Nuclear Physics News - NuPECC · Vol. 24, No. 4, 2014, Nuclear Physics News 1 Editor: Gabriele-Elisabeth Körner Editorial Board Maria José Garcia Borge, Madrid (Chair) Eugenio Nappi,

Nuclear Physics NewsInternational

Volume 24, Issue 4October–December 2014

FEATURING:Jyväskylä - Nuclear Lattice Simulations -

Cosmic Rays: Hurdles on the Way to Mars

10619127(2014)24(4)

Vol. 24, No. 4, 2014, Nuclear Physics News 1

Editor: Gabriele-Elisabeth Körner

Editorial Board Maria José Garcia Borge, Madrid (Chair) Eugenio Nappi, Bari Rick Casten, Yale Klaus Peters, Darmstadt and EPS/NPB Jens Dilling, Vancouver Herman Rothard, Caen Ari Jokinen, Jyväskylä Hideyuki Sakai, Tokyo Yu-Gang Ma, Shanghai James Symons, Berkeley Douglas MacGregor, Glasgow and EPS/NPB

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Nuclear Physics NewsVolume 24/No. 4

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2 Nuclear Physics News, Vol. 24, No. 4, 2014

NuclearPhysicsNews

Cover Illustration: The Jyväskylä Accelerator Laboratory - see article on page 4.

Volume 24/No. 4

ContentsEditorialThe Innovative Approach of the Last Born INFN Scientific-Technological Center

Fernando Ferroni and Graziano Fortuna ................................................................................................... 3Laboratory PortraitThe Jyväskylä Accelerator Laboratory

Ari Jokinen ................................................................................................................................................... 4Feature ArticlesA New Tool in Nuclear Physics: Nuclear Lattice Simulations

Ulf-G. Meißner ............................................................................................................................................ 11Nuclear Structure of Light Nuclei Near Threshold

Calem R. Hoffman and Benjamin P. Kay ..................................................................................................... 16Facilities and MethodsLight Exotic Nuclei at JINR: ACCULINNA and ACCULINNA-2 Facilities

Leonid Grigorenko, Andrey Fomichev, and Gurgen Ter-Akopian ............................................................... 22Nuclear Physics at Jožef Stefan Institute

Matej Lipoglavšek and Simon Širca ............................................................................................................ 28Impact and ApplicationsCosmic Rays: Hurdles on the Road to Mars

Marco Durante and Francis A. Cucinotta ................................................................................................... 32Meeting ReportThe First International African Symposium on Exotic Nuclei (IASEN2013)

Z. Vilakazi and Yu. Penionzhkevich ............................................................................................................. 35News and ViewsNuclear Physics Research Opportunities in Brazil

Mahir S. Hussein ......................................................................................................................................... 362012–2014 European Nuclear Physics Dissertation Award

Douglas MacGregor .................................................................................................................................... 37IBA-Europhysics Prize 2015 for Applied Nuclear Science and Nuclear Methods in Medicine Call for Nominations

Douglas MacGregor .................................................................................................................................... 38In MemoriamIn Memoriam: George Dracoulis (1944–2014)

Greg Lane, Andrew Stuchbery, Phil Walker, and Filip Kondev ...................................................................... 39

Calendar.......................................................................................................................................................... 40

editorial


In January 2013, INFN established a new scientific-technological Cen-ter in Trento, named Trento Institute for Fundamental Physics and Appli-cations (TIFPA). The foundation of TIFPA represents the achievement of a long journey of collaboration be-tween INFN and Scientific Institutions sited in the Trento area, among them, Trento University (UNITN) through the Physics Department (TPD), the Foundation Bruno Kessler (FBK) (former Istituto Trentino di Cultura), and The European Center for Theoreti-cal Studies in Nuclear Physics and Re-lated Areas (ECT*). It is worthwhile mentioning the important role of facil-itator played by the local government (Provincia Autonoma di Trento, PAT) which has provided substantial finan-cial and logistical support to most of the successful research programs car-ried out jointly by INFN, UNITN, and FBK. While the governance of TIFPA is under the responsibility of INFN, the Center activities are supported (for the moment) by three partners: UNITN, FBK, and APSS (formerly ATreP). The Center is open to other future partners. According to the new Statute of INFN and to the recommen-dations of PAT, the mission of TIFPA should comply with:

• Research activities conducted in international contests

• Research activities embedded in the territory

• Excellence of the expected re-sults

• Innovation triggered by institu-tional research activities

• Transfer of knowledge to the so-ciety

TIFPA is an environment struc-tured to intimately combine basic science (Particle, Astroparticles, and Nuclear Physics) activities with R&D programs; challenges of basic science trigger innovation; innovation makes it possible to attach new frontiers of knowledge. This vital circle is real-ized in TIFPA combining the virtues of the INFN Sections (research activities proposed by the scientific community through a bottom-up debate; such a de-bate is organized through the five Na-tional Scientific Committees that act as Advisory Boards of the INFN Coun-cil) with the modern organizations devoted to innovation and knowledge transfer (FBK). Day by day opera-tions and mid- to long-term programs are regulated by a Convention that also fixes the governance of the Center. Implementation Agreements define the specific role of every partner. Three important bodies are in charge to ad-vise the director of TIFPA:

• A Committee supervising the co-herence of the partner initiatives with the general planning of the Center. It is chaired by the direc-tor of TIFPA and composed by one representative per partner;

• A Council of the Center in sup-port of the director’s managing actions. It is composed by the traditional research group coor-dinators and by the supervisors of the new-born Technological Sectors (TSs). TSs are virtual laboratories that include all the infrastructures, tools, and pro-fessional skills needed to attach R&D strategic projects, optimiz-ing resources and timing;

• A Technical-Scientific Commit-tee monitoring the implementa-tion of the research programs and their position in the international contest.

TIFPA is an high priority initia-tive of the 2014–2016 Strategic Plan of Trento University, Department of Physics as a follow-up of the devel-opment strategy 2012–2014 approved by PAT directed to strengthen the joint initiatives between University and Research National Institutions in the Trento area. In particular, the pres-ence of INFN in Trento will contribute to the birth of a Center of excellence for in space and on ground Research in Astroparticle Physics and associ-ated technologies. Moreover, the birth of the proton therapy Center and the establishment in Trento of a new re-search group headed by a worldwide recognized scientist, will boost and expand the existing research activi-ties at the border of Physics, Biology, and Cancer treatment, attracting a new generation of skilled students and ex-ternal additional funds.

It is expected that TIFPA will be in full operation at the end of the year 2015.

Fernando Ferroni

INFN President

Graziano Fortuna

TIFPA Director

The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.

The Innovative Approach of the Last Born INFN Scientific-Technological Center

laboratory portrait


The Jyväskylä Accelerator Labo-ratory is a national center for nuclear and accelerator-based research and education. It is an integral part of the Department of Physics, University of Jyväskylä. The Accelerator Labora-tory and the Department Physics were moved to the current site in the early 1990s, as described in the previous Laboratory Portrait published in 1991 [1]. Since then the research program of the laboratory has been structured around the main instruments and re-search fields, which share the avail-able beam time. The present labora-tory layout is shown in Figure 1. In addition to basic research in nuclear and accelerator based materials phys-ics, beam time is reserved for com-mercial services.

Accelerator-based research began in Jyväskylä in the mid 1970s with the Scanditronix MC-20 cyclotron, which accelerated hydrogen (p, d) and helium (3He, 4He), running until 1991

when it was decommissioned. At that time the K130 cyclotron [2] was be-ing installed at the new location of the Accelerator Laboratory in Ylistö. The main components of the cyclo-tron were manufactured by Scanditro-nix, Sweden, with the magnet being jointly designed by JYFL and Scan-ditronix.

The cyclotron first accelerated beam in January 1992 and the first nu-clear physics experiment was carried out in 1993 when the measurement areas were available. By 1996 the cy-clotron usage exceeded 6000 h/year, a level maintained since then. At the end of 2013 the total run time of the K130 cyclotron since 1993 exceeded 130,000 h.

The K130 cyclotron was mainly designed and optimized for heavy ions although light ions can also be accelerated. The maximum energy is (q/A)2 130 MeV/nucleon for all other isotopes except protons, for which fo-

cusing limit restricts theoretical maxi-mum energy to 90 MeV.

The beam intensity for light ions at energies above 20 MeV/nucleon was originally limited by beam losses in the extraction region, the extraction efficiency being about 50%. To over-come this limitation the cyclotron was modified in year 2000 to allow extrac-tion of negative ions. After this modi-fication a proton beam current of 50 microA could be routinely provided for radioisotope production (123I).

High demand for light-ion beams triggered a project to acquire a dedi-cated cyclotron for protons and deu-terons. The plan became a reality when a 30 MeV H– cyclotron was ap-proved on the list of equipment as par-tial compensation of the former USSR debt to Finland. The contract for the 30 MeV H– cyclotron, MCC30/15, was approved in June 2007. The cyclo-tron was built by NIIEFA, D.V. Efre-mov-Institute, St. Petersburg, Russia [3].

Final acceptance tests were made at JYFL in April 2010, reaching or exceeding the specified values. The maximum proton current at both 30 MeV and 18 MeV was 200 microA. The maximum deuteron current at 15 MeV was 62 microA. The MCC30/15 cyclotron has two extraction ports, one on each side of the cyclotron (Figure 2). One beam-line serves the IGISOL facility and the other one for future radioisotope production.

The K130 cyclotron is served by three ion sources. Two ECR ion sources (6.4 and 14 GHz) produce highly charged heavy ions and a multi-cusp ion source LIISA produces nega-tive ions H– and D–. The ECR sources and the LIISA multicusp source were developed, designed, and (partially) built at JYFL.

The Jyväskylä Accelerator Laboratory

Figure 1. The present lay-out of the JYFL Accelerator Laboratory.

laboratory portrait


The 6.4 GHz ECRIS was the first ion source for the K130 cyclotron. Since then it has evolved through sev-eral upgrades and the performance has increased accordingly. Due to demand for higher charge states, a project to build a modern 14 GHz ECRIS was launched in 1999. Later, the 14 GHz ECRIS was equipped with an auxil-iary TWTA microwave transmitter to access higher charge states, like 35+ for 131Xe beam required for space electronics testing.

The multicusp ion sources for the K130 cyclotron (LIISA) and Pelletron (PELLIS) were designed and built at JYFL. In order to extend the time between filament changes a project to develop an RF-driven source (RA-DIS) was started in 2011 [4]. Replac-ing the filament with an RF antenna will extend the maintenance interval from about 150 hours at least to one month. This is rather crucial for reli-

able operation of the MCC30/15 cy-clotron for long physics experiments and for commercial runs.

The Ion Guide Isotope Separator On-Line facility at JYFL

In 2012 we celebrated three de-cades of research following the devel-opment of the ion guide technique in the early 1980s at the IGISOL facility. To acknowledge this achievement, a collection of articles, several of which contained a significant amount of original material, were published as a Topical Collection in the European Physical Journal [5] and a further 21 published in Hyperfine Interactions [6].

The novelty of the ion guide con-cept and its gradual evolution has always been driven by the pursuit of research on both sides of the valley of beta stability. Similar extraction effi-

ciencies for both volatile and non-vol-atile elements throughout the periodic table has resulted in the production of a rich variety of radioactive ion beams (RIBs) of short-lived exotic nuclei for fundamental nuclear structure re-search and applications.

During the 1980s, the main re-search activity at IGISOL was decay spectroscopy of fission products pro-duced in the proton-induced fission of uranium, with the discovery and study of approximately 40 new isotopes and isomers using beta-, gamma-, and con-version electron spectroscopy. Fol-lowing the move from the old Physics Department to the Science Campus of the University of Jyväskylä, the facility was reinstalled as IGISOL-2 and served the period from 1993 to 2003.

During this time a major upgrade to the instrumentation of the facil-ity was realized. The Universities of

Figure 2. A new MCC30 light-ion cyclotron.

laboratory portrait


Manchester and Birmingham installed a collinear laser spectroscopy station in 1994 for the study of ground state properties (nuclear spin, moments, and mean-square charge radii) of refrac-tory elements. In 1998 an RFQ cooler-buncher was installed to convert con-tinuous ion beams into bunches. This led to dramatic reductions in the scat-tered photon background, a technique that has since become standard prac-tice. The construction of the longitu-dinal Penning trap, JYFLTRAP, not only afforded unique opportunities for decay spectroscopy with isobari-cally purified beams, but resulted in a hugely successful mass measurement program.

From 2004 onward IGISOL-3 was in operation, coupling the improved yields with the new instrumentation to perform precision experiments. In par-allel, a rigorous development on reso-nance photo-ionization to address the

lack of elemental selectivity in the ion guide technique commenced. In addi-tion to selective RIB production, the possibility for in-gas-cell or in-gas-jet resonance ionization spectroscopy (RIS) has been pursued, providing a complementary approach to collinear laser spectroscopy for the study of nuclear structure. The backbone of the facility is a suite of three Ti:sapphire lasers, built in collaboration with the University of Mainz, pumped by an Nd:YAG laser operated at 10 kHz. In general, the laser system is capable of covering wavelengths ranging from ~690 nm to 1,000 nm and from ~500 nm to 205 nm with higher harmonic generation.

At IGISOL-3, experiments covered laser spectroscopy and decay spec-troscopy in collaboration with inter-national teams utilizing a variety of tools including beta and gamma spec-troscopy, total absorption spectrom-

etry, neutron spectroscopy, fast tim-ing methods and in-trap techniques, many experiments of which would increasingly request the purification capabilities of the Penning trap. The workhorse of the IGISOL facility be-came the JYFLTRAP Penning trap, employed in the measurement of almost 250 atomic masses of short-living nuclei, including measurements of the superallowed β-decay QEC val-ues for fundamental studies, with 14 QEC values measured to extremely high precision between 2005 and 2010.

Operation at IGISOL-3 concluded in June 2010. Over the following two years the facility was moved and re-constructed in a new experimental hall (850 m2), which also houses the MCC30/15 cyclotron. Primary beams can be delivered to the new IGISOL-4 facility from both cyclotrons (Fig-ure 3). The move has offered an op-

Figure 3. A schematic lay-out of the new IGISOL-4 facility.

laboratory portrait


portunity to dramatically improve the overall layout in order to overcome several shortcomings of the previous facility, as well as make use of a con-siderable increase in floor space for future developments and more sophis-ticated detector setups.

In the new layout, optical transport from two laser cabins situated directly above the target chamber has been im-proved, with separate paths for up to three laser beams to the target area for both in-source and in-jet ionization. A second ion source station is under con-struction on the second floor intended to provide stable beams of ions from a discharge-type and carbon cluster ion source.

Downstream of a new electrostatic switchyard at the mass separator fo-cal plane, the layout of the facility has dramatically changed. A more advanced beam distribution system will allow fast switching between three beam-lines, the first housing a permanent spectroscopic station for on-line yield monitoring, the second a line with additional electrostatic elements and diagnostics for future decay spectroscopy experiments not requiring the Penning trap, and the third leading to the RFQ. The collin-ear laser beam-line is now situated on the ground floor. The beam from the RFQ can either be transported left to-ward the laser spectroscopy station or right toward JYFLTRAP. Such separa-tion of collinear and trap beam-lines enables direct access of laser light into the RFQ for optical manipulation, ion resonance ionization, or even polar-ization of ion beams, all planned as part of an extensive laser spectroscopy program in the future.

Presently IGISOL-4 is undergoing full commissioning and a number of on-line experiments have been per-formed as different parts of the facility come on-line. The first experiments have shown improvements in the yield

of mass-separated fission fragments of up to a factor of three over IGISOL-3.

An important avenue of future re-search will be the push toward ever more exotic neutron-rich species. This will be met by a substantial research program utilizing neutron-induced fission of uranium and other actinide targets. Several topical applications related to nuclear energy including fis-sion product yields, reactor design and safety as well as the management of nuclear waste are all connected to this program. A neutron converter target is currently under construction follow-ing detailed studies in collaboration with Uppsala University.

Funding from the Finnish Acad-emy has been awarded for additional ion manipulation tools which can be directly connected to the beam-lines after the RFQ. One such device will be a multi-reflection time-of-flight mass spectrometer. Other devices un-der construction or planning include a cone trap for laser spectroscopy and a cryocooler. In close collaboration with the neighboring RITU/GAMMA group, plans are being made for the development of a gas cell for the focal plane of the new MARA recoil sepa-rator.

JYFL Nuclear Spectroscopy GroupOver the past fifteen years or so,

the “RITU” and “GAMMA” groups of JYFL have combined forces to great effect and made rapid advances in the experimental study of nuclear struc-ture of heavy and neutron-deficient nuclei. Assisted by close collaboration with a large number of international institutions, the instrumentation avail-able for in-beam and decay spectro-scopic studies has steadily expanded. Most notable of the collaborations is that with the UK community, which has resulted in the deployment of the GREAT spectrometer and associated

Total Data Readout (TDR) acquisition system at JYFL. In addition to these, the SAGE (Silicon And GErmanium) and LISA (Light Ion Spectrometer Ar-ray) spectrometers have been success-fully used in recent experimental cam-paigns (University of Liverpool and Daresbury Laboratory). The group at the University of York has been instru-mental in improving the sensitivity for challenging studies of N ≈ Z nuclei, through the so-called beta-tagging technique.

Further significant input has come from the French community, espe-cially IPHC Strasbourg, CEA Saclay, and CSNSM Orsay. The group at Strasbourg managed to produce an enriched volatile MIVOC compound containing 50Ti, which in turn led to the long-awaited in-beam study of 256Rf.

