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Forum: Hadronic Processes
Re: Question Regarding odd-even effect in heavy-ion interaction (Summit)
Date: 27 Jul, 2013
From: Jose Manuel Quesada <Jose Manuel Quesada>

   Dear Summit,

                             it's a matter of the physics included in 
such models: one should never expect what is beyond
their capabilities.  WilsonAbrasion model is a quite simplistic one, 
based in geometry and kinematics (geometric abrasion as initial stage 
followed by ablation,
emulating de-excitation).   If no pairing effects are included, detailed 
nuclear structure effects (as the odd-even effect) shoudn't   be expected
to be described. BIC and QMD use the same  models for the final 
de-excitation stage (where the pairing effects, and therefore the 
odd-even effects,
are included),   although their initial stages are  different: BIC is a 
intranuclear cascade model , whereas QMD is a quantum molecular dymamics 
one, with more physical content in it.   As for de-excitation, 
evaporation and fission  include pairing effects, but not the 
statistical  models  (Fermi break-up and statistical multifragmentation).
Fermi break-up can be activated or not (if yes, it takes care of 
de-excitation of light fragments, Z<9, A<17), this is
a user's choice (although in the latest releases it is on by default). 
If evaporation model plays its role, this would explain
why QMD is  partially  describes the odd-even effects  (for instance 
Ar+C @  8.5 GeV/u, page 18 of A. Ivanchenko's presentation).
On the other hand, BIC largely fails to describe the odd-even effects: 
that could be due to higher excitation energies in the population of
nuclei to be de-excited by evaporation (which would wash-out to some 
extent the  structure effects) with respect to the QMD case  or a 
dominating
role of Fermi break-up model for light fragment de-excitations.  But let 
me state once again that both, QMD and BIC, use in principle
the same de-excitation models.

  As for the suppresion of Z=9, this should come from the binding 
energies  (i.e. masses) of these nuclei (helped by pairing energies, if 
evaporation mechanism is the responsible), which make the probabilities 
for de-excitation chains ending up there , small. In this case these, 
the  models are  capable of reproducing experimental behaviour.


  Best regards

                          José Manuel

On 07/26/2013 08:16 AM, Summit wrote:
> *** Discussion title: Hadronic Processes
>
> Dear G4Users,
>
> I have tried to calculate partial fragmentation cross sections for 28Si
> + Pb using G4BinaryLightIonReaction, G4WilsonAbrasion and G4QMDReaction
> models. In the simulation work, no models exactly shows the odd-even
> effect as shown by experimental data. But BIC and QMD models well show
> the suppression for the fragment with the charge Z = 9. I have seen
> similar behavior in other interactions also. I need the explanation why
> they are not able to able the exactly odd-even effect and why they have
> show the suppression as shown by experimental data?
>
> Also in the presentation of A.Ivantchenko (Validation of Geant4 models
> with Ion/Ion interactions, page 18-21), similar type of behavior has
> been observed.
>
> Can anyone give me explanation regarding this?
>
> Thanking you,
>
> Summit.
>
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at:
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>

-- 
José Manuel Quesada Molina
Departamento de Física Atómica, Molecular y Nuclear
Universidad de Sevilla
Apartado 1065
41080 Sevilla, Spain
Tel:+34.954559508
Fax:+34.954554445
E-mail:quesada@us.es
Personal Web:http://personal.us.es/quesada/

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