Conseil Scientifique et Technique du Service de Physique Nucléaire

November 29, 2004 CEA/Saclay, DSM/DAPNIA/SPhN, Orme des Merisiers, Building 703

Contents

Contents 1

Agenda 3

List of members 5

COMPASS 7

Delayed neutron measurements from photo-fission 25

The Double Chooz experiment 41

A contribution of the SPALADIN experiment 49

Proton induced fission in the GeV domain with ALADIN, 59 MUSIC 4 and LAND

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Conseil Scientifique et Technique du Service de Physique Nucléaire

November 29, 2004 CEA/Saclay, DSM/DAPNIA/SPhN, Orme des Merisiers, Building 703

Agenda

Public Session (building 703, room 135) Monday, November 29 9:00 – 9:10 Introduction Michel Garçon (10') 9:10 – 9:30 - Physics at SPhN: the view from the DAPNIA Review Committee - Status of SPIRAL-II Jean Zinn-Justin (20') 9:30 – 10:15 COMPASS (Status and Prospects) Fabienne Kunne (35' + 10') 10:15 – 10:35 HAPPEX2 (Results) David Lhuillier (15' + 5') 10:35 – 10:55 Coffee break 10:55 – 11:40 Delayed neutron measurements from

photo-fission (Proposal) Danas Ridikas (35' + 10') 11:40 – 12:05 The Double-Chooz experiment (Letter of Intent) Alain Letourneau (20' + 5') 12:05 – 12:25 Study of 8He Valérie Lapoux (15' + 5') 12:25 – 13:50 Lunch break 13:50 – 14:10 Spallation studies Sylvie Leray (15' + 5') 14:10 – 14:35 A continuation of the SPALADIN experiment (Proposal) Jean-Eric Ducret (20' + 5') 14:35 – 15:00 Proton induced fission in the GeV domain with ALADIN, MUSIC4 and LAND (Proposal) Alain Boudard (20' + 5')

Closed Session (building 703, room 125) Monday, November 29 15:15– 18:00 Closed Session

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Conseil Scientifique et Technique du Service de Physique Nucléaire

Members Membres de droit: Nicolas Alamanos Jean Zinn-Justin Chef du SPhN Chef du DAPNIA CEA/Saclay CEA/Saclay DSM/DAPNIA/SPhN DSM/DAPNIA F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France Membres élus: Michel Garçon (chairman) Frank Gunsing (secretary) Wolfram Korten CEA/Saclay CEA/Saclay CEA/Saclay DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France France Jean-Marc Le-Goff Danas Ridikas CEA/Saclay CEA/Saclay DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France Membres nommés: Jean Barrette Piet van Duppen Dietrich von Harrach Department of Physics Inst. Kern- en Stralingsfysica Institut für Kernphysik McGill University Department Natuurkunde en Joh. Gutenberg Universität 845 Sherbrooke Street West Sterrenkunde J. J. Becher Weg 45 Montreal, Quebec University of Leuven D-55099 Mainz H3A 2T5 Celestijnenlaan 200 D Germany Canada B - 3001 Leuven Belgium

Marek Lewitowicz Yuri Oganessian Dan-Olof Riska GANIL Flerov Lab. of Nuclear Reactions P.O. Box 64 BP 55027 JINR FIN - 00014 University of Helsinki F-14076 Caen Cédex 141980 Dubna, Moscow region Finland France Russia

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Invités permanents: Françoise Auger Jean-Paul Blaizot Paul Bonche Adj. au Chef du SPhN Chef du SPhT CEA/Saclay CEA/Saclay CEA/Saclay DSM/SPhT DSM/DAPNIA/SPhN DSM / SPhT F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France France Gabriele Fioni Sydney Gales Yves Terrien Adjoint au Directeur Directeur Adjoint Adjoint au Directeur CEA/Saclay IN2P3 CEA/Saclay DSM/DIR 3, Rue Michel-Ange DSM/DIR F-91191 Gif-sur-Yvette F-75781 Paris Cédex 16 F-91191 Gif-sur-Yvette France France France Pascal Debu Pierre-Olivier Lagage François Damoy Chef du SACM Chef du SAP Chef du SDA CEA/Saclay CEA/Saclay CEA/Saclay DSM/DAPNIA/SACM DSM/DAPNIA/SACM DSM/DAPNIA/SDA F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France France Philippe Rebourgeard Pierre-Yves Chaffard Bruno Mansoulié Chef du SEDI Chef du SIS Chef du SPP CEA/Saclay CEA/Saclay CEA/Saclay DSM/DAPNIA/SEDI DSM/DAPNIA/SIS DSM/DAPNIA/SPP F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France France France

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Conseil Scientifique et Technique du SPhN

RESEARCH PROPOSAL Title: COMPASS Experiment carried out at: CERN

Spokes person(s): Alain Magnon, Gerhard Mallot

Contact person at SPhN: Fabienne Kunne

Experimental team at SPhN: J. Ball, Y. Bedfer, E. Burtin, N. d’Hose, F.Kunne, J.-M .Le

Goff, A. Magnon , C. Marchand , J. Marroncle, D. Neyret , S. Panebianco, S. Platchkov,

S.Procureur, M.Seimetz, E.Tomasi and J.Zhao.

List of DAPNIA divisions and number of people involved:

SPhN (16), SEDI, SACM, SIS

List of the laboratories and/or universities in the collaboration and number of people

involved:

26 institutes, ~220 participants

SCHEDULE

Duration of project: from 2005 to 2010 (6 years)

~ 30 months preparation time; beam foreseen mid 2006

Total beam time requested: 5 years (5 months/year)

Expected data analysis duration [months]: about 5x12 months

REQUESTED BUDGET

Total investment costs for the collaboration: 6.5 M€

Share of the total investment costs for SPhN: 480 k€

Investment/year for SPhN: 330 and 150 in 2005 and 2006 respectively

Total travel budget for SPhN: 690 k€ (4 years; 16 physicists + engineers and technicians)

Travel budget/year for SPhN: ~ 90 k€ in 2005, 120k€/year between 2006 and 2010

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If already evaluated by another Scientific Committee:

Experiment approved in 1997 by the SPSC at CERN for the muon and hadron programs.

Continuation 2006-2010 approved by the SPSC (Villars meeting, September 2004)

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COMPASS status and prospects Abstract : During its first phase (2002 to 2004) COMPASS has been running with polarized muons scattered on polarized deuterons in order to probe the gluon polarization in the nucleon. The first result for ΔG/G has already been obtained from the high pT hadron channel using 2002 + 2003 data. Adding the 2004 data, we should be able to extract ΔG/G from the D0 channel for the first time. The COMPASS collaboration is now preparing the completion and the upgrade of the spectrometer for the second phase of physics data taking (2006 to 2010). A detailed analysis of the present results shows the necessity of improving the performances of the first spectrometer (large angles) which is crucial for the D0 reconstruction. Apart from the work already agreed upon by a special MoU on the new target solenoid instrumentation and tests, Saclay contributions will focus on the construction of a large size drift chamber, the participation to the upgrade of the RICH electronics and the necessary upgrade of Micromegas for hadron beams. I – Introduction The main objective of the program using the high energy muon beam is the determination of the gluon polarization ΔG/G in the nucleon, which can be probed by measuring a spin asymmetry for the Photon Gluon Fusion (PGF) reaction, γ* g q qbar. The PGF process is identified either by detecting a charmed D meson (which results from the hadronisation of a c quark), or by selecting a pair of hadrons with large transverse momenta pT. Several other aspects of the spin structure of the nucleon are also studied in parallel, like longitudinally and transversely polarized parton distributions. In particular data on Δs (strange flavour), on A1 (inclusive spin asymmetry) and data on the transversity distribution functions are also collected. The COMPASS large angle and high flux spectrometer [1] has been designed and build for this muon physics program and for a complementary program of hadron spectroscopy using high energy hadron beams. It was commissioned in 2001 and 2002. Physics data were taken in 2002, 2003 and 2004 with polarized muons scattered off polarized deuterons. In 2005 there will be no beam at CERN. The COMPASS collaboration is now preparing the completion and the upgrade of the spectrometer in order to be able to start a second phase of physics data taking (2006 to 2010) with a larger acceptance and an improved efficiency of the particle detection and identification. Both physics programs with muons (measurement of ΔG/G, Δs and transversity) and hadrons (charmed hadron spectroscopy, exotics and glueballs) will be addressed in this second phase.

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II - Accomplishments COMPASS phase I i) Construction (1997-2001): The contribution from Saclay to the initial layout of the COMPASS spectrometer represents an investment of ~ 1.5 M€ devoted to: - the development and the construction of 12 Micromegas detectors [2], 40 x 40 cm2 with associated front-end electronics (12000 channels) . For this purpose the low noise preamplifier discriminator SFE16 was developed (DAPNIA/SEDI). - the construction of 3 drift chambers, 1.2 x 1.2 m2 with associated front-end electronics (3000 channels) [3]. - the reinstallation of the SMC solenoid for the polarized target. ii) Data taking (2002-2004) About 1000 Tbyte of data have been accumulated during the ~250 days of beam allocated in total between 2002 and 2004, with an approximate sharing of 80:20 for the longitudinally and transversely polarized target, and including a pilot hadron run of 21 days in October 2004. III - Saclay Responsibilities in COMPASS From the origin of the project up to now, Saclay has had important responsibilities in the COMPASS collaboration: Spokesperson : A.Magnon 02/2003 - 02/2005 Analysis coordination : J.-M. Le Goff 10/1999 – 06/2001 Deputy analysis coord : J.-M. Le Goff 2003-2005 Run coordination : F. Kunne 2002 – 2003 Technical coordination S. Platchkov 07/2003 – 07/2005 Publication committee F. Kunne 07/2001 – 07/2003 C. Marchand 07/2003 – 07/2005 Code management C.Marchand 2001-2002 Three Ph.D. thesis were defended in our group [2,3 and 6] and 2 more are in progress (Stefano Panebianco, fall 2005, and Sebastien Procureur, fall 2006). IV – First physics results All data taken in 2002 and 2003 have been produced and analysed. Saclay plays a leading role in the analysis which leads to promising results in the two most important sectors of the COMPASS spin physics program, the D0 channel and the high pT channel for the measurement of ΔG/G:

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1/- The open charm channel (γ* g c cbar) where a charmed quark hadronizes into a charmed meson D0 is the ‘golden channel’ for the measurement of ΔG/G . The signal is a clear signature of the photon gluon fusion process, and thus the theoretical interpretation is easier. However, experimentally the task is difficult: the cross section and the decay branching ratio are low. In addition, the impossibility of reconstructing the decay vertex of the D0, due to the target thickness, imposes to identify the D0 by reconstructing its mass from its decay products a pion and a kaon. The kaon is identified using a RICH. In order to improve the signal over background ratio, we reconstruct events where a parent D* decays into a D0 and a low energy pion which can be detected in the spectrometer.

Fig. 1 : Invariant mass of the K π system coming from the D0 decay via a D* tagging: D* D0 πs K π πs ( 2003 data).

Fig.1 shows the resonance peak for the D0 mesons produced via a D* meson (accompanied by a soft pion πs), and identified by their hadronic decay:

D* D0 πs K π πs .

Comparing the number of reconstructed D0 with detailed Monte Carlo simulations, we have identified the major sources of inefficiency in order to improve further data taking and analysis of this channel. Based on this work, between 2002 and 2003, the factor of merit of the experiment could already be improved by a factor of about 4 [4]. More work on the software is still ongoing. Adding all 2004 data (D0 and D*) and taking into account some software improvements, we expect to be able to extract the value of ΔG/G with a statistical

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uncertainty of about 0.24 (see Fig.2) .We expect that systematic and theoretical uncertainties will not dominate. 2/- The second channel which is used to tag the photon gluon fusion process is the production of a quark antiquark pair (γ* g q qbar) hadronizing in a high pT hadron pair. The two outgoing hadrons (mainly pions) are identified and their momentum measured. The pQCD scale is set by requiring large transverse momentum. The γ∗d spin asymmetry for high pT hadron pairs with longitudinal target polarisation has been extracted [5,6] using 2002+2003 data. We obtain a small value for the asymmetry:

A ( γ *d h h’) = - 0.015 ± 0.080 (stat) ± 0.013 (syst)

This channel provides high statistics. In order to extract ΔG/G from this asymmetry, a Monte-Carlo simulation is used to calculate the ratio of photon-gluon fusion (PGF) to the total cross section (0.34 ± 0.07). Other processes like γ*q q and γ*q qg compete with PGF but although their cross section is important, their contribution to the spin asymmetry is shown to be negligible: since it is proportional to the inclusive spin asymmetry A1

d, it is easily kept small by keeping only events with xBj < 0.05 for which we measure A1

d ~ 0. Using the analyzing power of PGF calculated at leading order, we find:

ΔG /G = 0.06 ± 0.31 (stat) ± 0.06 (syst) The above result uses only data with Q2 > 1 GeV/c2, in order to minimize theoretical uncertainties at low Q2. Data are from 2002+2003. The average value of xg is 0.13 ± 0.08. The result is shown in Fig.2 together with the two existing experimental points (SMC and HERMES) and the COMPASS projections for 2002-2004. Adding the data from all Q2 will increase the statistics by a factor of about 10, but

requires further calculations to estimate the contribution of processes involving resolved photons which may contribute significantly to the asymmetry. Note that the HERMES result was obtained without the cut Q2 > 1, and that no correction for the resolved photon contribution has been applied.

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Fig.2: First value of ΔG/G extracted by COMPASS in the high pT channel (red circles) at xg=0.13, with Q2>1 GeV2/c, compared to the published SMC and HERMES values. Note that the latter includes data at all Q2, and is thus affected by a large theoretical uncertainty. Expected error bars from COMPASS D0 channel for 2002-2004 data (blue triangle) and for the high pT channel (all Q2, 2002-2004 data; blue square) are also shown.