The main workhorse of the Nuclear Spectroscopy group is the RITU gas-filled recoil separator, which was orig-inally built to study the decay prop-erties of heavy nuclei [7] (Figure 4). At the time of construction, no-one would have imagined the versatile and wide-ranging use of the separa-tor today. For typical fusion evapora-tion reactions, RITU has a transmis-sion from around 10% to better than 50%. Almost continually since the late nineties, RITU has been coupled to an array of germanium detectors at the target position. This coupling allows the in-beam study of nuclei produced with low cross sections, by employing the Recoil-Decay Tagging (RDT) technique. From humble be-ginnings with the small DORIS array of TESSA detectors, the detection ef-ficiency for gamma rays at the target position has increased. The current array is JUROGAMII, which con-sists of 24 Clover detectors and up to 15 Tapered detectors along with their associated Compton-suppression shields. In parallel, the sensitivity of

laboratory portrait


the focal plane detection systems has also developed over the years. The first developments were made by the in-house group, with the addition of transmission gas detectors to allow the discrimination of scattered beam and other unwanted particles. The use of a transmission detector in “veto” mode also eliminated the need to use slow-pulsed beams in decay experiments. These developments were superseded with the installation of the GREAT spectrometer and the associated TDR acquisition system. The introduction of the triggerless TDR system elimi-nated problems due to common dead time and also eliminated the need to run “surrogate” reactions in order to set-up the timing electronics.

These developments meant that JYFL became one of the leading labo-ratories for studies of nuclei far from stability, with a very busy experimen-tal program. Currently the group per-forms something like 10–15 experi-ments per year, of typical duration one to two weeks.

In the past few years, our collabo-rations have again borne fruit, with the commissioning and exploitation of

new devices coupled to RITU. A col-laboration of the University of Liver-pool, Daresbury Laboratory, and the local group led to the development of the SAGE spectrometer, designed for simultaneous in-beam studies of inter-nal conversion electrons and gamma rays. The development of SAGE also relied on the parallel development of digital electronics to instrument the large number of channels of silicon and germanium detectors. Currently all channels are instrumented with Lyrtech VHS-ADC electronics, allow-ing the use of higher counting rates and further lowering the limit of sen-sitivity. SAGE has completed three campaigns of experiments, and data are under analysis.

The LISA spectrometer (again through Liverpool and Daresbury) completed a campaign of experiments in early 2013. LISA is an array of silicon detectors designed to observe charged particles emitted in the decay of short-lived (ns) states at the target position of RITU. Again, data from the campaign is under analysis and further experimental campaigns are being planned.

JYFL has had a very successful col-laboration with the group at Cologne, expert in lifetime measurements with plunger devices. This collaboration has made a number of experiments to study the lifetimes of nuclei close to 186Pb, one of the most well-known regions of nuclei exhibiting shape coexistence phenomena. Following on from this, an updated version of the Cologne plunger device has been constructed at the University of Man-chester, known as DPUNS. The col-laboration consisted of the Universi-ties of Manchester and Liverpool, the IKP Köln group, and the local group at JYFL. DPUNS has been successfully used in a number of experiments, and first results have been published. AQ1

As mentioned above, another line of study has been to employ the re-coil-beta tagging technique in order to investigate N ≈ Z in the mass 70 region. It is perhaps these studies that are the most surprising to be found in the RITU experimental program, given that RITU was developed for studies of heavy elements. The suc-cess here is largely due to the efforts of the group at the University of York, who have developed a variety of new detectors, both as extensions of the GREAT focal plane spectrometer and for use at the target position. The most recent of these is the “UoYTube” de-tector, an array of CsI detectors that is used to detect (and veto) charged particles emitted at the target position. The limit of sensitivity now such that studies of 66As and 66Se have recently been carried out.

The local group, in parallel to running the experimental campaign at RITU, is currently constructing the new Mass Analysing Recoil Ap-paratus (MARA) spectrometer. In the space vacated by IGISOL in the cave adjoining that of RITU, the new vacuum-mode mass spectrometer is taking shape. MARA will allow stud-

Figure 4. A gas-filled recoil spectrometer RITU.

laboratory portrait


ies of lighter nuclei than at RITU, broadening the region of the nuclear chart accessible for in-beam studies at JYFL. It is envisaged that the wide range of instrumentation available for use with RITU will also be used at MARA. The ion optics of the beam-line to MARA have also been planned to take this into account.

MARA consists of a magnetic quadrupole triplet, electrostatic di-pole deflector, and magnetic dipole, to separation of fusion-evaporation products according to their mass-to-charge ratio. The majority of compo-nents for MARA are already installed including the electrostatic deflector delivered by Danfysik earlier this year (Figure 5). It is hoped that the first beam tests will be made in the beginning of 2015.

Accelerator-Based Materials Research and Ion Beam Analysis

The two main focus areas in accel-erator-based materials research are the

understanding of the basic phenomena related to the ion–matter interaction, for instance energy straggling of ions [8], and utilizing these phenomena in materials modification and character-ization [9]. The main research instru-ment of the group is a 1.7 MV Pel-letron tandem accelerator (Figure 6), which can deliver beams of H to Au from three different ion sources with a final energy of 0.2–20 MeV. Four beam-lines are used for ion beam analysis and ion beam lithography.

The group is also a frequent user of the K130 cyclotron for instance, in ion track–related research.

The development of ion beam analysis techniques involves new de-tectors, data acquisition using direct digitization, and in-house analysis software development. The workhorse in ion beam analysis is a time-of-flight elastic recoil detection analysis (TOF-ERDA) setup, which can be utilized for depth profiling of all elements in thin films down to single nanometer depth resolution. This has proven to be a very powerful tool, especially in the analysis of atomic layer deposited (ALD) thin films, which often con-tain light impurities such as hydrogen and carbon. The latest development in 2013 was the installation of a super-conducting microcalorimeter detector in collaboration with a group from the NanoScience Center for particle- induced X-ray emission (PIXE) mea-surements. The detector has 3 eV en-ergy resolution at 5.9 keV, and there-fore offers unique possibilities for chemical analysis of thin films and also culture heritage artefacts.

The materials research group has close connections to Finnish indus-try via regular collaborative proj-ects. These projects have involved, for instance, detector development, biomimetic thin films, and ion beam analysis.

Figure 5. Installation of the electrodes of the high-voltage deflector of MARA separator.

Figure 6. A lay-out of the Pelletron laboratory with three ion sources and four beam-lines.

laboratory portrait


Industrial Applications at JYFL-ACCLAB

Isotope production with the K-130 cyclotron started in 2000 and in 2002 it was at a level of weekly production. The isotope 123I was produced for a local medical company, which sup-plied the final pharmaceuticals to all the biggest hospitals in Finland. Cur-rently, iodine production is halted, but plans to begin radioisotope production with the MCC30/15 accelerator are in progress.

The increased demands for radia-tion testing in Europe attracted ESA to the JYFL Accelerator Laboratory. In 2004 a contract between ESA and JYFL for the “Utilisation of the High-Energy Heavy Ion Test Facility for Component Radiation Studies” was signed. After the upgrade of the sta-tion was completed in May 2005, the RADiation Effects Facility, RADEF, qualified as one of ESA’s External European Component Irradiation Facilities (ECIF). RADEF includes

heavy-ion and proton beam-lines for the irradiation of space electronics in the same facility. It consists of a chamber whereby tests can be made either in vacuum or in air, and equip-ment for beam quality and dosimeter analysis is provided. A user interface for monitoring flux and fluence was also developed. A schematic picture of the set-up of beam-lines is shown Fig-ure 7. RADEF’s other specialty is the high penetration ion cocktail devel-oped during the upgrade. It consists of seven ion species with energies of 9.3 MeV/nucleon.

During its operation RADEF has served as a test site for about 35 com-panies and space organizations. In addition to ESA, the list of institutes includes NASA/JPL, JAXA, INTA, CNES, CEA, SANDIA, and ONERA.

From the beginning of 2008 RADEF has also irradiated mem-branes for a Swiss-German company. The final products are micro filters mainly manufactured for the needs

of the car and health care industries. For this application, stable and intense heavy ion beams have been devel-oped.

OutlookResearch and development has

been a priority at the JYFL Accelera-tor Laboratory since the first beams were delivered in the early 1970s. The last two decades have shown an increase of applied and commercial research utilizing the accelerators; reaching about 25% of the total beam time at present. The division between basic research and applications is ex-pected to stay at that level in the com-ing years. New installations under construction and planned upgrades will provide a firm basis for the suc-cessful operation of the Accelerator Laboratory well into the coming de-cade and beyond.

References1. J.Äystö and A. Pakkanen, Nucl. Phys.

News 1 (5) (1991) 6.2. E. Liukkonen, Proc. 13th Int. Conf.

On Cyclotrons and Their Applications (Vancouver, Canada, 1992) 22.

3. P. Heikkinen, Proc. 19th Int. Conf. on Cyclotrons and Their Applications (Lanzhou, China, 2010) 310.

4. T. Kalvas, O. Tarvainen, J. Komppula, et al., Recent Negative Ion Source Ac-tivity at JYFL, AIP Conf. Proc. 1515 (2012) 349.

5. European Physical Journal A 48 (4) (2012).

6. Hyperfine Interactions 223 (1–3) (2014).

7. M. Leino et al., Nucl. Instr. Meth.B 99 (1995) 653.

8. C. Vockenhuber, J. Jensen, J. Julin, et al., Europ. Phys. J. D 67 (2013) 145.

9. A. R. A. Sagari, J. Malm, M. Laitinen, et al., Thin Solid Films 531 (2013) 26.

Ari JokinenAQ2Affiliation???

Figure 7. A radiation test facility RADEF.

feature article


IntroductionThe nuclear many-body problem continues to be one of

the most interesting and demanding challenges in contem-porary physics. With the advent of FAIR, FRIB, and the many existing radioactive ion beam facilities, a detailed and accurate theoretical understanding of nuclear struc-ture and reactions is mandatory. A major breakthrough in nuclear theory was initiated through the work of Steven Weinberg [1], who made the first steps for an effective field theory (EFT) solution of the nuclear force problem. In this approach, two- and multi-nucleon forces as well as the re-sponse to external electromagnetic and weak probes can be calculated systematically, precisely, and consistently. In addition, the so important issue of assigning theoretical er-rors can be dealt with naturally. The very hot topic of the quest for three-nucleon forces was already addressed in this journal [2], which also contained a short introduction into the framework of chiral nuclear EFT. In this scheme, the nuclear forces are given in terms of one-, two-, … pion exchanges and smeared local multi-nucleon operators, that parameterize the short-distance behavior of the nuclear forces. These operators come with unknown coupling con-stants, the so-called low-energy constants (LECs) that must be determined from a fit to nucleon-nucleon scattering and a few three-body data. For systems up to four nucleons, these forces have been tested in extensive detail and scru-tinized. One of the present research foci is the calculation and investigation of higher order corrections to the three-nucleon forces as well as the construction of electroweak current operators. For reviews on the method and many re-sults see Refs. [3, 4].

But what about larger nuclei? There are two different venues. The first one is to combine these chiral forces, eventually softened using renormalization group methods, with well-developed many-body approaches like the no-core-shell model, the coupled cluster approach and so on. There have been quite a few activities in such type of ap-

proaches (see Refs. [5–10]) for some recent works. Another approach, and this is the one I will discuss in what follows, is to combine the chiral forces with Monte Carlo simulation techniques, that have been successfully applied in gauge field theory (lattice QCD), condensed matter systems and other areas of physics. This novel method will be called nuclear lattice simulations (or nuclear lattice EFT) in the following.

In this short review, I first introduce the formalism in a very simplified manner and discuss the scope of the method, then show a few assorted physics results and finally address the question about the viability of carbon-oxygen based life on Earth when one changes certain fundamental parameters of the Standard Model that control nuclear physics.

Formalism and ScopeThe basic ingredient in this framework is the discretiza-

tion of space–time (see Ref. [11] for details). Space–time is represented by a grid. This lattice serves as a tool to com-pute the nuclear matrix elements under consideration. More precisely, one first performs a Wick rotation in time so that the time evolution operator behaves as exp(-Ht), with H the nuclear Hamiltonian. Space–time is then coarse-grained as shown in Figure 1. In the three spatial directions, the small-est distance on the lattice is given by the lattice spacing a, so that the volume is L × L × L, with L = N a and N an inte-ger, whereas in the time direction one often uses a different spacing at, and Lt = Nt at is chosen as large as possible. Typical values are N = 6 and Nt = 10...15. As the Euclidean time becomes very large, one filters out the ground state as it has the slowest fall-off ~exp(-E0t), with E0 the ground state energy. Excited states can also be investigated. This, how-ever, requires some more effort. The nucleons are placed on the lattice sites as depicted in Figure 1. Their interactions are given by pion exchanges and multi-nucleon operators, properly represented in lattice variables. So far, nuclear lat-

A New Tool in Nuclear Physics: Nuclear Lattice SimulationsUlf-G. Meißner1,2,31 Helmholtz-Institut für Strahlen- und Kernphysik and BCTP, Universität Bonn, Nußallee 14-16, D-53115 Bonn, Germany

2Forschungszentrum Jülich, IAS-4, IKP-3, JCHP and JARA HPC, D-52425 Jülich, Germany3Kavli Institute for Theoretical Physics China, CAS, Beijing 100190, China

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tice simulations have been carried out using two- and three-nucleon forces at next-to-next-to-leading order (NNLO) in the chiral expansion. The Coulomb force and isospin-breaking strong interaction effects are also included, thus one has all required ingredients to describe the structure of nuclei. The lattice is used to perform a numerically exact solution of the A-nucleon system, where the atomic number A = N + Z counts the neutrons and protons in the nucleus under investigation.

It is important to realize that the finite lattice spacing entails a maximum momentum pmax = π/a, so that for a typical lattice spacing of a = 2 fm, one has a maximum momentum of about 300 MeV; that is, one deals with a very soft interaction. The main advantage of this scheme is, however, the approximate spin-isospin SU(4) symmetry of the nuclear interactions already realized by Wigner in 1937 [12]. Because of this approximate symmetry, the malicious sign oscillations that plague any fermion simulation at finite density are very much suppressed, quite in contrast to the situation in lattice QCD. A lucid discussion of this issue has been given by Chen, Schäfer, and Lee [13]. Consequently, alpha-type nuclei with N = Z, and spin and isospin zero can be simulated most easily. However, in the mean time our collaboration has developed a method that allows for a remarkable suppression of the remaining sign oscillations in nuclei with N ≠ Z. One more remark on the formalism is in order. The simulation algorithms sample all possible configurations of nucleons, in particular one can have up to four nucleons on one lattice site. Thus, the so important

phenomenon of clustering in nuclei arises quite naturally in this novel many-body approach.

In Figure 2, the phase diagram of strongly interacting matter is shown in the standard temperature versus density plot. Apart from nuclear structure research, nuclear lattice simulations can also be used to explore nuclear matter, neutron matter or other more exotic phases as indicated by the dark (blue) area. For comparison, the part of the phase diagram accessible to lattice QCD is depicted by the light (yellow) area, which is much narrower because of the sign oscillations discussed earlier. Therefore, we can systemati-cally explore many fascinating aspects of strongly interact-ing matter, but for this short review I concentrate on some recent results pertinent to the structure of nuclei.

Assorted ResultsBefore presenting results, we must fix parameters. We

have nine LECs related to the two-nucleon force that can be fixed from the low partial waves in neutron-proton scat-tering. Two further LECs from isospin-breaking four-nu-cleon operators are fixed from the nn and the pp scattering lengths, respectively. In addition, one has two LECs appear-ing in the three-nucleon force, that can, e.g., be fixed from

p

p

n

n a

~ 2 fmFigure 1. Two-dimensional representation of the space–time lattice. The smallest length on the lattice is the lattice spacing a, and the protons (p) and neutrons (n) are placed on the lattice sites.

Figure 2. Phase diagram of strongly interacting matter. Here, ρ denotes the density, with ρN the density of nuclear matter, and T is the temperature. For further details, see the text. Figure courtesy of Dean Lee.

10-110-3 10-2 1

10

1

100

T [

Me

V]

ρNρ [fm-3]

heavy-ioncollisions

quark-gluonplasma

gas of lightnuclides

earlyuniverse

nuclearliquid

superfluid

excitednuclei

neutron star coreneutron star crust

Accessible byLattice QCD

Accessible byLattice EFT

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the triton binding energy and the doublet neutron-deuteron scattering length. The first non-trivial prediction is then the binding energy difference of the triton and 3He, we find E(3H) - E(3He) = 0.78(5) keV, in good agreement with the empirical value of 0.76 keV [14]. That we can reproduce this small effect with good accuracy gives us confidence that we have all aspects of the strong and electromagnetic forces relevant to nuclear physics under control.

If one invents a new theoretical scheme, it is absolutely necessary to solve a problem which other methods could not deal with, otherwise this new approach is not accepted easily in the community. Therefore, the first nucleus we investigated was 12C, more precisely the ground state and its low-lying even-parity excitations. The most interesting excited state in this nucleus is the so-called Hoyle state that plays a crucial role in the hydrogen burning of stars heavier than our sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle [15] as a nec-essary ingredient for the fusion of three alpha particles to produce a sufficient amount of carbon at stellar tempera-tures. Without this excited state that is located very close to the 4He + 8Be threshold (thus leading to a resonant en-hancement of the production rate), much too little carbon would be generated and consequently also much too little oxygen, thus making life on Earth impossible. Although the Hoyle state was seen experimentally more than a half century ago [16], nuclear theorists have tried unsuccess-fully to uncover the nature of this state from first princi-ples. Using nuclear lattice simulations, we could perform an ab initio calculation of this elusive state [17]. Here, by ab initio we mean that all parameters appearing in the nuclear forces have been determined in the two- and three-nucleon systems and that the 12 particle problem has been solved numerically exactly using Monte Carlo techniques. The resulting spectrum of the lowest states with even par-ity is shown in Figure 3. One observes a nice agreement between theory and experiment. Not only does one get the Hoyle state at its correct position but also the much inves-tigated 2+ excitation a few MeV above it. Further insight into the structure of the Hoyle state was obtained in Ref. [18], where the structure of these states was investigated. In all these states, alpha clustering plays a prominent role. For the ground state and the first excited 2+ state, one finds a compact triangular configuration of alpha clusters. For the Hoyle state and its 2+ excitation, however, the domi-nant contribution is a “bent arm” or obtuse triangular alpha cluster configuration. A remaining challenge is the calcula-tion of radii and transition moments beyond leading order so as to make contact to the precise measurements of elec-

tromagnetic observables performed, for example, at the S-DALINAC in Darmstadt [19].

