1

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

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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

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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

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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

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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

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Pre-equilibrium cluster emission

10

Relative yield of pre-equilibrium composite particle emission

preliminary

11

Production cross sections

preliminary

preliminary

preliminary

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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

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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

//

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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

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Neutron multiplicity distributions in thin and thick targets

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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

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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

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Inelastic reaction cross section

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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

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Production cross sections

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Helium production cross sections - well known?

Discrepancies both for measured as well as for calculated

production cross sections

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Hydrogen and helium production cross sections

Hydrogen with Ep<25 MeVHelium

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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

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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

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Event-wise reconstruction of excitation energy

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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?

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Fission probability Pfiss(E*,Mn,Mlcp)

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Fission identification with BSiB

10 < Ai

50 < (A1+A2)

A1/(A1+A2) < 0.8

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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

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Probability of fission, IMF-emission, ... as a function of Mn and Mlcp

lcpn

incllcpn

fiss

lcpnfiss MMY

MMYMMP

,

,,

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Pfiss, IMF(Mlcp,Mn) for 2.5 GeV p + Au

255 IMFA

preliminarypreliminary

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preliminarypreliminary

Fission probability Pf as a function of light charged particle (p-α) multiplicity Mlcp for 2.5 GeV p+U

inclusive

fission

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Pfiss

preliminary

preliminary

Fission probability Pf as a function of light neutron multiplicity Mn for 2.5GeV p+U

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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