N U C L E A R PHYSICS A

t~1 ~:VH.:R Nuclear Physics A583 (1995) 51-60

IMPACT AND APPLICATIONS OF NUCLEAR SCIENCE: OPPORTUNITIES AND PERSPECTIVES

A.van der Woude KVI, Groningen, the Netherlands

ABSTRACT: Some highlights of the forthcoming NUPECC report on IMPACT AND APPLICATIONS of NUCLEAR PHYSICS will be discussed The role of accelerators is stressed. The discussion will not be limited to what has been achieved but will also indicate what opportunities there are and what that implies for research in nuclear physics and technology

1. INTRODUCTION A paper on "Applications of Nuclear Physics" in the proceedings of a conference on " Heavy-Ion Collisions" devoted primarily to basic issues, is a novelty. It is illustrative for the present situation in which scientific disciplines are not only appraised by their intrinsic value, the intellectual pleasure they give, but also by their embedment in the whole of science and by their contributions to the society at large. For our science there is an additional problem because of the general tendency to associate the word "Nuclear" with "weapons" with all the negative implications involved. It is thus very necessary for our community to show what present day Nuclear Physics and Technology has to offer for interesting and useful applications. This was why NUPECC (NUclear Physics European Collaboration Committee), which as part of its activities seeks to promote Nuclear Physics in Europe, took the initiative to produce a report on "Impact and Applications of Nuclear Physics: Opportunities and Perspectives". This report is sequential to the ones on "Nuclear Physics: Opportunities and Perspectives" issued in 1992 and "Radioactive Beams" issued in 1993. These two earlier reports were primarily meant to summarise and stimulate the fundamental issues in Nuclear Physics itself. The subjects covered in this report are shown in figure 1. With the ones in the upper part the relation with Nuclear Physics is one of mutual Impact and Interaction: progress in one often leads to progress in the other. On the other hand, with the ones in the lower part, the Applications, the relation is more uni- directional. Important fields like neutron physics and synchrotron radiation are not explicitly included since these disciplines are already well established and have their own community. The report will not only summarise the present status of the various inter-disciplinary activities but also identify what further developments can be expected or are desirable and what that would imply for research in nuclear physics or technology. For this report NUPECC got the help of 10 working groups of specialists, each covering one of the subjects shown in figure 1 (2 separate groups for medicine and radiobiology). In preparation of the report there was a 3'-day workshop in the French village of Dourdan, where the contribution of each working group was discussed. The edited proceedings of this workshop will form the main body of the report, which will be issued at the end of 1994. The present paper is a necessarily incomplete selection out of the large amount of interesting material presented at the workshop. The goal is to show that Nuclear Physics and Technology has much to offer indeed and that there is more to come.

0375-9474/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved. ¢ c F I ! I'Y2"7~_OA'TA[OAMM~Kaa A

52c A. van der Woude /Nuclear Physics A583 (1995) 51-60

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Figure 1. Sciences and Applications around Nuclear Physics and Technology

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A. van der Woude / Nuclear Physics A583 (1995) 51-60 53c

