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Question np-Elastic Cross-Section Discontinuity 

Forum: Physics List
Date: 09 Dec, 2014
From: Zach Miller <Zach Miller>

Hello,

I am working on characterizing a plastic neutron scintillation detector's efficiency. To do this, I throw neutrons into the detector and see at what rate they interact and are detected. Thus, my result is mostly dependent on np-elastic cross-section and light production. I'm getting a very strange result, and it seems to be tied to the np-elastic.

I am using FTFP_BERT_HP and am attempting to look at the efficiency for neutrons ranging from a 5 MeV up to 200 MeV (with a detection threshold of 4 MeV). When I do this, I get a discontinuity at 32.7 MeV (see attached picture). If I look at the code here: $GEANTINSTALL/source/process/hadronic/cross_sections/G4HadronCrossSections.cc it seems that 32.7 MeV is the point where the cross-section tables stop and, I'm assuming, a new model is selected. This discontinuity is fatal to my calculation, so I need to find a way to overcome it.

I see that there is a SAID database result for np-elastic that comes pre-packaged in the GEANT Data Files I installed upon installing GEANT... however, I'm unsure how I tell my physics list to use only this data instead of whatever it is using now. Is there a way for me to tell GEANT that I want it to use only that data (or perhaps the ENDF result for nH)?

Currently, I just register my PhysicsList as FTFP_BERT_HP in the Main() and register extra processes as necessary (OpticalPhysics or what-have-you). So, I'm not even sure what cross-sections GEANT is truly using. I have tried using G4EmCalculator, but it always returns 0 pbarns as the cross-section for "hadElastic" process, so I can't tell what it is selecting. I'm hoping to make the EmCalculator and will update with those values if I can figure out why it's returning 0.

Thanks for any and all help, Zach

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2014/12/09/05.47-93562-hotonEffeciency8_5_14.png

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1 Idea: Re: np-Elastic Cross-Section Discontinuity   (Vladimir Ivanchenko - 09 Dec, 2014)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 09 Dec, 2014)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (michel maire - 09 Dec, 2014)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 10 Dec, 2014)
(_ Question: Re: np-Elastic Cross-Section Discontinuity   (Andrea Dotti - 10 Dec, 2014)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 10 Dec, 2014)
(_ Question: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 10 Dec, 2014)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Alberto Ribon - 07 Jan, 2015)
(_ Question: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 08 Jan, 2015)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Michael H. Kelsey - 08 Jan, 2015)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 09 Jan, 2015)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Alberto Ribon - 12 Jan, 2015)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Zach Miller - 12 Jan, 2015)
(_ None: Re: np-Elastic Cross-Section Discontinuity   (Alberto Ribon - 12 Jan, 2015)
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