Measurements from the inclusive asymmetry for the deuteron A1

d [5] show the potential of the COMPASS apparatus: preliminary results from the 2002+2003 data are in agreement with previous SMC data (Fig.3a), and give more precise values at low xBj (Fig.3b), a region which is important to determine the integral of ΔΣ , the contribution of quarks to the nucleon spin.

a)

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b) Fig 3: The inclusive spin asymmetry A1

d as a function of xBj (2002+2003 data).

Semi inclusive data obtained with transverse polarization of the target have been analysed, and the first results for the Collins and Sivers asymmetries on the deuteron at several values of the xBj variable have been extracted [7]. More physics results have been derived from the 2002+2003 data. They concern the production of ρ0 and φ vector mesons at low Q2 [8], the measurement of polarization of Λ and Λbar and the flavour decomposition of polarized parton distribution functions using semi-inclusive events. The production of data taken in 2004 is in progress. Although all these physics results are promising, we can already anticipate that by the end of the 2004 run, the muon physics program will not be finished. Rather good statistics can be obtained on the spin asymmetry measurement for the high pT channel data, but theoretical uncertainties will limit the precision on the value extracted for ΔG/G. For the D0 channel, we expect to extract a first value of ΔG/G with statistical error of about 0.24, but more statistics will be needed to reach the error bar mentioned in the proposal (0.14). A significant increase of the acceptance of the spectrometer is thus foreseen after 2005 by the use of the larger acceptance target solenoid. Hardware improvements, especially in the first spectrometer (RICH, tracking,… ), are also foreseen in order to reach the necessary figure of merit of the experiment as discussed in [4]. Taking advantage of this major improvement, additional measurements of ΔG/G are planned. For the transversity measurement, the increase of acceptance (going from 70 to 180 mrad) will be particularly important in order to get statistics at high values of xBj, where models predict higher values for the transverse spin distributions.

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V – Target solenoid: slow control, safety system installation and tests (addendum to phase I)

The large radius solenoid (180 mrad acceptance) originally foreseen for the beginning of the experiment was not ready in time. In order to start the muon program, it had been decided to reinstall the old SMC solenoid (70 mrad acceptance) in 2001. This was successfully done by Saclay DAPNIA/SACM. Only thanks to this, it was possible to take data on ΔG/G until 2004. The new COMPASS large radius solenoid will soon be delivered by the Oxford-Dan Physics Company. A specific addendum to the initial MoU has recently been signed between Saclay, CERN and COMPASS. It defines the tasks taken by Saclay / DAPNIA in order to make the solenoid operational for COMPASS. The planning is the following: - Delivery to Saclay and installation (end 2004/ beginning of 2005) - Cryomagnetism and vacuum tests, cooling. Magnetic tests: field ramp up, reversal, field homogeneity, safety, slow control and quench detection. (2005) - Characterisation and delivery to CERN. - Installation at CERN, tests, magnetic measurements, polarisation - Magnet operational for the data taking : early spring 2006. Most of the costs are covered by COMPASS and CERN. Saclay provides the equivalent of 5 men years labour. VI – COMPASS phase II (2006-2010) The last SPS Committee meeting held in Villars in September 2004 examined the fixed target experimental programs at CERN. For COMPASS, the physics programme for the future with muon and hadron beams has been presented in three distinct talks [9-11] given in the session ’soft and hard hadron’. The Committee acknowledged the future of COMPASS up to 2010 with the aim of finishing the physics program described in the proposal, and recalled the priority of the ΔG measurement [12]. After the 2005 break, COMPASS will thus go on with the following program: i) Physics program - Spin structure of the nucleon: The new large acceptance solenoid for the polarized target will bring an increase of acceptance from 70 to 180 mrad, thus enlarging the kinematical domain for several observables, and the statistics for ΔG/G. Data taking on ΔG/G, A1, Δs and transversity will be resumed for 2 or 3 years with the high energy muon beam and polarized d and p targets. The deuteron target is more favourable for the measurement of ΔG/G, while the proton target is necessary to separate the various quark flavours especially for the transverse measurements.

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Estimations on expected error bars have been made [4]. They are based on 2002+2003 results and take into account the foreseen upgrades of the spectrometer. They show that a significant measurement of ΔG/G, close to the error quoted in the proposal (0.14), will be feasible in the D0 channel.

For the high pT channel , the estimation gives an error of about 0.07 when keeping only events at Q2>1. As stated before, about 10 times more statistics will be obtained at lower Q2. Provided that theoretical calculations on the contribution of resolved photons are well advanced, we could expect to divide the statistics into several bins of xg using data from this channel. Note that for the measurement of ΔG/G, the only competitor is the RHIC spin collaboration (STAR and PHENIX experiments). They use polarized pp collisions at high energy (200 and later 500 GeV) in order to probe the polarized parton distributions ΔG/G and Δq/q. Their ‘golden channel’ with a photon and a jet in the final state will require much more luminosity and higher beam polarization than what is available in the coming years. Nevertheless, they can already measure double spin asymmetries ALL from other channels, like the production of π0. They have published results from 2003 data [14] obtained with a luminosity of 0.3 pb-1, and a beam polarization of ~0.30 (Fig. 4a). These results are not yet conclusive for ΔG, since they are affected by large statistical and also systematic errors. For the future run, assuming a luminosity of 10 pb-1 and beam polarization of ~0.50, they expect to get a more precise measurement of the double spin asymmetry ALL (Fig. 4b).

Fig 4a: First measurement of the double spin asymmetry ALL in pp π0 X at PHENIX. Luminosity=0.3pb-1

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Fig 4b: Error bar projections for the double spin asymmetry ALL in pp π0 X at PHENIX in run 5 (year 2005, assuming a luminosity of 10 pb-1 and beam polarizations of 50%)) and in run 7 (100 pb-1, polarizations 70%). From this point of view, it is very important for COMPASS to be ready with the upgraded spectrometer already at the beginning of the 2006 data taking period, in order to fully take benefit from the long beam time period foreseen in 2006. For the transversity, measurements at high xBj will greatly benefit from the large acceptance of the new solenoid [13]. - Hadron spectroscopy : The physics program using high energy hadron beams, described in the proposal covers pion and kaon polarisability measurements, search for exotics and glueballs states, spectroscopy of double charm baryons, and possible pentaquark studies. The COMPASS spectrometer will be equipped with the two electromagnetic calorimeters for these measurements. Further improvements of the DAQ are also foreseen. During the pilot hadron run in 2004, CEDARS have been installed and tested. They will allow for the fast discrimination of pions and kaons in the incident beam. The specific target box has been installed in the place of the polarized target, and has been used with success. Adequate additional detectors have also been installed. First data on the polarisability of the pions have been taken.

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ii) Future Saclay investment and technical projects An addendum to the original MoU between the institutes participating in the collaboration and CERN is being prepared and should be signed in 2004. It concerns a total amount of 6.5 M€ devoted to the completion and upgrade of the spectrometer in view of the second phase of COMPASS. The DAPNIA participation would be of the order of 480 k€. A detailed and critical analysis of the global efficiency of the experiment, including running, tracking, and reconstruction efficiency has been made [4]. The comparison with the Monte Carlo simulation allows us to quantify most sources of losses compared to the original proposal, to calculate the performances of the spectrometer and to identify the necessary improvements for the future. In particular the effort will focus on upgrades which ensure a significant measurement of ΔG/G from the D0 channel. The weakest points of the present setup have been identified. It has been shown that the performances of the first spectrometer (large angles) are crucial for the efficiency of the reconstruction of the D0 meson from its decay particles. In addition, reducing the background and improving the resolution on the D0 reconstructed mass is also essential for the statistics. This is why most of the upgrade will focus on improving the performances of the first spectrometer in terms of acceptance, tracker efficiency and stability, and of course efficiency and purity of the RICH detector. The goal is to improve the global figure of merit of the experiment by a factor of about 2. Based on these arguments, and apart from the work on the new target solenoid (slow control and safety system, installation and tests) already decided upon in a dedicated MoU, we have identified the following projects for Saclay: 1) Construction of a large drift chamber 2 x 2 m2 covering the new acceptance 2) Participation to the RICH read-out electronics upgrade 3) Upgrade of Micromegas for the hadron beam VII – Large drift chamber In 2001, in absence of the large acceptance COMPASS magnet (180 mrad), it was decided to reinstall the old SMC magnet of reduced acceptance (70 mrad) in order to proceed with the measurements foreseen with a polarized target without delay. The initial layout of the spectrometer which had been designed for the COMPASS magnet had also to be modified since all straw detectors were not ready at that time. In consequence a modified version of the layout, using the SMC magnet was adopted and used between 2002 and 2004 (see Fig.5). In this modified version, only one drift chamber is left upstream of SM1, since the Micromegas detectors can cope for the whole acceptance at the exit of the SMC magnet. In order to track particles behind SM1, it was decided to use the second drift chamber in combination with one straw detector and a third identical drift chamber urgently ordered by the Collaboration to Saclay.

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Fig. 5: Schematic layout of the first spectrometer for tracking at large angle. Upper Fig.: (Initial) layout designed to fit the acceptance of the COMPASS magnet, using two 1.2x1.2 m2 Saclay Drift Chambers (SDC - dark blue) upstream of the SM1 dipole, and large size Straws (green) downstream; the new 2x2m2 SDC (red) will cover the acceptance downstream of SM1. Lower Fig.: modified setup, used in 2002, 2003 and 2004, showing the reduced acceptance of the SMC magnet and the three 1.2x1.2 m2 drift chambers (dark blue) covering the whole acceptance. The performances of the three 1.2x1.2 m2 Saclay Drift Chambers match the requirements of the COMPASS proposal, namely an efficiency above 99 % and a spatial resolution of 100 µm. In addition, they introduce a very small amount of material in the spectrometer ( 6 times less than a straw detector) thus minimizing multiple scattering and production of secondary events. During the 3 years of data taking, the 3 drift chambers operated with a high reliability and were very stable : this is essential for the measurement of small asymmetries which requires the stability of the apparatus during long periods. Another interesting property of these detectors, is that their central area can be deactivated for the use in high intensity beams (normal data taking), and can be activated for low intensity calibrations runs. This allows for precision alignment runs, where data from the drift chambers are associated to small area tracking detectors (GEMS or Micromegas).

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In addition, it was shown that those drift detectors are essential for the continuous calibration of the straw detectors. Indeed the position of the individual wires of the straw detectors is not stable: it changes dramatically with temperature and not in the constant way over the whole plane. In addition, this wire position is poorly known. Although some calibrations of the straw wire positions have been performed using x-raying (in a limited spatial zone of 36 cm!), the straw information cannot be used alone. Without the information from the drift detectors, the straws provide an insufficient spatial resolution of several hundreds of microns. Finally, the total number of straws (15 double layers) is not sufficient to make the necessary 3 stations, which would require 18 double layers in total. Let us also recall that among the existing double layers, two of them show bad performances. All the experience gained with the present setup mixing efficiently drift chambers and straws, points to the necessity of adjusting the initial proposed layout. We propose for the second phase of COMPASS to build a new drift chamber of large size, to replace the station of straws immediately downstream of SM1 (Fig5a). It will also replace de facto the present third SDC, as this one is of too small size to cope with the larger acceptance of the COMPASS magnet. This large drift chamber should have similar performances, in terms of efficiency and resolution, as the smaller ones. A preliminary design exists for the large size drift chamber. The main characteristics are the following: - 8 planes XX’, YY’, UU’, VV’ (angle 10°) - Drift cell: width 9 mm, gap 8 mm - Active area 2. x 2. m2 - Central dead zone: φ 30 cm - Front End electronics (taken from old chamber): ASD8 + F1 TDC cards The chamber can be build within 18 months. The total budget needed is estimated to be of 250 k€ (chamber 200 k€ + set of tools 50€). VIII – RICH read-out electronics The COMPASS RICH detector has presently limited performances due to the large beam halo and to an insufficient chamber gain. One of the present limitations of the COMPASS RICH read out comes from the large integrating time of the GASSIPLEX chip which reads the Photon Detector signal. This integrating time of 3.2 µs results in a very high occupancy for the background muon halo events which the RICH sees. We recall that the incident muon flux is 2.108 muons per spill (4.8s), i.e. ~40 MHz. Integrated over the full RICH acceptance and given the central dead zone of the RICH, we expect a few % of this flux to be seen as halo by the RICH, i.e. 5% would give 2 MHz of halo flux. Indeed this muon halo corresponds to parallel tracks with a momentum close to the beam momentum (160 GeV), and due to the focusing properties of the RICH, leads to a concentration of rings at a fixed position in the central photon

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detectors. A further reduction factor of the flux comes from photon statistics. This leads to a maximum occupancy of ~200 kHz per pad. The presence of this high number of background photons which are indistinguishable from the signal photons make the analysis of the RICH response problematic. In consequence, the Figure of Merit (FoM) of the RICH, which depends on its efficiency and purity, is below the design expectations. In order to solve this problem an R&D project has been developed by the SPhN and SEDI groups, in collaboration with a TUM (Munich) group. The idea is to replace the GASSIPLEX by the APV chip. The APV is a fast, low noise, 128 channel chip which is already being used for other COMPASS detectors by the TUM group. Its operation, including its integration in the COMPASS data acquisition system, is fully under control. This has largely simplified all the present development and tests. The APV provides three samples of each signal. From the correlation between these three samples it is possible to have a time measurement of the signal, which allows for the discrimination between the signal and background photons. Simulations show that a time resolution around 400 ns would lead to a substantial reduction of the background and an increase of the signal; we estimate that this corresponds to an increase of around 1.5 - 2 in the RICH global FoM. An illustration of this is given in Fig.6 where the reconstructed kaon mass is shown for several values of the RICH front end integrating time between 400 ns and 3200 ns (present GASSIPLEX value).

