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Question Re: Cross Sections used to determine Elastic Scattering 

Forum: Hadronic Processes
Re: Question Cross Sections used to determine Elastic Scattering (Evan Askanazi)
Re: None Re: Cross Sections used to determine Elastic Scattering (Joel Long)
Date: 26 Jun, 2011
From: e askan <e askan>

Thank you for showing that. Do you know if geant4, when it upgraded the cross sections to 3.14, also changed those for Aluminium or do you think that is possible ? Because then I use geant4 version 4.9.4 with libraries updated to 3.14, I got that the rate of elastic scattering does NOT stay the same for geant4 as the neutron energy drops below 2.5 mev or so. In that range the rate of elastic scattering, and therefore the cross section, increase at essentially the same rate as the ENDF data sets.

 In fact, I used the cross sections from the ENDF files, in the national nuclear data center, and used them to determine the mean free path length for elastic scattering and used it to determine the theoretical rate of elastic scattering for neutrons of 2 mev or lower in Aluminum and then used geant4 to calculate the rate of elastic scattering of 2 mev neutrons in aluminum as well. I used the method lambda = sigma*n where n is the number of atoms per unit of volume, sigma is the elastic scattering cross section and lamba is the resulting mean free path length.  And used sigma as determined by EDNF/B-VI data files, which is what my version of geant4 uses, to determine the values of lambda.  Then used lambda to calculate, for a given number of neutrons launched into a slab of Aluminum, the number of neutrons that would be expected to scatter over the given length of Aluminum.  And then I used geant4 to launch the same number of neutrons of the same energy into a slab of Aluminum of the same dimensions as used in the theoretical model.   And the same number of neutrons scattered over the length of Aluminum as was predicted in the theoretical model for neutrons above and below 2.5 mev;  geant4 produced the same results in predicting how many neutrons would scatter in Aluminum as the predicted model, using mean free path lengths based on cross sections, gave.  

Do you think they also upgraded the cross sections for Aluminum and/or used a new method to calculate elastic scattering rate for neutrons of energy 2.5 mev or lower in Aluminum ? I just find this interesting is all. Because when I use geant4, I get that the effective cross section determined by geant4 for neutrons of 2 mev or lower in Aluminum is the same as the ENDF/B-V1.

Unless somehow the physics list G4HadronElastic* elasticModel = new G4HadronElastic() uses Aluminum cross sections that are the same as the ones you showed and then uses them to determine the rate of elastic scattering in Aluminum and then, for neutrons below 2.5 mev or so, somehow adjusts the calculations for the rate of elastic scattering or uses different cross section data in order to find out how many neutrons, out of a given initial neutron set, would elastically scatter in Aluminum. Is that possible ?

In any event, my goal for Aluminum at 300 K was to ensure that if a given set of neutrons was launched into a slab of Aluminum that, for neutrons of 2 mev, 5 mev , 10 mev, 100 mev and 0.2 mev, that Geant4 would correctly predict the rate at which neutrons would elastically scatter in Aluminum and Geant4 did predict it correctly for neutrons of all these energies.

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1 None: Re: Cross Sections used to determine Elastic Scattering   (Joel Long - 27 Jun, 2011)
(_ Feedback: Re: Cross Sections used to determine Elastic Scattering   (Evan Askanazi - 27 Jun, 2011)
(_ Feedback: Re: Cross Sections used to determine Elastic Scattering   (Joel Long - 28 Jun, 2011)
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