Thermal neutron scattering with NIST materials

I’m trying to simulate a source of Cf-252 moderated by polyethylene and a Li-6 based thermal neutron detector and have some questions about how to ensure thermal neutron scattering is handled correctly:

  1. Currently I have G4HadronElasticPhysicsHP and G4HadronPhysicsQGSP_BIC_HP (among other standard physics) in my modular physics list. I also need to add the thermal scattering libraries (G4NeutronHPThermalScatteringData) as shown in Section 5.2 of the Book for Application Developers, correct?

  2. I’m using the NIST G4_POLYETHYLENE material for my moderator. Do I understand correctly that automatically overrides the hydrogen content of the NIST material with the correct thermal scattering version? Or do I need to build it myself from elements using TS_H_of_Polyethylene?

In addition, can anyone comment on the expected accuracy of neutron thermalization in Cf-252? I found this paper by Shin et al that shows up to 40% discrepancies between simulated and measured doses when using polyethylene shielding, but much better agreements in other materials. And van der Ende et al found a 15% discrepancy between both geant4 and mcnpx vs measured thermal neutron count rates.

Have there been any documented improvements since 2014?

See example Hadr04: DetectorConstruction

Hadr04 shows how to build the material manually, but I want to know whether I need to build it manually or whether the NIST polyethylene automatically uses the TS version of hydrogen when the TS libraries are loaded.

So far as I’ve been able to tell, none of the NIST materials are named with the “TS” prefix/suffix. You have to do it yourself :frowning:

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In case anyone else runs into this, it seems I had to first remove the G4HadronElasticPhysicsHP physics list before adding the thermal physics manually (as in Section 5.2 of the Book for Application Developers), otherwise two elastic processes would exist.