2 AN EXAMPLE OF IMPACT AND INTERACTION: NUCLEAR ASTROPHYSICS The impact of Nuclear Physics on Nuclear Astrophysics is very strong. The major problem is that the required nuclear physics input refers to circumstances which are difficult to meet on earth. At the same time this is a great challenge. This is especially true for the reactions which play a role in the energy production, which form a key to the evolution of a large variety of astrophysical objects and also to the closely connected subject of "Nucleosynthesis", the processes which lead to the observed abundance of elements in the solar system and in other stars and galaxies. Energy production and light element formation occurs via thermo-nuclear reactions in non-explosive events. These are charged particle reactions which take place at energies far below the Coulomb barrier. Consequently they are characterised by very small cross-sections ("almost no-event region"). Recently it became clear that under these circumstances the effect of electron-screening t can considerably effect the cross section at the very low energies involved. For the 3He(d,p)4He a straightforward extrapolation of data in the 25-40 keV energy range to the <10 keV range would give errors of 20 to 50% in the astronomical S-factor. It implies that in order to obtain the relevant reaction rates, one has to extract from the laboratory measurements the bare-nuclei cross section and then convert these to reaction rates under circumstances characteristic for the stellar atmosphere. At present there seems to be a deviation of about 10% between experiment and theory 1 which, if true, poses a serious problem. The well-known solar neutrino-problem relates to the fast neutrino's produced in the 7Be(p,'/)SB capture reaction. The cross-section for this crucial reaction has been measured 1 directly by using a radioactive 7Be-target, but the uncertainty estimated from the data remains large, about 28%. Recently a measurement of the inverse process was performed 2 allowing to distinguish between the conflicting experiments. For this experiment the technique of inverse Coulomb break-up reactions was used in which a beam of radioactive 8B projectiles impinges on a heavy, high-Z target thus creating a strong and virtual v-beam which breaks up the projectile. This technique might also be used in determining reaction rates of other processes of interest, like the 12C(~,V)160 reaction which is of crucial importance in the Helium burning phase of stars 3. A direct measurement of the cross section for this reaction at the relevant energy of 300 keV is quite difficult if not impossible, due to the extreme low cross section. The usual procedure is to extrapolate the measurements at higher energies to the energy region of interest, but this procedure is not straightforward due to the presence of a few interfering resonance states in this energy range. But also the interpretation of the data for the inverse Coulomb break-up reaction will be complicated because of the interference between electromagnetic and nuclear break-up processes. For the thermonuclear reactions in explosive events like in novae, supernovae and the Big Bang the energy can be of the order of the Coulomb barrier with cross sections typical in the micro- and millibarn range. Within a short time interval the high local flux in combination with the sizable cross section cause the reaction path to be in the region of neutron rich or deficient nuclei, far from the region of stability. Moreover the target nuclei can be in excited states. In order to determine the relevant reaction rates one has to rely heavily on theoretical models and predictions, which then should be tested experimentally for specific cases. This is the field where radioactive beams can make a major impact, as is discussed in the contribution of J.Vervier to this conference 4. It should be clear from this discussion that the measurement and prediction of reaction rates of relevance to stellar evolution, elemental abundance, cosmology and energy production in the Universe is a real challenge to nuclear physicists. This is a vast field which requires the most advanced experimental techniques and theoretical methods nowadays available.

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3. APPLICATIONS: THE ROLE OF ACCELERATORS 3.1 INTRODUCTION In many applications accelerators play an essential role. As figure 2 shows, this is true for the whole energy range from 0.1 to 1000 MeV. Although I will concentrate here on accelerator-based applications, one should realise though that important work is going on using tracers, especially in biology, or low-level counting techniques of natural radioactivity. Well-known examples are 14C dating and the study of Radon abundance in dwellings.

3.2 ACCELERATORS AND ANALYSING TECHNIQUES For analysing purposes high sensitivity and/or precise localisation are needed. These requirements have stimulated the development of (sub)-micron beams in combination with sensitive element-specific analysing techniques like PIXE (Proton Induced X-ray Emission). With present day technology it is now possible to produce beams with a diameter of 0.4 I.tm and currents of 10 pnA. With the PIXE technique the absolute detection limit for Z>ll is between 10.12 and 10 -15 g and the relative limit as low as 0.1 I.tg/g. With techniques like Rutherford Back Scattering (RBS) or Nuclear Resonance Analysis (NRA), it is possible to perform in- depth profiling of elements with an accuracy in the few nanometer range which make them useful analysing tools for instance in the semi-conductor industry. Accelerator mass spectrometry (AMS) is a relatively new and very sensitive technique for measuring isotopes and isotope ratios 5. With a few exceptions all AMS measurements are performed with tandem accelerators. In essence its principle is to accelerate all the various isotopes to a well defined final energy and then separate them in a magnetic analyser system where they can be counted with a suitable detection system. The advantage of starting with negative ions is the suppression of a number of stable-isobar interferences like 14N because of their inability to form negative ions. The method was initially developed as an alternative for l'~2-dafng by radioactive decay, but at present it is also used for other long living isotopes like t°Be, Z6A1, 36C1 and 41Ca with half-lives between 102 and 108 years. The obvious advantage of this method over counting decay-products is that in the relative short time interval typical for a measurement, there are many more surviving atoms present than decay products. The detection limit for stable isotope

concentration is - 10.12, for the ratio radioisotope/ stable-isotope - 10 16 and for

exotic particle concentrations - 10 tg- The large difference is due to the difference in the background one has to deal with 5. In principle AMS can also be done with other kind of accelerators. Especially for heavier elements, energies of the order of 10MeV/nucleon or higher are desirable in order to obtain good isotope and isobar separation. For this one can use a tandem + linear accelerator combination like the ATLAS facility at Argonne National Laboratory or any of the new superconducting isochronous cyclotrons.

