nuclear reactions at high energiesindico.ictp.it/event/a0149/material/1/5.pdf · 2014. 5. 5. ·...

»*-»*« abdus salameducational, scientificand cultural

theiinternational centre for theoretical physics

international atomicenergy agency SMR/1325-7

Workshop on

Nuclear Data for Science fii Technology: AcceleratorDriven Waste Incineration

10-21 September 2001

Miramare - Trieste, Italy

Nuclear Reactions at High Energies

Sylvie LerayDAPNIA/SPhN CEA/ Saclay

France

strada costiera, I I - 34014 trieste italy - tel.+39 04022401 I I fax +39 040224163 - [email protected] - www.ictp.trieste.it


Nuclear Reactions at High

EnergiesSylvie LERAY

DAPNIA/SPhN CEA/Saclay

Design of spallation targets for ADShas raised needs for reliablenumerical simulation codesoImprovement of high energy nuclear

reaction models (above 150-200 MeV)

o Validation on the bulk of newlyavailable high energy data

Other applications:• spallation neutron sources

• radioactive beams• radiation damage in space+ astrophysics

Sylvie LERAY (CEA/Saclay) Trieste, Sept. 10-21, 2001


Outline

1. Importance of spallation reactions forapplications- Definition of spallation

- Data needed for Accelerator-Driven Systems

- Other applications

2. High energy nuclear models- Models and codes for high energies

- Intra-nuclear cascade models

- The Liege INC model

3. Comparison of models to available highenergy data- Neutrons

- Charged particles

- Residues

- Coincidence measurements

4. Conclusions



Spallation reactions

p(lGeV)

Intra-Nuclear Cascad Excited nucleusEyappration

a, JJ, y decay

Definition:interaction of a high energy (> 100 MeV) lightparticle with a nucleus leading to emission oflight particles and leaving a heavy residue.

History:*> observation of particle cascades in cosmic

rays interactions (G.Rossi, ZP82 (1933) 151)

^ first accelerators: many nucleons emitted bythe target nucleus ( Cunningham, PR72 (1947) 739)

**TWO Step mechanism (Serber, PR72 (1947) 1114)



Data required for the design ofspallation targets

Accelerator

Protons 1 GeV10-100 m A

Sub-critical reactor JfL

• • * ^^^ • • *

\ \ t / I \ / .0 Spa llation target

^

•-̂ (R

/ v \neutrons * *

\

transmutation

Neutron production4 number -• power of the system / needed

accelerator intensityenergy, spatial distribution -4 targetoptimisation, damage in window and structureshigh energy neutrons -4 shielding

Charged particle production+ gas (H2, He) production -» embrittlement,

swelling• energy ^ DPA, energy deposition


Shape optimisation of a spallation target

p + Pb, E = L2 GeV, L = 80 cm

Ea>20MeV

• cylindrical surface• Back surface* Front surface

Total

100 190 200 150Diameter (Cm)

Number of low and high energy neutrons emitted through the different faces of a

cylindrical lead target as a function of the target diameter.

500 1000 1500 2000 2500 3000 3500 4000E(MeV)

Number of low energy neutrons emitted from the lateral face of a cylindrical lead

target for fixed or an optimised geometry.

From F. Lavaud. stage DEA. CEA/SPhN (1998)


Data required for the design ofspallation targets

Accelerator

Protons 1 GeV10-100 rn A

Sub-critical reactor

N

"^hr * *

/

neutrons

yH fission

Vw# Spa llation target

*

V \

" transmutat

/

ton

Residual nuclide production+ element distribution -• corrosion, change in

metallurgical properties+ isotope distribution -> activity (short lived

isotopes), radiotoxicity (short livedisotopes), decay heat

• recoil energies -* DPA in window andstructures, energy deposition


Pb target (50x100)Proton energv 0.8 GeVI = 30 mAOne year irradiation

10 "4 10 "a 10 "2 10 "*2 1 0 * 10 4 10 5 1 0 * 10 7 10of cool ing (day)

1 0 * 10

Fig. 4. Total and partial activiiiiaits; rflead target as a function of cooling time.

