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Warning Seemingly incorrect (n,alpha) cross section on Cu65 

Forum: Hadronic Processes
Date: 14 Mar, 2012
From: Ben Loer <Ben Loer>

I'm shooting fast neutrons through a copper cryostat using the Shielding physics list in geant4.9.4.p02, and with verbose tracking on, I see a high rate of events like the following:

*********************************************************************************************************
* G4Track Information:   Particle = neutron,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0 -4.21e-07 9.06e-07 4.86e-08     0.636        0        0         0      Vessel initStep

.. skip a bunch ...

   37      436     27.9      637      0.44        0 0.000136       869 Vessel/LoadVacuum Transportation
   38      434     26.8      634         0        0     3.89       873 Vessel/LoadVacuum NeutronInelastic
    :----- List of 2ndaries - #SpawnInStep=  2(Rest= 0,Along= 0,Post= 2), #SpawnTotal=  4 ---------------
    :       434      26.8       634     0.112              alpha
    :       434      26.8       634  0.000206          Co62[0.0]
    :----------------------------------------------------------------- EndOf2ndaries Info ---------------

There is a real (n,alpha) process, but the cross section on Cu65 should be 0 below a few MeV, at least according to the ENDF/B-VII.1 cross sections in the NNDC database (http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15032&mf=3&mt=107&nsub=10) I've seen this behavior with both G4NDL3.14 and 4.0. We're using the NIST definition for G4_Cu.

Any thoughts? This looks like a bug to me...

Thanks, ~Ben

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1 None: Re: Seemingly incorrect (n,alpha) cross section on Cu65   (Koi, Tatsumi - 15 Mar, 2012)
1 None: Re: Seemingly incorrect (n,alpha) cross section on Cu65   (Ben Loer - 15 Mar, 2012)
2 None: Re: Seemingly incorrect (n,alpha) cross section on Cu65   (Ben Loer - 16 Mar, 2012)
1 None: Re: Seemingly incorrect (n,alpha) cross section on Cu65   (Dennis H. Wright - 29 Mar, 2012)
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