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