Pb-Bi target (50x100)Proton energy 0.8 GeVI = 30 mAOne year irradiation

7io " " J O * " i 6 * i o s i o ' 10 T i o * JO • i oof cooling (day)

Fig. 5. The same assinIFig- 3 for lead-bismuth target.

Analysis of the Contributions ofiheJvwton avid Neutron Spectral Components to theAcxMirruktting Activity

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Astrophysics

10c

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- 1 1 1 I J I I 1 1 I I I ' 1

- • - Satellite Measurements- 3 - Solar System abundances

i • • { ' •

o 10 15 20 25 30N u c l e a r C h a r g e

• Secondary reactions of cosmic rays ininterstellar medium (90% of hydrogen)*> explanation of abundance of isotopes

t» decide among models for galacticnucleosynthesis

*» origin of cosmic rays

• Composition of meteorites


\o

Nuclear Reactions at KBgJi Energies

Spallation reactions in space instruments

10

Cosmic ray bombardment of thespacecraft and instruments*• Noise due to secondary gammas, neutrons

and spallation residues

t» ex: spectrometer of the INTEGRAL missiondevoted to high resolution y - ray astronomy

determination of the flux of secondaryparticlesbackground due to radioactive residues



Rare isotope production

• Direct methods*• ISOL p (1 GeV) + A =*> low energy RIB

t* fragmentation of GeV/A heavy ions -> highenergy RIB

• Converter methodst» use of moderated spailation neutrons to

induce fission



Spaiiation neutron sources

Shielding

Moderation of spaiiation neutrons in(heavy) water

Reflectors to direct escaping neutronsinto beam tubes*> pulsed sources: well-defined time structure,

high peak flux o tof experiments*» continuous sources: high neutron flux in a

large volume o irradiation experiments



Spallation target modelling

p (1 GeV)

Internuclear cascade

Fission OR Evaporation

©—,

Monte-Carlo transport codes*» propagation of all particles created in elemen-

tary interactions (HETC + MCNP type)

Nuclear physics models (above 150-200MeV*» generating cross-sections (Intra-Nuclear

Cascade followed by evaporation-fission)

Evaluated data files (below 150-200 MeV)t» providing all reaction channels



What is needed above 150-200 MeVfor ADS and other applications

Objective: to reliably predictproduction rates of all producednuclei with their energy andangular distributions• Elementary cross-sections measu-

rements

*> to test the physics models

• Improvement of models and/ordevelopment of new ones

*• validation on experimental data

• Integral measurements

test and validation of transportcodes



Models for spallation reactions

p(lGeV)

Intra-Nuclear Cascad Excited nucleusEvaporation

TWO Step mechanism (Serber 1947):

t» Intra-Nuclear Cascade

sequence of independent N-N collisions

Ade Brogiie= hc^P « X = 1/paw mean free path

fast process (» 30 fm/c)

=> Heating of the nucleus - thermalisation

*> De-excitation by evaporation or fission

statistical evaporation models

slow process (hundreds of fm/c)


;:lii^^

Intra-Nuclear Cascade

p (1 GeV)

Determines the number and direction of

the high energy particles*» shielding against energetic neutrons

t» inter-nuclear cascade propagation

for lead INC neutrons = 15% total nb

but carry 80% of the energy

Determines initial conditions forevaporation-fission

• Excitation energy

• Z, A of the pre-fragment

• Angular momentum


n


Intra-Nuclear Cascade models

p(lGeV)•

Common features*> linear trajectory between collisions

t* nuclear potentiel

** free N-N cross-sections

*• inelastic collisions N+N-* N+A -» N+ N+n

*+ Pauli blocking

Main available INC models• Bertini (Phys. Rev. 131 (1963) 1801)

• Isabel (Yariv and Frankel, Phys. Rev. C20 (1979) 2227)

• Cugnon (Cugnon et al., Nucl. Phys. A620 (1997) 457)


\%


Differences between the different INC models

^ 7C

Fig. 3 : Schematic representat ion of the INC models of the first type (left) and of second type {.right !. In thelat ter case, nucleons promoted from the continuum are. indicated by he.nvy dots.

