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Question neutron detection with 3He tube 

Forum: Hadronic Processes
Date: 21 Jun, 2011
From: hemiao <hemiao>

I'm simulating the He3 tube(with G4.9.3.p01) for detection neutron source which from 252Cf source and thermol energy(2.5e-8MeV).
Now the problems I meet with 2:
1st:detection efficiency  
    with the thermal neutron energy 2.5e-8MeV, the He3 tube(in Vacuum) can detect neutron with about 100% efficiency;
    with the Cf source spectrum(max energy about 12MeV), after moderated by polyethene, the He3 tube can detect neutron with about 30% efficiency;

    As I know that the detection efficiency of He3 tube is about 10%. 
    In order to know what's wrong, I debugged the program and found that a lot of proton and triton are produced with reaction 3He(n,p),
    but the Q value of most are not equal to 0.764MeV, even after minus neutron energy by sum of proton Energy and triton energy;
    why my program can produce reaction n+3He->t+p+gamma+Q?(for example I and II) Do I need to change my physics process for hardronprocess?
    It would be very helpful for some idea or advise.

exampleI

*********************************************************************************************************
* 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     -579     67.2    -34.1     0.227        0        0         0     world_P initStep
    1      -85     67.2    -34.1     0.227        0      494       494 polyethene Transportation
    2      -77     67.2    -34.1     0.219        0     8.04       502 polyethene hElastic
    3    -60.6     69.2    -31.7    0.0825        0     16.6       519 polyethene hElastic
    4    -54.9     65.7      -24    0.0237        0     10.2       529 polyethene hElastic
    5    -45.3       67    -23.6    0.0237        0     9.74       539        detector Transportation
    6    -43.7     67.3    -23.6    0.0237        0     1.63       540       detector Transportation
    7    -43.7     67.3    -23.6         0        0 7.34e-06       540       detector NeutronInelastic
Track (trackID 1, parentID 0) is processed with stopping code 2
Track #2 of proton E(MeV)= 0.0082 in polyethene
Track #3 of proton E(MeV)= 0.136 in polyethene
Track #4 of proton E(MeV)= 0.059 in polyethene
Track #5 of proton E(MeV)= 0.59 in detector
Track #6 of triton E(MeV)= 0.136 in detector
Track #7 of gamma E(MeV)= 0.00173 in detector
Track #8 of gamma E(MeV)= 0.0296 in detector
Track #9 of gamma E(MeV)= 0.0296 in detector

exampleII

*********************************************************************************************************
* 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     -579     32.3    -35.3      5.09        0        0         0     world_P initStep
    1      -85     32.3    -35.3      5.09        0      494       494 polyethene Transportation
    2    -44.6     32.3    -35.3      5.09        0     40.4       534        detector Transportation
    3    -43.2     32.3    -35.3      5.09        0     1.45       536       detector Transportation
    4    -43.2     32.3    -35.3      4.92        0 4.87e-05       536       detector hElastic
    5    -43.2     32.3    -35.3      3.78        0 1.43e-05       536       detector hElastic
    6    -43.2     32.3    -35.3      3.43        0 1.02e-05       536       detector hElastic
    7    -43.2     32.3    -35.3         0        0 1.41e-05       536       detector NeutronInelastic
Track #2 of He3 E(MeV)= 0.172 in detector
Track #3 of He3 E(MeV)= 1.144 in detector
Track #4 of He3 E(MeV)= 0.345 in detector
Track #5 of proton E(MeV)= 1.57 in detector
Track #6 of triton E(MeV)= 1.97 in detector
Track #7 of gamma E(MeV)= 0.004 in detector

2nd: the track drawing picture

    with the thermal energy neutron beam through He3 tube directely, I can get  all particles' tracking line in the He3 tube, no problem;
    but after moderated Cf source spectrum by polyethene, I only get the neutron tracking in the moderator, and empty in the He3 tube,
    thanks for any points for track-drawing!

hemiao

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1 Question: Re: neutron detection with 3He tube   (Vladimir Ivanchenko - 22 Jun, 2011)
1 Feedback: Re: neutron detection with 3He tube   (hemiao - 23 Jun, 2011)
2 News: Re: neutron detection with 3He tube   (hemiao - 30 Jun, 2011)
2 More: Re: neutron detection with 3He tube   (hemiao - 23 Jun, 2011)
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