Another alpha cluster-type nucleus is 16O, that also plays an important role in the formation of life on Earth. Since the early work of Wheeler [20], there have been sev-eral theoretical and experimental works that lend further credit to the cluster structure of 16O. However, no ab initio calculations existed that gave further support to these ideas. This gap was filled in Ref. [21] where nuclear lattice simu-lations have been used to investigate the low-lying even-parity spectrum and the structure of the ground and first few excited states. It is found that in the spin-0 ground state the nucleons are arranged in a tetrahedral configuration of alpha clusters (Figure 4). For the first 0+ excited state, the predominant structure is given by a square arrange-ment of alpha clusters, as also shown in Figure 4. There are also rotational excitations of this square configura-tions that include the lowest 2+ excited state. These cluster configurations can be obtained in two ways. First, one can investigate the time evolution of the various cluster con-figurations shown in Figure 4 and extract, for example, the corresponding energies as the Euclidean time goes to infin-ity. Second, one can also start with initial states that have no clustering at all. One can then measure the four-nucleon correlations. For such initial states, this density grows with time and stays on a high level. For the cluster initial states, these correlations start out at a high level and stay large as a function of Euclidean time. This is a clear indication that the observed clustering is not build in by hand but rather

Figure 3. Even-parity spectrum of 12C. On the left, the empirical values are shown, whereas the right column dis-plays the nuclear lattice simulation results from Ref. [16].

2+

Exp Th

−92

Hoyle

2+

0−84

−86

−88

−90

−87.72

−84.51 −85(3)

−82

0 +

−92(3)

−88(2)

2+

−82.6(1)2 +

0 + +−83(3)

E [

MeV

]

0 +

−92.16

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constant)? This can be answered by employing the chiral EFT approach to the nuclear forces. In fact, as in QCD the pion mass squared is proportional to the sum of the light up and down quark masses, we simply need to study the varia-tion of the forces under changes of the pion mass. This has been done to NNLO in the chiral expansion in Ref. [23], where also constraints on quark mass variations from the abundances of the light elements from the Big Bang were derived. Armed with that, in Ref. [24] a detailed study of the resonance condition in the triple alpha process was per-formed, leading to the conclusion that quark mass varia-tions of 2 to 3% are not detrimental to the formation of life on Earth. However, this number is afflicted with a sizeable uncertainty that can eventually be overcome from lattice QCD studies of the nucleon-nucleon scattering lengths. It could also been shown that the various fine-tunings in the triple alpha process are correlated, as had been speculated before [25]. Further, the possible variation of the fine struc-ture constant can be also derived, changes in αEM of ±2.5% are consistent with the requirement that ΔE changes by at most 100 keV in magnitude.

Consequently, the light quark masses and the fine struc-ture constant are fine tuned. Beyond these rather small changes in the fundamental parameters, the anthropic prin-ciple appears necessary to explain the observed abundances of 12C and 16O. For a recent review on the applications of the anthropic principle, the reader is referred to Ref. [26].

Summary and ConclusionsIn this article, I have given a short review about the

novel method of nuclear lattice simulations and showed some first promising results for nuclei. In addition, an ap-plication to testing the anthropic principle, which has con-sequences much beyond nuclear physics, was discussed. Of course, there remains much work to be done. In particu-lar, the removal of lattice artefacts through the finite lattice spacing and the finite volume has to be further improved (see, e.g., the recent work on the restoration of rotational symmetry for cluster states [27]). In addition, the methods to reduce the errors in the extraction of the signals from the Euclidean time interpolation have to be sharpened, at present ground state energies of nuclei up to A = 28 can be extracted with an accuracy of 1% or better [28]. The computing time scales approximately as A2, so that heavier nuclei can also be investigated in the future. Further, the underlying forces have to be worked out and implemented to NNNLO in the chiral expansion. Another line of research is to allow for the continuum limit a → 0 by formulating the EFT with a cut-off on the lattice. A first step was done in Ref. [29]. Another area of research concerns the equation

Figure 4. Schematic illustration of the alpha cluster states in the tetrahedral (left panel) and the square (right panel) configuration.

(a) (b)

follows from the strong four-nucleon correlations in the 16O nucleus.

Anthropic ConsiderationsAnother fascinating aspect of this method is that it al-

lows one to test the changes of the generation of the life-relevant elements under variations of the fundamental constants of the Standard Model. For the case of nuclear physics, these are the light quark masses and the electro-magnetic fine structure constant αEM. While the light quarks generate only a small contribution to the mass of the nucleon—showing that mass generation is not entirely given by the Higgs boson—their masses are comparable to the typical binding energy per nucleon. Therefore, varia-tions in the quark masses will lead to changes in the nuclear binding. In fact, nuclear binding appears to be fine-tuned by itself. A deeper understanding of this particular fine-tuning in Nature has so far been elusive.

The already discussed Hoyle state has often been her-alded as a prime example of the anthropic principle, that states that the possible values of the fundamental param-eters are not equally probable but take on values that are constrained by the requirement that life on Earth exists. A crucial parameter in the triple-alpha reaction rate is the dif-ference between the Hoyle state energy and three times the alpha nucleus mass, ΔE = 380 keV. Already in 2004, Schlattl et al. [22] showed that ΔE could be changed by about ±100 keV so that one still produces a sufficient amount of carbon and oxygen in stars. This is a 25% modification that does not appear very fine-tuned. But how does this translate into the fundamental parameters of the Standard Model (i.e., into changes of the light quark mass and the fine structure

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of state of neutron and nuclear matter and the possibility of various pairing phenomena in such dense systems. Finally, preliminary investigations toward the inclusion of hyperons are also done to tackle problems in hypernuclear physics. There is a bright future for applying and improving nuclear lattice simulations and I would like to see more groups em-ploying this powerful tool.

AcknowledgmentsI thank all members of the NLEFT collaboration for

sharing their insight into the topics discussed here, espe-cially Dean Lee, Timo Lähde, and Evgeny Epelbaum. I also thank Evgeny Epelbaum and Dean Lee for comments on the article and for help with this strange type-setting sys-tem. Computational resources were provided by the Jülich Supercomputer Center and the RWTH Aachen. Work sup-ported in part by the BMBF, the DFG, the HGF, the NSFC and the EU.

References 1. S. Weinberg, Nucl. Phys. B363 (1991) 3. 2. N. Kalantar-Nayestanaki and E. Epelbaum, Nucl. Phys. News

17 (2007) 20. 3. E. Epelbaum, H.-W. Hammer and U.-G. Meißner, Rev. Mod.

Phys. 81 (2009) 1773. 4. D. Entem and R. Machleidt, Phys. Rep. 503 (2011) 1. 5. G. Hagen et al., Phys. Rev. Lett. 109 (2012) 032502. 6. D. Jurgensen et al., Phys Rev. C87 (2013) 054312. 7. R. Roth et al., Phys. Rev. Lett. 107 (2011) 072501. 8. H. Hergert et al., Phys. Rev. C87 (2013) 034307 . 9. V. Soma et al., Phys. Rev. C87 (2013) 011303.10. A. Lovato et al., Phys. Rev. Lett. 111 (2013) 092507

11. B. Borasoy et al., Eur. Phys. J. A31 (2007) 105.12. E. Wigner, Phys. Rev. 51 (1937) 106.13. J.-W. Chen et al., Phys. Rev. Lett. 93 (2004) 242302.14. E. Epelbaum et al., Phys. Rev. Lett. 104 (2010) 142501.15. F. Hoyle, Astrophys. J. Suppl. 1 (1954) 121.16. C. W. Cook et al., Phys. Rev. 107 (1957) 508.17. E. Epelbaum et al., Phys. Rev. Lett. 106 (2011) 192501.18. E. Epelbaum et al., Phys. Rev. Lett. 109 (2012) 252501.19. M. Chernykh et al., Phys. Rev. Lett. 98 (2007) 032501.20. J. A. Wheeler, Phys. Rev. 52 (1937) 1083.21. E. Epelbaum et al., Phys. Rev. Lett. 112 (2014) 102501.22. H. Schlattl et al., Astrophys. Space Sci. 291 (2004) 27.23. J. C. Berengut et al., Phys. Rev. D87 (2013) 085018.24. E. Epelbaum et al., Phys. Rev. Lett. 110 (2013) 112502; Eur.

Phys. J. A49 (2013) 82.25. S. Weinberg, Facing Up (Harvard University Press, Cam-

bridge, USA, 2001).26. A. N. Schellekens, Rev. Mod. Phys. 85 (2013) 1491.27. B.-N. Lu et al., Phys. Rev. D 90 (2014) 034507.28. T. Lähde et al., Phys. Lett. B732 (2014) 110.29. I. Montvay and C. Urbach, Eur. Phys. J. A48 (2012) 38.

Ulf-G. Meißner

Filler?

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2 3 4 5 6 7 8

–5

–4

–3

–2

–1

0

1

2

3

4

2 3 4 5 6 7 8 2 3 4 5 6 7 8

1/2+5/2+

N = 5 7 8 9 10 11 13

Z Z

E n (M

eV)

Z

1/2–

3He 4He 5He 6He 7He 8He 9He 10He

4Li 5Li 6Li 7Li 8Li 9Li 10Li 11Li 12Li

13Be 14Be6Be 7Be 8Be 9Be 10Be 11Be 12Be 15Be 16Be

13B 14B 17B7B 8B 9B 10B 11B 12B 15B 16B 18B 19B

13C 14C 17C 20C 21C9C 10C 11C 12C 15C 16C 18C 19C 22C

13N 14N 17N 20N 21N 23N 24N11N 12N 15N 16N 18N 19N 22N 25N

13O 14O 17O 20O 21O 23O 24O 26O 27O15O 16O 18O 19O 22O 25O 28O

Stable

Unstable

Unbounds and d knownp, s, and d known

Nuclear Structure of Light Nuclei Near ThresholdCalem R. Hoffman and Benjamin P. Kay

Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA

IntroductionMoving toward an understanding of nuclei at the thresh-

old of nuclear binding is a major theme of contemporary experimental and theoretical nuclear physics. The challenge to the former is to probe nuclei at the limits of existence requiring a variety of different techniques such as nucleon transfer, nucleon knockout, and Coulomb dissociation, and so on. And to the latter, a question of framing the problem: What role does finite binding play? What role does the con-tinuum play? How can the action of these effects be isolated when interpreting the experimental data? Is it even possible to disentangle these?

The last few decades have seen an explosion in the amount of available data on such systems, from heavy neutron-deficient systems, to light nuclei-rich nuclei, pav-

ing the way for systematic studies. In this article we focus our attention on the neutron excitations in neutron-rich nu-clei between helium and oxygen. It is within this relatively small range of protons, two to eight, that we see the de-mise and creation of shell gaps [1], perhaps most notably remarked on by Talmi and Unna in 1960 with regards to the anomalous 1/2+ 11Be ground state [2], the existence of halos [3], and cluster structures [4]. It is clear that this re-gion offers a fertile ground for nuclear-structure studies and why it has been capturing the attention of the field over half a century.

Figure 1 shows the landscape in which these nuclei re-side as a function of proton and neutron number. The in-set is a compilation of single-particle neutron 0p1/2, 1s1/2, and 0d5/2 excitations relative the neutron threshold for the

Figure 1. A portion of the Segre chart for isotopes between helium and oxygen highlighting the isotopes for which there is information available on the energies of the neutron 0p1/2 (1/2–), 1s1/2 (1/2+), and 0d5/2 (5/2+) orbitals. These data are shown in the plots relative to neutron threshold. The dashed lines are merely to guide the eye. The origins of the data are summarized in Ref. [5].

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We have studied the 15Cðd; pÞ16C reaction in inversekinematics using a beam of short-lived (T1=2 ¼ 2:45 s)15C ions from the In-Flight facility at ATLAS at ArgonneNational Laboratory [20]. The beam was produced bybombarding a cryogenic D2 gas cell with a 100 p nA 14Cprimary beam with an energy of 133 MeV. The resulting15C beam, from the 14Cðd; pÞ15C reaction, had an energy of123 MeV, corresponding to a deuteron energy of 16.4 MeV,where the ðd; pÞ reaction is well understood. The intensityranged from 1 to 2 106 15C per second.

Protons from the 15Cðd; pÞ16C reaction were detectedwith the Helical Orbit Spectrometer (HELIOS) [21,22].HELIOS is a new device designed to study reactions ininverse kinematics. It consists of a large-bore, supercon-ducting solenoid with its axis aligned with the beam direc-tion. The magnetic field was 2.85 T, and a 110 g=cm2

deuterated polyethelyne [ðC2D4Þn] target was used. Protonsemitted at forward angles in the center-of-mass frame(lab > 90) were transported in the magnetic field anddetected with a position-sensitive silicon-detector arraysurrounding the beam axis upstream of the target. Thesilicon-detector array measured the protons’ energy, dis-tance z from the target, and flight time (equal to the cyclo-tron period Tcyc ¼ 2m=Bq). The recoiling 16C ions were

detected in coincidence with protons in an array of silicon-detector E E telescopes that covered 0.5–2.8 in thelaboratory. All events with a particle detected in the up-stream silicon array were recorded. The beam intensity wasmonitored by using a silicon detector placed at 0 behind amesh attenuator that reduced the beam flux by a factor of1000. The widely spaced holes in this attenuator made thismeasurement sensitive to the alignment and the shape ofthe beam spot, giving an estimated 30% systematic uncer-tainty for the absolute beam flux.

Figure 1(a) shows a spectrum of proton energy versusposition z from the 15Cðd; pÞ16C reaction for p-16C co-incidence events. The diagonal lines correspond to differ-ent excited states in 16C, and the excitation-energy spec-trum derived from these data is shown in Fig. 1(b). Theresolution is approximately 140 keV FWHM, determinedby a combination of intrinsic detector resolution, energyloss of the beam in the target, and the energy spread of thebeam from straggling in the production cell and the kine-matics of the production reaction. This resolution wasinsufficient to resolve the closely spaced 2þ2 =3

þ1 doublet

near EXð16CÞ ¼ 4 MeV, though the width of this peak is20% greater than those of the other three excitations.

Angular distributions for the three resolved transitions in16C and the unresolved 2þ2 =3

þ1 doublet are shown in Fig. 2.

The proton solid angle was defined by the geometry of theupstream silicon-detector array. The efficiency for thecoincident proton-16C-recoil detection was calculated byusing Monte Carlo simulations of particle transport inHELIOS as described in Ref. [21] with the measured fieldmap of the solenoid magnet. This efficiency was typically

80%, with an estimated 5% systematic uncertainty fromdetector misalignment. The absolute cross-section scalewas determined by using the 0 monitor detector as de-scribed above; the plotted uncertainties reflect only thecombined statistical uncertainties from the data andMonte Carlo simulations. The horizontal bars representthe angular range included in each data point. The angulardistributions for the ground and second-excited states showclear ‘ ¼ 0 character, confirming the tentative assignmentof J ¼ 0þ [23] for the second-excited state. The first-excited state and the presumed doublet near 4 MeV areconsistent with ‘ ¼ 2.Relative spectroscopic factors were obtained by compar-

ing the experimental cross sections with distorted-waveBorn approximation calculations done with the codePTOLEMY [24]. The curves in Fig. 2 represent calculations

done with four sets of optical-model parameters, and eachcurve was normalized to the experimental cross sections.The deduced spectroscopic factors are listed in Table I.Because of the uncertainty in the absolute cross sections,the results were normalized by requiring the sum of the 0þ

spectroscopic factors to add up to 2.0. The values obtainedwith each of the four parameters sets were averaged toobtain the results in Table I. The errors are dominated by

Z (mm)-400 -350 -300 -250 -200 -150 -100 -50 0

(M

eV)

PE

0

1

2

3

4

5

6

7

8

1+0.000; 0

1+1.766; 2

2+3.027; 0

2+3.986; 2

1+4.088; 3

(a)

C) (MeV)16 (XE

0 1 2 3 4 5 6

Co

un

ts/8

keV

0

50

100

150

200

250

(b)

1+0

1+2

2+0

1+/32

+2

FIG. 1 (color online). (a) Proton energy versus positionspectrum for the 15Cðd; pÞ16C reaction measured in inversekinematics with HELIOS. The target is at z ¼ 0 mm, and zincreases in the beam direction. The different groups correspondto different final states in 16C, as is indicated on the figure.(b) 16C excitation-energy spectrum.

PRL 105, 132501 (2010) P HY S I CA L R EV I EW LE T T E R Sweek ending

24 SEPTEMBER 2010

132501-2

our estimate of the uncertainties from the normalizationand the variations among the different parameter sets.While the 2þ2 and 3þ1 states could not be resolved, theirrelative contributions could be estimated from the widthsof the lower excitations (0.140 MeV FWHM) and thecentroid of the doublet peak, 4.077(.005) MeV. The esti-mated maximum possible contribution to this doublet fromthe 2þ2 state is 23%. This limit is used to derive the

maximum spectroscopic factor for the 2þ2 state and the

allowed range of values for the 3þ1 state consistent with that

limit as given in Table I.The excitation energies and spectroscopic factors ob-

tained from the LSF wave functions, and from shell-modelcalculations using the Warburton-Brown (WBP) interac-tion [25], also appear in Table I; this interaction was used inRef. [3] to reproduce the 2þ1 ! 0þ1 transition data for

several neutron-rich C isotopes. The present data for thethree lowest states in 16C are in good agreement with theWBP calculations. The estimated values for the 2þ2 and 3þ1levels are also consistent with shell-model predictions.The strength of both 0þ states in the ðd; pÞ reaction

indicates that each has a substantial ð1s1=2Þ2 component,

revealing strong mixing between the ð1s1=2Þ2 and ð0d5=2Þ2configurations. Also, while in 15C the 1=2þ groundstate may be identified with the 1s1=2 configuration, and

the 0.74 MeV 5=2þ state with the 0d5=2 one, in 16C the

ð1s1=2Þ2 configuration is dominant in the excited 0þ level.