Fig 6 : Simulation of the reconstructed kaon mass for several values of the RICH front end integrating time: 3200 (blue), 800 (green) and 400 ns (red).

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The R&D on this option, started in April 2004, consisted in the fabrication of a prototype FEE card with 4 APV chips, made by SEDI, which was tested in a test-bench at CERN and on a photon detector (PD) chamber with a particle source. These tests showed a very low noise level, around 600 e- (to be compared with a mean noise of 1000 e- for the GASSPIPLEX), and a clear in-time response of the chip to the chamber signal. The APV parameter can be varied to a rise-time between 150 and 300 ns, with a time interval between the three samples between 75 and 150 ns. In parallel with the test on the prototype card, a detailed work on simulation was also performed in SEDI in order to choose the best parameter configuration for the APV and to estimate the ballistic deficit and the effect of the ionic tail on the APV response at high flux.

During the last days of muon beam, a set of 12 APV FEE cards equipped half of a PD chamber, i.e. ~5000 channels, and was tested with hadron and high intensity muon beam. The first results from on-line analysis are that the noise level in the real RICH environment is below 650 e- and not sensitive to the presence of the GASSIPLEX FEE and other detectors nearby. Moreover the correlation between the three samples is clearly visible, which gives the felling that a timing resolution of 400 ns is certainly reachable. The offline analysis is currently ongoing. The global project of exchanging the RICH FE electronics will consist in producing 150 FEE cards corresponding to 60000 channels of the RICH. With a cost of about 5 Euro per channel, the project amounts to about 300 kEuros. We estimate the Saclay part to be of about 150 kEuro dedicated to Front End cards, plus 20 kEuro for R&D. IX – Micromegas upgrade for hadron beam The Micromegas detectors have been initially designed and optimized to operate in a muon beam. When used in the high energy and high flux ( 107-108 hadron/spill) hadron beam, they are exposed to about 100 times more discharges. In consequence they cannot be used at their nominal gain without modifications. In order to reduce the discharge rate, we can use a different gas mixture. Our initial R&D on Micromegas had shown that the discharge rate depends on the atomic weight of the gas [2]. This is why we have decided to suppress the CF4 in the mixture, when working with hadron beams. Data are now taken in this condition and will be analyzed. Another way to lower the discharge rate is to modify the geometrical characteristics of the detector, in order to operate the detector at a lower gain. We have thus modified one of the Micromegas detectors, enlarging the ionization gap from 3.2 mm to 5.5 mm. First online results show indeed a reduction of the discharge rate which has to be quantified precisely. The performances of this modified detector have also to be analyzed. Based on these results, we will have to decide on an adequate modification of the present Micromegas detectors, in order to be able to use them for the whole hadron programme. Let us recall that this project is partially financed by the JRA 4 on gaseous detectors.

22

X – Conclusion For this second phase of COMPASS, the Saclay team consists in 16 physicists (11 staff, 2 postdocs and 2 PhD students), out of which 15 work full time on the project. The total required investment amounts to 480 kEuro (250 for the large drift chamber, 170 for the RICH electronics, 20 for the Micromegas upgrade, and 10% reserve). The R&D on the RICH electronics upgrade has progressed very fast. The first results in real beam conditions are quite promising. Concerning the large size drift chamber, a preliminary design exists. Nevertheless, starting the complete drawing is now urgent in order to guaranty that the detector will be operational at the beginning of the 2006 data taking period. XI – References 1. COMPASS proposal to the CERN SPSC 1996 2. D.Thers et al. NIM A469 (2001) 133; C.Bernet et al. NIM A 2004 in print. 3. H.Pereira, Ph. D. thesis 2001. 4. J.-M. Le Goff et al. COMPASS note 2004 – 02 5. Y.Bedfer on behalf of COMPASS coll., contribution to BARYONS 2004 conference 6. C.Bernet Ph.D. thesis 2004. 7. R.Webb on behalf of COMPASS coll., contribution to BARYONS 2004 conference 8. E.Burtin et al. COMPASS note 2004-12. D.Neyret on behalf of COMPASS coll., contribution to SPIN 2004 conference 9. COMPASS with muon beam ‘Status and future’, A.Magnon, Villars SPSC meeting, September 2004 10. ‘The COMPASS hadron programme’, S.Paul, Villars SPSC meeting, September 2004 11. ‘COMPASS physics with high intensity muon beams’, N.d’Hose, Villars SPSC meeting, September 2004 12. CERN seminar, J.Dainton, October 2004. 13. ‘Prospects for the COMPASS muon programme’, A. Magnon, in Workshop on Future Physics at COMPASS, CERN yellow report, p.31. 14. PHENIX collaboration, contribution to SPIN 2004 conference

23

24

Conseil Scientifique et Technique du SPhN

PROJECT PROPOSAL

Title: Delayed neutron measurements from photo-fission

Experiment carried out at: CEA/DIF Bruyères-le-Châtel

Spokes person(s): D. Ridikas

Contact person at SPhN: D. Ridikas (ridikas@cea.fr)

Experimental team at SPhN:

J.-C. David, D. Dore, M.-L. Giacri (PhD student), D. Ridikas, A. Van Lauwe (PostDoc)

List of DAPNIA divisions and number of people involved: DAPNIA/SIS (2)

List of the laboratories and/or universities in the collaboration and number of people involved:

X. Ledoux (CEA/DIF), M. Gmar (CEA/DRT), M. Chadwick (LANL), K.H. Schmidt (GSI-Darmstadt),

J. Benlliure (Univ. of Santiago), P. Schillebeeckx (EC-JRC-IRMM, Geel)

SCHEDULE

Estimated total duration of the proposed experiment: 2005-2007

Possible starting date of the experiment: 2005

Expected duration of the data analysis: ~4 months after each measurement campaign with 1 target

ESTIMATED BUDGET

Total investment costs for the collaboration: 84 kEuros + electron beam time (~120 kEuros)

Share of the total investment cost for SPhN: ~84 kEuros

Total Travel Budget for SPhN: ~24 kEuros

25

Introduction

Recently a renewed interest in photonuclear processes has appeared. It is motivated by a number of different applications where progress in reliable and, in some cases, very high intensity electron accelerators was awaited [1]. A particular today’s interest is linked to the nuclear material interrogation and non-destructive nuclear waste characterization, both based on delayed neutron emission from photo-fission. In the same context our participation in the European Security project NUMADE is planned in 2005 (if accepted by the European Commission). Major problems in modeling photonuclear reactions are the lack of photonuclear data on corresponding cross sections despite the huge efforts of the IAEA [2], where data are available for 164 isotopes only. In addition, no material evolution-depletion code including photonuclear reactions is available. For this reason, in a close collaboration with the LANL, we have been working on the development of a new photonuclear activation data library to be included into the CINDER’90 evolution code [3]. HMS-ALICE [4] and GNASH [5] have been used to calculate photonuclear reaction cross sections for more than 500 isotopes. For photo-fission fragment distributions in collaboration with GSI we employ the fission-evaporation code ABLA [6] known to give good results in the case of high energy spallation reactions. The photonuclear activation data library should also include full information on photo-fission delayed neutrons. Therefore, due to the lack of consistent data on photo-fission delayed neutron yields we propose to start an experimental program in collaboration with CEA/DIF. Both absolute yields and time characteristics of delayed neutrons will be measured for a number of high priority nuclei as uranium and plutonium isotopes including some minor actinides (Am and Np). The energy range of Bremsstrahlung photons available are from the photo-fission threshold of ~6 MeV up to 19 MeV covering the entire Giant Dipole Resonance (GDR) region. Part I: Evaluations CINDER’90 initially was developed to perform the material activation analysis in neutron fluxes. By adding a photonuclear activation data library the calculations can be done both in neutron and photon fluxes making the code a multi-particle activation program. The following strategy to construct the photonuclear library was chosen:

a) we use the IAEA evaluations explicitly for the major 164 isotopes; b) due to the rapidity and simplicity of the calculation procedure, the latest version of the ALICE

code (HMS-ALICE) written by M. Blann is employed to complete the library for nearly 600 isotopes;

c) in some particular cases the evaluations GNASH code are performed (e.g., 235U, 239Pu, 237Np); d) the GSI fission-evaporation code ABLA is used to provide the photo-fission fragment

distributions; e) an independent code (developed at SPhN and using intermediate ABLA results and nuclear

data tables) is employed to construct delayed neutron tables. The energy range of incident photons is between 0 and 25 MeV, and an extension of the present activation library up to 150 MeV is planned in the future. Our primary task during the construction of the data library was to test the accuracy of the calculated cross sections through comparisons with the existing experimental data and IAEA evaluations. Below we present our major results and important progress made since the last “Letter of Intent” presented for the CSTS on 5 April 2004. We should note that the 1st version of the photo-activation data library for CINDER’90, containing more than 600 isotopes and nearly 2000 reaction channels, is now operational. Recently, we have applied it for

26

the 1st time in the characterization of activated concrete and metallic structures in the case of the decommissioning of LURE accelerator at IPN Orsay. Our predictions gave very satisfactory results compared to the experimental measurements of irradiated samples, what validates in part our approach for non-fissile nuclei. The remaining part of the activation data library should include the information on actinides (reaction cross sections, fission fragment distributions and delayed neutron tables). Below we present some progress made in this context. HMS-ALICE predictions [7] The problem of total photo-absorption cross section based on a single Lorentzian was solved in the case of HMS-ALICE code for deformed nuclei. The photo-absorption cross section, expressed as a sum of two Lorentzians was recently implemented into HMS-ALICE, and all separate channels are being recalculated with this new parameterization in the case of actinides and other deformed nuclei. The widths and positions of GDR are taken from the internationally recommended data library RIPL-2. The quality of our new results in the case of 235U is presented in Fig. 1. All these newly recalculated cross sections for actinides are being added to the photo-activation data library for CINDER’90.

Figure 1: Comparison of the original HMS-ALICE model for photo-absorption (solid line) with the IAEA evaluations (dashed line) and the updated HMS-ALICE using RIPL 2 parameters (dotted line) in the case of 235U.

Figure 2: Comparison of the GNASH results with data for (γ,n), (γn) in the case of 239Pu. Evaluations with GNASH [7] For the most important actinides as 235U, 238U, 237Np, and 239Pu we use GNASH evaluations. This choice was mainly motivated by the fact that GNASH, in addition to the separate reaction channels, provides also with the emission of the energy spectra and angular distributions of all secondary particles up to alphas. In other words, this evaluation tool will provide required information to construct the ENDF

27

format data files to be used by different particle transport codes. The quality of our GNASH calculations in the case of 239Pu is presented in Fig. 2. Naturally, we will include these new GNASH evaluations into the photo-activation data library under construction. In addition, our goal for the next year is to prepare these new evaluations for 235U, 238U, 239Pu, and 237Np in the ENDF format to be released with a new version of the ENDF/B-VI data library (version 8) in collaboration with LANL. Recent ENDF data files also require fission fragment distributions, where we plan to use the ABLA code as long as it is fully benchmarked in the case of photo-fission. Predictions of photo-fission yields [8] Our modeling using ABLA code can be divided into two parts: the γ absorption and the de-excitation of the nucleus. The γ excitation of the nucleus is based on the giant dipole resonance principally, but also on the giant quadrupole resonances. The absorption cross section is the sum of these components, each of them determined from empir abs based on the RIPL-2 data library as discussed above was successfully tested with ABLA and will be added to the code for all actinides in the near future). The nucleus de-excitation within ABLA is based on a statistical model, where fission is in competition with particle emission. In other words, the complete code provides neutron (proton) emission, fission cross sections and also fission yields. Multi-chance fissions are taken into account as well.

To check the validity of the ABLA code we compare our theoretical results to available data. These data are the cross sections (absorption, particle evaporation and fission), the fission yields, and the delayed neutrons. We will focus on Uranium isotopes, since they are the nuclei experimentally investigated most of the time. Other calculations for 237Np and 239Pu are also in progress.