3.3 APPLICATIONS IN MEDICINE 3.3.1. INTRODUCTION Major applications in medicine are radiation therapy and imaging. Radiation therapy has already a long history, a well known example being the treatment of thyroid malignancies with ~3~I. The main requirement for radiation treatment is that it should concentrate the damage in the tumor and spare the healthy tissue around it as much as possible. Moreover its method of administering should be reliable and "cheap". The traditional and well-proven method to do this is with "~-radiation from electron linear accelerators. However there is now an increasing interest in using protons and light heavy ions instead of T-radiation. The present trend is towards a therapy in which different techniques are combined, like high precision therapy for

A. van der Woude /Nuclear Physics A583 (1995) 51-60 55c

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t he primary solid mass and a regional or systematic therapy for the spread of the disease. This can be achieved with hadron (proton or heavy ion) therapy combined with a targeted radionuclide therapy like Boron Neutron Capture Therapy. A more sophisticated treatment technique requires refined diagnostic techniques like Positron Emission Tomography (= PET).

3.3.2 EIADRON THERAPY The advantage of "heavy" panicles over "/-my treatment is illustrated in figure 3 which shows the dose or damage as function of depth in tissue for ~'s and protons: for hadrons maximal ionisation is concentrated at the end of the track, in the Bragg peak, while for 7's such a localisation does not occur. By varying the particle energy a homogeneous distribution in depth can be obtained. The other advantage is small lateral spreading so that the beam width remains well defined. Protons of 200 MeV and light heavy ions of 300-500 MeV/nucleon have a range of about 25 cm in tissue, so that in principle with such beams any deep-seated tumor can be treated. Up till now most experience has been obtained with protons using

56c A. van der Woude / Nuclear Physics A583 (1995) 51-60

accelerator facilities still in use or already abandoned by nuclear physicists: well known examples are the 160 MeV synchro-cyclotron at Boston and the PSI facility at Villingen, Switzerland. There is only one dedicated facility operating, which is located at Loma-Linda, California. Another dedicated facility in the U.S.A. will be the Northwest Proton Therapy center at Boston where a consortium headed by the Belgian firm IBA will supply a 235 MeV proton cyclotron-based facility. At Chiba in Japan, the HIMAC (Heavy-ion Medical Accelerator) facility with light heavy ion beams up to 800 MeV/nucleon Argon, just started to operate. Many more facilities are now in operation or planned, among them the Hadron therapy Project launched by the INFN in Italy, which combines a large central facility with several regional ones. Up till now approximately 15.000 patients have been treated with hadron (mostly proton) therapy, in some cases like melanomas in the eye with spectacular success. The new development in this field is conformal treatment: delivery of the required dose in a three dimensional volume conform the tumor distribution in the body. This can be done by using a spot scanning system as shown in figure 4 which illustrates the way adopted at GSI for their heavy-ion therapy facility 6. The target volume is dissected into slices of equal particle range and each slice is treated independently by scanning a narrow particle beam of a few mm cross section in a two dimensional raster using a fast magnetic steering system. The different particle ranges = energies can be obtained by putting absorbers of varying thickness in the beam. By adjusting for each pixel the integrated current, one can get any prescribed dose distribution. A total of 104 pixels may be necessary and in order to keep the treatment time per patient reasonable, each pixel radiation including change over to the next one should be performed in 10-50ms. This is technically feasible. A further improvement in sparing healthy tissue is possible if this technique is combined with a gantry so that the radiation can be performed from different directions of incidence. The challenges are: (i) to develop the conformal treatment itself, that is to translate the tumor distribution determined with techniques like PET, MRI or CT scans, into a treatment planning prescription, (ii) to design an optimal (gantry + pixel) delivery system including a full-proof safety system and (iii) to develop an on-line monitor system that measures the actual dose distribution delivered, compares it with the desired distribution and couples that information back to the beam delivering system. Although hadron therapy seems to have at least for specific cases clear advantages over conventional y-therapy, it is not yet sure whether this is also true in general. Also in ?-therapy conformal treatment is progressing. Clinical studies in which the most advanced techniques for 7- and particle treatment are compared, are necessary to decide what kind of therapy is optimal and most economical for a specific case. These clinical studies should be supported by more basic radio- biological research on the effect of various types of radiation on a specific type of tumour ceil. For large scale hadron therapy application in hospitals it will be desirable to design an integrated facility of accelerator, beam guiding, gantry and monitoring system. Reliability, ease of operation and low price will be the main criteria.