This result agrees qualitatively with those of Ref. [11],although the predicted configuration mixing between thetwo 0þ states is less than what is observed. Other calcu-lations [6,10] give even larger mixing; in Ref. [10] theð1s1=2Þ2 is larger in the ground state, and in Ref. [6] the twoconfigurations carry approximately equal amplitudes. Theobserved mixing also conflicts with the conclusions ofRef. [2] that the ground state is dominantly ð1s1=2Þ2 and

that the first-excited level is largely a single-neutron(1s1=20d5=2) excitation. Our spectroscopic factor for the

2þ1 excitation agrees with the strongly configuration-mixed

wave functions of the LSF and WBP shell-model analyses.The measured spectroscopic factors, excitation energies,

and the energies of the 1s1=2 and 0d5=2 levels from 15C

yield matrix elements for the ðsdÞ2 residual interaction fortwo sd-shell neutrons coupled to J ¼ 0þ. By ignoringany contributions from the higher lying d3=2 orbital, the

wave functions may be written as j0þ1 i ¼ ð1s1=2Þ2 þð0d5=2Þ2 and j0þ2 i ¼ ð1s1=2Þ2 þ ð0d5=2Þ2, where

2 þ 2 ¼ 1. The two amplitudes and may then be

1

10

1

10

1

10

0 10 20 30 40 50 60

θc.m. (deg)

10

100

dσ/d

Ω (

mb/

sr)

(a)

(b)

(c)

(d)

0+

2+

0+

2+ /3

+

1

1

2

2 1

FIG. 2 (color online). Angular distributions for different tran-sitions in 15Cðd; pÞ16C. The curves represent distorted-waveBorn approximation calculations described in the text, usingoptical-model parameters from Refs. [27] (solid line), [28](dashed line), [29] (dot-dashed line), and [30] (dotted line).The cross-section uncertainties are statistical and do not reflectsystematic errors in the absolute scale, as described in the text.

TABLE I. Experimental and theoretical spectroscopic factors for states in 16C and 15C from the 15Cðd; pÞ16C and 14Cðd; pÞ15Creactions. The values labeled LSF and WBP correspond to those obtained from Ref. [18] and shell-model calculations with the WBPinteraction described in the text, respectively. Experimental uncertainties are in parentheses.

Nucleus State Eexp (MeV) ELSF (MeV) EWBP (MeV) Sexp SLSF SWBP

16C 0þ1 0.000 0.000 0.000 0.60(.13) 1.07 0.6016C 2þ1 1.766 2.354 2.385 0.52(.12) 0.63 0.5816C 0þ2 3.027 3.448 3.581 1.40(.31) 0.93 1.3416C 2þ2 3.986 4.052 4.814 0:34a 0.40 0.3316C 3þ1 4.088 5.857 0.82–1.06a 0.9215C 1=2þ 0.000 0.000 0.88(.18)b 0.9815C 5=2þ 0.740 0.380 0.69(.14)b 0.94

aLimiting values, assuming that at most 23% of the 2þ2 =3þ1 doublet yield can be attributed to the 2þ2 state.

bExperimental values for 14Cðd; pÞ15C from Ref. [16].


24 SEPTEMBER 2010

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(mb/

sr)

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0.000, 0+

1.766, 2+

3.027, 0+

3.986/4.088, 2+/3+

1

1

2

2 1

T. AL KALANEE et al. PHYSICAL REVIEW C 88, 034301 (2013)

TABLE I. Comparison between the results for 16O(d, p)17O in inverse kinematics and the adopted excitation energies (Ex) and previouslypublished spectroscopic factors (C2S) for the observed states. The uncertainties on the C2S for this work here are estimated to be of the orderof ±20% (see text).

J π Ex(keV) C2S This work

(Adopted values [37]) (Refs. [39,40]) Ex C2S

5/2+ 0 1.07 − 0.84 5 ± 2 0.71/2+ 870.73 ± 0.10 1.14 − 0.91 865 ± 9 1.43/2+ 5084.8 ± 0.9 1.2 5089 ± 1 0.87/2− 5697.26 ± 0.33 0.15 5692 ± 7 0.13

(DWBA) calculations were carried out using the code FRESCO

[42]. These employed the same global deuteron and neutronoptical model parameters for the distorting potentials inthe entrance and exit channels, respectively, as used in thed(8He,p) calculations described later. The binding potentialsfor the ⟨d|n + p⟩ and ⟨17O|16O + n⟩ overlaps also employedthe same parameters as for the d(8He,p) calculations, the16O + n values being similar to those of Refs. [39] and [40].

The four angular distributions obtained in the test mea-surement were well reproduced and the resulting angulardistribution for the first excited state is shown, as an example,in the insert of Fig. 2. This demonstrates the validity of ourexperimental approach. Note that a systematic 10% error wasassigned to the cross sections to take into account the effect ofthe uncertainties in: target thickness, detector efficiencies, andsolid angles.

Finally, the corresponding spectroscopic factors C2S werededuced by the normalization of the DWBA calculations to themeasured angular distributions. The error on the normalizationdue to statical and systematic errors are ∼ 10%, and theuncertainties arising from the choice of potential in the DWBAcalculations are estimated to be ∼ 20% [43]. Table I lists theC2S, which are in reasonable agreement with those taken fromthe literature.

IV. RESULTS

The analysis procedure for the d(8He, 9He)p measurementwere identical to the test experiment. The missing massspectrum is presented in Fig. 3. Since the experimentalresolutions obtained with the 320 and 550 µg/cm2 targetswere similar, we present here the sum of the spectra obtainedwith both targets. Note that here the rest mass m4 in Eq. (1)is defined as the sum of the 8He and free neutron rest masses.The calculated missing mass energy (denoted here as Er ) isthus defined from the neutron threshold of 9He.

Two peaks can clearly be seen: one approximately 200 keVabove threshold which we identified as g.s. and another around1.5 MeV. We also observe a shoulder around 3 MeV. Giventhat the broad structure around 6 MeV is related to the protonenergy cutoff and therefore not a real state, we concluded thatthe shoulder around 3 MeV is due to a second excited state.The presence and the position of the two excited states arecompatible with several previous reports [7,8,23,24,26].

Using these energies as a first estimate of the resonanceenergies of the states, a fit was performed employing “Voigt

profiles” [41]. The Lorentzian widths are energy dependent

= 0

√EER

[44]. The Gaussian component takes into account

the experimental energy resolution. The widths were deducedfrom the results for the 16O (d, p) test measurement at thecorresponding proton energy. Only the last structure around6 MeV was considered as a simple Gaussian function. Physicalbackgrounds associated with three-, five-, and seven-bodyphase spaces corresponding to 8He + d → 8He + p + n,6He + p + 3n, and 4He + p + 5n were taken into account.Finally, a linear background arising from reactions of thebeam with the carbon of the target and reactions in the plasticscintillator beam stopper was added. The results are listed inTable II.

We will discuss these results in detail in the next section,although we note here that the ground state of 9He is found at180 ± 85 keV above the neutron threshold. This is compatiblewith the other (d, p) reaction [26,27] studies. Both the positionand the rather small width of the first excited state are alsocompatible with several previous experiments [8,10,22,23,26].

[MeV]E-2 -1 0 1 2 3 4 5 6 7

Cou

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10

20

30

40

50

60

70

80

90

100

110

3-body 5-body7-body

-1 0 1 20

5

10

15

20

FIG. 3. (Color online) Experimental missing mass spectrum forthe (p,8 He)p reaction which is described with three states: groundstate (red), first excited (green), and second excited (blue) states.The solid gray line models the acceptance cutoff. The solid blackline denotes the sum of the three-, five-, and seven-body phasespace contributions, whose respective breakup energies are noted.The dotted line indicates the physical background due to reactions ofthe beam with the plastic scintillator. The thin solid line is the sumof all contributions. The region around the threshold is shown in theinset.

034301-4

STRUCTURE OF UNBOUND NEUTRON-RICH 9He . . . PHYSICAL REVIEW C 88, 034301 (2013)

TABLE II. Position and width of 9He states obtained in this work. Spectroscopic factors were deduced using DWBA calculations (see text),the uncertainties originate from the different Woods-Saxon n + 8He binding potentials used in the calculations.

Er (keV) (keV) C2S

p1/2 p3/2 d3/2 d5/2

180 ± 85 180 ± 1601235 ± 115 130+170

−130 0.02−0.05 0.01−0.03 0.006−0.01 0.005−0.0073420 ± 780 2900 ± 390 0.03−0.04 0.02−0.03

The second excited state is slightly higher in energy than theaverage of previous experimental observations [7,8,22,23,26,27]. This could be due to the uncertainty in the shape of thestructure located at 6 MeV, and a deviation of up to severalhundred keV might be possible. The error on its position hasbeen estimated by assuming different widths for the 6 MeVstructure.

The experimental angular distributions for these three statesare presented in Fig. 4. Error bars take into account uncer-tainties due to the subtraction of the different backgrounds.These angular distributions are compared with the results offull finite range DWBA calculations, similar to those carriedout for the d(16O,p)17O reaction. The normalization for eachenergy and transferred angular momentum L was obtainedwith a log-likelihood fit.

The entrance channel d+ 8He optical model potential wascalculated using the global parameters of Daehnick et al. [45]and the exit channel p+ 9He potentials employed the sys-tematics of Koning and Delaroche [46]. The deuteron internalwave function, including the small D-state component, wascalculated using the Reid soft-core interaction [47] as theneutron-proton binding potential. We used the weak bindingenergy approximation (WBEA) where the 9He internal wavefunctions were calculated by binding the neutron to the 8Hecore with a standard Woods-Saxon potential with reducedradius r0 = 1.25 fm, and diffusivity a0 = 0.65 fm, the well

10-2

10-1

100

101

L = 0L = 1L = 2

0 5 10 15 20 25θc.m. (deg)

10-2

10-1

100

dσ/d

Ω (

mb/

sr)

0 5 10 15 20 25 30

)ABCC( .S.G)ABWD( .S.G

Er≈ 1.3 MeV (DWBA) Er≈ 3.4 MeV(DWBA)

(a) (b)

(c) (d)

FIG. 4. (Color online) Angular distributions for the ground state(a) and the two first excited states of 9He [(c) and (d)] compared toL = 0, 1, 2 (respectively red, green, and blue) DWBA calculations.(b) Angular distribution of the g.s. compared to CCBA calculations.

depths being adjusted to give a binding energy of 0.0001 MeVin all cases. Note that test calculations were performed withdifferent sets of (r0, a0) values with ranges of 1.25−1.50and 0.65−0.75, respectively, without noticeable effect on ourconclusions.

We chose to employ the WBEA to calculate the n+ 8Heoverlaps for two reasons: firstly, when the unbound neutron isin a relative s state with respect to the 8He core this resultsin a virtual state rather than a conventional resonance, due tothe absence of either a Coulomb or a centrifugal barrier inthe “binding” potential, thus rendering a more sophisticatedmodeling of the form factor for such states problematic.Secondly, while states with L > 0 may be modeled in FRESCO

as true resonances with finite widths, in practice it is oftendifficult to achieve consistent results using this procedure. Wetherefore chose to use the WBEA to calculate all the n+ 8Heoverlaps for the sake of consistency.

The procedure adopted was to perform calculationsassuming angular momentum L = 0, 1, and 2 for the neutronrelative to the 8He core for all three states, and to comparethe resulting angular distributions to the experimental pointsto deduce the best-fit values of L, thus providing clues asto the spin-parities of the respective states in 9He, as wellas spectroscopic factors. All calculations included the fullcomplex remnant term and thus yielded identical results foreither post- or prior-form DWBA.

Since the incident 8He energy is relatively high, theinfluence of deuteron breakup effects could be important. Totest this we performed a coupled-channels Born approximation(CCBA) calculation for stripping to the ground state of 9He.The CCBA calculation was similar in all respects to the DWBAcalculations with the exception that the entrance channeloptical potential was replaced by a continuum discretizedcoupled channels (CDCC) calculation similar to that describedin Ref. [48]. The necessary diagonal and transition potentialswere calculated using Watanabe-type folding based on theglobal nucleon optical potential of Ref. [46] and the deuteroninternal wave function of Ref. [47]. As Fig. 4(b) shows, theshapes of the L = 0, 1, 2 angular distributions are almostidentical to those for the corresponding DWBA calculations,suggesting that the influence of deuteron breakup on the shapeof the angular distribution is small in this case, justifying ouruse of the DWBA to infer spins and parities.

V. DISCUSSION

We present the 9He states obtained in the present worktogether with all published results in Fig. 5. This confirms

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Column 57Column 58WS fitExp dataColumn 10

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WS calculationdata tensor force

nuclei highlighted in the Segrè chart. These data, with the exception of the N = 11 and 13 isotones, were the subject of a recent study exploring the role of finite binding on shell structure changes [5]. Most striking is the behavior of the 1/2+ excitations (1s1/2) compared to both the 1/2– (0p1/2) and 5/2+ (0d5/2) trends, with the first showing a tendency to linger below the neutron threshold, changing in energy by only ~4 MeV, while at the same time the 5/2+ state changes by ~8 MeV. It is on this unique feature of neutron s states that we will focus, complementing the recent Nuclear Physics News article on physics beyond the neutron drip-line [6].

Experimental DataThe neutron energies, En, relative to threshold are de-

fined as the centroid of the single-particle neutron excita-tion energy minus the one-neutron separation energy, En = Eexc – Sn, and as such, centroids above threshold have positive values. The data are shown in Figure 1 for the 1/2– (black), 1/2+ (red), and 5/2+ (blue) states for nuclei from helium to oxygen (Z = 2–8) having N = 5, 7, 8, 9, and 10, each of which have only one neutron in the 1s0d shell. We show additional data for N = 11 and 13 (open symbols), which though they behave in a remarkably similar manner, cannot be put on equal footing with the data deduced from N < 11 due to the additional neutrons in the 1s0d shell.

For many of the cases shown in Figure 1, the determina-tion of the neutron excitation-energy centroid was straight-forward from neutron transfer data, an ideal probe of sin-gle-particle states, with relative spectroscopic-factor and statistical weightings. In total, there are 19 sets of 1s1/2 and 0d5/2 data, far more than the limited information available on the 0p1/2 states. Details of their origins are given in Ref. [5]. Similar compilations have been made over the years, perhaps with the most recent detailed one being in 1995 [7], discussing the trends in the context of Coulomb displace-ment energies. Since then, a great deal more data has been gathered. We highlight two recent cases here.

9He Neutron Energy Centroids9He is one of the most exotic nuclei observed possessing

a neutron-to-proton ratio of 3.5 and having no bound states. The single-neutron centroids of interest were extracted from a recent neutron transfer (d, p) measurement. It was carried out a GANIL with a 8He beam in inverse kinematics and us-ing the MUST2 detector setup at the SPIRAL ISOL facility [8]. The experimentally determined missing-mass spectrum and angular distributions from this work are shown in Fig-ure 2. The authors have determined that the ground state is

an unbound 1/2+ state with missing-mass energy 0.18 MeV, hence Sn = –0.18 MeV, and the lowest-lying resonance at 1.24 MeV has ℓ = 1 character making it the p1/2 state. While tentative in the work of Ref. [8], combined with previous measurements (summarized in Figure 5 of Ref. [8]), the 5/2+ state at 3.24 MeV was adopted as the d5/2 centroid.

N = 10 CentroidsCentroid information for the 1s1/2 and 0d5/2 states was

available for two nuclei with N = 10, 16C and 18O, based on single-neutron transfer data and the fact that the 3+ states in these nuclei are of a pure sd configuration while the 4+ states have pure d2 configurations. Data for the for-mer was acquired recently in a measurement of the 15C(d,

Figure 2. (Top) Missing-mass spectrum for 9He as mea-sured by the (d,p) reaction on 8He [8]. (Bottom) Angular distributions corresponding to the observed strength, sup-porting the assignments made. These data were used for the s and d states at 9He, the only Z = 2 data point available in this study. See Ref. [8] for further details.

feature article


p) reaction carried out at Argonne National Laboratory in inverse kinematics using the ATLAS accelerator, with 15C produced via the in-flight technique, and the HELIOS spectrometer [9, 10]. Figure 3 shows the angular distribu-

tions for the states populated in that work [11]. The 18O data come from normal kinematic data, in particular that of Ref. [12]. However, because there are two neutrons in the sd shell, the interaction energy between them must be removed to extract the single-neutron energy comparable to the odd-N data. A model independent method for apply-ing this correction is to deduce the interaction from one set of N = 10 centroids and apply the correction to the other resulting in a single N = 10 data point. The interaction energies (two-body matrix elements) extracted for 18O in Ref. [12] were therefore applied to the centroid energies of 16C. Combining the corrected energies, 3.49(20) MeV for the 3+ state and 4.49(20) MeV for the 4+ state (from the (t,p) reaction data of Ref. [13]), with an Sn value of 4.25 MeV [14] results in the data for the 1s1/2 and 0d5/2 energies of Figure 1 for 16C.

The Role of Finite BindingA simple question to ask is to what extent is the sepa-

ration of the s1/2 and d5/2 orbitals driven by the effects of finite binding? The behavior of states in a finite potential had been studied before by many; for instance, Bohr and Mottelson considered the behavior of neutron orbits in a static nuclear potential for heavier systems [15], remarking on the s states, which approach the threshold much more slowly than other states. In this vain, the role of this prox-imity to the neutron threshold was explored by explicitly comparing the data to the equivalent states calculated in a Woods-Saxon potential with standard parameters (e.g., r0 = 1.25 fm, a = 0.63 fm, VSO = 4.03 MeV) [5]. For each individual isotope the depth of the Woods-Saxon potential was varied until the calculated single-neutron energy re-produced the binding energy of the experimentally known 0d5/2 orbital. The spin-orbit parameters were fixed such that they reproduced the 1/2+ - 5/2+ energy splitting in 17O. The energy of the 1s1/2 orbital was then deduced within the same potential. The experimental energy difference be-tween the two states, ΔEexp, is shown in Figure 4a, with the red line showing a fit that was derived from the computed values for only those nuclei with N less than 10. One im-mediately notices that the calculated difference describes remarkably well the gross trend between experimental en-ergy differences as a function of neutron binding, even for the N = 11 and 13 isotones. This is a strong suggestion that finite binding plays a dominant role in the trends of these states.