DATAABLA

235U15 MeV 25 MeV

Fragment Mass (A) Fragment Mass (A)

YIE

LD (%

) YIE

LD (%

)

DATAABLA

235U

DATAABLA

235U15 MeV 25 MeV

Fragment Mass (A) Fragment Mass (A)

YIE

LD (%

) YIE

LD (%

)

15 MeV 25 MeV

Fragment Mass (A) Fragment Mass (A)

YIE

LD (

%) Y

IELD

(%)

DATAABLA

238U

DATAABLA

238U

Figure 3: Photo-fission fragment mass distributions in the case of 15 MeV and 25 MeV Bremsstrahlung photons on 235U and 238U (see the legends for details). Figure 3 shows the yields of fission fragments for Uranium 235 and 238. Our predictions (histograms) are compared to 15 and 25 MeV Bremsstrahlung data (squares). The widths of the peaks are well reproduced by the calculations (lines) while the heights are slightly different. We also observe a better

28

agreement for 235U at 15 MeV than at 25 MeV, while it is somewhat opposite for 238U. We note that for the next step (delayed neutron yield calculations) it is important to reproduce the relative yields of the precursors which are more abundant at the peaks of the mass distributions. Predictions of photo-fission delayed neutron yields [8] It is well known that the time dependence of the number of fission delayed neutrons YDN(t), emitted after infinite irradiation as a result of β-decay of various fission products, known precursors, can be represented as a sum of exponentials:

( ) ( ) i tDN c DNDN i i i

i i

Y t Y t Y P eλ−= =∑ ∑ (1)

where the decay constant is equal to ln2/Ti1/2 with Ti

1/2 being the half-life of the ith precursor, Yic – the

cumulative fission yield, PiDN – the probability of emission of a delayed neutron during β-decay. The

sum is over all delayed neutron precursors. Because the number of delayed precursors is very large (at present more than 270 are known), the above equation is usually approximated by lumping precursors with similar half-lives into smaller number of groups (so called a few groups model). The most widespread few-group model is the 6-group model first introduced by Keepin et al. (1957) for neutron induced fission. In a number of detailed studies it was shown that a set of 12 parameters (averaged 6 decay constants λ and 6 weighting constants a =Yc PDN) should be sufficient to describe with a desired precision the time dependence of the number of fission delayed neutrons. All critical reactor kinetics (reactor control and accident simulations) is based on this assumption and validated by a number of criticality experiments. For this reason a similar approach was adopted to describe the photo-fission delayed neutrons. In our case the following steps to calculate the photo-fission delayed neutron yields were employed

• independent photo-fission yields are calculated with the ABLA code • cumulative photo-fission yields are estimated by the use of the CINDER’90 evolution code • delayed neutron precursors are identified and selected according to the nuclear data tables • delayed neutron yields for all precursors are calculated using emission probabilities from the

nuclear data tables (more than 250 precursors are taken into account in our calculations) • all precursors are merged into 6 delayed neutron groups, characterised by the corresponding

averaged group half-life T i1/2 and time integrated delayed neutron yield ai

(with i = 1,6). Calculation results (Calc.) for 235U and 238U at 15 MeV are presented in Table 1 and compared with the existing data (Data). As expected, results for the decay constants are closer to the data than the yields are. The calculated total number of delayed neutrons is in good agreement with data, especially for 238U. For both isotopes, the groups 2 and 4 are overestimated while the 5 and 6 are underestimated. It is clear that the relative contributions of the different isotopes inside each group have to be investigated in detail. In addition, although the ABLA code predicts quite reasonably the mass distribution of the fission fragments as shown above, this result in not sufficient to guarantee reliable estimates of the isotopic fission yields, and those on the neutron rich side in particular (delayed neutron precursors are in this particular region). Another reason for this disagreement could be that delayed neutron emission probabilities Pn are not known precisely for the very short lived precursors with T1/2 < 100 ms. (See the disagreement between data and calculations for the 6th group in Table 1).

29

2.9583.119±0.41.1930.962TOTAL

0.170.19±0.020.0750.502±0.0200.170.19±0.040.010.083±0.256

0.470.70±0.060.4130.552±0.0800.470.50±0.100.0740.134±0.0305

1.922.15±0.101.3320.970±0.1502.132.01±0.250.3810.354±0.0704

5.465.50±0.200.4700.545±0.0705.215.45±0.600.2430.146±0.0303

20.3321.3±0.30.6380.489±0.07019.1020.3±1.00.4240.193±0.0402

55.6056.2±0.80.0300.061±0.01055.6054.7±2.50.0610.052±0.0101

T1/2 (s)Data Calc.

Yield Data Calc.

T1/2 (s)Data Calc.

YieldData Calc.

GROUP

238U (Ee=15 MeV)235U (Ee=15 MeV)

2.9583.119±0.41.1930.962TOTAL

0.170.19±0.020.0750.502±0.0200.170.19±0.040.010.083±0.256

0.470.70±0.060.4130.552±0.0800.470.50±0.100.0740.134±0.0305

1.922.15±0.101.3320.970±0.1502.132.01±0.250.3810.354±0.0704

5.465.50±0.200.4700.545±0.0705.215.45±0.600.2430.146±0.0303

20.3321.3±0.30.6380.489±0.07019.1020.3±1.00.4240.193±0.0402

55.6056.2±0.80.0300.061±0.01055.6054.7±2.50.0610.052±0.0101

T1/2 (s)Data Calc.

Yield Data Calc.

T1/2 (s)Data Calc.

YieldData Calc.

GROUP

238U (Ee=15 MeV)235U (Ee=15 MeV)

Table 1: 6-group model parameters for photo-fission delayed neutrons in the case of 15 MeV Bremsstrahlung photons on 235U and 238U: both sets of parameters extracted from the experiment (Data) and based on the ABLA code predictions (Calc.) are presented. Part II: Motivation for the experimental program Systematic from neutron induced fission We tried to establish a direct link between neutron and photon induced fission in terms of the same composite nucleus and similar excitation energy. The best example in this case would be n(4 MeV)+ 234U and e(15MeV)+ 235U giving in both cases the same composite nucleus (235U) and the excitation energy around 10 MeV. Indeed, the total number of delayed neutrons is comparable, i.e. within 10 % (see Tables 1 and 2). On the other hand, averaged decay constants and some of the single group weighting constants are very different. By inserting these two sets of parameters into Eq. 1 we obtained that delayed neutron decay curves as a function of time would differ up to 30 % in some temporal regions, although error bars for both data sets are below 20 %. From this example it seems that a “simple logics” in terms of the same composite nucleus and similar excitation energy is not so evident.

Group

I

Half-life

(s)

n(fast) + 234U

(Ref. values)

1 55.60 0.058

2 23.10 0.227

3 9.71 0.109

4 3.30 0.382

5 1.39 0.223

6 0.30 0.061

All 1.06 ± 0.12

Table 2: Reference values of delayed neutrons within the 6-group model from fast neutron (~4 MeV) induced fission on 234U.

30

We also note delayed neutron yields from neutron induced fission follows certain systematic as a function of composite nucleus mass number A and charge Z, i.e. so called 3Z-A dependence as shown in Fig. 4 by solid line. Some of the photo-fission data are consistent with this relationship, however in some cases they “escape” from the expected systematic (note the logarithmic scale). Finally, data of composite nuclei like 232Th, 237Np, 238Pu, 241Am and some others in the case of neutron induced fission would be extremely difficult to obtain, while it is a “usual” experiment in the case of photo-fission. Indeed, in the case of neutron induced reactions, fission of 237Np, for example, would correspond to the 2nd chance fission from n+237Np 238Np*. It is clear that excitation of 237Np with gammas without adding a supplementary neutron is the simplest way to proceed. Figure 4: Delayed neutron yield systematic as a function of composite nucleus mass and charge for neutron induced fission (solid line) for a comparable excitation energy. Data from photo-fission are presented by blue triangles. Status of the photo-fission delayed neutron data (yields) In the case of photo-fission we collected all available delayed neutron data for 238U, which are presented in Fig.5 (on the left). Data seems to be more-or-less consistent within error bars suggesting no dependence on excitation energy. On the other hand, one expects a decrease of delayed neutron yields as soon as the energy threshold of the 2nd chance fission is passed (this channel opens at the excitation energy of ~12.3 MeV as shown on the right of the same Fig. 5). The same observation is always seen for delayed neutron yields in the case of neutron induced fission (see Fig.11 at the end of this paper). D e layed n eu tro n y ie ld

1

2

3

4

5 10 15 20 25 30Ee , M eV

n/f

iss

, %

da ta U-238

A B LA U-238

Figure 5: on the left – photo-fission delayed neutron yields as a function of electron energy; on the right – ratio of (,fiss)/[(,fiss)+(,n fiss)] as a function of photon energy, where (,n fiss) is the notation for 2nd chance fission with emission of extra neutron (from Caldwell et al. 1980).

U-236Th-232

U-238

Pu-239

U-233

Np-237

U-234U-235

Th-233

Am-241

0,1

1

10

36 37 38 39 40 41 42 43 44 45

3*Z-A

nd

/ fis

s, %

Photofission data

lnY=lnC1-C2(3Z-A)

31

As a matter of fact, the ABLA code predicts this expected decrease of delayed neutron yield as a function of excitation energy as shown in the same Fig. 5 (on the left – solid line). Experimental confirmation is clearly needed with data precision better than 10 % to confirm this dependence. We note separately that ABLA also predicts correctly the behaviour of the experimental ratio as shown on the right of the same Fig. 5 (on the right). Finally we add that there are no data at all for other actinides above the threshold energy of the 2nd chance fission, what corresponds to electron energies higher than ~17 MeV (equivalent to averaged excitation energies higher than ~12 MeV). Status of the photo-fission delayed neutron data (time spectra) It seems that decay constants of photo-fission delayed neutrons are known even with worse precision than delayed neutron yields as presented in Fig. 6 (on the left). First of all, big dispersion of data is seen for nearly all groups. Secondly, one cannot conclude if the decay constants are dependent on the excitation energy, although at these excitation energies no such dependence would be expected. It would be very interesting to confirm if the decay constants of photo-fission delayed neutrons are different below and above the threshold of the 2nd chance fission as it was observed in the case of neutron induced fission. For some applications as “isotopic identification” of different actinide vectors with unknown masses in the sample (see on the right of Fig. 6) not only the total absolute delayed neutron yields but also separate group weight and decay constants should be known with the best possible precision. As an example we performed the following analysis. We assumed that we know delayed neutron spectra for single isotopes with a precision of 10 %. It seems that in this case one is able to separate 235U and 239Pu masses within error bars of ~20 %. One should be aware that this is rather simple example, and in some cases even better initial data precision will be required (e.g., the sample contains three or even more different isotopes). Finally, most of the applications will employ Bremsstrahlung photons mainly due to high fluxes available, simplicity and attractive costs of low energy electron accelerators. Therefore, the Bremsstrahlung data is directly applicable in these cases. With mono-energetic photon data one would need to cover the entire energy region of GDR in finite energy steps, being very difficult to realize in practice, and finally to fold it back with the Bremsstrahlung spectrum. At the moment no data at all on delayed neutrons are available with mono-energetic photons, mainly due to low beam intensities available. Figure 6: on the left – photo-fission delayed neutron weight constants ai (%) within the 6-group model; on the right – “isotopic separation” of 235U and 239Pu using delayed neutron decay curves (from Xi et al. 2004).

U-238

0

5

10

15

20

25

30

35

40

45

0 1 2 3 4 5 6 7Group number

Gro

up fr

actio

n Fi

, %

8.0 MeV

10.0 MeV

11.4 MeV

12.5 MeV

15 MeV

32

Improvement of ABLA using good quality delayed neutron data Although delayed neutrons can be considered as integral observable of the fission process, however, at the same time, it seems to be quite sensitive parameter to tune fission models at low excitation energies. This we already saw in Fig. 5, where the dependence of delayed neutron yields as a function of excitation energy is presented. From this data analysis one could obtain the information on the 2nd chance fission, mainly its importance for the total fission cross section including the threshold energy and transition region. However, better quality data is needed in this case. Having a good quality delayed neutron data, including decay and weight constants within 6-group model, one could also extract some information on the fission fragment distributions, and on the wings of the distribution on the neutron rich side in particular.

Groupe Isotope Contribution (%)1 Br87 1002 I137 59,2

Br88 12,46Ba144 20,8

3 Br89 30,42I138 47,29Rb93 10,94

4 Rb94 21Br90 10,9Sb135 13,5I139 16,41

5 Rb95 32,84I141 10,45C145 19,06

6 Rb97 32,84Cs147 10Kr94 16

Table 3: Major precursors contributing to the separate groups within the 6-group model for 15 MeV Bremsstrahlung photons on 238U as predicted by the ABLA code. This is seen from Table 3 where we present major contributors to the delayed neutron yields within each group. For example, the 1st group will tell us directly the fission yield of 87Br. Similarly, relative contributions of I or Rb isotopes for different groups could be also compared directly to the code predictions. (Here we assume that delayed neutron emission probabilities Pn are known). In the same context, 6-group delayed neutron tables could be changed into 12 or higher number delayed neutron tables in order to have less precursors in each group (e.g., so called 12-group model for Iodine or Bromine isotopes; Piksaikin et al. 1999). The above argumentation is clearly in the support of an experimental program aiming to measure photo-fission delayed neutron yields and their time characteristics. In most of the cases discussed above data precision needed should be better than 10 % both for absolute values of total delayed neutron yields as well as individual group decay and weight constants.

33

Part III: Experimental The following stages were previewed for the proposed experimental program:

• calibration of neutron detectors with Cf-252 and AmBe neutron sources (finished) • calibration of neutron detectors with mono-energetic neutron beams in the energy range from 100

keV to 2.0 MeV (finished) • measurements of delayed neutron yields from neutron (2 MeV) induced fission on U-238

(finished) • measurements of delayed neutron yields from photon (Bremsstrahlung energy spectrum) induced

fission on U-238 (experiment finished; data analysis in progress) • proposal of a complete 3 year experimental program on systematic measurements of photo-

fission delayed neutron yields and corresponding time spectra as a function of (A,Z) for actinides and as a function of electron energy (Bremsstrahlung energy spectrum).

