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Question Geant4 9.5 beta Decay missing energy 

Forum: Hadronic Processes
Date: 03 Jul, 2012
From: Andrew Brown <Andrew Brown>

Hi all,

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).

Any ideas?

Andrew

Macro begins:

/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

/run/beamOn 1000000

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2012/07/03/14.31-32921-MacroResults.png

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1 None: Re: Geant4 9.5 beta Decay missing energy   (michel maire - 05 Jul, 2012)
(_ None: Re: Geant4 9.5 beta Decay missing energy   (Andrew Brown - 05 Jul, 2012)
(_ None: Re: Geant4 9.5 beta Decay missing energy   (michel maire - 10 Jul, 2012)
(_ None: Re: Geant4 9.5 beta Decay missing energy   (Andrew Brown - 12 Jul, 2012)
(_ None: Re: Geant4 9.5 beta Decay missing energy   (Andrew Brown - 01 May, 2013)
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