To explore this further, one can subtract out the effects that appear to be due to the finite binding of the s state. Figure 4b shows this subtraction of the experimental dif-






þ1 doublet









Z (mm)-400 -350 -300 -250 -200 -150 -100 -50 0

(M

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24 SEPTEMBER 2010

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0.000, 0+

1.766, 2+

3.027, 0+

3.986/4.088, 2+/3+

1

1

2

2 1

Figure 3. The top plot shows the characteristic proton en-ergy versus target-detection distance as recorded using the HELIOS spectrometer [9,10] at ATLAS. The lines corre-spond to states populated in the 15C(d,p) reaction [11]. The corresponding angular distributions are shown below. The extraction of the s- and d-state centroid for this N = 10 sys-tem is discussed in the text.

feature article







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24 SEPTEMBER 2010

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T. AL KALANEE et al. PHYSICAL REVIEW C 88, 034301 (2013)

TABLE I. Comparison between the results for 16O(d, p)17O in inverse kinematics and the adopted excitation energies (Ex) and previouslypublished spectroscopic factors (C2S) for the observed states. The uncertainties on the C2S for this work here are estimated to be of the orderof ±20% (see text).

J π Ex(keV) C2S This work

(Adopted values [37]) (Refs. [39,40]) Ex C2S

5/2+ 0 1.07 − 0.84 5 ± 2 0.71/2+ 870.73 ± 0.10 1.14 − 0.91 865 ± 9 1.43/2+ 5084.8 ± 0.9 1.2 5089 ± 1 0.87/2− 5697.26 ± 0.33 0.15 5692 ± 7 0.13

(DWBA) calculations were carried out using the code FRESCO

[42]. These employed the same global deuteron and neutronoptical model parameters for the distorting potentials inthe entrance and exit channels, respectively, as used in thed(8He,p) calculations described later. The binding potentialsfor the ⟨d|n + p⟩ and ⟨17O|16O + n⟩ overlaps also employedthe same parameters as for the d(8He,p) calculations, the16O + n values being similar to those of Refs. [39] and [40].

The four angular distributions obtained in the test mea-surement were well reproduced and the resulting angulardistribution for the first excited state is shown, as an example,in the insert of Fig. 2. This demonstrates the validity of ourexperimental approach. Note that a systematic 10% error wasassigned to the cross sections to take into account the effect ofthe uncertainties in: target thickness, detector efficiencies, andsolid angles.

Finally, the corresponding spectroscopic factors C2S werededuced by the normalization of the DWBA calculations to themeasured angular distributions. The error on the normalizationdue to statical and systematic errors are ∼ 10%, and theuncertainties arising from the choice of potential in the DWBAcalculations are estimated to be ∼ 20% [43]. Table I lists theC2S, which are in reasonable agreement with those taken fromthe literature.

IV. RESULTS

The analysis procedure for the d(8He, 9He)p measurementwere identical to the test experiment. The missing massspectrum is presented in Fig. 3. Since the experimentalresolutions obtained with the 320 and 550 µg/cm2 targetswere similar, we present here the sum of the spectra obtainedwith both targets. Note that here the rest mass m4 in Eq. (1)is defined as the sum of the 8He and free neutron rest masses.The calculated missing mass energy (denoted here as Er ) isthus defined from the neutron threshold of 9He.

Two peaks can clearly be seen: one approximately 200 keVabove threshold which we identified as g.s. and another around1.5 MeV. We also observe a shoulder around 3 MeV. Giventhat the broad structure around 6 MeV is related to the protonenergy cutoff and therefore not a real state, we concluded thatthe shoulder around 3 MeV is due to a second excited state.The presence and the position of the two excited states arecompatible with several previous reports [7,8,23,24,26].

Using these energies as a first estimate of the resonanceenergies of the states, a fit was performed employing “Voigt

profiles” [41]. The Lorentzian widths are energy dependent

= 0

√EER

[44]. The Gaussian component takes into account

the experimental energy resolution. The widths were deducedfrom the results for the 16O (d, p) test measurement at thecorresponding proton energy. Only the last structure around6 MeV was considered as a simple Gaussian function. Physicalbackgrounds associated with three-, five-, and seven-bodyphase spaces corresponding to 8He + d → 8He + p + n,6He + p + 3n, and 4He + p + 5n were taken into account.Finally, a linear background arising from reactions of thebeam with the carbon of the target and reactions in the plasticscintillator beam stopper was added. The results are listed inTable II.

We will discuss these results in detail in the next section,although we note here that the ground state of 9He is found at180 ± 85 keV above the neutron threshold. This is compatiblewith the other (d, p) reaction [26,27] studies. Both the positionand the rather small width of the first excited state are alsocompatible with several previous experiments [8,10,22,23,26].

[MeV]E-2 -1 0 1 2 3 4 5 6 7

Cou

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220

keV

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10

20

30

40

50

60

70

80

90

100

110

3-body 5-body7-body

-1 0 1 20

5

10

15

20

FIG. 3. (Color online) Experimental missing mass spectrum forthe (p,8 He)p reaction which is described with three states: groundstate (red), first excited (green), and second excited (blue) states.The solid gray line models the acceptance cutoff. The solid blackline denotes the sum of the three-, five-, and seven-body phasespace contributions, whose respective breakup energies are noted.The dotted line indicates the physical background due to reactions ofthe beam with the plastic scintillator. The thin solid line is the sumof all contributions. The region around the threshold is shown in theinset.

034301-4

STRUCTURE OF UNBOUND NEUTRON-RICH 9He . . . PHYSICAL REVIEW C 88, 034301 (2013)

TABLE II. Position and width of 9He states obtained in this work. Spectroscopic factors were deduced using DWBA calculations (see text),the uncertainties originate from the different Woods-Saxon n + 8He binding potentials used in the calculations.

Er (keV) (keV) C2S

p1/2 p3/2 d3/2 d5/2

180 ± 85 180 ± 1601235 ± 115 130+170

−130 0.02−0.05 0.01−0.03 0.006−0.01 0.005−0.0073420 ± 780 2900 ± 390 0.03−0.04 0.02−0.03

The second excited state is slightly higher in energy than theaverage of previous experimental observations [7,8,22,23,26,27]. This could be due to the uncertainty in the shape of thestructure located at 6 MeV, and a deviation of up to severalhundred keV might be possible. The error on its position hasbeen estimated by assuming different widths for the 6 MeVstructure.

The experimental angular distributions for these three statesare presented in Fig. 4. Error bars take into account uncer-tainties due to the subtraction of the different backgrounds.These angular distributions are compared with the results offull finite range DWBA calculations, similar to those carriedout for the d(16O,p)17O reaction. The normalization for eachenergy and transferred angular momentum L was obtainedwith a log-likelihood fit.

The entrance channel d+ 8He optical model potential wascalculated using the global parameters of Daehnick et al. [45]and the exit channel p+ 9He potentials employed the sys-tematics of Koning and Delaroche [46]. The deuteron internalwave function, including the small D-state component, wascalculated using the Reid soft-core interaction [47] as theneutron-proton binding potential. We used the weak bindingenergy approximation (WBEA) where the 9He internal wavefunctions were calculated by binding the neutron to the 8Hecore with a standard Woods-Saxon potential with reducedradius r0 = 1.25 fm, and diffusivity a0 = 0.65 fm, the well

10-2

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101

L = 0L = 1L = 2

0 5 10 15 20 25θc.m. (deg)

10-2

10-1

100

dσ/d

Ω (

mb/

sr)

0 5 10 15 20 25 30

)ABCC( .S.G)ABWD( .S.G

Er≈ 1.3 MeV (DWBA) Er≈ 3.4 MeV(DWBA)

(a) (b)

(c) (d)

FIG. 4. (Color online) Angular distributions for the ground state(a) and the two first excited states of 9He [(c) and (d)] compared toL = 0, 1, 2 (respectively red, green, and blue) DWBA calculations.(b) Angular distribution of the g.s. compared to CCBA calculations.

depths being adjusted to give a binding energy of 0.0001 MeVin all cases. Note that test calculations were performed withdifferent sets of (r0, a0) values with ranges of 1.25−1.50and 0.65−0.75, respectively, without noticeable effect on ourconclusions.

We chose to employ the WBEA to calculate the n+ 8Heoverlaps for two reasons: firstly, when the unbound neutron isin a relative s state with respect to the 8He core this resultsin a virtual state rather than a conventional resonance, due tothe absence of either a Coulomb or a centrifugal barrier inthe “binding” potential, thus rendering a more sophisticatedmodeling of the form factor for such states problematic.Secondly, while states with L > 0 may be modeled in FRESCO

as true resonances with finite widths, in practice it is oftendifficult to achieve consistent results using this procedure. Wetherefore chose to use the WBEA to calculate all the n+ 8Heoverlaps for the sake of consistency.

The procedure adopted was to perform calculationsassuming angular momentum L = 0, 1, and 2 for the neutronrelative to the 8He core for all three states, and to comparethe resulting angular distributions to the experimental pointsto deduce the best-fit values of L, thus providing clues asto the spin-parities of the respective states in 9He, as wellas spectroscopic factors. All calculations included the fullcomplex remnant term and thus yielded identical results foreither post- or prior-form DWBA.

Since the incident 8He energy is relatively high, theinfluence of deuteron breakup effects could be important. Totest this we performed a coupled-channels Born approximation(CCBA) calculation for stripping to the ground state of 9He.The CCBA calculation was similar in all respects to the DWBAcalculations with the exception that the entrance channeloptical potential was replaced by a continuum discretizedcoupled channels (CDCC) calculation similar to that describedin Ref. [48]. The necessary diagonal and transition potentialswere calculated using Watanabe-type folding based on theglobal nucleon optical potential of Ref. [46] and the deuteroninternal wave function of Ref. [47]. As Fig. 4(b) shows, theshapes of the L = 0, 1, 2 angular distributions are almostidentical to those for the corresponding DWBA calculations,suggesting that the influence of deuteron breakup on the shapeof the angular distribution is small in this case, justifying ouruse of the DWBA to infer spins and parities.

V. DISCUSSION

We present the 9He states obtained in the present worktogether with all published results in Fig. 5. This confirms

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ferences from the calculated differences. Note that 17O lies at zero due to the spin-orbit parameters chosen and the N = 11 and 13 data points lie systematically higher, by only a small amount, as a result of the extra neutrons in the 1s0d shell. Naively, this difference of differences must highlight effects not related to finite binding. One sees that the remaining deviations from zero are on average an order of magnitude smaller (~0.5 MeV) than the experimental changes (over 4 MeV) over the sampled range. These re-maining contributions are of the same direction and mag-nitude as those expected from the monopole component of the tensor force [16]—the shaded region in Figure 4b highlights this.

Impact of s State Behavior

Single-Neutron OrderingThe behavior of the sd neutron orbitals in the light

neutron-rich nuclei presented in Figure 1 can be reliably

described by the Woods-Saxon potential calculations as shown in Figure 4, with the ordering (s orbital moving be-low the d orbital) implicit in the sign change of ΔEexp. The binding energy effects account for the over 4 MeV change in the differences between the s and d orbitals across Z = 2–8, while the action of the tensor force, for example, only accounts for a small fraction of the total energy change. Shell-model calculations have been remarkably successful in describing these features also, but one notes that the ef-fects of the binding energy will be inherently included in the effective interactions used. Other approaches may also be successful in describing these data; for example, those that treat deformation explicitly, or include coupling to the continuum.

This near-threshold effect must play a role in the reduc-tion of the traditional N = 8 shell gap being that the neutron s states move below the p1/2 orbital at, for example, 11Be. In this case, however, the monopole part of the tensor in-teraction is expected to be larger, about the same order of magnitude as the binding energy effects.

Figure 4. (a) The difference in energy between the 1/2+ and 5/2+ states (red), ΔEexp, as a function of the energy of the 5/2+ relative to threshold as determined from the experimental data. The curve state is a fit to calculations of the energy differ-ence using Woods-Saxon potentials. The general trend reproduces that of the experimental data. The N = 11 and 13 data points were not included in the calculations, although the experimental data are added here. (b) The difference between the experimental and calculated differences as a means of showing what is not accounted for by the effects of finite bind-ing. The orange shaded region, calculated using different interactions, shows the possible contribution of the tensor force on the d orbital.

feature article


Neutron Halo NucleiThe lingering of the neutron s state at the neutron

threshold is the same phenomenon responsible for the halo states in weakly bound light systems such as in 11Li and 11Be [3]. Two other neutron-rich regions of the chart, where the higher lying s orbitals may appear sufficiently close to threshold, are just outside N = 50 around 78Ni and outside N = 126 below 208Pb. As shown in Figure 5, Woods-Saxon potential calculations qualitatively describe similar features as those present in the quite limited ex-perimental data sets around 78Ni, showing hints that the 2s1/2 orbital may “dip” below the 1d5/2 orbital close to the threshold. The large uncertainty in the experimental one-neutron separation energy in 79Ni lends itself to the possibility of a neutron halo in this nucleus. In addition, nuclei with smaller Z, such as the neutron-rich Ca isotopes highlighted in recent theoretical work [17], may also form halos. Far more exploratory work is needed to understand how well a neutron-halo is defined in such large systems as those around N = 126; however, the strong influence of finite binding on the neutron s state in the weakly bound systems is clear.

SummaryA detailed study of data on the 1s1/2 and 0d5/2 states in

light neutron-rich nuclei, greatly aided by recent studies with radioactive ion beams at facilities around the world, emphasizes a notable trend in the separation of these or-bitals. Over a relatively small range of neutron excess, be-tween isotopes of He and O, the states diverge by over 4 MeV. It has been shown that a significant fraction of this deviation can be attributed to the behavior of the neutron s state near threshold, with the action of the tensor force playing only a small role. While the former has been dis-cussed before, an explicit comparison to the experimental data, much of which is new, is revealing. It is tempting to surmise that this effect plays a significant role in the break-down of the N = 8 shell gap, but matters are complicated somewhat by the overlap between the p1/2 neutrons and p-shell protons. Such behavior also leads one to speculate the existence of halo states in heavier systems, with the 78Ni region being most tantalizing.

Detailed spectroscopic information, such as that pre-sented in the measurements discussed above, allows one to elucidate specific aspects of nuclear structure that may otherwise be masked. It is highly likely that the wealth of data already available in this region will be added to sig-nificantly in the near future, as well as the first glimpses of

data on heavier nuclei exhibiting the identified threshold characteristics.

AcknowledgmentsThis material is based on work supported by the U.S.

Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.

References 1. R. V. F. Janssens, Nature 459 (2009) 1069. 2. I. Talmi and I. Unna, Phys. Rev. Lett. 4 (1960) 469. 3. I. Tanihata et al., Prog. Part. Nucl. Phys. 68 (2013) 215. 4. M. Freer, Nature 487 (2012) 309. 5. C. R. Hoffman et al., Phys. Rev. C 89 (2014) 061305. 6. T. Aumann and H. Simon, Nucl. Phys. News 24 (2014) 5. 7. H. T. Fortune, Phys. Rev. C 52 (1995) 2261.

28 32 36 40 44

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1/2+

Figure 5. (Left) The energy of the 1/2+ and 5/2+ orbitals outside N = 50. The solid data points are from single-nu-cleon transfer on the stable isotones [18], while the empty data points are from transfer with radioactive ion beams [19] or other probes. The grey data point represents the binding energy of 79Ni [14]. (Right) For illustrative pur-poses we show Woods-Saxon calculations of the energy of the same states as a function of the radius of the potential, using the prescription described in the text (except fixing the spin-orbit parameters to 91Zr).

feature article


8. T. Al Kalanee et al., Phys. Rev. C 88 (2013) 034301. 9. J. C. Lighthall et al., Nucl. Instrum. Methods A622 (2010) 97.10. B. B. Back and A. H. Wuosmaa, Nucl. Phys. News 23 (2013)

21.11. A. H. Wuosmaa et al., Phys. Rev. Lett. 105 (2010) 132501.12. T. K. Li et al., Phys. Rev. C 13 (1976) 55.13. H. T. Fortune et al., Phys. Lett. B70 (1977) 408 and D. P.

Balamuth et al., Nucl. Phys. A290 (1977) 65.14. G. Audi et al., Chin. Phys. C 36 (2012) 1287.15. A. Bohr and B. R. Mottelson, Nuclear Structure (W. A. Benja-

min, Inc., New York, 1969), Vol. 1, 240.16. T. Otsuka et al., Phys. Rev. Lett. 95 (2005) 232502.17. G. Hagen et al., Phys. Rev. Lett. 111 (2013) 132501.18. D. K. Sharp et al., Phys. Rev. C 87 (2013) 014312.19. J. S. Thomas et al., Phys. Rev. C 76 (2007) 044302.

Calem R. Hoffman

Benjamin P. Kay

Filler?

facilities and methods


Light Exotic Nuclei at JINR: ACCULINNA and ACCULINNA-2 FacilitiesJoint Institute for Nuclear Research (JINR)

JINR is an international scientific centre covering a broad range of ac-tivities in the nuclear, particle, theo-retical physics, and biophysics. It is located in Dubna, 130 km to the north of Moscow. The JINR Laboratory Por-trait can be found in a recent Nuclear Physics News article [1].