The concept of Boron Neutron Capture Therapy (BNCT) has potentially very nice properties. It is based on the high thermal neutron capture cross section of 3840 barns for the process tOB(n,o07Li, with a total energy release of 2.8 MeV. The combined range of the heavy particles of 15 ~tm roughly corresponds to the size of a cell. If a tumour could be loaded wi,,, lOB and /hen irradiated with thermal neutrons, a great deal of energy would be released at exactly the right place, including metastases. The challenge is to find Boron-carrying pharmaceuticals which are preferentially absorbed in the tumor. Moreover, application in hospitals requires the development of cheap, reliable, low-energy and high-current proton accelerators and target+moderator technology to produce the neutrons.

A. van der Woude / Nuclear Physics A583 (1995) 51-60 57c

3.3.3 POSITRON EMISSION THERAPY (PET) With PET functional in vivo imaging in a quantitative way is possible. In cancer therapy its use would be to determine the distribution of viable cells before and after treatment. It employs short-lived, positron emitting, radio-pharmaceuticals in which one of the nuclei ~1C, 13N, tsO, or ~SF with t~a = 20, 10, 2 and 110 min respectively, is built in. These radionuclei emit positrons which annihilate with an electron under emission of two "~'-quanta with an energy of 511 keV under a relative angle of 1800 . Its principle is illustrated in figure 5.

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A measurement of the two y's in coincidence determines the line on which the annihilated positron was located, the position of a point source can then be located by measuring several events. Using a multiplane system of BGO block detectors and modern computer analysing programs the three dimensional shape of an extended source can be located with a precision of 5mm FWHM or better. Due to the short half- lives the synthesis of the radiopharmaceuticals has to be done on site, implying the availability of a cyclotron for isotope production in combination with a facility for radiochemistry.

Figure 5. The principle of PET.

Woddwide there are about 100 PET centers, which are used for clinical purposes as well as for research. Its main drawback in comparison with other imaging techniques is the relative high cost and the need for highly qualified personnel to run the facility. Physicists can contribute to further progress first all by designing cheaper isotope production facilities, for instance by using small superconducting cyclotrons or Radio Frequency Quadrupole accelerators. A major improvement would be if fast and efficient crystals for y-ray detection would be available: with 10 ps time resolution, time-of flight measurements can be used to locate the source of positron emission. This would mean a considerable simplification in data analysis and an increase in position resolution to the ultimate limit of - 2 mm, dictated by the path length of a positron in material.

3.4 NUCLEAR PHYSICS AND THE ENERGY PROBLEM Nuclear Physics has had a large impact on energy-production methods. A considerable part, about 17 %, of the world's electricity production is already generated by nuclear power. With the increasing demand for power combined with the fear for the greenhouse effect, nuclear power generation might even become more important. This will be especially true if one would succeed in overcoming the .main objections against nuclear power: the inherent safety of the reactors, the nuclear waste problem and the possibility to produce weapon-grade material. At present there are two new concepts for large scale energy production in which nuclear physics techniques are used, both based on the use of accelerators. In "Inertial Confinement Fusion Driven by Heavy Ion Beams", small 10mm pellets

58c A. van der Woude / Nuclear Physics A583 (1995) 51-60

containing a few milligrams of a deuterium-tritium mixture are subjected to simultaneous bombardment of several 10-20 nsec wide pulsed beams of for instance 10 GeV Bi-ions with a total power of 5 MJ and a peak power of 250-500 TW. As is clear from several recent review papers 7, this concept may well be the only alternative to magnetically confined fusion. It has several advantages like: no radio-active actinide production, no complex magnetic configuration system, etc., but it requires very sophisticated accelerator and target technology. Recently a novel breeder reactor concept s has emerged which is based on a Thorium fuel cycle with accelerator- produced neutrons injected in the reactor core in order to supply the extra neutrons needed to equilibrate the neutron balance. In this concept the main breeder reaction chain to produce the fissionable nucleus 233U is:

232Th + n ~ 233Th + 7 2~m 233p a + ~. 27a 233U + I~" By keeping the neutron flux at a value of about 1014 n/cm2.s, the competing reaction : 233pa + n ~ 234U +~, which bypasses the production of the fissionable "33U, has only a small yield. In equilibrium the ratio of 233U/ 232Th = 1%, independent of the exact value of the flux, while the yield of Pu isotopes is ~ 10 "4. The thermal power production P for a reactor loaded with 5 ton of Thorium would be around 300 MW. The main problem in this concept is the neutron balance. In the breeder process every neutron causing fission has to produce effectively at least two other neutrons, one to replace the fissioned nucleus through the capture process and one for the next fission process. A key parameter is thus the ratio k between the neutrons at the end of a complete cycle to the number starting the generation. In a realistic design of a reactor based on the Thorium breeder concept 0.9 < k < 0.95, making it necessary to add ,neutrons from an external source. The idea is to realise this by injecting neutrons produced by bombarding a heavy target with a high intensity proton beam of say 1.5 GeV and 10 mA. Such an accelerator should be feasible with present day accelerator technology.

