[Gate-users] Compton interactions in the crystal show energy deposited as zero

[Marc Verderi]

Hello,

It is normal that a Compton interaction does not deposit energy. It 
surprises sometimes, but a at the time the Compton interaction occurs, 
Geant4 has no way to guess what will be the deposited energy in the 
volume where the Compton interaction occured. Assume this volume is very 
thin, then the Compton electron will escape this volume, leaving very 
few of its initial energy in the volume. On the contrary, if the volume 
is large, then all the energy lost by the photon will be deposited by 
the electron in the volume where the interaction occured : to figure out 
that, Geant4 must track the Compton electron. Properly said, and this is 
what Geant4 does, this is not the Compton interaction that deposits the 
energy, but the electron produced by this Compton interaction.

Cheers,
Marc

KB a écrit :
> Hello All,
>
>    Going by event Id, I printed all the hits corresponding to a given
> LOR and the interactions. It looks like all the compton interactions
> deposit 0 MeV and this doesn't sound right.  The other point is adding
> the energy deposited from the hits do not add up to what energy1 and
> energy2 are for the coincidence. What am I missing here? Thanks.
>
> The relevant physics lines from the macro file are :
>
> /gate/physics/gamma/selectRayleigh lowenergy
> /gate/physics/gamma/selectPhotoelectric standard
> /gate/physics/gamma/selectCompton standard
> /gate/physics/setElectronCut 30. cm
> /gate/physics/setXRayCut 1. GeV
> /gate/physics/setDeltaRayCut 1. GeV
> /gate/physics/verbose 0
>
> and here is the printout from the hits corresponding to some LORs. In
> each block (separated by ------ lines) the first line is the data from
> the coincidence tree and the
> subsequent lines are hits with the same eventID.
>
> ---------------------------------------------------------------------
>  Pos1=[ 452.6   70.8   9.0] Rad=  458.1, Pos2=[-451.4  -71.3  -11.5]
> Rad=  457.0, CID1 = 555, CID2=440, E1=0.498,E2=0.494
>         Position=[318   452.5   70.8    9.0] Energy=0.0170380007
> CrystalID=555  phot
>         Position=[319   452.6   70.8    9.0] Energy=0.4935308695
> CrystalID=555  eIoni
>         Position=[320  -451.3  -71.3  -11.5] Energy=0.0000000000
> CrystalID=440  compt
>         Position=[321  -451.5  -69.3  -12.8] Energy=0.0000000000
> CrystalID=417  LowEnRayleigh
>         Position=[322  -452.4  -55.5  -23.1] Energy=0.0633139983
> CrystalID=368  phot
>         Position=[323  -452.4  -55.5  -23.1] Energy=0.1834079325
> CrystalID=368  eIoni
>         Position=[324  -451.4  -71.3  -11.5] Energy=0.0341149680
> CrystalID=440  msc
>         Position=[325  -451.4  -71.3  -11.5] Energy=0.0263256542
> CrystalID=440  msc
>         Position=[326  -451.4  -71.3  -11.5] Energy=0.2042667121
> CrystalID=440  eIoni
> Energy deposited through hits:  0.510569 0.511429
> ---------------------------------------------------------------------
>  Pos1=[ 247.7 -377.7  64.9] Rad=  451.7, Pos2=[-245.3  379.3  -46.6]
> Rad=  451.7, CID1 = 852, CID2=230, E1=0.529,E2=0.460
>         Position=[327   247.7 -377.7   64.9] Energy=0.0000000000
> CrystalID=852  compt
>         Position=[328   245.2 -374.8   67.6] Energy=0.0000000000
> CrystalID=875  LowEnRayleigh
>         Position=[329   244.9 -374.5   68.0] Energy=0.0633139983
> CrystalID=875  phot
>         Position=[330   244.9 -374.5   68.0] Energy=0.1242482439
> CrystalID=875  eIoni
>         Position=[331   247.7 -377.7   64.9] Energy=0.3213312924
> CrystalID=852  eIoni
>         Position=[332  -245.4  379.2  -46.5] Energy=0.0000000000
> CrystalID=230  compt
>         Position=[333  -245.2  379.4  -46.6] Energy=0.0633139983
> CrystalID=230  phot
>         Position=[334  -245.2  379.4  -46.6] Energy=0.2265119106
> CrystalID=230  eIoni
>         Position=[335  -245.4  379.2  -46.5] Energy=0.2232786566
> CrystalID=230  eIoni
> Energy deposited through hits:  0.508894 0.513105
> ---------------------------------------------------------------------
>  Pos1=[ 403.8 -206.3 -35.2] Rad=  453.4, Pos2=[-398.8  204.0   30.3]
> Rad=  448.0, CID1 = 307, CID2=675, E1=0.516,E2=0.507
>         Position=[368   402.2 -203.8  -33.3] Energy=0.0000000000
> CrystalID=308  compt
>         Position=[369   403.7 -206.4  -35.2] Energy=0.0633139983
> CrystalID=307  phot
>         Position=[370   403.8 -206.3  -35.2] Energy=0.2492854297
> CrystalID=307  eBrem
>         Position=[371   403.8 -206.3  -35.2] Energy=0.0118946973
> CrystalID=307  eIoni
>         Position=[372   404.7 -205.9  -33.9] Energy=0.0170380007
> CrystalID=308  phot
>         Position=[373   404.7 -205.9  -33.9] Energy=0.0625219345
> CrystalID=308  eIoni
>         Position=[374   402.3 -203.8  -33.3] Energy=0.1059423536
> CrystalID=308  eIoni
>         Position=[375  -398.8  204.0   30.2] Energy=0.0170380007
> CrystalID=675  phot
>         Position=[376  -398.8  204.0   30.3] Energy=0.4949637055
> CrystalID=675  eIoni
> Energy deposited through hits:  0.509996 0.512002
> ---------------------------------------------------------------------
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