K.-H. Schmidt for the CHARMS collaboration Gesellschaft für Schwerionenforschung (GSI) Darmstadt,...
-
Upload
lorin-roxanne-melton -
Category
Documents
-
view
220 -
download
0
description
Transcript of K.-H. Schmidt for the CHARMS collaboration Gesellschaft für Schwerionenforschung (GSI) Darmstadt,...
K.-H. Schmidt for the CHARMS collaborationGesellschaft für Schwerionenforschung (GSI)
Darmstadt, Germany
Spallation ReactionsSpallation Reactions--
Physics and ApplicationsPhysics and Applications
work supported by EU (EURISOL and EUROTRANS)
Spallation reactions – physics and Spallation reactions – physics and applications applications
- Definition- Applications- Experiments- Physics and models- Conclusion
Outline
DefinitionDefinition
What is a spallation reaction ?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.
ApplicationsApplications
Importance of spallation reactions 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
Neutron sourcesNeutron sourcesType Facility Proton
beamNeutron energy
Time structure
Neutron flux
Purpose
Fission reactor
ILL Grenoble ---
cold, thermal, epitherm
al
continuous 1.3 1015 n/(cm2 s)
mostly solid state
Spallation
neutron source
SINQ Villigen
500 MeV,1.8 mA continuous 1.1 1014
n/(cm2 s)mostly
solid stateISIS
Rutherford800 MeV,200 μA
50 Hz, 400 ns
mostly solid state
SNS Oak Ridge
1 GeV,1.4 mA
60 Hz, 695 ns
mostly solid state
n_TOF CERN
200 GeV/c
thermal – several
100 MeV0.42 Hz,
6 nsnuclear physics
Example:Layout of SINQ →(Study of condensedmatter.)
ISOL-based secondary-beam facilitiesISOL-based secondary-beam facilitiesFacility Proton
beamOutput
ISOLDE CERN ≤ 1.4 GeV Rare isotopesTRIUMF Vancouver 200 MeV Rare isotopes, neutrons, pions,
muonsEURISOL project 1 GeV Rare isotopes
ADS (Accelerator-driven system)ADS (Accelerator-driven system)
Proton accelerator (≈ 1 GeV)
Subcritical fission reactor
Spallation neutron source
Purpose: Incineration of nuclear wastePrototype: Myrrha (Mol, Belgium)
ExperimentsExperiments
Detector systemsDetector systems• Normal kinematics (particle on nucleus)
• Inverse kinematics (nucleus on light target)
• Neutrons (d2Y/(dE dθ)) (kinematical detectors)• Neutrons (total yield) (moderation and capture of neutrons)• Light charged particles (d2Y/(dE dθ)) (ΔE -E, e.g. silicon)• Heavy residues (a few independent yields, cumulative yields)(irradiation, off-line gamma spectroscopy / accelerator mass spectrometry)
• Heavy residues (Y(Z,A), dY/dv) (in-flight identification Bρ – ToF – ΔE)• Neutrons and light charged particles (advanced installations at FAIR@GSI)
Double-differential neutron spectraDouble-differential neutron spectra
SATURNE experiment,S. Leray et al. (2002)
Neutrons in forward direction reach up to the energy of the projectiles.
Spectra of light fragmentsSpectra of light fragments
PISA experiment, Jülich, F. Goldenbaum et al. (2003)
Almost thermal energy spectrum of light fragments.
Excitation functions of heavy residues Excitation functions of heavy residues
Titarenko et al, 2005
Independent and cumulative yields by off-line gamma spectroscopy
GSI facility GSI facility → inverse kinematics→ 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
Fragment Separator (FRS) Fragment Separator (FRS)
max = 15 mradp/p = 1.5 %
ZAB
ecm0
Resolution: - ()/ 5·10-4 - Z 0.4 - A / A 2.510-3
ToF
x1, x2 B
E Z
Nuclide identification (238U + p, M. V. Ricciardi)
Benefit of inverse kinematics Benefit of inverse kinematics
Protons (553 MeV) on lead 208Pb (500 A MeV) on hydrogenExperiments in inverse kinematics:
Complete overview on nuclide production (T1/2>100 ns) ; E > several 100 A MeV
Spallation of Spallation of 238238U – complete overviewU – 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
Velocity distributionsVelocity distributions
Typical velocity profiles arecharacteristic for thereaction mechanism (evaporation,fission andmultifragmentation)
P. Napolitani, 2007
Systematic studiesSystematic studies
www.gsi.de/charms/data.htm
CollaborationCollaborationGSI P. Armbruster, A. Bacquias, T. Enqvist, L. Giot, K. Helariutta, V.
Henzl, D. Henzlova, B. Jurado, A. Kelić, P. Nadtochy, R. Pleskač, M. V.