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Figure 6. The energy balance of the Thorium breeder concept s .

The energy balance as illustrated in figure 6 results from the following considerations: N injected neutrons produce N x k(*-t) in the n th cycle and a total of N / (l-k) for k ~ ,,*. Every neutron costs about 35 MeV while about 40% of them cause fission with an energy release of 190 MeV. The energy gain is thus G - 2.2 / (l-k) - 20 to 40.

A. van der Woude / Nuclear Physics A583 (1995) 51-60 59c

Another feature is that once the supply of extra neutrons is stopped, the energy

production decreases, at least if the neutron flux is kept around 10 t4 so that the amount of 233pa which is produced but not yet converted into 233U is not too large. This concept has in principle a few advantages over the traditional reactor concept: (i) there is plenty of 23:Th around, (ii) the production of weapon grade material is negligible small, (iii) two well-known technologies, reactor and accelerator, are combined and (iv) the operation is inherently safe. Of course a lot of detailed studies have to be done before this attractive concept can be transformed into a realistic design. One the main issues will be (target + moderator) design. But also the economics of the system should be studied carefully, especially since also in this concept radio-active waste is produced.

4.CONCLUSIONS This overview has out of necessity been incomplete. Nevertheless. it may have sufficed to show that Nuclear Physics, its techniques and methods, has found a steadily increasing number of applications in a great variety of fields and that this multi-disciplinary work is interesting in itself. Progress in nearly all fields is strongly dependent on further refinement and improvement of Accelerators (including ion-sources) and Detection Equipment. With respect to Accelerators the development has to concentrate on Precision, Power and Price. The key word is phase-space density. For analytical techniques and material modification this should result for instance in sub-micron beams with sizable beam- currents of light and heavy ions while in the Energy sector the proposed concepts need nigh-power GeV beams. Also reliability and ease of handling is essential for any large-scale medical and industrial application. Applying technologies like superconductivity, pulsed magnets and computer-control should result in smaller, cheaper and more reliable machines. Electron cooling of particle beams in synchrotrons, already applied in several facilities, will continue to be developed, resulting in very "cold" beams with which high precision experiments will be done. Many applications will profit from further development of detectors and data. handling techniques. High density, fast detectors, together with sophisticated data handling and analysing systems will find a direct application in PET. Higher resolution will improve the sensitivity of analysing techniques. Low level counting techniques are equally important in studies of natural and artificial radioactivity as in basic physics. In fact, any new feature which will originate from the demands in basic nuclear research will find its application in another field. An interesting aspect of much of the work described in the report is that it is relatively small-scale requiring only modest investments with which first-rate multi-disciplinary research can be conducted. This makes this kind of work attractive for research at Universities and also suitable for introducing Nuclear Physics and Technology in developing countries. A point of great concern is the tendency at several Universities to omit Nuclear Physics from the curriculum. This may have the result that in not too long a time from now we may be facing a shortage of physicists who are familiar with the basic ingredients of Nuclear Physics and Technology. This is. not only regrettable because on the long run it will hamper the understanding of the physical world around us, but also highly undesirable because Nuclear Technology can contribute much to a modern industrial society. The community of Nuclear Physicists should try to avoid this by making responsible authorities aware of the present trend and the consequences that might have. I am grateful to all the colleagues of the working groups who have contributed to what is going to be the NUPECC Report on "Impact and Applications of Nuclear Physics". Without their input I would not have been able to present here this short

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and necessarily incomplete list of what I consider quite interesting Nuclear Physics.

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W.Kutschera and M.Paul, Ann. Rev. Nucl. Part. Sci. 40 (1990), 411 6. G.Kraft, Europhysics News 25 (1994), 81

Th. Haberer et al., Nucl.Instr. and Meth. A330 (1993), 296 7. R.Bock, Europhysics News 23 (1992), 83

C.Rubbia, Nucl. Phys. A553 (1993), 375c 8. F.Carminati et al., CERN/AT/93-47 (ET)

applications of