Neutron detectors and calibration with Cf and Am-Be sources Neutron counters we use are standard He-3 gas detectors under pressure of 4 atmospheres working on the principle of gas ionization via (n,p) reaction (Canberra: type 48NH30; sensitivity ~44 counts/s per n/(s cm2) ). The He-3 tubes of 30 cm long and 2.5 cm diameter (active dimensions) are surrounded by polyethylene (CH2) in order to increase the neutron detection efficiency in terms of neutron moderation. Our Monte Carlo simulations showed that an optimal CH2 thickness is around 5 cm for neutrons in the energy range of 100keV – 1 MeV, i.e. an expected delayed neutron energy range. To avoid the background due to the thermal neutrons reflected from the concrete walls, the polyethylene was coated by 1 mm cadmium foils. In this way energetic delayed neutrons passing through the cadmium barrier (the cadmium energy cut off is around 0.417 eV) are partly thermalized in the polyethylene before being detected by the He-3 counters. The He-3 counter signal is amplified and shaped using an industrial charge amplifier (Canberra: type DEXTRAY ACHP96). The analog signal is transmitted out of the irradiation hall to a multi-channel scalar and transmitted from the analyzer to a PC. Detector efficiency was already measured for a single counter using the Cf-252 (average neutron energy ~2.0 MeV) and Am-Be (average neutron energy ~4.2 MeV) neutron sources located at variable distances from the detector unit. The intrinsic detector efficiency was found to be around 5 %, what was confirmed by the Monte Carlo simulations. Test experiment with mono-energetic neutrons It is known that delayed neutrons are emitted in the energy range of 100keV – 1 MeV. Our Monte Carlo simulations have shown that our detector efficiency will not depend (within ~5 %) on the delayed neutron energy. To know more precisely this dependence we decided to perform detector calibration with mono-energetic neutrons produced by the p+Li reaction (resulting available neutron energy between 100 keV and 700 keV) and the p+T reaction (available neutron energy between 700 keV and 2.0 MeV). This experiment was successfully realized at CEA/DIF of Bruyères-le-Châtel by using the 4 MV proton accelerator. In brief, we confirmed that in the energy region from 100 keV to 1.0 MeV our detector efficiency is not dependent (within ~5 %) on neutron energy. Feasibility experiment with neutron induced fission There are much more systematic data available on delayed neutrons in the case of neutron induced fission. Having an access to the mono-energetic neutron beam we also performed a feasibility experiment in order to measure delayed neutrons emitted from fission of U-238 induced by ~2 MeV neutrons. In this case the fission cross sections, fission fragment distributions and delayed neutron yields are known precisely from independent experiments. We used a depleted 400 g uranium target (with 0.2 % of U-235

34

remaining) of metallic density (3 cm diameter and 3 cm thick). The sample was placed at ~30 cm from the neutron production target (tritium), while the He-3 counters were situated at the distance of ~15 cm from the uranium target as shown in Fig. 7. At the same angle the reference neutron detector (BF3) was placed for the instantaneous neutron flux measurements.

Figure 7: Schematic view of the test experiment for delayed neutron measurements from neutron induced fission. The target was irradiated for ~2 min and measurements were done without the beam for another ~2 min afterwards in a periodic fashion to accumulate statistics. In this way reduced decay curves of delayed neutrons were obtained. Another data taking campaigns with shorter irradiation-decay periods were tried in order to enhance the contribution of short-lived delayed neutron precursors. All data from this experiment was already analyzed. We were able to extract the total delayed neutron yield d = 0.044±±±±14% (this work) to be compared with a corresponding reference value d = 0.0466±±±±3.6% (JENDL). In addition, from the measured time spectra we could also obtain the sets of the (λ i, ai) parameters for 4 delayed neutron groups, which again coincide well with reference values. Unfortunately, due to the limited beam time we could not obtain enough statistics for the full set of data with desired error bars. Nevertheless, this experiment validated our detection system, calibration of the detector and chosen experimental strategy. In addition, this was also direct confirmation of our Monte Carlo simulations. Feasibility experiment with photon induced fission In this experiment we used the ELSA electron accelerator of CEA/DIF at Bruyères-le-Châtel to produce Bremsstrahlung photons. The electron accelerator consists of a 144 MHz photo-injector followed by three 422 MHz accelerator sections. The rf sources and main power supply limit the duty cycle to a 150 µs macro-pulse at a repetition rate of 10 Hz. For low currents (10 mA), the maximum beam energy is 2.7 MeV at the injector exit and 19 MeV at the linac exit. Bremsstrahlung photons were produced by electrons interacting with the Ta target-converter (0.12 cm thick). The remaining electrons were stopped by a thick Al layer (~5 cm). The photon background in the experimental area was strongly attenuated by ~50 cm thick Pb collimators. Behind the Pb collimators the 400 g uranium target was placed (see Fig. 8). The depleted uranium target is a cylinder defined by 3 cm diameter and 3 cm thickness. Similarly like in the experiment with neutron induced fission, delayed neutrons were measured between periodic irradiations with an electron beam off. Our Monte Carlo simulations showed that number of fissions due to the secondary neutrons will be of the order of 1 % compared to all fission events. We also predicted that the background neutrons (re-scattered from the concrete walls) could contribute up to 5 % to the signal, therefore the use of He-3 counters surrounded by Cd envelopes was employed to decrease this contribution to the minimum.

protons T

3He

Ref. BF3

238U

protons T

3He

Ref. BF3

238U

35

Figure 8: Schematic view of the feasibility experiment for delayed neutron measurements with the 15 MeV Bremsstrahlung photons inducing fission on 238U. Relative data. Like in the experiment with neutron induced fission, data taking campaigns with long (~300 s), short (~10 s) and very short (~50 ms) irradiation periods were tried in order to enhance the contribution of different periods of delayed neutron precursors. Part of the data (accumulated for ~6 hours) in the case of the 300 s irradiation-decay cycle is presented in Fig. 9. It seems that this time we will have enough statistics to extract all 6-group parameters of delayed neutron spectra with desired precision. For comparison on the same Fig. 9 we added the theoretical decay curve (solid line), based on the 6-group parameters extracted from the equivalent experiment by Nikotin et al. 1966. One notes that both data points and the parametric curve coincide nearly perfectly. Data analysis of this experiment is still in progress. Figure 9: Experimental (preliminary) delayed neutron spectrum (data points) with the 15 MeV Bremsstrahlung photons inducing fission on 238U. The red solid line is the parameterized decay curve using 6-group parameters extracted from the equivalent experiment by Nikotin et al. 1966. Absolute normalization. In order to obtain the absolute normalization of delayed neutron yield one needs to know the number of fission events taking place in the target (see the equation below). We employed 2 independent techniques for this purpose. First of all, the fission rate was measured directly by standard fission chamber (with the 4.7 mg deposit of U-238), operating in a pulsed mode. In this case, the obtained fission rate will be scaled to the corresponding uranium mass in the case of delayed neutron experiment. Secondly, we activated a sample of natCu at exactly the same position where our uranium target was were created (62 !"# $$#%

electrons

Ta

3He

238U

Al

Pb

3

3 3

( 0 )Hed

fiss He He

N t s

Nν

ε==

⋅ ⋅Ω

36

64 $#$&''%()*+,way by the use of the experimental photo-fission cross section for U-238 and calculated Bremsstrahlung spectra (now validated by Cu-activation experiment), a number of fission events in the uranium sample will be obtained. The analysis of data with the fission chamber, activated Cu sample and corresponding estimates of fission rates are in progress. Work plan of the future experimental program 2005. It seems we will obtain 3 weeks of the ELSA beam time in 2005. With the existing experimental setup we could start our experiment with available “massive” actinide targets (~100 g) like 232Th (15 MeV and 19 MeV electrons) and 238U (only 19 MeV since the 15 MeV measurements were already performed in 2004). For other actinide targets (1-10 g), one will build a much more efficient detection system, which is presented in Fig. 10. According to our Monte Carlo simulations with this new delayed neutron detection system one would obtain comparable statistics with 10 g target instead 400 g target as it was the case during our last experiment (see Fig. 9). Therefore, by the end of the next year we will be able to take data with the ~6 g 237Np target (15 MeV and 19 MeV electrons). 2006. ELSA accelerator is supposed to increase its authoriz($-.$/-. in 2006. This would allow us performing the measurements with targets of ~1 g without further update of the detection system and without additional beam time, i.e. 3 weeks per year. In this case the measurements with 235U, 239Pu and 240Pu are planned using 15 MeV and 19 MeV electrons. 2007. Finally, the remaining targets of 241Pu, 242Pu and 241Am of ~1 g would be used both with 15 MeV and 19 MeV electrons. Again 3 weeks of the beam time would be needed. Figure 10: Cross sectional view of the optimized delayed neutron detector: 12 independent He-3 counters (circles) are placed into polyethylene moderators (hexagons), which are organized into a compact hexagon lattice. One has to note a possibility to add another 6 counters if necessary to increase further the detection efficiency.

13 cm13 cm13 cm13 cm

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Budget and manpower The detailed budget of this experimental project and technical resources needed are provided in Table 4.

He-3 counters 12 tubes 4 cross connectors 3 connectors 3 preamplifiers 3 amplifiers 2 time cards Polyethylene Cd foils Detector disposal/assembling Cables

10.8 kEuros 3.2 kEuros 2.0 kEuros 3.0 kEuros 3.0 kEuros 3.0 kEuros 2.0 kEuros 4.0 kEuros 3.0 kEuros 2.0 kEuros 36 kEuros

Fission chamber 1 with 237Np deposit and 1 without deposit Mass analysis Pre-amplifier and amplifier Cables/connectors Transport

20.0 kEuros 5.0 kEuros 3.0 kEuros 2.0 kEuros 2.0 kEuros 32 kEuros

Targets Transport of 8 targets

16 kEuros

Summary Minimum investment budget for 3 years 84 kEuros Minimum travelling budget for 3 years 24 kEuros

Table 4: Investment and travelling budget of the project. 3 permanent physicists of SPhN are involved in part in this project, all together making 1.2 man/year. In addition, 1 PostDoc and 1 PhD student will contribute at full time, both finishing their contracts by the end of 2005. The manpower required would be 1 PostDoc (2006-2007) and 1 PhD student (2005-2007). A preliminary agreement was reached with our collaborators from CEA/DIF for this project. Their contribution would be 0.4 man/year in terms of physicists and engineers during our experiments at Bruyères-le-Châtel, technical and infrastructure support including electron beam time (~3 weeks/year). We also will need some support in terms of ~0.2 man·year from DAPNIA/SIS in 2005 for the realisation of our combined delayed neutron detector (construction of support, preparation of polyethylene envelopes and assembling of 12 He-3 counters).

Summary and outlook In brief, we propose 3 year experimental program to measure photo-fission delayed neutron yields and their time characteristics for a number of high priority nuclei as uranium and plutonium isotopes (including some minor actinides) in the energy range of Bremsstrahlung photons from the photo-fission threshold of ~6 MeV up to 19 MeV. The main goal of this initiative would be a release of a consistent delayed neutron data library to be used in material evolution codes as CINDER’90 and photon transport codes as MCNP(X). These delayed neutron data could be also employed independently for a number of different applications as nuclear material interrogation and non-destructive nuclear waste characterization, isotopic identification via photo-activation in particular.

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In parallel, we will continue our efforts on photonuclear reaction modeling and related data evaluations. The CINDER’90 activation data library will be completed for most of the actinides using the IAEA data, the HMS-ALICE predictions and the GNASH code evaluations. By now we finalized our benchmarks of the ABLA fission-evaporation code using the experimental (existing but very scarce) fission fragment distributions and delayed neutron yields in the case of photo-fission. Some important changes were made in the present version of ABLA in collaboration with GSI, making our predictions coincide much better with experimental data. In this context, the above experimental program will be able to provide us with consistent data to test and tune the theoretical approaches used to model photo-nuclear reactions in general and photo-fission delayed neutron yields in particular. Finally we note that as long as a high efficiency delayed neutron detector is constructed we could extend our experimental program on delayed neutron measurements, but this time from neutron induced fission. We note that the measurements of delayed neutron yields and time spectra relative to innovative critical reactors (e.g., Generation IV initiative) are urgently needed for some of the Pu isotopes, minor actinides and nuclei contributing to the Th fuel cycle (according to the last recommendations of the 6th subgroup of OECD/NEA NSC working party on International Evaluation Cooperation). As an example in Fig. 11 we present the status of the delayed neutron data and evaluations for 233U and 232Th. It is evident that some new data points would guide much better the evaluators in this particular case. These measurements would be feasible at CEA/DIF of Bruyères-le-Châtel, using their proton accelerators to produce mono-energetic neutron beams of variable energies (from 200 keV to 14 MeV) and our new high efficiency delayed neutron detector.

Figure 11: Status of delayed neutron data for neutron induced fission on 233U (on the left) and 232Th (on the right). References [1] D. Ridikas, P. Bokov, M.-L. Giacri, “Potential Applications of Photonuclear Processes: Renewed Interest in Electron Driven Systems”, Proc. of the Int. Conf. on Accelerator Applications/Accelerator Driven Transmutation Technology and Applications (AccApp/ADTTA'03), 1-5 June 2003, San Diego, California, USA. [2] Handbook on photonuclear data for applications, “ Cross sections and spectra”, IAEA-TECDOC-Draft No 3. [3] W. B. Wilson, T. R. England and K. A. Van Riper “Status of CINDER’90 Codes and Data”, Los Alamos National Laboratory, report LA-UR-99-361 (1999). [4] M. Blann, “New pre-compound decay model”, Phys. Rev. C 34 (1996) 1341. [5] P. G. Young et al., “ Comprehensive nuclear model calculation”, Theory and use of GNASH in “Nuclear reaction data and nuclear reactor – Physics, design and Safety – Vol 1”, Int. Centre for Theoretical Physics, Trieste, Italy, 15 Apr.-17 May 1999. [6] A. R. Junghans et al., “ Projectile-fragment yields as a probe for the collective enhancement in the nuclear level density”, Nucl. Phys. A 629, 635 (1998); J. Benlliure et al., “Calculated nuclide production yields in relativistic collisions of fissile nuclei”, Nucl. Phys. A 628, 458 (1997). [7] M.L. Giacri, D. Ridikas, J.C. David, D. Dore, M.B. Chadwick, W. B. Wilson, “Status of the Photonuclear Library for CINDER’90”, Proc. of the Int. Conference on Nuclear Data for Science and Technology (ND2004), 26 Sept.– 1 Oct. 2004, Santa Fe, New Mexico, USA. [8] J. C. David, D. Dore, M.L. Giacri, D. Ridikas, “Fission Fragment Distributions and Delayed Neutron Yields from Photon Induced Fission”, Proc. of the Int. Conference on Nuclear Data for Science and Technology (ND2004), 26 Sept. – 1 Oct. 2004, Santa Fe, New Mexico, USA.

