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Question Energy conservation in G4NeutronHP for n(d,p)2n deuteron breakup 

Forum: Hadronic Processes
Date: 14 Nov, 2016
From: Joseph Turko <Joseph Turko>

Hello,

I am trying to simulate the response of a BC537 deuterated scintillator to fast neutrons with the QGSP_BERT_HP (and therefore G4NeutronHP) physics package. When looking at the energy deposition spectrum in the detector from a 10 MeV neutron beam, I see quite a few events that deposit > 10MeV in the detector. Some of these can be attributed to capture reactions with positive Q-values (ie n-capture on protons/deuterons). however looking at the output from "/tracking/verbose 1" seems to indicate the vast majority of these interactions come from deuteron breakup (n + d -> n + n + p), or the "neutronInelastic" process name, which has a negative Q-value. An example event is:

*********************************************************************************************************
* 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        0        0      500        10        0        0         0       World initStep
    1        0        0        1        10        0      499       499 av_1_impr_1_testcan_alum_casing_log_pv_0 Transportation
    2        0        0        0        10        0        1       500 av_1_impr_1_testcan_scintillator_log_pv_1 Transportation
    3        0        0    -21.5         0        0     21.5       522 av_1_impr_1_testcan_scintillator_log_pv_1 neutronInelastic

*********************************************************************************************************
* G4Track Information:   Particle = proton,   Track ID = 4,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0        0        0    -21.5      10.8        0        0         0 av_1_impr_1_testcan_scintillator_log_pv_1 initStep
    1   -0.305  -0.0291    -21.9       8.9     1.88    0.469     0.469 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni
    2   -0.551   -0.049    -22.2      7.13     1.77    0.375     0.844 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni
    3    -0.75  -0.0688    -22.4      5.44     1.69    0.299      1.14 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni
    4   -0.908  -0.0806    -22.6      3.67     1.78    0.235      1.38 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni
    5    -1.02  -0.0835    -22.7      1.68     1.99    0.172      1.55 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni
    6    -1.06  -0.0815    -22.7         0     1.68   0.0621      1.61 av_1_impr_1_testcan_scintillator_log_pv_1 hIoni

*********************************************************************************************************
* G4Track Information:   Particle = neutron,   Track ID = 3,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0        0        0    -21.5      1.64        0        0         0 av_1_impr_1_testcan_scintillator_log_pv_1 initStep
    1     17.2    -7.89    -25.4      1.64        0     19.4      19.4 av_1_impr_1_testcan_quartz_window_log_pv_2 Transportation
    2       29    -13.3      -28      1.58        0     13.1      32.5 av_1_impr_1_testcan_quartz_window_log_pv_2 hadElastic
    3     30.9    -15.9    -31.8      1.58        0     4.94      37.4       World Transportation
    4 2.56e+03 -3.55e+03   -5e+03      1.58        0  6.6e+03  6.64e+03  OutOfWorld Transportation

*********************************************************************************************************
* G4Track Information:   Particle = neutron,   Track ID = 2,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0        0        0    -21.5      1.71        0        0         0 av_1_impr_1_testcan_scintillator_log_pv_1 initStep
    1     9.13     6.62    -25.4      1.71        0     11.9      11.9 av_1_impr_1_testcan_quartz_window_log_pv_2 Transportation
    2     24.1     17.5    -31.8      1.71        0     19.6      31.5       World Transportation
    3    5e+03 3.62e+03 -2.14e+03      1.71        0  6.5e+03  6.53e+03  OutOfWorld Transportation

*********************************************************************************************************
* G4Track Information:   Particle = O16,   Track ID = 5,   Parent ID = 3
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng  NextVolume ProcName
    0       29    -13.3      -28    0.0588        0        0         0 av_1_impr_1_testcan_quartz_window_log_pv_2 initStep
    1       29    -13.3      -28         0   0.0588 0.000317  0.000317 av_1_impr_1_testcan_quartz_window_log_pv_2 ionIoni
    2       29    -13.3      -28         0        0        0  0.000317 av_1_impr_1_testcan_quartz_window_log_pv_2 RadioactiveDecay

Is this a result of non-conservation of energy in the G4NeutronHP package? I can't seem to figure out what else could be causing these events. Any help/ideas would be greatly appreciated.

Cheers, Joey

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