Radioactive Ion Beam Studies at FLNR

Flerov Laboratory of Nuclear Re-actions (FLNR) is a JINR subdivision, most famous for the super-heavy ele-ment program. Through the last few years new elements with atomic num-bers Z = 114–118 were discovered here in the study performed jointly with the three U.S. research centers (Lawrence Livermore National Labo-ratory, Oak Ridge National Labora-tory, and Vanderbilt University). Two of these new elements are recog-nized officially by IUPAC and have got their names: 114Flerovium and 115Livermorium. FLNR possesses two high-current cyclotrons: the U-400 (3–30 A MeV heavy-ion beams) used mainly for the heavy element study and U-400M (higher energy, 6–60 A MeV beams). The latter machine has broader research objectives includ-ing the radioactive ion beam (RIB) program implemented at the ACCU-LINNA fragment separator.

ACCULINNA

Facility LayoutThe ACCULINNA fragment sepa-

rator (http://aculina.jinr.ru) was ini-tially aimed for the study of light neu-

tron-rich RIBs. It has a compact and comparatively simplistic design with a 14 m long achromatic stage, contain-ing a wedge degrader in its dispersive focus, and a 8.5 m ToF stage provid-ing particle-by-particle identification of the RIB (Figure 1). Finally, the beam is transferred into the low-back-ground target hall (Figure 2). Despite its modest size the facility gains on the high-intensity primary beams of the U-400M cyclotron. The obtained RIB energies of 20–40 A MeV fit well direct reaction studies. Lower-energy and stopped beam experiments are feasible as well. The ACCULINNA beam line hosts installations used by the JINR Laboratory of Radiation Bi-ology and by the material radiation studies carried out for the Russian Federal Agency RosCosmos.

Available InstrumentsThe ACCULINNA group develops

or participates in the development of

a broad range of detector arrays re-quired for the low-energy nuclear-re-action studies (Figure 3).

Various types of high-granularity detector telescopes are manufactured and used depending on the kinematical conditions of experiment. Previously our group used a subset of the neutron detector array DEMON. Now an array of 32 stilbene scintillation detectors (each crystal being 5 cm thick and 8 cm in diameter) is developed and cur-rently available. The GADAST target-area γ-detector array consisting of 64 CsI(Tl) and 16 LaBr3(Cr) modules was built by the ACCULINNA group within the program of infrastructure upgrade for the FRS facility at GSI. The GADAST array can also be avail-able for ACCULINNA experiments.

The ACCULINNA group partici-pates in the development OTPC tech-nology. The idea of time-projection chamber with optical readout was pro-moted by the group of Warsaw Uni-

Figure 1. Layouts of the ACCULINNA and constructed ACCULINNA-2 facilities in the U-400M cyclotron hall.



versity led by Professor M. Pfützner. It provided in the recent years very important results on rare decay modes, which include the first measurements of momentum distributions inherent

to the 2p radioactive decay and dis-covery of the beta-delayed 3p emis-sion (in 45Fe and 31Ar). The camera R&D and tests are partly conducted in Dubna and the observation of rare de-

cays for light exotic nuclei 8He, 14Be, 27S were performed at ACCULINNA.

The ACCULINNA group has tra-dition of using cryogenic gas/liquid targets for reaction studies. Most in-

Figure 2. View of ACCULINNA low-background target hall with (from left to right) reaction chamber, DAQ, and neutron array DEMON. People in protective suits prepare the tritium gas system to operation. Cryogenic tritium cell with double-shielding.



teresting is a massive instrumentation connected with the cryogenic tritium target (Figure 2). Tritium target opens additional opportunities for achieving extreme neutron-rich nuclear systems and detailed studies of their excita-tions (also discussed below). The use of gas/liquid targets allows low-back-ground experiments with low-intensity (≥103 pps) secondary beams. Techni-cally, the use of pure (not chemically confined) tritium is a great challenge and subject of serious security regula-tions. The special conditions of work with tritium, according to the national security standards, allow the use of “free” (gas, liquid, or solid) tritium for research only in a few laboratories in the world. One of few such laborato-ries in Russia is the All-Russian Re-search Institute of Experimental Phys-ics (Sarov). The technical base for the gas/liquid tritium target operation was successfully developed in JINR since the mid 1990s in close collaboration and with a leading role of colleagues

from Sarov. This collaboration is a nice example of the conversion of military technology for the benefit of fundamental science.

Scientific IdeologyThe current period in the RIB re-

search is marked with massive up-grade and construction of new fa-cilities all over the world. The “new generation” RIB factory at RIKEN is operating for several years and such upgrades as FAIR, FRIB, and SPI-RAL-2 are actively promoted and will define the tomorrow of the research in this field. What should be the place of the minor facilities? Our vision is that important opportunities and com-petitive scientific programs can be provided by minor facilities if one fo-cuses on a narrow research field.

For the ACCULINNA group such a field of choice is associated with direct reactions with exotic beams leading to the population of particle-unstable states in the nuclear systems

located near and beyond the drip-lines. The relatively low-energy RIBs (~20–40 MeV/nucleon) are suitable for the production of exotic nuclei in few-nucleon transfer reactions, which are well-understood due to their clear mechanism. Compared to the frag-mentation and knockout reactions oc-curring at higher energies (~70–500 A MeV), which become increasingly popular at the modern RIB factories, the “old school” transfer-reaction ap-proach supplies additional prospects. Figure 4 gives some qualitative illus-tration that the initial state (and con-sequently the reaction mechanism) contributions should be different in the “high-energy” and “low-energy” approaches.

The study of few-body decays makes a special field of interest for our group. Few-body dynamics is wide-spread in the drip-line systems due to paring interaction. In certain condi-tions it gives rise to exclusive quan-tum mechanical phenomena. Among

Figure 3. Some instrumentation available at ACCULINNA. Opened reaction chamber view, charged particle telescopes, stilbene neutron detector array, GADAST γ-detector array, and Warsaw OTPC.



these, the most known are the Borro-mean type of three-body halo systems and two-proton radioactivity. Notions of such a phenomenon as two-neutron and even four-neutron radioactivity were recently promoted and some two-neutron emitters beyond the neu-tron drip line are now investigated at the leading RIB facilities. Compared with the two-body decays, where in-ternal properties of the decaying sys-tem come to light only via the reso-nance position and width, the decays with emission of few particles also provide access to information encoded in the correlations among the decay products. This field is not well investi-gated now and opens broad opportuni-ties for pioneering research.

As a special approach, not broadly developed elsewhere, we promote correlation studies in continuum as a spectroscopic tool. For example, the angular distributions of the products in the direct reactions are a standard basis for spin-parity identification. Less widespread but very powerful alternative method here relies on the usage of induced by the transfer re-action mechanism strong alignment

of products (particle-unstable states). The powerful methods developed by our group for the three-body decays of aligned states were so far not applied elsewhere.

Recent ExperimentsBelow we give examples of some

key experiments of the last decade underlying opportunities connected with correlation studies of continuum decay of exotic nuclei. These results are based on the following physical peculiarity of the transfer reactions: the single-step reaction mechanism imposes strong restrictions on the an-gular momentum transfer. Namely, only zero projection of the angular momentum can be transferred in the frame associated with the transferred momentum. As a result, for the total momenta J > 1/2 strongly aligned states are typically populated. The strong alignment of the whole system produces expressed angular correla-tion pattern for the emitted fragments in the transferred momentum frame.

The 5H produced in the 3H(t, p) re-action [2]. This was the pilot experi-ment aimed for the three-body decay

Figure 4. Population of “superheavy” He isotopes in high-energy reactions by particle (cluster) removal reactions (red) and at lower energies by the transfer reactions (blue).

of broad aligned states. The feature to be emphasized here is the opportu-nity to disentangle the contribution of very poorly populated 5H g.s. from the strong background of the higher-lying states, where it is otherwise com-pletely lost (Figure 5). The most no-table examples of further application of this technique include spin-parity identification in the spectra of 9He [3] and 10He [4] produced in the (d, p) and (t, p) reactions. For 10He this allowed us to demonstrate that shell structure breakdown, known so far for 12Be, also extends further in the N = 8 iso-tone (Figure 6).

The mentioned examples portray the results obtained exclusively uti-lizing “technologies” available at our group. However, the research in-terests are not limited by these and close cases. In recent years we have obtained a number of results on struc-ture, decay dynamics, and rare decay modes of relatively light nuclei from 4H to 26S using variety of methods like transfer, charge-exchange, and QFS reactions (http://aculina.jinr.ru/ publications.php).

Collaboration

Local ExperimentsUsually ACCULINNA has around

2 months of beam time per year and hosts on average 1–2 guest experi-ments. These are mainly experiments performed by other Flerov lab groups and groups from JINR member states. It is expected that the new facility AC-CULINNA-2 will operate as “user fa-cility” with easy access for users from outside.

External Experimental ProgramsThe members of our group are in-

volved in experimental works on the RIB study at GSI, GANIL, RIKEN, and MSU.



There is a broad program of col-laboration with the FRS group of GSI. The ACCULINNA group par-ticipated in works on the hardware development for the FRS and future SuperFRS facilities. These activities are now concentrated on the EXPERT setup initiative for SuperFRS@FAIR (http://aculina.jinr.ru/pdf/topic8_ expert.pdf). The FAIR-Russia Re-search Centre foundation supports now a team of young scientists work-ing on the FAIR-related projects within our group.

ACCULINNA-2 Project StatusThe research program of the AC-

CULINNA facility was recognized as successful and prospective. To en-force this program a major upgrade of the facility was initiated in 2008. This resulted in the construction of a new fragment separator, ACCU-LINNA-2. This facility should deliver the RIBs produced by means of 35–60 A MeV primary heavy-ion beams with atomic numbers 3 ≤ Z ≤ 36. The AC-CULINNA-2 design is optimized for larger RIB intensities and for high-precision studies of direct reactions leading to the population of nuclear systems near and beyond the drip lines having in mind sophisticated correla-tion experiments.

At the moment the manufacture of the ACCULINNA-2 components by the ion-optics solution provider SigmaPhi (Vames, France) is in the final stage. Construction work has started in the U-400M hall. The instal-lation should be completed by the end of 2014, and we plan the commission-ing and first experiments running in 2015.

To provide broader experimental opportunities the auxiliary “massive” instrumentation should be delivered together with the separator “body.” The ACCULINNA group is working

Figure 5. Excitation spectrum of 5H and angular correlations of 3H fragment in the system of transferred momentum. Dots show data and histogram provide Monte-Carlo results. The 1/2+ g.s. contribution at about 1.9 MeV is practically invisible on the thick “background” of the higher-lying states. Only correlation analysis allows extracting this information.

Figure 6. Anomalous level ordering demonstrated for 10He indicate the shell structure breakdown known in 12Be extends also further to the most neutron-rich part of N = 8 isotone.



now on the development and financ-ing options for several of the most important items. (i) The zero-angle spectrometer (“sweeper magnet”) is required for a number of experiments, where heavy reaction products go forward close to the secondary beam direction. This option becomes im-portant in experimental conditions with intense or strongly contaminated secondary beams (>>105 pps). (ii) The ion optics of the ToF stage of ACCU-LINNA-2 is optimized to accommo-date an RF-kicker. This option is es-sential for purifying secondary beams on the proton-rich side. (iii) The cryo-genic tritium target gas system is one of the really unique opportunities pro-vided at FLNR. Unfortunately, the ex-isting system is “bound” to its physi-cal location by certification conditions concerning hazardous radioactive substances. The advanced next-gener-ation tritium system is planned to be constructed in the ACCULINNA-2 target area.

Having the ACCULINNA-2 sepa-rator fully put into operation the Flerov lab will convert the present-day ACCULINNA for biophysics and applied studies.

WelcomeThe operation of the new ACCU-

LINNA-2 fragment separator since 2015 at the Flerov Laboratory of JINR will open new opportunities for sci-entific collaboration with JINR in the field of RIB research. The research program of ACCULINNA-2 for the first years of operation is not yet final-ized, and we welcome new ideas and experimental proposals for the arriv-ing facility.

AcknowledgmentsThis work was supported by the

Russian Foundation for Basic Re-search 14-02-00090a grant. Leonid Grigorenko acknowledges the support of the Russian Ministry of Education and Science NSh--932.2014.2 grant.

References1. B. Starchenko and Y. Shimanskaya,

Nuclear Physics News 22 Phys. Rev. C (2012) 7.

2. M. S. Golovkov et al., Phys. Rev. C 72 (2005) 064612.

3. M.S. Golovkov et al., Phys. Rev. C 76 (2007) 021605(R).

4. S. I. Sidorchuk et al., Phys. Rev. Lett. 108 (2012) 202502.

Leonid GriGorenko

Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear

Research, Dubna, Russia, and Natinal Research Center "Kurchatov

Institute", Moscow, Russia

Andrey Fomichev


Research, Dubna, Russia

GurGen Ter-AkopiAn


Research, Dubna, Russia



Nuclear Physics at Jožef Stefan Institute

includes a research reactor TRIGA Mark II (Figure 2), that recently cel-ebrated its 40th anniversary of contin-ued operation.

Nuclear physics research is cur-rently performed only at the Depart-ment of Low and Medium Energy Physics. During the last decade the department has consisted of about 40 staff members and their work can roughly be divided into three groups: atomic physics, environmental radio-activity measurements, and a rela-tively small group performing basic and applied nuclear physics research. The atomic physics group operates and utilizes the department’s own 2 MV tandetron accelerator built by High Voltage Engineering Europa B.V. (Figure 3). The accelerator is equipped with three ion sources that enable it to accelerate many different ion beams, from very intense proton

beams from a multicusp ion source, specialized duoplasmatron source for low consumption 3He beams, to vari-ous light- and heavy-ion beams from the sputtering source. The main ad-vantage of the accelerator is its stable operation that enables us to obtain high-quality ion beams.

The research at the accelerator is conducted at four beam-lines (Fig-ure 4), where various ion-beam analy-sis techniques are applied. One beam-line is devoted to particle-induced X-ray analysis (PIXE) in air. This technique is mainly used in archeom-etry to study cultural heritage objects that cannot be placed in vacuum. The second beam-line is the micro-beam-line, where the PIXE technique is applied with ion beams with a diam-eter of less than one micrometer. The state-of-the-art at this beam-line is the MeV-range secondary ion-mass

The Jožef Stefan Institute (Institut “Jožef Stefan”) was founded by the Slovenian Academy of Sciences and Arts in 1949 as the Physics Institute for Nuclear Research. In 1952 it was renamed in honor of the Slovenian physicist Jožef Stefan (1835–1893), mostly known today for the law de-scribing the energy flux of black-body radiation as a function of tem-perature,

j = σT4,

which is named after him and his stu-dent Ludwig Boltzmann. The Stefan’s constant σ has been immortalized in the institute’s logo (Figure 1), which represents the letters I, J, and S in the International Telegraph Alphabet, while also resembling the letter σ.

After its early stages of a dedicated nuclear physics facility, the institute’s research became quite diversified. Al-though it still remains the country’s only national physics institute, its almost one thousand staff members work in the fields of physics, chemis-try, computer science, robotics, mate-rials research, and biochemistry. The institute is heavily involved in the ed-ucational process since more than two hundred of its members are also Ph.D. students. Currently the largest depart-ments at the institute are the Con-densed Matter Physics Department and the Environmental Sciences De-partment. The institute’s infrastructure

Figure 1. The logo of Jožef Stefan In-stitute.

Figure 2. The research reactor TRIGA of the Jožef Stefan Institute.



spectrometry (i.e., SIMS with an MeV-range ion beam), where the dis-tribution of large organic molecules in biological samples can be studied with great precision.

The third beam-line is devoted to nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA) methods. These two meth-ods are mainly used for depth profil-ing of hydrogen isotopes in materials exposed to tokamak plasma within the European Fusion Development Agreement. The rightmost beam-line in Figure 4 is usually connected to a special scattering chamber for high-resolution X-ray spectroscopy. How-ever, this scattering chamber has often been traveling to various European synchrotrons, where synchrotron ra-diation is used instead of protons to achieve high resolution in X-ray spec-troscopy. The accelerator belongs to the SPIRIT network through which outside users can apply for beam time and, if successful, have all their ex-penses covered.

Many of the environmental radio-activity measurements are performed in our High Resolution γ-ray Spec-trometry Laboratory. The labora-tory is market-oriented and measures activities of γ-ray emitting isotopes in samples collected in the environ-

ment. Many samples come from the vicinity of the only Slovenian nuclear power plant at Krško. The laboratory cooperates with the Comprehensive Nuclear-Test-Ban Treaty Organization and the International Atomic Energy Agency. Supplementing high resolu-tion γ-ray spectrometry is the Liquid Scintillation Spectrometry Laboratory in which activities of tritium in water with extremely low detection limits are measured, as well as 14C compo-nents in biodiesel fuels. This labora-tory is compliant with the European Commission Council Directive 98/83/EC on measuring gross α/β emitters in drinking water and will already be prepared once Slovenia imple-ments it in its own legislation. We also have a secondary standard laboratory that maintains the national reference standard for absorbed and equivalent doses of gamma radiation. Our cali-bration and measurement capabilities are being loaded into the database of Bureau International des Poids et Mesures.

In spite of being the smallest group at the Department, its Nuclear Physics Group conducts research in three dif-ferent but closely related fields. We are members of two major international collaborations, Hall A at Thomas Jef-ferson National Accelerator Facility

(TJNAF or Jefferson Lab), Newport News, VA, USA and the A1 Collabo-ration at the Mainz Microtron MAMI, hosted at the Institute of Nuclear Physics of the Johannes-Gutenberg University, Mainz, Germany. In both of these research centers, we are ac-tively involved in designing, planning, and conducting of electron scattering experiments, as well as their calibra-tions and subsequent data analyses.