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40

Conseil Scientifique et Technique du SPhN

LETTER OF INTENT

Title: Characterization of the Anti-Neutrino energy spectra emitted from a nuclear reactor

– The Double Chooz experiment. Experiment carried out at: High Flux Reactor of ILL (Grenoble) and Chooz reactor (Ardenne)

Spokes person(s): A. Letourneau Contact person at SPhN: A. Letourneau

Experimental team at SPhN: A. Letourneau, D. Lhuillier, F. Marie, A. Vacheret List of DAPNIA divisions and number of people involved:

SPhN (4), SPP (3), SIS (2), (SEDI for the development of the β-spectrometer and electronic)

List of the laboratories and/or universities in the collaboration and number of people involved:

ILL (2) SUBATECH Nantes (3)

SCHEDULE

Estimated total duration of the proposed experiment: 4 years

Possible starting date of the experiment: mid 2005 for the experiences at ILL Expected duration of the data analysis:

ESTIMATED BUDGET

Total investment costs for the collaboration: not yet evaluated

Share of the total investment cost for SPhN: not yet evaluated Total Travel Budget for SPhN: not yet evaluated

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Characterization of the anti-neutrino energy spectra emitted from a nuclear reactor – The Double-Chooz experiment

A. Letourneau, D. Lhuillier, F. Marie, A. Vacheret

CEA/DAPNIA/SPhN M. Cribier, Th. Lasserre, J.P. Meyer

CEA/DAPNIA/SPP H.Faust, P.Mutti

ILL Abstract In the framework of the Double-Chooz project dedicated to the precise measurement of the

13θ neutrino mixing angle and also dedicated to non-proliferation oriented studies, we propose

to study and to characterize the anti-neutrino energy spectrum emitted by a nuclear reactor. Both proposed experiments and proposed modelisations will serve to precisely characterize the anti-neutrino emission sources in order to reduce systematic errors in the oscillation measurements as well as to study the effective possibility to use anti-neutrinos as probes to control the isotopic composition of nuclear power plant fuel elements. 1. Introduction Neutrinos play a crucial role in fundamental particle physics and have a huge impact in astroparticle physics and cosmology. The strong evidence for non-zero neutrino masses [1] clearly indicates the existence of physics beyond the minimal Standard Model and provides insights into possible modifications of the current electroweak interaction descriptions. Besides these fundamental interests, recently the International Atomic Energy Agency (IAEA) asked members states to make a feasibility study to determine whether antineutrino detection methods might provide practical safeguards tools for selected applications. The high penetration power of antineutrinos and the detection capability might provide a means to make “remote”, non-intrusive measurements of plutonium content in reactors and in large inventories of spent fuel. The antineutrino flux and energy spectrum depend upon the thermal power and the fissile isotopic composition of the reactor fuel. Based on predicted

[2,3] and observed [4-6] beta spectra, the number of eν per fission from 239Pu is known to be

less than the number from 235U (see table 1). This variation has been directly measured in reactor antineutrino experiments [7]. This may offer a means to monitor changes in the relative amounts of 235U and 239Pu in the core and in freshly discharged spent fuel. The antineutrino energy spectrum is less energetic for 239Pu than for 235U (see table 1). The shape of the antineutrino spectrum can provide additional information about core fissile isotopic composition. 235U 239Pu 241Pu

eν /fission 6.2 5.6 6.4

End point (MeV) 9.0 7.4 9.3 Table 1: Number and mean end-point of anti-neutrino emitted from different fissile isotopes.

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This safeguard aspect has been developed in the Double-Chooz project [8] which is dedicated to a precise measurement of the 13θ mixing angle. Thanks to the close position of one detector

from the reactor the possibility of using anti-neutrino for safeguards applications will be explored. 2. The Double-Chooz experiment and the implication of the SPhN The Double-Chooz experiment [9] will be installed at the EDF nuclear power reactor of Chooz. Two identical neutrino detectors will be placed at 100-200 m and 1 km from the reactor. The objectives of this project are in priority to search for the value of 13θ neutrino

mixing angle. The required sensitivity for this measurement implies to reduce systematic

errors and control the background. The knowledge on the eν fluxes and energy spectra as a

function of time, space and fuel burn-up is one of the systematic errors that has to be reduced. In particular a precise characterization and follow-up of the fuel evolution during the years of experience are obviously required to know the relative part of 235U, 239Pu and other fissile isotopes in the fissions and the impact on the evolution of the energy spectra. As shown on Fig.1 the anti-neutrino energy spectrum produced by a PWR at the very begin of the irradiation (after 1s) is completely different from the energy spectrum after 2 years of irradiation, due to the accumulation of long-lived fission product. This variation has its importance when looking for example at the unloading and replacement of the spent fuel element.

Moreover as already mentioned previously, the shape and the intensity depend on the fissile emitter and on the precise knowledge of the energy spectra, for all relevant fissile isotopes that contribute to the source emission is obviously required. From the present knowledge of

the eν spectrum emitted by the fission product, we see that the most energetic part offers the

best possibility to disentangle fission from 235U and 239Pu, in particular. Unfortunately the

10-5

10-4

10-3

10-2

10-1

1

0 2 4 6 8 10 12

Energy (MeV)

N_Β

(/f

issi

on/M

eV)

10-5

10-4

10-3

10-2

10-1

1

0 2 4 6 8 10 12

Energy (MeV)

N_Β

(/f

issi

on/M

eV)

Figure 1: Simulated anti-neutrino energy spectra emitted by 235U (left) and 239Pu (right) after 1s, 1 day and 2 years of irradiation in a PWR.

44

present uncertainties in that high energy region of energy is rather large, due to difficulties of -.Thus, the Double-Chooz project will allow to

measure the correspondence between the eν energy spectra emitted by a PWR (N4) and the 239Pu contained of the core in different functioning regimes. In the frame of the Mini-INCA project dedicated to transmutation studies at SPhN [10], experimental tools have been developed to perform quasi on-line α- and γ-spectroscopy analyses on irradiated isotopes and to monitor on-line the neutron flux in the high flux reactor of ILL. Also competences have been developed on the Monte-Carlo simulations of complex systems and in particular nuclear reactors. We propose to use these competences to provide the community with:

• a set of new and detailed β energy spectra relevant for the Double-Chooz experiment and for safeguards studies related to the AIEA missions,

• to characterize the eν sources (spatial distribution, energy distribution, …) and to

determine the possible sources of fluctuations in the eν energy spectra originated

from the reactor changing (spent fuel unloading, burn-up of the fuel element, …),

• to study the feasibility of using eν as a tool for non-proliferation controls.

3. 3. 3. 3. Energy spectra measurements Measurements of the β energy spectra coming from the thermal fission of fissile isotopes will be done at the ILL reactor and could be completed at a neutron source (SINQ, GELINA, N-TOF,...) to study 238U fission. They are decomposed into three complementary experiments:

• measurement of the individual β energy spectrum for each fission products on the Lohengrin spectrometer,

• measurement of integral “prompt” β energy spectra for different fissile targets (233U, 235U, 239Pu, 241Pu, 243Cm) on a neutron guide,

• measurement of integral “delayed” β energy spectra for different fissile targets (233U, 235U, 239Pu, 241Pu, 243Cm) on H9, using the Mini-INCA chamber.

All these measurements are complementary and will provide a complete characterization of the anti-neutrino spectrum produced in the fuel element by taking into account the fuel evolution and the burn-up. But they require the development of a compact β-spectrometer that has to be adaptable to all the experiments.

β-spectrometer The key element for all the measurements is the development of a large dynamic (from 100 keV to 10 MeV) β-spectrometer to cover the full energy range of interest. It should have either an absolute resolution of 10-50 keV or a relative resolution (∆E/E) of 1%, and an intrinsic efficiency of 100% whatever the β-energy is. As far as the precision on the shape of the β-spectrum is concerned (1%), we have estimated that a fast electronic is needed to support a maximum counting rate of about 105 count/s. This

45

estimation was done by considering a segmentation of 1000 bins and an acquisition time corresponding to 10% of the half-live of the isotopes that we want to measure.

Measurements on Lohengrin The Lohengrin spectrometer is connected to the H9 irradiation tube where a fissile (235U, 239Pu and 243Cm) target can be irradiated. Fission fragments that leave the target are selected via a dipole magnet and collected few meters farther where detectors are installed. By implanting selected fission products into a layer in front of the β-spectrometer or simply into Si detectors one can measure the individual energy spectrum for each fission product. We propose to measure these spectra for all the fission products coming from 235U and/or 239Pu. This information, is really important to deconvoluate and to convert the β-energy spectra into

eν energy spectra within the integral measurements that are described in the following. As

the individual β-energy spectrum can easily be converted into eν energy spectrum, it is the

way to construct an eν energy data base. Moreover these measurements should give new

information on the beta-decay and on the shell structure of neutron-rich isotopes.

Measurements on Neutron guide The neutron guides at ILL provide pure thermal neutron beams with intensities of about 109

n/cm2/s. We propose to place different fissile targets (235U, 239Pu, 241Pu, 243Cm) into the neutron beam and to record the in-beam β “prompt” with the β-spectrometer. These measurements are important because they give access to the high energy part of the spectra (see Fig.1) that are created by short-lived exotic fission fragments. Moreover there are characteristic of a fresh 235U, after refueling of the combustible.

Measurements on H9 The Mini-INCA α- and γ-spectroscopy station is connected to the H9 irradiation channel. It offers the possibility to perform irradiations in a quasi thermal neutron flux up to 20 times the nominal value in a PWR. The irradiation can be followed by measurements and repeated as many time as needed. It offers then the unique possibility to characterize the evolution of the β spectrum as a function of the irradiation time and the irradiation cooling. The expected modification of the β spectrum as a function of the irradiation time is connected to the transmutation induced by neutron capture on the fissile and fission fragment elements. It is thus related to the “natural” evolution of the spent-fuel in the reactor. The modification of the β spectrum as a function of the cooling time is connected to the decaying chain of the fission products and is then a means to select the emitted fragments by their lifetime. This information is important because long-lived fission fragments accumulate in the core and after few days mainly contribute to the low energy part of the antineutrino-spectra. We propose to add the β-spectrometer to the Mini-INCA chamber and to record the β-energy spectra for 235U, 239Pu, 241Pu and 243Cm for different irradiation and cooling times. Due to the mechanical transfer of the sample from the irradiation position to the measurement station an irreducible delay of 30 mn is imposed leading to the loss of short-live fragments.

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4. Characterization of the anti-neutrino source

Modelisation of the reactor By the means of Monte-Carlo (MCNP - TRIPOLI) and determinist codes used for neutron flux calculation and isotopic evolution at ILL and for various types of transmutation scenario studies, we propose to modelize the complete history of the Chooz reactor cores during the year of operation. It should help to characterize the barycenter of the eν source and to

characterize the eν flux variations when completed with a reactivity monitoring. Moreover it

can serve to study the sensitivity of the eν spectrum to the isotopic composition and fuel

burn-up also related to non-proliferation studies and used to understand the physics of the both Double-Chooz detectors. The new experimental data will be included in the simulation.

Non-proliferation studies The modelization of the Chooz reactor can serve as a starting point for the non-proliferation studies. By varying the Pu content of the core in relevant IAEA scenarios one could estimate

the variations on the eν energy spectra and the sensitivity of the method. Moreover the

precise measurement of the eν spectra done by the near detector of the Double-Chooz

experiment will be correlated with the simulations when the discharge of parts of the core will happen in order to monitor the sensitivity of the method. 5. Schedule and Manpower The far detector of the Double-Chooz experiment will be installed in the fall of 2006 in order to start data taking in the beginning of 2007. The near detector will be installed one year later and will start data taking beginning 2008. Nevertheless, reactor simulations, sensitivity studies and β-spectrometer conception for the experiments at ILL can start from 2005. Two post-docs, starting from 2005, are needed to start the experimental activities, in particular the definition and the conception of the detector and of the experiments, and to start the modelisation of the reactor and the sensitivity studies as required by IAEA. A Ph.D thesis will be proposed in 2005. References [1] S. Fukuda et al. (coll. Super-Kamiokande), Phys. Lett. B539 (2002) 179; K. Eguchi et al. (coll. KamLAND), Phys. Rev. Lett. 90 (2003) 021802. [2] V.I. Kopeikin, Sov. J. Nucl. Phys. 32, (1980), 780. [3] P. Vogel, G.K. Schenter, F.M. Mann, R.E. Schenter, Phys. Rev. C24 (1981) 1543. [4] F.v. Feilitzsch, A.A. Hahn, K. Schreckenbach, Phys. Lett. B118 (1982) 162 [5] K. Schreckenbach, G. Colvin, W. Gelletly, F.v. Feilitzch, Phys. Lett. B160 (1985) 325 [6] A.A. Hahn, K. Schreckenbach, W. Gelletly, F.v. Feilitzch, G. Colvin, B. Krusche, Phys. Lett. B218 (1989) 365. [7] M. Apollonio et al., Eur.Phys.J. C27 (2003) 331.

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[8] Th. Lasserre, The Double-Chooz project, proposal to the Scientific and Technical Council of SPP (CSTS), March 10th 2004. [9] Letter Of Intent for Double-Chooz and US Letter Of Intent for Double-Chooz, http://www.neutrinooscillation.org/. [10] G. Fioni, The Mini-INCA project, Proposal to the Scientific and Technical Council of SPhN (CSTS), June 1st 1999.

