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None Problem neutron time-of-flight simulation 

Forum: Hadronic Processes
Date: 19 Sep, 2012
From: Anders Hjalmarsson <Anders Hjalmarsson>

Dear all,

I simulate a neutron time-of-flight spectrometer using the QGSP_BERT_HP physics list and have encountered a problem (geant4-09-05-patch-01). The time-of-flight is between two sensitive volumes, (S1PV and S2PV), the first volume is positioned in a neutron beam and the second volume is positioned with an angle and some distance away from the in-beam one. By using my own SteppingAction class I retrieve the time, using GetGlobalTime, when neutrons interact in these volumes.

For one incoming neutron, interacting in both volumes, the time-of-flight is constructed by subtracting the time from the second volume with the time obtained from the in-beam volume. The problem I encountered is that the time-of-flight I get by subtracting these two times from each other do not agree with the time I get if I calculate the time-of-flight analytically, the time-of-flight from simulations is shorter than the time-of-flight from analytical calculations. It seems to me that the true flight path of the scattered neutron is not taken into account.

I also attach results of one source neutron the scatter ones in the in-beam volume and ones in the second volume, which can be compared with an analytical calculation. The extra text in the attached file is the information generated from my own SteppingAction class, used for the time-of-flight calculation.

Hope someone have the time to look in to this problem or explain what Iím doing wrong.

I have also tried to use version 9.6.0 and get the same result.

Regards, Anders

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2012/09/19/04.07-63236-Simresult.pdf

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