At MAMI we are primarily in-volved in all experiments devoted to pion electro-production on protons, both near the production thresh-old (test of low-energy theorems of chiral perturbation theory in the neutral-pion channel, extractions of the axial form factor of the proton in the charged-pion channel) and in the nucleon resonance region (determina-tion of electric and Coulomb quadru-pole contributions to the Delta (1232) excitation, studies of the N(1440) (Roper) resonance); many of these experiments, running at the standard three-spectrometer setup of the A1 Collaboration, exploit polarization degrees of freedom (polarized beam, proton recoil polarimetry) in order to amplify the appropriate physics sensi-tivities. A large fraction of our recent efforts, however, was directed at the newly implemented KAOS spectrom-

Figure 3. The 2 MV tandetron accelerator at the Jožef Stefan Institute.



eter, in particular in its primary role in the physics studies of hypernuclei, for which we have designed and built an aerogel Cherenkov counter. We are also involved in virtual Compton scat-tering experiments at low momentum transfers, the main goal of which are the generalized polarizabilities of the proton (the extensions of the usual static electric and magnetic polariz-abilities to virtual photons); a part of this program was also conducted by using polarized beam and/or focal-plane proton polarimetry (single-spin and double-spin asymmetries). The group has also collaborated in bench-mark determinations of electric and magnetic elastic form-factors of the proton as well as measurements of neutron electric form-factor at high momentum transfer. Our involvement at MAMI further extends to dark pho-ton searches and exploiting the initial-state radiation method to access pro-ton elastic form-factors at extremely

low momentum transfers not accessi-ble directly; the latter effort is closely related to the “proton radius puzzle” that has been permeating the field for the past several years.

At Jefferson Lab our primary in-volvement in the past five years or so has been in the so-called BigFamily of experiments comprising, among oth-ers, a set of measurements utilizing the large-acceptance (approximately 100 msr) spectrometer BigBite in addition to the standard two high-resolution spectrometers of Hall A, together with a polarized beam and a high-density, optically pumped polarized 3He target. Our main focus was the measurement of electron-target double-polarization asymmetries (in-plane target polariza-tion) in deuteron, proton, and neutron knockout from 3He in the quasi-elastic region, a set of processes that consti-tute an extremely sensitive probe of spin and isospin structure of the 3He nucleus and its dynamics, but a large

part of our collaboration extended to studies of single-spin inclusive as well as exclusive asymmetries (neutron knockout) when the target was polar-ized out of plane. All these experi-ments have been devised to test the most precise available theories of few-nucleon systems, in particular regard-ing the question whether, or to which accuracy, the polarized 3He nucleus may be regarded as an effective polar-ized neutron target.

Meson electro-production in the first, second, and third nucleon reso-nance region, both in the non-strange and strange sector, is also the subject of our theoretical investigations, in which we exploit various chiral quark models of the nucleons, in particular those with explicit non-quark degrees of freedom (i.e., those that incorporate meson-cloud effects). In these studies we collaborate with the co-workers from the institute’s Theoretical Phys-ics Department. In the past few years we have calculated the meson elec-tro-production multipole amplitudes (both the electro-magnetic vertex and the strong decay, including the appro-priate complex phases) for all major (positive and negative parity) nucleon resonances up to an energy of about 1.8 GeV in a coupled-channel frame-work that can accommodate any un-derlying quark model to compute its matrix elements.

Some nuclear physics research is also performed at our tandetron accel-erator. We are especially interested in nuclear astrophysics, more precisely in the role of electron screening in nuclear reactions at low energies. We have confirmed the previous sugges-tion that the accepted static picture of electron screening inadequately de-scribes the process. This is especially evident in experiments on implanted hydrogen in metallic targets, where many measured values of the elec-tron screening potential in different

Figure 4. The four beam-lines of the tandetron accelerator at the Jožef Stefan Institute.



nuclear reactions are more than an or-der of magnitude above the adiabatic limit inferred from the static picture. To figure out which dynamic process is responsible for the large electron screening, we are trying to deduce the dependence of the electron screening potential on the proton number Z of the reactants. Previous measure-ments have failed to confirm the ex-pected linear dependence. We also observed that the strength of electron screening depends on the position of the hydrogen nuclei in the metallic lattice.

We are also active in radiation de-tector development with activities in novel materials for neutron detection. We are developing new algorithms for digital pulse processing, where our focus is in pulse shape analysis for separating neutron and γ-ray sig-nals. However, our main specialty is the development of novel algorithms for high count rate spectroscopy from

both scintillator and semiconductor detectors.

Thanks to two Slovenian high tech companies, Instrumentation Technol-ogies and Cosylab, Slovenia became a founding member of FAIR GmbH in Darmstadt, Germany. Since this membership is such a promising op-portunity, the Slovenian scientific community and in particular the Nu-clear Physics Group at Jožef Stefan Institute are turning toward FAIR-related research. We are especially interested in the NUSTAR collabo-ration, where our expertise in pulse processing at high count rates might prove useful.

To conclude, the nuclear physics group at the Jožef Stefan Institute is small but young and very much alive and kicking. In June 2015 we are or-ganizing together with our Croatian colleagues the next one in the inter-national conference series Nuclear Structure and Dynamics. Simon Širca

Faculty of Mathematics and PhysicsUniversity of Ljubljana,

Ljubljana, Slovenia

matej LipogLavŠek

Jožef Stefan Institute, Ljubljana, Slovenia

Filler?


impact and applications

Space radiation has long been rec-ognized as a major health hazard for human space exploration. Unlike ter-restrial radiation, space radiation com-prises high energy protons and high charge and energy (HZE) nuclei, which produce distinct forms of biological damage to biomolecules, cells, and tis-sue compared to terrestrial radiation, making risk predictions highly uncer-tain [1]. While the crews in low Earth orbit (LEO), such as the International Space Station (ISS), are partially pro-tected by the Earth’s magnetic field, for interplanetary missions in deep space the risk of acute effects caused by solar particle events (SPE) and late effects induced by protons and HZE nuclei in the galactic cosmic rays (GCR) is sig-nificant. Intense SPE can be lethal for unprotected crews, but shielding is ef-fective against solar protons. Chronic exposure to GCR represents instead a very serious risk of carcinogenesis [2]. It is not clear if the health risks associ-ated with long-term exposure to HZE nuclei can be adequately estimated by epidemiological studies, as done for ra-diation protection on Earth, due to both quantitative and qualitative differences in biological damage. Therefore, risk estimates, mostly based on ground-based cell or animal studies, are af-fected by large uncertainties. More-over, shielding from very energetic CGR nuclei tends to be poor given the weight constraints of spacecraft.

In 2006, the National Council on Radiation Protection and Measure-ments (NCRP) concluded that no rec-ommendations for specific radiation protection limits could be provided to NASA regarding long-term explor-atory-class missions, because of the high uncertainty associated with the risk of late effects [3]. Since that re-port, many new developments demand a re-analysis of the problem:

1. The one-year mission to the ISS (2015) and the Mars mission (In-spiration Mars, 2018) are now scheduled, and all exploration scenarios foresee a long perma-nence of humans in space.

2. NASA implemented a radiation protection standard that limits astronauts’ exposure in LEO to a 3% risk of exposure-induced death (REID) within the 95% confidence interval (CI), and uses a specific model for the REID calculation in different mission scenarios [4].

3. The Mars Science Laboratory (MSL), carrying the Curiosity rover (Figure 1), measured for the first time the radiation field

on the route to Mars [5] and on the planet’s surface [6], sup-porting previous estimates and demonstrating that radiation dose rates in space are indeed 200–400 times higher than on Earth.

4. New ground-based radiobiology experiments at high-energy par-ticle accelerators, supported by NASA at the Brookhaven Na-tional Laboratory (Upton, NY, USA) and by ESA at the GSI Helmholtz Center (Darmstadt, Germany), show that, in addition to cancer [2], HZE nuclei can induce late tissue degenerative effects, especially CNS damage and cardiovascular diseases.

Cosmic Rays: Hurdles on the Road to Mars

Figure 1. Sand dunes and rocks around the “Dingo gap” on Mars. The photo-graph was taken by the Curiosity rover, which landed on Mars on 6 August 2012, following a 253-day, 560-million-kilometer space trip. The Curiosity rover, with the Radiation Assessment Detector (RAD) mounted to its top deck, was inside the Mars Science Laboratory spacecraft. RAD measured the space radiation doses during the cruise in deep space [5] and on the Mars surface [6]. Image Credit: NASA/JPL-Caltech/MSSS.



Based on these new data, is it ac-ceptable to plan long-term ISS mis-sions and planetary exploration? What are the scientific and ethical issues?

Radiation LimitsGeneral public and professionally

exposed workers are subject to spe-cific radiation dose limits set by law. Although current recommendations are risk-informed, they are not based directly on assumed limits on risk and do not directly account for uncertain-ties in estimates of risk associated with given doses. For example, the dose limits recommended by the Interna-tional Commission on Radiological Protection for the public is set to 1 mSv/year, while for radiation work-ers it is 20 mSv/year [7]. Emergency exposures (generally up to 100 mSv) are permissible in case of nuclear acci-dents, as it happened in the Fukushima nuclear power plant disaster in 2011. Higher doses (around 1 Sv) may only be justified if they involve the saving of human lives. A simple dose-limit approach is also implemented by the Russian and European Space Agen-cies, with an astronaut’s career limit

set at 1 Sv, independently of the age at exposure and sex [1].

In contrast, the radiation protection standard for astronauts currently used by NASA is expressed directly in terms of a limit on risk of lifetime exposure-induced mortality, and include the un-certainty on the risk estimate: 3% REID at 95% upper CI [4]. This approach has not been applied to the general public or Earth based worker, where dose lim-its are preferred for practical reasons, but it is clearly more scientific and ap-propriate for a small group of workers such as the astronauts, and of growing interest on Earth [8]. In fact, the expo-sure limits and risk model are gener-ally considered prudent, appropriate, and scientifically sound, and they were positively evaluated by the National Research Council [9].

However, by applying these stan-dards many exploratory missions would exceed the limits. In Figure 2, estimates using the NASA model [4, 10]. for four space missions are com-pared to terrestrial exposures, includ-ing the 1-Sv career limit used by the Russian and European space agency, where the uncertainty is calculated us-

ing the U.S. Environmental Protection Agency model [11]. The estimates in Figure 2 are for a 45 year old, male, never-smoker, and include the risk for late cardiovascular effects. The lower background cancer rates of a never-smoker population reduce radiation risk estimates compared to estimates for the U.S. average population. More-over, risk estimates will be higher for females and younger astronauts. Even for the ISS, missions longer than 1-year may exceed the current guide-lines for astronauts involved in mul-tiple missions, depending on age, sex, and mission duration [10]. The fixed career dose limit at 1-Sv limit adopted by the Russian and European Space agencies have not received external re-view; however, they would far exceed the NASA guidelines, even assuming the uncertainty level of terrestrial ex-posures [11].

Ethical IssuesThe high risk predicted for many

missions may push toward simple so-lutions, such as an ease of the dose limits and the adoption of “informed consent” strategies. However, these approaches pose serious ethical and le-gal concerns. On Earth, in addition to the dose limits, the regulatory agencies adopt the so-called ALARA principle, which means that all unjustified expo-sures should be avoided and all mea-sures should be taken to keep the expo-sures as-low-as-reasonably-achievable [7]. A recent report from the Institute of Medicine recommends several eth-ics principles should be applied to the NASA health standards for decisions regarding long-duration and explora-tion spaceflights [12]. NASA should systematically assess risks and benefits and the uncertainties attached to each, drawing on the totality of available scientific evidence, and ensure that benefits sufficiently outweigh risks. In any case, the principle of “avoid harm” should be applied, which implies that NASA should minimize the risks to astronauts from long-duration and ex-

Figure 2. Estimates of cancer mortality risk and 95% CI for four different space mission scenarios compared with terrestrial exposures. Estimates are for a 45-year-old, male, never-smoker. Estimates for Mars asteroid mission, Mars opposition-class mission, and the Mars Design Reference Mission (DRM) pro-posed by NASA are assumed in a solar minimum and are detailed in Ref. [4]. Details of the ISS missions are in Ref. [10]. Annual dose for a radiation worker is assumed to be 20 mSv and 100 mSv for an emergency exposure (acute) [7]. Es-timates of the excess cancer mortality risk for a 1-Sv dose limit are also reported, assuming terrestrial exposure [11].



ploration spaceflights and address un-certainties through approaches to risk prevention and mitigation that incorpo-rate safety margins. These recommen-dations are of course of general value, and should therefore be considered by all space agencies, which can poten-tially be engaged in long-duration and exploratory missions. ESA is indeed currently supporting several modeling and experimental research programs in space radiation protection. An interna-tional effort would be extremely useful in this respect, to avoid astronauts from different countries being subject to dif-ferent standards, which is intrinsically an ethical problem. From our view-point, it is only upon the completion of a significant fraction of the scientific studies that can be reasonably sug-gested to reduce uncertainties and de-velop mitigation measures, that space agencies can argue they have made a significant effort. At this time, perhaps higher levels of space radiation risk could be accepted, while at the same time consistency with the many efforts to reduce the much lower risks from flight failures, which are now esti-mated at less than 1 in 250, would have been demonstrated.

Scientific IssuesReducing uncertainty is clearly the

highest priority for understanding the risk of exploratory missions. Recent evidence of tissue degenerative ef-fects has led to further increasing the risk estimates [4], previously based on cancer risk alone [3]. High priority should therefore be given to radiobiol-ogy research on cancer and non-cancer effects induced by HZE particles in accelerator-based experiments. Even though very much has been learned in the past 10 years, the translation of in vitro or animal experiments to human protection remains problematic if the mechanisms are not well understood.

Estimates in Figure 2 suggest that, even with a reduced uncertainty, explo-ration will hardly be possible without appropriate countermeasures both in

the near future (applying the ethical standards recommended by the Insti-tute of Medicine [12]) and especially in the medium-term future, when spaceflight will be extended to a much larger fraction of the population (space tourism, workers on planetary bases). At the moment, biomedical counter-measures (radioprotective drugs or di-etary supplements) have only limited efficacy, and it is not expected that they will solve the problem [2]. Crew selec-tion for radiation resistance may be-come more likely as knowledge is in-creased, however possibly constrained by the small pool of candidates and other selection criteria. Passive shield-ing also has limited effects, because of the severe weight constraints in space flight, yet the use of light, highly hy-drogenated materials is a simple and effective way for reducing risk [13], and in situ material can be exploited for safe shielding in planetary bases. Active shielding (e.g., the use of a magnetic field similar to the Earth’s protection of the Van Allen belts), is very promising but technically imma-ture, and probably will not be realis-tic for the next 10–20 years. Mission design can gain large factors. Moving the missions to solar maximum drasti-cally reduces the GCR dose (by up to 50%), even though the risk of intense SPE is higher. Reducing the transit time is clearly the best solution, both for minimizing radiation exposure and for the other medical issues caused by microgravity and isolation. This can be achieved by innovative propulsion sys-tems and choice of appropriate flight windows. In any case, the recent MSL data [5, 6] confirm that cosmic rays are high hurdles on the way to Mars, and an international effort is clearly ur-gently needed to address the problem. Experts in medicine and space radia-tion will gather at the Ettore Majorana Foundation in Erice in October, in the framework of the International School on Heavy Ions, to discuss this issue and hopefully to produce a consensus

document to be implemented by the space agencies [14].

References 1. M. Durante and F. A. Cucinotta. Rev

Mod Phys. 83 (2011) 1245. 2. M. Durante and F. A. Cucinotta. Nat

Rev Cancer. 8 (2008) 465. 3. NCRP. Information Needed to Make

Radiation Protection Recommenda-tions for Space Missions beyond Low-Earth Orbit. NCRP Report No. 150, Bethesda, MD, 2006.

4. F. A. Cucinotta, M. H. Kim, L. J. Chap- pell, and J. L. Huff. PLoS One. 8 (2013) e74988.

5. C. Zeitlin, D. M. Hassler, F. A. Cuci-notta, et al.. Science. 340 (2013) 1080.

6. D. M. Hassler, C. Zeitlin, R. F. Wim-mer-Schweingruber, et al. Science. 343 (2014) 1244797.

7. ICRP. Recommendations of the Inter-national Commission on Radiologi-cal Protection. ICRP Publication No. 103, Ann. ICRP 37(2–4), Elsevier, NY, 2007.

8. J. Preston, J. D. Boice, A. B. Brill, et al. J. Radiol. Prot. 33 (2013) 573.

9. National Research Council. Techni-cal Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation (The National Acad-emies Press, Washington, DC, 2013).

10. F. A. Cucinotta. PLoS One. 9 (2014) e96099.

11. D. J. Pawel. Health Phys. 104 (2013) 26.

12. Institute of Medicine. Health Stan-dards for Long Duration and Ex-ploration Spaceflight: Ethics Prin-ciples, Responsibilities, and Decision Framework (The National Academies Press, Washington, DC, 2014).

13. M. Durante. Life Sci. Space Res. 1 (2014) 2.

14. International School on Heavy Ions, III Course on: Hadrons in Therapy and Space, Erice, Italy, 1–4 Octo-ber 2014. Frontiers in Oncology, in press. http://journal.frontiersin.org/ ResearchTopic/3520

Marco Durante GSI Helmholtz Center for

Heavy Ion Research and Darmstadt University of Technology

Darmstadt, GermanyFrancis a. cucinottaUniversity of Nevada,

Las Vegas, Nevada, USA

meeting report


The First International African Symposium on Exotic Nuclei (IASEN2013)

The first International African Symposium on Exotic Nuclei (IA-SEN-2013) was held on 1–6 Decem-ber 2013, not far from Cape Town (Republic of South Africa). This Sym-posium was organized by two scien-tific centers—the iThemba Laboratory for Accelerator-Based Sciences, South Africa and the Joint Institute for Nu-clear Research, Russia.

The symposium grew out of the 6th Symposium on Exotic Nuclei (EXON 2012), which was held in Vladivo-stok, Russia, when the then director of iThemba LABS, Zeblon Vilakazi, had an idea to organize a similar confer-ence in South Africa. This idea was supported during a round table discus-sion by almost all leading participants of the symposium. IASEN-2013, similar to the EXON symposia, was devoted to the investigation of nuclei in extreme states; the following topics were discussed: exotic nuclei and their

properties, shell structure, collectivity, rare processes and decays, nuclear astrophysics, applications of exotic beams in material research, and pres-ent and future facilities.

