|Message: Geant4 9.5 beta Decay missing energy||Not Logged In (login)|
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I'm having problems reproducing the full expected energy in a "perfect" detector for beta decays - some energy is always lost during gamma emission during a beta decay.
I take as an example Pb210 in Geant4 9.5. The full energy seen in a perfect detector (one that sees all electron, gamma/X-ray and nuclear recoil kinetic energy) should see precisely the beta decay Q value (63.1 keV) minus the neutrino energy, yet I cannot reproduce this energy.
I managed to reproduce the problem using the rdecay02 example using the macro included at the end of this message. I use an absurdly large detector (actually just multiplied all the dimensions in rdecay02's ne24.mac by 100,000) so as all non-neutrino kinetic energy should be recorded. In relaxations of the Bi210[46.5] product (84% chance) of Pb210[0.0] decay, there is almost always missing energy of ~a few keV. The figure I attach illustrates this showing the expected Q minus neutrino energy in red, and the detected energy in black.
I tried this in versions 9.3 and 9.4 and got differing (still not expected) results. It turns out that if I turn ICM off using G4RadioactiveDecay::SetICM(false) in my own code, I can recover the correct spectrum in both 9.5 and 9.4, though of course this is un-physical (only 4% of Pb-210 decays give a 46.5 keV gamma according to http://www.orau.org/ptp/PTP%20Library/library/DOE/bnl/nuclidedata/MIRPb210.htm).
/exrdm/det/setTargetRadius 0.001 km /exrdm/det/setTargetLength 0.001 km /exrdm/det/setDetectorThickness 20 km /exrdm/det/setDetectorLength 40 km /run/initialize /run/setCutForRegion Target 10 km /run/setCutForRegion Detector 50 km /run/verbose 0 /event/verbose 0 /tracking/verbose 0 /grdm/verbose 0 /grdm/noVolumes /grdm/selectVolume Target
/process/em/fluo true /process/em/auger true
/gps/position 0 0 0 /gps/energy 0 keV /gps/particle ion
/grdm/nucleusLimits 210 210 82 82 /gps/ion 82 210 0 0
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