K.H. Schmidt for the CHARMS collaboration

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Spallation Reactions - Physics and Applications

• K.-H. Schmidt for the CHARMS collaboration
• Gesellschaft für Schwerionenforschung (GSI)
• Darmstadt, Germany

work supported by EU (EURISOL and EUROTRANS)
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Spallation reactions physics and applications
Outline
- Definition - Applications - Experiments -
Physics and models - Conclusion
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Definition
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What is a spallation reaction ?
Violent collision of nucleons (or particles) with
heavy nuclei. First studied with cosmic rays.
Schopper et al. Naturw. 25 (1937) 557
Collision of a µ of 41.2 GeV with an iron
nucleus, recorded by the KARMEN detector.
Disintegration (spallation) of the nucleus in
many pieces. Production of a variety of different
particles and fragments.
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Applications
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Importance of spallation reactions

• EOS of nuclear matter - Spallation is a way
  to heat nuclear matter ? thermal break-up
• Astrophysics - Reactions of cosmic rays with
  interstellar medium ? origin of c.r. -
  Nucleosynthesis in turbulence of Supernova
  explosions
• Spallation neutron sources - Efficient way
  for producing neutrons
• ADS (Accelerator-driven system) - Project
  for incinerating radioactive waste
• Secondary-beam facilities - Production of
  rare isotopes
• Radioprotection and medicine

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Neutron sources
Example Layout of SINQ ? (Study of
condensedmatter.)
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ISOL-based secondary-beam facilities
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ADS (Accelerator-driven system)
Proton accelerator ( 1 GeV)
Subcritical fission reactor
Spallation neutron source
Purpose Incineration of nuclear waste Prototype
Myrrha (Mol, Belgium)
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Experiments
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Detector systems

• Normal kinematics (particle on nucleus)

• Neutrons (d2Y/(dE d?)) (kinematical detectors)
• Neutrons (total yield) (moderation and capture
  of neutrons)
• Light charged particles (d2Y/(dE d?)) (?E -E,
  e.g. silicon)
• Heavy residues (a few independent yields,
  cumulative yields)(irradiation, off-line gamma
  spectroscopy / accelerator mass spectrometry)

• Inverse kinematics (nucleus on light target)

• Heavy residues (Y(Z,A), dY/dv)
  (in-flight identification B? ToF ?E)
• Neutrons and light charged particles (advanced
  installations at FAIR_at_GSI)

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Double-differential neutron spectra
Neutrons in forward direction reach up to the
energy of the projectiles.
SATURNE experiment,S. Leray et al. (2002)
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Spectra of light fragments
Almost thermal energy spectrum of light fragments.
PISA experiment, Jülich, F. Goldenbaum et al.
(2003)
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Excitation functions of heavy residues
Independent and cumulative yields by off-line
gamma spectroscopy
Titarenko et al, 2005
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GSI facility ? inverse kinematics

• UNILAC Up to 20 A MeV
• SIS 50 2000 A MeV, up to 1011
  particles/spill
• Beams of all stable nuclides
  up to 238U

