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Forum: User Requirements
Re: Question Doubt about simulation type (Cristian Acuņa)
Date: 07 Jan, 2014
From: Pedro Arce <Pedro Arce>

Dear Cristian,

To do your job first you have to get the number of times each reaction happens. This is not easy in Geant4, becuase you should use the neutron_hp physics and in this physics there is no information about the nucleus that suffered the collision. You can get it by summing up the secondary particles produced; this works always for neutron_hp except for a few exceptions, none of them Si or O. The exposure time has to be translated to number of events, changing the initial time of each event. The half lifes are also not easy to take into account, because Geant4 may decay the isotopes for you, but assigning them a time sampled from the decay time distribution, so you will have to count by yourself how many are inside the time you selected.

I have developed some tools to do what you want, which I have put in the GAMOS framework, and I honestly think you would save a lot of time by using it. Counting isotopes can be easily done by getting the number of times each reaction happens. This job will be done by a simple script like this:

/gamos/setParam GmGeometryFromText:FileName test.geom /gamos/geometry GmGeometryFromText /gamos/physicsList G4QGSP_BIC_HP /gamos/generator GmGenerator


/gamos/generator/addSingleParticleSource source neutron 10.*MeV

/gamos/userAction GmCountTracksAndStepsUA GmClassifierByHadronicReaction

/run/beamOn 1000

and a geometry using Geant4 ASCII format:

:ELEM Silicon Si 14 28.0855
:ELEM Oxygen O 8 15.9994
:MIXT_BY_NATOMS SiO2 2.648 2
  Silicon 1
  Oxygen 2
:VOLU world BOX 1000. 1000. 1000. SiO2

(put your cylinder instead...) which will produce a table of this sort:

%%% COUNT_STEPS: Si28(n,p)Al28 = 123 %%% COUNT_STEPS: Si28(n,n)Si28 = 448 %%% COUNT_STEPS: O16(n,a)C13 = 180 %%% COUNT_STEPS: Si28(n,a)Mg25 = 72 ...

To take into account the time, look at the activation example, exercise 4a of tutorials/ShieldingTutorial


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