The first African Symposium was attended by 140 scientists from 16 countries and 42 institutions. A school for young participants and students from several SA universities, where leading scientists gave lectures, was organized the day before the open-ing of the Symposium. Thomas Auf der Heyde, deputy director-general of the Department for Science and Technology of South Africa, officially opened the symposium; in his detailed report he presented the perspectives of nuclear physics and technology in South Africa. He was followed by re-ports of progress and plans at facilities around the world: R. Bark (iThemba LABS), M. Thoenissen (MSU), M. Lewitowicz (SPIRAL 2, GANIL), K.

Johnston (ISOLDE/CERN), H. En’yo (RIKEN), R. Tribble (Texas A&M), F. Weissbach (GSI/FAIR), S. Galés (ELI-NP), A. Popeko (JINR/DRIBs3), R Kruecken (TRIUMF), and G. de Angelis (SPES/INFN).

At the end of the Symposium, a discussion of cooperation between South African research centers with the world’s leading laboratories was organized. A joint memorandum of cooperation was adopted that en-dorsed a proposal by iThemba LABS for an ISOL based radioactive beam facility in South Africa.

The last day of the symposium was marked with a minute’s silence for the loss of a world leader—Nelson Roli-hlahla Mandela.

Z. VilakaZi and Yu. PenionZhkeVich

Co-Сhairmen of IASEN2013AQ1

Filler?

news and views


Nuclear Physics Research Opportunities in BrazilResearch in nuclear physics in

Brazil is strong and well-recognized internationally. There are researchers in several Brazilian states, with most of them confined to the Rio–São Paulo axis. Historically, since the early 1950s, these researchers were sta-tioned in universities such as the Uni-versidade de São Paulo (USP), and the Centro Brasileiro de Pesquisas Físicas (CBPF), in Rio de Janeiro. A quite ac-tive program in experimental nuclear physics was in place at USP, which produced precise results on inelastic scattering data such as the (d, p), (d.n) reactions. This effort was enhanced by the installation of the 8 MV Pel-letron Accelerator Laboratory, which entered into operation in 1970. The realm of heavy ion physics was then made available to Brazilian nuclear physicists and several international collaborations were put into place. It allowed the study of light and me-dium heavy-ion reactions at low ener-gies. Among these we mention charge exchange reactions, which aimed to probe isospin symmetry breaking, fusion, and breakup reactions. Three decades later the study of the physics of neutron rich and proton rich nuclei became possible through the installa-tion of a twin solenoid system coupled to the 8 MV Pelletron, baptized by the name RIBRAS. This system has been in operation since 2003 and reactions with 6He and 8He were extensively studied. In the electron accelerator ef-fort, I mention the ongoing effort in the construction of a MICROTRON, also at the University of São Paulo.

Applied nuclear physics has also been a strong area of activity in Bra-zil. Medical applications, 14C dating, AMS use for dating and other appli-cations in material science, and reac-tor physics have been under intense

investigation by the Brazilian nuclear scientists. Many international collab-orations in these areas are in course and being intensified. Research op-portunities in the AMS program are currently enhanced through the instal-lation of a state of the art apparatus at the Universidade Federal Fluminense (UFF) in Rio.

Research in nuclear theory has been strong in Brazil over many de-cades. Very active groups working on the many facets of the nuclear theory (high spin states, giant resonances in stable and exotic nuclei, multi-phonon excitation of giant resonances), and especially reaction theory are consid-ered leaders in the field. Low energy reaction theory and relativist heavy-ion reaction theory using hydrody-namical models are in the frontline of physics. Hadron physics and relativ-istic description of nuclear structure and reactions are also actively re-searched. Application of nuclear tech-niques to atomic and molecular phys-ics (Bose-Einstein Condensation, one and multi-phonon excitation in metal and atomic clusters), as well as to nanophysics and mesoscopic systems (quantum dots, grapheme) have been actively studied. Last, but not least, research in nuclear astrophysics has been pursued both theoretically and experimentally in collaboration with colleagues in Europe and the United States. A group on nuclear astrophys-ics has been formed at the Institute for Advanced Studies of the University of São Paulo, which includes among its members several of these colleagues (see www.iea.usp.br/pesquisa/grupos/astrofisica-nuclear/integrantes).

The interaction between the theo-rists and the experimentalists in all the above areas has been of fundamental importance in advancing the research

of both. It resulted in several widely used models and concepts; to cite a few we mention the São Paulo Optical Model Potential (SPP), the Breakup Threshold Anomaly (BTA), and the Universal Fusion Function (UFF).

The nuclear physics community holds annual meetings during the first and second weeks of September with the participation of several in-vitees from overseas. This has been a tradition since the 1970s. Several international topical meetings are also organized almost every one or two years. The community hosted and still hosts imported international meet-ings, such as the INPC in 1989, and the NN2006 and the Few-Body Con-ference in 2006. In these conferences, hundreds of international participants attended and helped in the success of the events.

The international collaboration is greatly valued by the Brazilian nuclear physics community. Several important research centers and labo-ratories have had an important role in making these collaborations a suc-cess. Among these are: GSI, MIT, Harvard, LHC, RHIC, MSU, Yale, Madison, Texas A&M, Notre Dame, Berkeley, Ganil, ULB, and Surrey, to cite a few. Current opportunities for the continuation of these collabora-tions have been bolstered through the establishment by the Brazilian federal government of the program Science Without Borders, which enables undergraduates and begin-ning graduate students to spend six months in universities in Europe and the United States to get familiar with the teaching programs and research. These visits are fully supported by the federal funding agency CNPq (see www.cnpq.br). Further, the program supports the visit of senior academics

news and views


and researchers from oversees uni-versities to visit one of the research universities in Brazil for up to three months or more, also well and fully supported by the CNPq. It is hoped that our international colleagues will be encouraged to get in touch with the contact persons listed below and inquire about postdoc positions in Brazil and senior scientists visits. I should mention that for postdoc posi-tions and visits to São Paulo, the State Funding Agency, FAPESP (see www.fapesp.br) has the means to support postdocs for a period of two years, renewable for one or two more years, and one year visits by senior scientists renewable for one more year.

Contact Persons

Alika Lepine Szily ([email protected])Experimental nuclear physics, Pel-

letron and RIBRAS, Microtron, nuclear astrophysics

Paulo R. S. Gomes (paulogom@if. uff.br)

Applied nuclear physics, AMS, exper-imental nuclear physics

Yogiro Hama ([email protected])Relativistic heavy ion reaction theory,

Hadron Physics, LHC, RHIC

Mahir S. Hussein ([email protected])Theoretical nuclear physics, low en-

ergy reaction theory, heavy ion re-actions, nuclear astrophysics

It is hoped that the above account of the nuclear physics research cur-rently done in Brazil will give a clear picture of what our community is pur-suing to enhance the knowledge in our field and will encourage further intensification of the already quite healthy international collaboration.

Mahir S. huSSein

Instituto de Estudos Avançados, Universidade de São Paulo,

São Paulo, Brasil

The board of the European Physi-cal Society (EPS) Nuclear Physics Division calls for nominations for the 2012–2014 European Nuclear Physics Dissertation Award. The award recog-nizes the excellency of a recent Ph.D. in Nuclear Physics. Nominations are open to any person who has received a Ph.D. degree in experimental, theo-retical, or applied nuclear physics in a country that is a member of the EPS and where the degree has been awarded within the three-year period 1 January 2012–31 December 2014. The deadline for applications is 1 Jan-uary 2015.

Nominations, which should be made via the Dissertation Prize website (http://www.eps.org/?NPD_prizes_ PhD), should include details of the nominee, an electronic copy of the Ph.D. Diploma showing the date it was awarded, a 4–5 page summary of the Dissertation/Thesis written in English, an electronic copy of the The-sis, a copy of any publication directly related to the candidate’s Ph.D. stud-ies, a letter of support (max. 2 pages) from the candidate’s thesis advisor, and two additional letters of support (max. 1 page each) from physicists

2012–2014 European Nuclear Physics Dissertation Award

who are familiar with the candidate and the research.

The prize winner will be given a di-ploma from the EPS, offered a plenary talk at the 2015 European Nuclear Physics Conference, 31 August–4 September, Groningen, The Nether-lands, and 1000 € to cover their con-ference travel and subsistence costs.

DouglaS Macgregor

Chair, EPS Nuclear Physics Division

news and views


The board of the European Physi-cal Society (EPS) Nuclear Physics Division calls for nominations for the 2015 IBA-Europhysics prize spon-sored by the IBA company, Belgium. The award will be made to one or sev-eral individuals for outstanding con-tributions to Applied Nuclear Science and Nuclear Methods and Nuclear Re-searches in Medicine.

The board welcomes proposals that represent the breadth and strength of Applied Nuclear Science and Nuclear Methods in Medicine in Europe.

Nominations forms, available on the IBA prize website (http://www.eps.org/?NPD_prizes_IBA), should be accompanied by a brief CV of the nominee(s) and a list of relevant pub-lications. Up to two letters of support from authorities in the field, outlining the importance of the work, would also be helpful. Nominations will be treated in confidence and, although they will be acknowledged, there will be no further communication. Nomi-nations should be submitted by e-mail

to Douglas MacGregor, Chair, IBA Prize Committee:

[email protected]. uk

The deadline for the submission of the proposals is 16 January 2015.

Prize Rules 1. The Prize shall be awarded every

two years. 2. The Prize shall consist of a Di-

ploma of the EPS and a total prize money of 5000 € (to be shared if more than one laureate).

3. The money for the prize is pro-vided by the IBA company.

4. The Prize shall be awarded to one or more researchers.

5. The Prize shall be awarded with-out restrictions of nationality, sex, race, or religion.

6. Only work that has been pub-lished in refereed journals can be considered in the proposals for candidates to the prize.

7. The NPB shall request nomina-tions to the Prize from experts

in Nuclear Science and related fields who are not members of the Board.

8. Self-nominations for the award shall not be accepted.

9. Nominations shall be reviewed by a Prize Committee appointed by the board. The Committee shall consider each of the eligible nominations and shall make rec-ommendations to the board, tak-ing also into account reports of referees who are not members of the board.

10. The final recommendation of the board and a report shall be sub-mitted for ratification to the Ex-ecutive Committee of the EPS.

DouglaS Macgregor

Chair, EPS Nuclear Physics Division

IBA-Europhysics Prize 2015 for Applied Nuclear Science and Nuclear Methods in Medicine Call for Nominations

in memoriam


In Memoriam: George Dracoulis (1944–2014)

Professor George Dracoulis, a pillar of the Australian National University’s Department of Nuclear Physics and a highly respected researcher interna-tionally, passed away on 19 June 2014, after a brief battle with an aggressive kidney cancer.

Born in Melbourne, Australia, to Greek immigrant parents, George graduated from the University of Mel-bourne with a Ph.D. in nuclear physics in 1970. His thesis research involved particle spectroscopy, but it was during his three years as a research associate at the University of Manchester, UK, that he began the gamma-ray spec-troscopy investigations that dominated his research career. In 1973, he joined the Australian National University as a Research Fellow in the Depart-ment of Nuclear Physics, where the world’s largest tandem Van de Graaff heavy-ion accelerator was under con-struction. George played an integral role in the accelerator’s development and worked tirelessly to build up the laboratory’s research infrastructure and exploit it to perform world-class

research. He was appointed to a Chair in Physics in 1991 and became Head of Department in 1992, a position he held until he retired in 2009.

The great contributions that George made to the Department helped estab-lish it as one of the world’s most re-spected nuclear physics laboratories. He was renowned for the thorough-ness of his experimental approach and it was his clever use of isomeric states as a sensitive probe that underpinned many of his important contributions to our understanding of nuclear phenom-ena. George demonstrated the key role of octupole vibrations in the trans-lead region and showed how the inclusion of particle-vibration coupling is es-sential to reproduce the state ener-gies and isomeric transition strengths, while his substantial body of research on high-K isomers and associated rota-tional structures gave profound insight into both the purity of the K quantum number and the nature of nuclear pair-ing. His clever alternative approach to experimental problems is amply dem-onstrated by his identification of char-acteristic isomers in neutron-deficient lead nuclei that can only occur at dif-ferent nuclear shapes, providing some of the best experimental evidence for nuclear shape coexistence.

An excellent public speaker, George was in high demand to give after din-ner and summary talks at international conferences, and was known for his urbane manner and fondness for red wine, good food, fine jazz and interest-ing conversation. He was the recipient of numerous awards, being a Fellow of both the Australian Institute of Phys-ics and the American Physical Society, an Honorary Fellow of the Royal So-ciety of New Zealand and an elected Fellow of the Australian Academy of Science. He received the Academy’s Lyle Medal in 2003 for outstanding

contributions to our understanding of the structure of atomic nuclei and in 2004 he won the Boas Medal of the Australian Institute of Physics.

In the public arena, George served as a member of the Australian Prime Minister’s Select Task Force on Ura-nium Mining, Processing & Nuclear Energy during 2006 and continued to remain active afterward in the pub-lic discussion of nuclear technology. George also continued his research work until only a few weeks before he died, including finishing the draft of a comprehensive and long-awaited re-view on nuclear isomers that promises to be essential reading.

George was a gifted scientist who we knew in various guises and roles. To his family he was a loving father and husband, while to his colleagues he was variously a supervisor, col-laborator, fierce competitor, and, for many of us, a dear friend who will be greatly missed. George would be pleased to have the last word, and in his acceptance speech for a Lifetime Achievement Award received from the Hellenic-Australian Chamber of Commerce and Industry in Novem-ber 2013, he left us with the following advice: “My advice to those who fol-low: Keep up with the new literature, but go back and read the old papers. Always be self-critical. Always try and do things that you feel are a little bit beyond your reach.”

GreG Lane and andrew Stuchbery

Australian National University, Canberra, Australia

PhiL waLker

University of Surrey, Guildford, United Kingdom

FiLiP kondev

Argonne National Laboratory, Chicago, Illinois, USA

George Dracoulis

calendar


2015January 19–30

Les Houches, France. Winter School on the Physics with Trapped Charged Particles

http://indico.cern.ch/event/315947/

January 26–30Bormio, Italy. 53rd International

Winter Meetinghttp://www.bormiomeeting.com/

February 25–27Madrid, Spain. The Energy and

Materials Research Conference - EMR2015

http://www.emr2015.org/

March 2–6Valparaiso, Chile. 7th Interna-

tional Conference Quarks and Nu-clear Physics - QNP2015

http://indico.cern.ch/event/304663/

May 1–6Casta-Papiernicka, Slovakia.

Isospin, STructure, Reactions and energy Of Symmetry 2015 (IS-TROS2015)

http://istros.sav.sk/

May 11–15Grand Rapids, MI, USA. Inter-

national Conference on Electro-magnetic Isotope Separators and Related Topics (EMIS-2015)

http://frib.msu.edu/EMIS2015

May 18–23Oslo, Norway. 5th Workshop on

Nuclear Level Density and Gamma Strength

http://tid.uio.no/workshop2015/

May 25–29Urabandai, Fukushima, Japan.

5th International Conference on the Chemistry and Physics of the Trans-actinide Elements (TAN 15)

http://asrc.jaea.go.jp/conference/TAN15/

May 31–June 5New London, New Hampshire,

USA. Gordon Research Conference on Nuclear Chemistry

https://www.grc.org/programs.aspx?id=11762

June 7–12Hohenroda, Germany. EURO-

RIB2015http://www.gsi.de/eurorib-2015

June 7–13Victoria, BC, Canada. 6th Inter-

national Symposium on Symmetries in Subatomic Physics SSP 2015

http://ssp2015.triumf.ca/

June 8–12Budva, Montenegro. Third Inter-

national Conference on Radiation and Applications in Various Fields of Research (RAD 2015)

http://www.rad-conference.org/

June 14–19Portoroz, Slovenia. Nuclear Struc-

ture and Dynamicshttp://ol.ijs.si/nsd2015/

June 14–20Crete, Greece. 2015 Interna-

tional Conference on Applications of Nuclear Techniques CRETE15

http://www.crete13.org/

June 15–19Varenna, Italy. 14th Interna-

tional Conference on Nuclear Reac-tion Mechanisms

http://www.fluka.org/Varenna2015/

June 21–26Catania, Italy. 12th International

Conference on Nucleus-Nucleus Collisions (NN2015)

http://www.lns.infn.it/link/nn2015

June 29–July 3Pisa, Italy. Chiral Dynamics 2015http://agenda.infn.it/event/cd2015

July 20–24Pisa, Italy. 30 years with RIBs

and beyondhttp://exotic2015.df.unipi.it/index_

file/slide0003.htm

July 28–30Liverpool, UK. Reflections on the

atomic nucleus http://ns.ph.liv.ac.uk/

Reflections2015

August 31–September 4Groningen, The Netherlands.

European Nuclear Physics Confer-ence (EuNPC 2015)

http://www.eunpc2015.org/

September 6–13Piaski, Poland. 34th Mazur-

ian Lakes Conference on Physics “Frontiers in Nuclear Physics”

http://www.mazurian.fuw.edu.pl/

September 14–19Kraków, Poland. 5th Interna-

tional Conference on “Collective Motion in Nuclei under Extreme Conditions” (COMEX5)

http://comex5.ifj.edu.pl/

September 27–October 3Kobe, Japan. Quark Matter 2015http://qm2015.riken.jp/

December 1–5Medellín, Colombia. The XI

Latin American Symposium on Nu-clear Physics and Applications

http://www.gfnun.unal.edu.co/LASNPAXI/

More information available in the Calendar of Events on the NuPECC website: http://www.nupecc.org/

Documents

Nuclear Physics News - NuPECC · Vol. 24, No. 4, 2014, Nuclear Physics News 1 Editor: Gabriele-Elisabeth Körner Editorial Board Maria José Garcia Borge, Madrid (Chair) Eugenio Nappi,