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Question Puzzling angular distribution of proton and triton tracks in the reaction n + 3^He --> p + t (with thermal neutrons) 

Forum: Physics List
Date: 14 Dec, 2016
From: Latif Kabir <Latif Kabir>

Dear Geant4 Users,

I was simulating the energy deposition in the ion chamber filled with Helium-3 gas at 0.5 atmosphere and room temperature which is hit by thermal neutrons (range 2meV to 9meV) producing proton and triton through the capture reaction : n + 3^He ---> p + t . I was using modular based Physics list QGSP_BERT_HP with Geant4 v10.02 . While the simulation produces some aspects as expected , but the angular distribution of proton and triton tracks are puzzling to us. Helium-3 at room temperature (298K) of the experiment gives proton and triton tracks heavily biased towards -z and +z axis respectively ( where z axis is the direction of neutron beam) as shown in the attachments. We get correct angular distribution if we set Helium-3 temperature to 0K and in the later case the energy deposition in the chamber from the simulation agrees with the experiment but it distorts other validated features.

I am not sure if something wrong with the PhysicsList or I am missing something ?

Any input will be appreciated.

Regards,

Latif

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/12/14/19.46-74441-rack_Polar_Angle_Dist.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/12/14/19.46-32123-Helium_298K.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/12/14/19.46-69256-Helium_0K.png

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