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Conseil Scientifique et Technique du SPhN

RESEARCH PROPOSAL Title: A continuation of the SPALADIN experiment Experiment carried out at: GSI-Darmstadt (Allemagne) Spokes person(s): J.-E. Ducret Contact person at SPhN: J.-E. Ducret Experimental team at SPhN: A. Boudard, J.-E. Ducret, E. Le Gentil, S. Leray, S. Pietri, C. Volant List of DAPNIA divisions and number of people involved: SPhN (6), SEDI (1 ou 2), SACM (2), SIS (1) List of the laboratories and/or universities in the collaboration and number of people involved: IN2P3/IPN-Orsay, GANIL, Univ. de Saint-Jacques de Compostelle, GSI-Darmstadt (Allemagne), Université Technologique de Munich (Garching, Allemagne)

SCHEDULE

Possible starting date of the project and preparation time [months]: End of 2005, 6 months of preparation Total beam time requested: 7 days

Expected data analysis duration [months]: 3 years

REQUESTED BUDGET

Total investment costs for the collaboration:

Share of the total investment costs for SPhN: Investment/year for SPhN: 150 000 euros (common to this proposal & the proposal ‘Proton induced fission in the GeV domain with ALADIN, MUSIC IV & LAND’ of A. Boudard et al.) Total travel budget for SPhN: 20 000 euros in 2005, 10 000/year in 2006 & 2007 Travel budget/year for SPhN: ~ 13 000 euros

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50

1

PROPOSAL TO THE C.S.T. SPhN

Exclusive measurements in spallation reactions:

A continuation of the SPALADIN experiment

J.-E. Ducret1, A. Boudard1, E. Le Gentil1, S. Leray1, S. Pietri1, C. Volant1

in collaboration with :

C.-O. Bacri1, A. Lafriakh1, F. Rejmund2, J. Benlliure3 T. Aumann4, A.Kelic4, A. Le Fevre4, W. F. J. Muller4, K.-H. Schmidt4, W. Trautmann4, O.Yordanov4 M. Bohmer5, R. Gernhauser5

(1) Institut de Physique Nucleaire d’Orsay, IN2P3-CNRS, F-91406 OrsayCedex, France(2) GANIL, CEA et IN2P3-CNRS, B.P. 5027, F-14076 Caen Cedex, France(3) Univ. de Santiago de Compostela, E-15706 Santiago de Compostela,Spain(4) Gesellschaft fur Schwerionenforschung, D-64291 Darmstadt, Germany(5) Physik-Department E12, TU Munchen, D-85748 Garching, Germany

Abstract: We propose to extend the exclusive measurement of spallation reac-tions already performed on 12C and 56Fe with the SPALADIN experiment toboth lighter and heavier nuclei. For the lighter nuclei, we propose to chooseAl or Si (A ' 25) and for the heavier one, Xe or Nb (A ' 100). The aimof the measurement on the lighter system is to test the description of thespallation mechanism in terms of a Fermi break-up, this system being toosmall for a proper statistical description of its decay. The going-on analysisof the SPALADIN data indicates that the experiment with isotopic identifica-tion of the projectile fragments is feasible. The measurement with Xe or Nbwill be at the limit of performances of the detection set-up in terms of massidentification. However, it will allow to determine if de-excitation channelslike very asymmetric fission or multifragmentation play a role in these sys-tems as suspected from recent FRS data. It will aim at testing the spallationmechanism on more exclusive experimental observables in the A ' 100 massregion. These experiments are parts of a long term program of the Saclayspallation group. This program was presented to the CSTS in June 2003 andwas given support then. Its aim is to develop an experience in the use ofmulti-track detectors to be able to perform exclusive measurements of spalla-tion on nuclei as heavy as 208Pb or 238U with the mass identification of the

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fragments. It is part of a European collaboration R3B / RHIB which has incharge the high-energy branch to be installed downstream of the new Super-FRS of the future GSI heavy-ion facility. These experiments will complete theset of data necessary to ensure a quantitative understanding of the spallationmechanism.

Spallation reactions are important due to their applications in variousfields of research such as astrophysics, spatial technologies, accelerator drivensystems (ADS), neutron sources and production of radioactive beams. To ob-tain a quantitative understanding of the spallation mechanism and improveits modelisation, large experimental efforts have been done during the lastyears. Since 1996 at the FRS, in GSI (Darmstadt, Germany), the residualnuclei production has been studied in inverse kinematics using SIS heavy-ionbeams impinging on a liquid-hydrogen target [1-9]. These data have led to im-provements of nuclear models but also raised new questions which appearedimpossible to answer with inclusive experiments alone. This is why a morecomplete experiment, called SPALADIN, has been proposed which aims atmeasuring as exclusively as possible the final states of the spallation reactions[10]. This experiment, accepted by the experimental advisory committee ofGSI in 2000, has the goal of studying the spallation reaction 56Fe+p in re-verse kinematics. Besides the fact that 56Fe was a rather light system wellaccessible to our experimental device (resolution of detection, multiplicityand bending capability of the ALADIN magnet), it was also chosen becauseit is the most used structural material in spallation sources, the most criticalpart of them in terms of proton irradiation being the window between theproton beam vacuum and the spallation target. Understanding of the pri-mary 56Fe+p interactions is therefore of crucial importance. Furthermore,the more exclusive data from SPALADIN on 56Fe+p will be complementarywith the extensive study of the residual nuclei production at five differentenergies which was performed at the FRS [9] and will give new insight intothe spallation mechanism on 56Fe.

The SPALADIN data taking was performed at the beginning of 2004.The main goal of this experiment is to reconstruct, as completely as possi-ble, the primary fragment after the first stage of the reaction in mass, chargeand excitation energy. For this, the heavy residues are detected as well as thelight particles, the nature and the energies of which are determined to permita calorimetry of the primary fragments. This experiment is concentrated onthe study of the evaporative particles in coincidence with the residual nuclei.Nevertheless, the reconstruction of the excited nucleus characteristics beforeevaporation permits to check how the modelisation of the first stage of the re-action, generally described by intra-nuclear cascade models, is able to predict

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these characteristics. Furthermore it allows to study the various decay modesof the reconstructed excited nucleus and to test the modelisation of the sec-ond stage of the reaction: Evaporation models for 56Fe or evaporation-fissionwhen such an experiment will be done with heavy beams. Also, the questionsof other possible de-excitation channels such as very asymmetric fission ormultifragmentation could be addressed. Such channels have recently beeninvoked to explain our most recent FRS results [11,12].

The detection of the evaporation residues is performed using the AL-ADIN magnet associated with various detectors: An ionisation chamber fortheir charge identification, a ring imaging Cerenkov (RICH) to determinetheir velocity, high resolution position detectors (drift chambers) for the re-construction of the magnetic rigidity. The evaporated neutrons are detectedwith LAND. The light charge particles were initially thought to be identi-fied in mass and charge and their momentum measured by a set of multi-wire chambers and a scintillator array behind the ALADIN magnet. Duringtwo years, in-beam tests have been performed to check the capability of thevarious detectors on a step-by-step basis, each following test approachingthe final design. It appeared that the multiwire chamber set-up originallyplanned was too challenging a device to detect the light charge particles inthe heavy-ion environment with the beam passing through the detectors.The best alternative solution appeared to be the use of the TP-MUSIC IVdetector (time projection chamber, TPC) associated with its ToF-wall ho-doscope from the ALADIN collaboration. Feasability tests were performedin November 2003 with the full experimental set-up shown in Fig. 1, includ-ing the liquid hydrogen target. In the on-line analysis, the coupling of thevarious detection systems has been checked as well as the performances of thedetectors. Physics data were taken at the beginning of 2004 in two periods:A first measurement with 12C beam at 1 A.GeV energy in January and asecond one, with 56Fe beam at 0.5 and 1 A.GeV in February and March. Thedata analysis is in progress on each part of the detection system. We takefull advantage of our collaboration with the S254 experiment [13] in whichwe are involved and with which we share the use of the large TP-MUSIC IV,the ToF scintillator wall and the LAND detector (in a quite high neutronmultiplicity mode). A status report of this analysis will be done during theoral presentation in front of the committee.

As presented to the committee in June 2003, our mean-long range pro-gram is to perform further measurements in order to complete our under-standing of the spallation reaction mechanism with beams which are also ofinterest for applications. This will allow to test the ability of the theoreticalmodels to describe the reaction in a large mass range. Our ultimate goalis, as explained then, to perform exclusive experiments on Pb and U with

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TP MUSIC IV

light charged particles

START

ALADINmagnet

heavy fragments & beam

position detectorshigh resolution

SPALADIN @ GSI

RICH

MUSIC

liquidhydrogentarget

HODOSCOPE

LAND

neutrons

Figure 1: Layout of the SPALADIN experimental set-up

the mass identification of both heavy and light fragments. For such heavynuclei, the new superconducting magnet GLAD of the R3B / RHIB projectwill be necessary as well as an upgrade of the detection to achieve the re-quired mass resolution and to have a sufficient granularity. Such spallationmeasurements could also be seen as complementary to more complicated ex-periments looking for example for isospin effects in fission of exotic nuclei orin multifragmentation in heavy ions induced reactions as it is being studied inthe S254 experiment. It has to be underlined for example that in spallationreactions, there exists only one hot source of emitted particles (compared toup to three in ion-ion reactions) and that centrifugal forces on fission barriersare small. Thus, a proper description of the spallation mechanism is neces-sary to understand precisely collective effects in ion-ion collisions at theseenergies.

To reach this goal, a road-map was defined, based on physics as well ason detector experience to be gained to fullfil it:- The measurement of spallation on a system lighter than 56Fe, a measure-ment on an A ' 100 with the existing detection with small upgrades whennecessary;- The design of a new multi-track detector to be installed downstream ofthe future R3B / GLAD superconducting magnet to improve momentumand angular resolutions as well as event reconstruction of charged-particlemultiplicities up to 20-30 which requires higher granularities for the chargecollection with a large signal dynamics (1:10000). Such a detector, by thevolume it will have to cover at the exit of the magnet and the continuoustracking it will have to ensure will be most probably of the TPC type, as

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TP-MUSIC IV;- The measurement of Pb and U spallation with this new facility with massidentification of the fragments (both light and heavy ones).

Since then, an extra experiment has been designed to be performed withthe existing ALADIN / TP-MUSIC IV / LAND set-up and is proposed tothe C.S.T.-SPhN : the measurement of fission channels in the spallation ofthree heavy nuclei (238U, 208Pb and 181Ta at 1 A.GeV). This experiment isthe purpose of another proposal to the same committee and is presented ina separate paper.

Lighter systems are well inside the performances of our detection and areof physical and technological interests. These small systems are a challenge tothe modelisations which are based on Monte-Carlo and statistical methods.For instance the statistical evaporation model would have to turn towardsother methods like the Fermi break-up [14] which has still to be validated. Inthis respect, the 12C data we took in January are of big interest. Moreover,Si and Al are commonly used materials, Al as a structural material and Siin the electronics components of in-flight experiments that could suffer fromspallation reactions in space due to the cosmics rays. There exists alreadysome data on residual nuclei produced in these spallation reactions [15,16],but the present device will permit to characterize the complete events. Thesedata are needed to develop the spallation models on light systems required inthe European Integrated Project on Transmutation (EUROTRANS) in theNUDATRA sub-project.

However, the present experimental device is limited to masses around100 for a proper identification. We would like to make a first experimentwith nuclei of mass around this limit, exploratory in terms of mass iden-tification (experimental performances of the set-up) but useful in terms ofunderstanding the spallation mechanism. Possible projectiles could be Xefor which the residual nuclei production has been studied at various energieswith the FRS [17] or Nb, which is the material of superconducting cavitiesused in the proton accelerator to be coupled with the sub-critical reactorin an ADS facility. According to the results of the FRS experiment [15], itseems that the production of light fragments in the reaction 136Xe+p at 1A.GeV cannot be explained by present spallation models which reproducewell the 56Fe+p data and that extra mechanisms are required to that. Mea-suring this reaction at the ALADIN set-up, with a much larger angular andmomentum acceptance is important to confirm the FRS data. However, thesmaller Nb mass (A = 98) makes the Nb+p experiment easier to do thanthe Xe+p experiment whose mass is relatively larger (A = 136). The finalchoice between Nb and Xe beams will take into account the performances ofthe set-up as determined by the data analysis of SPALADIN. Furthermore,

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such a measurement would give us quantitative and experimental indicationson the improvements which could be necessary from the present TP-MUSICIV detector to a detector capable of providing efficient tracking of spallationevents with A ' 200 projectiles.

The three experiments mentioned above in the experimental program inthe mid-term range will be performed at the ALADIN / TP-MUSIC IV /LAND set-up after its move to the new experimental area ”Cave C” in GSI.

The spallation measurement on Al/Si will be performed in a rather sim-pler set-up than the 56Fe+p experiment. We will not need, upstream ofALADIN, the RICH detector and the first ionisation chamber (”MUSIC” onFig. 1). The drift chambers we used during the 56Fe run can be used as beamtrackers in front of the target. Their high position resolution, confirmed inbeam during the experiment, will be very useful for the event reconstruction.Furthermore, it appears in the TP-MUSIC IV data analysed sofar that theisotopic identification is feasible up to Al/Si. This makes us believe that sucha measurement is already feasible. With respect to the models, the differ-ence between Al and Si is small. The choice of one of this nuclei will dependmainly on the availability of the beams (Al or Si) at GSI.

The spallation experiment on the heavier system will be done with aset-up quite comparable to that of the 56Fe run, as on Fig. 1.

For these experiments, we need to develop our experience on two de-tectors: TP-MUSIC IV and the ToF wall. We need also to take part intheir moving from Cave B, where they still are, to Cave C where the AL-ADIN magnet and the LAND detector are already. To that end, we need thesupport of detector engineers and technicians from SEDI. Time projectionchambers (TPC) are in fact quite complicated detectors to handle, tune aswell as to analyze. The support we need for TP-MUSIC IV will serve as abasis on which we will be able to rely to develop this new multi-track detectormentioned above and needed for A ' 200 nuclei.

