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Investigation of GeV proton-induced spallation reactions
•Motivation•Experiment
•PE cluster-emission•Neutron multiplicities
•Inelastic reaction cross sections•Production cross sections of LCPs
•Decay of hot nuclei as a function of excitation energy •Fission probability
•Summary
D. Hilscher, C.-M. Herbach, U. Jahnke, V.G. Tishchenko, HMI-Berlin
J. Galin, B. Lott, A. Letourneau, A. Péghaire, GANIL
D. Filges, F. Goldenbaum, K. Nünighoff, H. Schaal, G. Sterzenbach, FZ-Jülich
L. Pienkowski, U. of Warsaw
W.U. Schröder, J. Tõke, U. of Rochester
D. Hilscher for the NESSI collaboration
2
Nuclear data for the target station of a spallation neutron source
GeV p
60 cm W, Hg, Pb
20 cm
25 n/p GeV
Window Fe .. Ta
Reaction length 18 cm (Pb) Preac = 1-exp(-z/Lreac)
Range 60 cm (1 GeV) nuclear stopping
cooling: 30 MeV/n reactor: 200 MeV/n
GeV proton induced
neutron production, multiplicity distributions
production cross sections of n, 1,2,3H, 3,4 He, 6,7 Li ... energy spectra in thin targets
excitation energy distributions of post INC residues
Validation of models/codes: LAHET, HERMES, INCL, FLUKA
Beam-induced radiation damage in window materials (Fe,Ta)
helium, hydrogen gas production
displacements per atom
3
Experiment
4
N I @ COSY
GeV p
5
Investigation of spallation reactions at COSY/FZJ
NESSI Collaboration: HMI-Berlin, FZ-Jülich, GANIL, Univ. Warsaw, Univ. Rochester
Cooler synchrotron and storage ring for protons p = 600 - 3400 MeV/c Ekin= 175 - 2600 MeV
6
NESSI detector
U. Jahnke et al., Nucl. Instr. Meth. A 508 (2003) 295C.-M. Herbach et al., Nucl. Instr. Meth. A 508 (2003) 315
BSiB: 162 detectors, particle separation of H, He, IMF, FF via TOF-E
Neutron multiplicity
7
Two step spallation reaction: INC+PE plus evaporation
ER2.5 GeV p + Au FF
()
n
n
n
p
p
n
E*GeV p
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INC protons
Too many low energetic INC protons, cutoff should be at ~20 MeV
preliminary
9
Pre-equilibrium cluster emission
10
Relative yield of pre-equilibrium composite particle emission
preliminary
11
Production cross sections
preliminary
preliminary
preliminary
12
Coalescence model 2.5 GeV p+Au
jiij rrr
jiij ppp
2
1
cMeVfm
prpr ijij
/300336
00
Improvement of PE composite particle spectra but at the expense of INC nucleon spectra
300
A. Letourneau et al., Nucl. Phys. A 712 (2002) 133
13
Systematics of PE emission
preliminary
The yield of PE deuterons seems to depend on the N/Z ratio only and not in addition also on the nuclear size R
1.2 GeV p + X
d
t
α
3He
TT
TTTT ZN
ZNAN
/1
//
14
Systematics of PE emission
The yield of PE deuterons and tritons seems to depend on the N/Z ratio only and not in addition also on the nuclear size R
TT
TTTT ZN
ZNAN
/1
//
preliminary
15
Neutron multiplicity distributions in thin and thick targets
16
Neutron multiplicity (Z): thin targets
1.2 GeV p + ZT
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Neutron multiplicity in thin and thick targets
Increase of Mn with target thickness due to inter nuclear cascade
thin targets
A. Letourneau et al., Nucl. Instr. Meth. B170 (2000) 299
18
Validation of HE-transport codes: Neutron multiplicity distributions
Preac probability to produce in BNB Mn neutrons/p in 5, 15, and 15 cm long Hg cylinders with a diameter of 15 cm
While for 1.2 GeV protons Mn distributions are well described by MCNPX and HERMES considerable deviations are observed at 2.5 GeV in particular with the MCNPX code
2.5 GeV p + Hg
D. Filges et al., Eur. Phys. J. A 11 (2001) 467
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Hadron induced neutron production in thick Pb-targets
Available energy: Ep + 2mpc2
35 cm
15cm
thick target
D. Hilscher et al., Nucl. Instr. Meth. A414 (1998) 100
20
Inelastic reaction cross section
21
BNB as a reaction detector
inelasticity > 10-15 MeV
H.P. Wellish, D. Axen PRC 54 (1996) 1329 R.E. Prael, M.B. Chadwick LA-UR-97-1745
Energy dependence of σinel
smaller than expected from systematics
preliminary
preliminary
22
Production cross sections
23
Helium production cross sections - well known?
Discrepancies both for measured as well as for calculated
production cross sections
24
Hydrogen and helium production cross sections
Hydrogen with Ep<25 MeVHelium
25
Window lifetime at different proton energies
He production in window materials per neutron produced in a thick Pb spallation target
He production per neutron produced decreases for Fe-like windows, for Ta only above 3 GeV
Average n-multiplicity per GeV
60 cm, 20cm
D. Hilscher et al., J. of Nucl. Materials 296 (2001) 83
26
Decay of hot nuclei as a function of excitation energy
Proton induced spallation reactions generate thermal excitation energy with a minimum of
compression
deformation
spin
27
Event-wise reconstruction of excitation energy
28
heating efficiency
LAHET Code (INC) overestimates the deposited excitation energy E*
INCL Code predicts E* relatively well10-20%
Heating efficiency of nuclei with GeV protons?
29
Fission probability Pfiss(E*,Mn,Mlcp)
30
Fission identification with BSiB
10 < Ai
50 < (A1+A2)
A1/(A1+A2) < 0.8
31
Fission probability Pf as a function of excitation energy E* for 2.5GeV p+U
preliminarypreliminary
fiss
ion
pro
bab
ility
excitation energy
inclusive
fission
32
Probability of fission, IMF-emission, ... as a function of Mn and Mlcp
lcpn
incllcpn
fiss
lcpnfiss MMY
MMYMMP
,
,,
33
Pfiss, IMF(Mlcp,Mn) for 2.5 GeV p + Au
255 IMFA
preliminarypreliminary
34
preliminarypreliminary
Fission probability Pf as a function of light charged particle (p-α) multiplicity Mlcp for 2.5 GeV p+U
inclusive
fission
35
Pfiss
preliminary
preliminary
Fission probability Pf as a function of light neutron multiplicity Mn for 2.5GeV p+U
36
Summary
• detailed, exclusive, and systematic data needed for validation of models
• excitation energy distributions sensitive test of INC models
• no satisfactory description of pre-equilibrium cluster-emission
• neutron production in thick targets reasonably well described by different models (compensation effect)
• H, He production cross-sections large differences between different models
• radiation damage of the window due to He production decreases with p-energy
• preliminary results of p-induced fission of U as a function of Mlcp, Mn and E*
D. Hilscher for the NESSI collaboration
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