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Forum: Hadronic Processes
Re: Question Gammas from neutron capture on Cd113 (Camille B.-Champagne)
Date: 03 Aug, 2016
From: Camille B.-Champagne <Camille B.-Champagne>

Hello experts,

I have a follow up on this topic after spending quite some time digging through the various hadronic processes.

G4NDL4.5 does not contain 113Cd data in the Capture/FS directory so Geant defaults to the photon evaporation model in all cases (this explains why setting G4NEUTRONHP_USE_ONLY_PHOTOEVAPORATION=1 has no effect on the observed gamma spectrum)

In the PhotonEvaporation files (I've looked at versions 3.1 and 3.2), the list of energy levels for 114Cd (the nucleus that is deexcited after capture on 113Cd) only goes up to 4.6052 MeV while the Q-value of the capture reaction is 9.043 MeV.

It seems like a gamma is emitted to bring down the energy to this uppermost level (4.4 MeV gamma from the difference of 9-4.6MeV available energy) and that in most cases, to match the most likely emission multiplicity of 3 gammas, this highest energy state is deexcited through the only listed possibility (emitting a 578 keV gamma into the 4.027MeV level) and then all remaining excitation energy is emitted as a single 4.027 MeV gamma. (I believe that because it runs into these limits at both ends of the emission process, the emissions are exact and this is why setting G4NEUTRONHP_DO_NOT_ADJUST_FINAL_STATE=1 has no effect either)

These are completely unphysical emissions and the photon evaporation model is clearly not adequate for this case where not enough level information is known.

I have looked for alternative sources of emission data. I see from: https://www-nds.iaea.org/geant4/ that both JENDL330 and CENDL-31 both have *some* Capture/FS files for either 113Cd or nat_Cadmium. I was able to use these databases in Geant 4.10.1p1 to obtain results. The code runs without crashing but there is no information on the IAEA page about compatibility with this particular version of geant. Many of the older versions of Geant had incompatibilities or bugs related to these alternate data files. Is someone able to confirm that I can use these data files with an out-of-the-box version of Geant 4.10.1p1?

It also appears that while more realistic than the photon evaporation results, these files do not result in the correct narrow dominant gamma emission lines at the expected energies of 558 and 651 keV. (see attached files).

Is there any support/documentation/information about the G4DNL format that I can consult to try to understand how the input data results in the observed gamma spectrum? And more generally, is there a better way to study the gamma emission from thermal neutron capture on cadmium? Do you have any other suggestions to reach realistic results?

Thank you,

Camille

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/08/03/01.50-9073-113Cd-JENDL330.gif
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/08/03/01.50-89579-113Cd-CENDL-31.gif

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1 None: Re: Gammas from neutron capture on Cd113   (Koi, Tatsumi - 03 Aug, 2016)
(_ None: Re: Gammas from neutron capture on Cd113   (Camille B.-Champagne - 05 Aug, 2016)
(_ None: Re: Gammas from neutron capture on Cd113   (Koi, Tatsumi - 08 Aug, 2016)
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