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Fragment Separator (FRS)
Nuclide identification (238U p, M. V.
Ricciardi)
?max 15 mrad ?p/p ? 1.5
ToF ? ?? x1, x2 ? B? ?E ? Z
Resolution - ?(??)/?? ? 510-4 - ?Z ?
0.4 - ?A / A ? 2.5?10-3
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Benefit of inverse kinematics
Protons (553 MeV) on lead
208Pb (500 A MeV) on hydrogen
Experiments in inverse kinematics Complete
overview on nuclide production (T1/2gt100 ns) E
gt several 100 A MeV
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Spallation of 238U complete overview
Data measured at GSI
Ricciardi et al, Phys. Rev. C 73 (2006) 014607
Bernas et al., Nucl. Phys. A 765 (2006) 197
Armbruster et al., Phys. Rev. Lett. 93 (2004)
212701 Taïeb et al., Nucl. Phys. A 724 (2003)
413 Bernas et al., Nucl. Phys. A 725 (2003) 213
www.gsi.de/charms/data.htm
More than 1000 different nuclides
observed. Features of spallation-evaporation /
-fission / -IMF emission
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Velocity distributions
Typical velocity profiles arecharacteristic for
thereaction mechanism (evaporation,fission
andmultifragmentation)
P. Napolitani, 2007
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Systematic studies
www.gsi.de/charms/data.htm
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Collaboration
GSI P. Armbruster, A. Bacquias, T. Enqvist, L.
Giot, K. Helariutta, V. Henzl, D. Henzlova, B.
Jurado, A. Kelic, P. Nadtochy, R. Pleskac, M. V.
Ricciardi, K.-H. Schmidt, C. Schmitt, F. Vives,
O. Yordanov IPN-Paris L. Audouin, M. Bernas, B.
Mustapha, P. Napolitani, F. Rejmund, C. Stéphan,
J. Taïeb, L. Tassan-Got CEA-Saclay A. Boudard,
L. Donadille, J.-E. Ducret, B. Fernandez, R.
Legran, S. Leray, C. Villagrasa, C. Volant, W.
Wlazlo University Santiago de Compostela J.
Benlliure, E. Casarejos, M. Fernandez, J.
Pereira CENBG-Bordeaux S. Czajkowski, M.
Pravikoff
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R3B_at_FAIR (New project at GSI)
- Full identification of heavy residues with
simultaneous measurement of neutrons, light
charged particles and gammas with new R3B
magnetic spectrometer. ? Aiming for a
kinematically complete experiment.
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Physics and models
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Nucleon-nucleus collision at 1 A GeV
No consistent uniform description of the
spallation process available.
Decisive parameter de Broglie wavelength of a
nucleon ?h/p
Compared to nuclear radius (r 1.16 fm ? A1/3)
or range of nuclear force ( ? 1 fm)
Spallation reaction collisions of individual
nucleons !
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Modeling of spallation reactions
Specialized codes for different steps of the
reaction
1. Intranuclear cascade (INCL, ISABEL,
...) (quasi-free nucleon-nucleon collisions
?high-energy n, p ..)
2. Exciton model (sequence of particle-hole
excitations ?pre-equilibrium emission,included
in INCL) ----------------------------
4. Evaporation code(ABLA07, ...) (evaporation of
particles and fragments, fission)
3. Multifragmentation (expansion and thermal
break-up)
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Thermal expansion
Statistical model The nucleus assumes the
configuration which offers maximum number of
states. This is also true for the volume.
?eS level density S2v(aE)Fermi
gas aVlevel-density parameter grows
withvolume E E0 - c(V-V0)2 parabolic
dependence of nuclear binding onvolume or
density Sv(V(E0-c(V-V0)2)
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Multifragmentation
Expansion may lead to multifragmentation. (SMM,
ABLA07)
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The evaporation corridor
Decisive influence of evaporation on the nuclide
distribution.
Residues tend to follow the evaporation corridor
(Dufour, Charity).
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Fission
Fission barrier ? Interplay of surface and
Coulomb energy.
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General features of fission
Potential barrier as a function of mass asymmetry.
Symmetric fission for heavy systems
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Experimental information low energy
Experimental survey at GSI by use of secondary
beams
K.-H. Schmidt et al., NPA 665 (2000) 221
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Modeling multi-modal fission
E 60 MeV
20 MeV
10 MeV
black data, red simulation with ABLA07
Many different nuclei with different E
contribute to fission.
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Dynamics of fission
Fission is a dynamical process, described by the
Langevin equation.
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Langevin trajectories
Fission barrier
Groundstate
Fission is hindered by dynamics with respect to
evaporation.
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Generalized fission
Potential barrier as a function of mass asymmetry.
Continuous mass distribution from particle
evaporation to symmetric fission (Moretto)
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Emission of intermediate-mass fragments
(only n,p,a) (n, p, all fragments)
Data 209Bi p Yu. E. Titarenko et al., Nucl.
Instrum. Methods A 562 (2006) 801
Evaporation of IMF (very asymmetric fission) must
be considered.
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Model Calculation
INCL4 ABLA07
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Conclusions
Spallation reactions
- Many fields of application ? high interest for
good understanding - Two experimental
approaches - Direct kinematics - light
particles yields and energy distributions
heavy residues only long-lived species and
cumulative yields - Inverse kinematics
heavy residues complete overview (1000 nuclides
/ system) - velocity spectra information
on reaction mechanism - new-generation
(complete) experiments at R3B_at_FAIR - Elaborate
codes for the reaction stages (e.g. INCL4
ABLA07) - INC ? (Exciton) ? (Thermal break-up)
? Evaporation-fission
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Additional slides
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Experimental challenge
Short-lived as well as stable nuclei have to be
detected.
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Excitation functions
Independent and cumulative yields
- About 100 nuclei/system - Uncertainty 7 30
Additional information - Miah et al, Nucl. Sc.
Tech. Suppl. 2 (2002) 369 - Schiekel et al, Nucl.
Instr. Meth. B114 (1996) 91 - Adilbish et al,
Radiochem. Radioanal. Lett. 45 (1980) 227 - Chu
et al, Phys. Rev. C 15 (1977) 352
Titarenko et al, 2005
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Velocity distributions
238U (1 AGeV) 2H
FISSION
FRAGMENTATION
For each nucleus production cross section,
velocity and production mechanism
Pereira, PhD thesis
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Experimental progress by inverse kinematics
More than 1000 nuclei/system measured

• Data accuracy
• Statistic below 3
• Systematic 9 - 15

Data available at www.gsi.de/charms/data.htm