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Forum: Hadronic Processes
Re: Question Neutron Detection - No Neutron Interactions (Eric)
Date: 11 Jul, 2011
From: Zach Hartwig <Zach Hartwig>

Hi Eric,

Two main suggestions: first, if your geometry hierarchy is full of errors (overlapping volumes, daughter volumes outside of mother volumes, etc) Geant4 transportation becomes extremely confused. Often, particles are transported through the geometry as if it's not there because the transportation manager cannot correctly step particles through an invalid geometry. Try running the geometry tests at the command line of your simulation. For example: /geometry/test/cylinder_test true

Second, unless you have explicit reason to build your own physics lists entirely from scratch, there are two preferred methods now in Geant4 for the incorporation of physics into your simulation:

1. Use on of the pre-built physics list included with Geant4. These lists are extremely easy to use and highly validated by Geant4 collaboration and user community. For a description and use cases of these physics lists, see:
http://geant4.web.cern.ch/geant4/support/proc_mod_catalog/physics_lists/referencePL.shtml
http://geant4.web.cern.ch/geant4/support/proc_mod_catalog/physics_lists/useCases.shtml

If you require neutron physics (as all as standard transportation, electromagnetic, hadronic physics, ...), most recommend are the QGSP_BERT and QGSP_BIC lists ("BERT" and "BIC" refer to 2 different model for spallation or hadronic cascases...if this physics is unimportant to you, just use either list). These lists include parametrized neutrons models, ie, theory or equation-driven models are used to neutron transport. If you require high precision neutron transport, use the QGSP_BERT_HP or QGSP_BIC_HP list, which includes data-driven neutron transport based on the G4NDL data library (which must be downloaded and built with your Geant4 installation)

2. If you'd like more control over your physics lists, you can assembled "modules" of the relevant physics using the "builder" method of the G4ModularPhysicsList class. For an example of how to build these physics lists (with use of parametrized or high-precision neutron physcis, see: $G4Install/examples/extended/hadronic/Hadr01/

Hope this helps.

~ZSH

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