Ricciardi, K.-H. Schmidt, C. Schmitt, F. Vives, O. Yordanov
IPN-ParisL. Audouin, M. Bernas, B. Mustapha, P. Napolitani, F. Rejmund, C. Stéphan, J. Taïeb, L. Tassan-GotCEA-SaclayA. Boudard, L. Donadille, J.-E. Ducret, B. Fernandez, R. Legran, S.
Leray, C. Villagrasa, C. Volant, W. Wlazło
University Santiago de CompostelaJ. Benlliure, E. Casarejos, M. Fernandez, J. Pereira
CENBG-BordeauxS. Czajkowski, M. Pravikoff
14 PhD
R3B@FAIR (New project at GSI)R3B@FAIR (New project at GSI)
Neutrons
Heavy fragmentsExotic beam
from Super-FRS
Protons
Target
-raysNeutronsProtons
Tracking detectors: E, x, y, ToF, B
Neutrons
High-resolution spectrometer
- 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.
Physics and modelsPhysics and models
Nucleon-nucleus collision at 1 A GeVNucleon-nucleus collision at 1 A GeV
E p
10 MeV 137 MeV/c 9.03 fm100 MeV 443 MeV/c 2.79 fm
1 GeV 1692 MeV/c 0.73 fm
Decisive parameter:de Broglie wavelength of a nucleon: =h/p
Compared tonuclear radius (r = 1.16 fm A1/3) orrange of nuclear force ( 1 fm)
Spallation reaction ≈ collisions of individual nucleons !
No consistent uniform description of the spallation process available.
Modeling of spallation reactionsModeling of spallation reactions
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)
Specialized codes for different steps of the reaction
Thermal expansionThermal expansion
ρ~eS level densityS=2√(aE*)Fermi gasa~Vlevel-density parameter grows withvolumeE* = E0* - c·(V-V0)2 parabolic dependence
of nuclear binding onvolume or density
S~√(V(E0*-c·(V-V0)2)
Statistical model: The nucleus assumes the configuration which offers maximum number of states. This is also true for the volume.
MultifragmentationMultifragmentation
Expansion may lead to multifragmentation.
(SMM, ABLA07)
The evaporation corridorThe evaporation corridorDecisive influence of evaporation on the nuclide distribution.
Residues tend to follow the evaporation corridor (Dufour, Charity).
FissionFissionFission barrier → Interplay of surface and Coulomb energy.
General features of fissionGeneral features of fissionPotential barrier as a function of mass asymmetry.
Symmetric fission for heavy systems
Experimental information – low energyExperimental information – low energy
K.-H. Schmidt et al., NPA 665 (2000) 221
Experimental survey at GSI by use of secondary beams
Modeling multi-modal fissionModeling multi-modal fission
E* = 60 MeV
20 MeV
10 MeV
Many different nuclei with different E* contribute to fission.
black: data, red: simulation with ABLA07
Dynamics of fissionDynamics of fission Fission is a dynamical process, described by the Langevin equation.
Langevin trajectoriesLangevin trajectories
Fission is hindered by dynamics with respect to evaporation.
Fission barrier
Groundstate
Generalized fissionGeneralized fissionPotential barrier as a function of mass asymmetry.
Continuous mass distribution from particle evaporation to symmetric fission (Moretto)
Emission of intermediate-mass fragmentsEmission of intermediate-mass fragments
Evaporation of IMF (very asymmetric fission) must be considered.
(only n,p,α) (n, p, all fragments)
Data: 209Bi + p Yu. E. Titarenko et al., Nucl. Instrum. Methods A 562 (2006) 801
Model CalculationModel Calculation
INCL4 +ABLA07
ConclusionsConclusions
- 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@FAIR
- Elaborate codes for the reaction stages (e.g. INCL4 + ABLA07)
- INC → (Exciton) → (Thermal break-up) → Evaporation-fission
Spallation reactions
Additional slidesAdditional slides
Experimental challenge Experimental challenge
Short-lived as well as stable nuclei have to be detected.
Excitation functions Excitation functions
Titarenko et al, 2005
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
Velocity distributions Velocity distributions 238U (1 AGeV) + 2H
Pereira, PhD thesis
For each nucleus: production cross section, velocity and production mechanism
FISSION
FRAGMENTATION
Experimental progress by inverse Experimental progress by inverse kinematicskinematics
Projectile Target Energy [A GeV] 56Fe 1H, 2H 0.2 - 1.5
136,124Xe 1,2H, Be, Ti, Pb 0.2, 0.5, 1 197Au 1H 0.8208Pb 1,2H, Ti 0.5, 1238U 1,2H, Ti, Pb 1
Data accuracy:Statistic: below 3% Systematic: 9 - 15 %
More than 1000 nuclei/system measured
Data available at: www.gsi.de/charms/data.htm