Medium '

Cascade 'propagation••

Collision',criteriuraStoppingcrit.eriivn

Surface

Pauli blocking

Bertini

continuous

collidedparticles

mean free path

energy

diffuse (3density regions)

strict

Isabel

continuous

time steps

mean free path

energy

diffuse

not fully strict

Cugnon

particles

time steps

minimum distanceof approach

time

sharp

statistics


id


The Liege INC model (INCL)

First developed for heavy ion collisions (Cugnon et

ai., Nuci. Phys. A352 (1981) 505) then applied to proton

induced reactions (Cugnon, Nucl. Phys. A462 (1987) 751)

standard INCL2 model(Cugnon et al., Nucl. Phys. A620 (1997) 457)

• succession of binary collisions well separated inspace and time

• generation of initial positions of target nucleonsat random inside a sharp surface sphere

• stochastical generation of initial momenta oftarget nucleons inside a Fermi sphere

• straight line trajectories until minimum distanceof approach or hitting of the wall of the potential

• statistical Pauli blocking

• inelastic collisions, pion production andabsorption: N+N

(chwjeJaffect 0° iA (p,x>r\)

10 r • r n r

CO -IO Io

•-- H.W.Bertini,PRC131(63)1801•- J.Cugnonetal,NPA352(81)505- New parametrisationo M.LEvans et al,PRC26(82)2525* Y.Terrien et al,PRL59(1987)1534

Elab=650 MeV

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o Data n-p scattering at 0 deg.

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— Cugnon angular distribution

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p(1600 MeV)+Pb[0-5]degre

En(MeV)



The new INCL4 version(Boudard et al., to be published)

• diffuseness of the nuclear surface:Wood-Saxon distribution with parameters in

accordance with experimental values

good total reaction cross-sections

better prediction of peripheral collisions

• consistent dynamical Pauli blocking:phase space occupation probability evaluated

collisions leading to energy Eej > EGS(AR) forbidden

-> no more negative excitation energies

• collisions between spectators forbiddenno spurious nucleon evaporation

dynamical evolution of the phase spacepreserved

• angular momentum of the remnant calculated-> important for input in evaporation-fission

• possibility of composite incident particleswith realistic momentum distribution


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• no really free parameters:stopping time fixed by consideration on thevariation rate of several observables

-> results insensitive to a variation of ± 5fm/c

Potential = 45 MeV (EF+S)

-> could be slightly varied

• Further possible improvements

^realistic momentum density

^•medium effect on N-N cross-sections

êmission of composite particles (d, t, a, IMF)

^special treatment of the first collision

(quasi-elastic reactions)

ênergy dependence of the potential

împrovement of pion dynamics

• Implementation in LAHET3 in progress


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Models for the de-excitation

+ Evaporation: statistical modelsEmission probability of one particle governed by

*> inverse capture cross-section (detailed balanceprinciple)

t» Coulomb barriers

*» density of available states

+ Most widely used model: Dresner (ORNL-TM-196 (1962))

t» Weisskopf-Ewing formalism

*> all types of LCP evaporation

** GCC-lgnatyuk level density parameter (-> A/8)

** Coulomb barriers lowering with E*

+ GSI (K.H.Schmidt) model (Nucl. Phys. A629 (1998) 635)

*> Weisskopf-Ewing formalism

^ only n,p,a evaporation

*• Level density parameter -> ~ A/12

t» realistic Coulomb barriers

Fermi-Break-up* • For A < 22

^ break-up probabilities from available phase space



Models for the de-excitation

• Fission:+ Models used in high-energy transport codes

*» Bohr-Wheeler formalism

t» phenomenological parameterisation of barriers

t» phenomenological parameterisation of Z and Adistribution of fission fragments

*» only n/fission competition

> ORNL, Z>91 (Alsmiller, ORNL-7528 (1981))

>̂ RAL, Z>70 (Atchison, KFA Julich conf-34 (1981))

+ GSI modelt» friction introduced through a delay time

t» full particle/fission competition

*» Z and A distribution of fission fragments based onpotential energy surface at saddle

ty

+ GEMINI model (Moretto et al., NP A247 (1975) 211)

*> Transition state method

*» particle, IMF and fission treated on an equal footing


nuclear reactions at high energiesindico.ictp.it/event/a0149/material/1/5.pdf · 2014. 5. 5. ·...

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