The work to be done to prepare these experiments with the TP-MUSICIV and the ToF wall is the following:- To take part in the moving of the two detectors from Cave B to Cave C,which requires uncabling, cabling of all the channels and of the gas handlingsystem and the HV power-supply (SEDI or perhaps SIS for the electrical andgas system cabling);- To install the liquid hydrogen target in Cave C (from Cave B) for the Al /Si experiment;- To check all the readout electronics once the detectors are installed in CaveC and learn the software to control them;- To take part in the repair of some of the phototubes and rebuild the elec-tronics readout and the updating of the power supplies;

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- To work on a new liquid hydrogen target, thinner to reduce the amont ofsecondary reactions inside the hydrogen and the contribution of the targetwalls, new target required by the A ' 100 experiment as well as by the fissionexperiment to be done with the TP-MUSIC IV / ALADIN / LAND set-upand already reffered to here (equivalent one person full time over 12 months);

This has to be done starting at the beginning of 2005. This is a threemonths equivalent full time work for the part related to the moving of thedetectors. The installation of the liquid hydrogen target in Cave C is a threeweeks work for two persons of SACM and/or SIS.

The financial part of this proposal comprises travel expenses and invest-ments. The travel expenses amount to 20 keuros, a part of which cominginto the GSI / IN2P3 / DSM agreement concerning travel expenses. Theinvestments have to be foreseen for the ToF wall and the new target. In fact,around 30 phototube bases have to be changed on this wall. The high voltagepower supply is also aging and has to be changed. These expenses of around70 keuros could be our contribution to the updating of the ToF-wall andits moving to Cave C. The investment for the new target is approximately80 keuros.

Our aim, if the committee agrees on this proposal, is to perform the firstexperiment (on the lighter system) at the end of 2005. These experimentswill be presented, in case of approval by the CST-SPhN, to the GSI programadvisory committee during its next meeting (21-22 March 2005).

[1] W. Wlazlo et al., Phys. Rev. Lett. 84, 5736 (2000)[2] J. Benlliure et al., Nucl. Phys. A 683, 513 (2001)[3] F. Rejmund et al., Nucl. Phys. A 683, 540 (2001)[4] T. Enqvist et al., Nucl. Phys. A 686, 481 (2001)[5] T. Enqvist et al., Nucl. Phys. A 703, 435 (2002)[6] J. Benlliure et al., Nucl. Phys. A 700, 469 (2002)[7] J. Taieb et al., Nucl. Phys. A 724, 413 (2003)[8] M. Bernas et al., Nucl. Phys. A 725, 435 (2003)[9] C. Villagrasa-Canton, these de doctorat, universite Paris XI - Orsay (2003)[10] J.-E. Ducret et al., EA-GSI, Dec. 2000, S. Pietri et al., to be published inthe proceedings of the International Conference on Nuclear Data, Santa-Fe,USA (2004)[11] P. Napolitani et al., submitted to Phys. Rev. C

[12] C. Volant et al., to be published in the proceedings of the InternationalConference on Nuclear Data, Santa-Fe, USA (2004)[13] W. Trautmann et al., proposal to the EA-GSI (2000), C. Sfienti et al.,Communication to the 18th nuclear division conference of the EPS, Prague,

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Czech Republic (2004)[14] E. Fermi, Prog. Theor. phys. 5, 570 (1950), J.P. Bondorf et al., Phys.Rep. 257, 133 (1995)[15] W.R. Webber et al., Phys. Rev. C, 520 (1990)[16] R. Michel et al., Nucl. Instr. Methods B 103, 183 (1995)[17] P. Napolitani, these de doctorat, universite Paris XI - Orsay (2004)

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Conseil Scientifique et Technique du SPhN

RESEARCH PROPOSAL Title: Proton induced fission in the GeV domain with ALADIN, MUSIC 4 and

LAND Experiment carried out at: GSI-Darmstadt

Spokes person(s): Alain BOUDARD

Contact person at SPhN: Alain BOUDARD Experimental team at SPhN: Groupe Spallation (6 personnes)

List of DAPNIA divisions and number of people involved: SEDI(1 or 2), SACM(2), SIS(1) List of the laboratories and/or universities in the collaboration and number of people involved:

GSI (11), Univ. Santiago de Compostela (3), IN2P3 (IPNO,GANIL,CENBG) (3).

SCHEDULE

Possible starting date of the project and preparation time [months]: End 2005

Total beam time requested: 10 days Expected data analysis duration [months]: 2-3 years

REQUESTED BUDGET

Total investment costs for the collaboration: Share of the total investment costs for SPhN: 150 kEuros (common with “Exclusive

measurements in spallation reactions: A continuation of the SPALADIN experiment.)

Investment/year for SPhN: 150 kE in 2005 Total travel budget for SPhN: 40 kEUROS

Travel budget/year for SPhN: 20 kE/year

If already evaluated by another Scientific Committee: (GSI EA, accompanying letter)

If approved Allocated beam time: Possible starting date: If Conditionally Approved, Differed or Rejected please provide detailed information:

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CSTS/ SPhN November the 29th, 2004

GSI Proposal: Proton induced fission in the GeV domain with ALADIN, MUSIC 4 and LAND.

This proposal has been submitted to the GSI Experimental Committee (EA) of September 27 (deposit the 31 August). Usually there are two Committees per year, one in June and one in December which would have been synchronised with our Fall CSTS. This year, only one in September has been scheduled. Shortly notified, our aim was to submit a Letter of Intent, but our collaborators have insisted for a full Proposal. We apologize for this irregular way to proceed. Presently, no beam time has been allocated by the GSI EA to this experiment, and we will have to submit it again to the next EA in March 2005. The referees were J. Aichelin (Subatech) and S. Paul (TU-Muenchen). We have not yet received the official answer of the EA. Note that M. Lewitowicz (GANIL) is a member of the CSTS and of the GSI-EA. From our private discussions especially with J. Aichelin, the main critics were on the definition of the physics case. In particular, questions were asked about the optimal way to use our observables to constraint more clearly the various possible reaction mechanisms. The Tantalum study, beam time consuming, was especially questioned during the oral presentation. It was not clear enough that the experiment could measure the (weak) fission part, and also all more exotic channels, by selecting events with a suitable trigger, actually, the rejection of events leading to a heavy residue. It seems that the experimental device was not otherwise criticized. The motivation of this experiment is in the framework of the systematic spallation study and the tuning of precise and predictive codes for its description. After the neutron spectra (double differential cross sections in energy and angle in the full phase space) at SATURNE and the nuclear residues (inclusive production cross section of all significant isotopes) at GSI, we are now involved with SPALADIN in measurements of the nuclear de-excitation as exclusively as possible. This will allow various balances and correlations testing especially the delicate link between the high energy intra nuclear cascade and the nuclear de-excitation. With this setup, we have recently measured the spallation of carbon and iron. A continuation with other nucleus will be discussed during this CSTS. The Xe is the heaviest nucleus that we could tentatively measure at SPALADIN with a reasonable mass identification of the evaporation residues. Heavier projectiles like lead will need the supraconducting magnet R3B/GLAD and the granularity of its associated detection foreseen in the framework of the R3B collaboration. Adding detectors around the target, we could also foresee a complete detection of the low energy (inverse kinematics) particles from the cascade phase. In the meanwhile and with the present device, we want to focus on the measurement of the two fission products of heavy nuclei, identified in charge, in coincidence with neutrons and light charged particles..

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To summarise, we propose: 1) A measurement with Lead, a crucial nucleus for spallation studies in the framework of

ADS applications, at 500 MeV/A where our absolute fission cross section measured with FRS was found almost twice larger than expected, and at 1 GeV/A. With regard to the cross section, it should be noted that FRS detects only one fission product with a 5% to 10% acceptance. Here we will detect the two fission products, covering 85% of the acceptance.

2) A measurement with Uranium at 500 MeV/A and 1 GeV/A and with Tantalum at 1 GeV/A. These two nuclei will provide a good range on the fissility parameter and so a good constraint on the fission description. The counting rate on Ta is rather weak and so only one energy is proposed. However a measurement with Ta is also justified by the large under prediction of our model (INCL4-ABLA) compared to the production cross section of intermediate nuclei measured by γ–spectrometry.

In coincidence with the two fission products we will detect around 50% of the evaporated protons and almost all other charged particles produced in the de-excitation stage. The multiplicity of evaporated neutrons will be measured with LAND, giving access to the excitation energy at the end of the intra nuclear cascade phase. A specific trigger will exclude all channels with a heavy residue. These contributions with large cross-sections are more specifically studied in the S184 SPALADIN experiment and its continuation with R3B/GLAD. Other decay channels, as very asymmetric fission or possible multifragmentation that could explain the discrepancy of our model with light evaporation residue production cross-sections will also be investigated and will complement for heavy nuclei the similar study foreseen in the Xe experiment. These production cross sections are largely polluted by reactions on the target Ti windows and by secondary reactions. While this can be more or less solved for cross section determinations applying correction factors, for mechanism study, one would like a cleaner selection of the real events. Therefore, we would need a new liquid Hydrogen target of smaller thickness and with thinner windows. The support required from the DAPNIA is common with the other SPALADIN proposal. It includes especially the new liquid target based on a pressure regulation. If the experiment is fully accepted, it will be probably divided in 3 runs, one for each type of beam. So we will need for this experiment specific travel expenses around 40 000 Euros on 2 years.

A. Boudard 01 69 08 43 44

aboudard@cea.fr

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Date of Receipt: GSI Exp. No.

Proposal for an Experiment at GSI, Darmstadt

1. Title of Proposal: Proton induced fission in the GeV domain with ALADIN, MUSIC4 and LAND.

X New Proposal

Continuation of Previous Experiment (Exp. No.:..........................)

2. Spokesperson: A. Boudard & J. Benlliure

Full Address: DAPNIA/SPhN CEA/Saclay 91191 Gif-sur-Yvette FRANCE

Telephone/Fax: (33-1) 69 08 43 44

email: aboudard@cea.fr j.benlliure@usc.es

Participants: J. Benlliure (Full list on the first

page of the proposal)

Address: Dep. de Fisica de

particulas, Univ. Santiago de Compostela,

E-15706 Santiago De Compostela

SPAIN

Telephone: (34) 981563100 ext 13967

email: j.benlliure@usc.es

3. GSI Contact Person: W. Trautmann UNILAC:

SIS: X

ESR:

Requested Beam Properties and Experimental Equipment:

a) Ion Species (Charge State): 238U (6 BT), 208Pb (9 BT), 181Ta (15 BT) b) Intensity (Particle nA): ~5000 particles/second c) Energy (MeV/u): 500 MeV/u and 1 GeV/u d) Target Station: Cave C e) Special Requests on Beam Properties: Good focalization on target (Ø < ~7 mm) f) Special Target Requirements: Liquid Hydrogen target (e=1cm, 7 cm3) g) Electronic Pool: h) GSI Computers: ALADIN standard acquisition system i) Further Assistance Requested from GSI:

For Safety Aspects of the Proposal please fill in the Extra Form. Requested Beam Time (in Shifts of 8 Hours each) Total: 30 B.T. units + Parasitic Number of Runs: Possibly 2 or 3 Prefered Dates:

After september 2005 Dates when you cannot run:

Before oct. 2005

Detailed description of the Proposal: Please attach an experiment description (max. 10 pages including figures) which should summarize the scientific justification and relevant technical details for the proposed experiment. For a continuation request, a brief status report of the previous as well as an outline of the future experiments should be given.

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Date:______________ (Do not fill in) GSI Exp.No.:______________

SUPPLEMENTARY FORM FOR SAFETY ASPECTS OF A PROPOSAL

Title: Proton induced fission in the GeV domain with ALADIN, MUSIC4 and LAND Spokesperson: A. Boudard, J. Benlliure GSI-Contact Person: W. Trautmann 1. General Safety

a. Do you use combustible or hazardous gases within your experiment Yes X No (e.g. gas target, gas detectors)? What sort of gases? Standard ALADIN Liquid Hydrogen target Which quantities or flow rates? Closed circuit (~ 15 cm3) b. Do you use other dangerous (e.g. toxic, inflammable, biologically hazardous Yes X No

etc.) materials within your experiment? What sort of materials? P10 in MUSIC4 Which quantities? c. Is your vacuum set-up equipped with fragile parts like thin glass or foil Yes X No windows etc. (danger of implosion)? Brief description of the construction: Standard ALADIN-MUSIC4 vacuum tank d. Is it intended to move heavy parts for setting-up your experiment or during Yes X No the experiment? Brief description of the equipment and working procedure: Before the Experiment: setting of MUSIC4, TOF and the liquid Hydrogen target.

2. Radiation Safety a. Do you use radioactive sources or materials on-site? Yes No X What sources? Which activities? b. Is it intended to direct the beam through air or other gases? Yes X No Beam sort, energy, intensity: 208 Pb, 1 GeV/u, ~ 5000 particles/sec Distance through air or gas: ~ 1m before ALADIN, ~ 8 m before beam dump

3. Electrical/Laser Safety

a. Do you use electrical instruments on-site? Yes X No Max. Voltage/max. current: Standard MUSIC4, LAND electronics

b. Do you use high-intensity radio frequency (RF) sources on-site? Yes No X Frequency region/power:

c. Do you use lasers in your experiment? Yes X No Laser-type, max. power: Standard TOF laser

4. Is there any other special safety aspect to be considered in connection with Yes No X your proposal ? Date: Spokesperson of the experiment: 25/8/2004 A. Boudard

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