Annihilation photon energies from GPS

[onrptk]

Hello everyone,

I use Na-22 source by GPS. From the decay of Na-22 source there is positron occur. In the crystal this positron annihilate. When I get pre kinetic energy of this annihilate gammas it gives below 511 keV energy(sometimes it gives 510.99 keV but moslty below this). I’m confused I think they should have 511 keV energy.

For instance:

G4WT0 > PreVol: Crystal | CopyNo: 0
G4WT0 > PrePointKinEn: 510.999 keV
G4WT0 > PostVol: Crystal | CopyNo: 0
G4WT0 > PostPointKinEn: 0 eV
G4WT0 > EdepSD: 138.23 eV
G4WT0 > ParName: gamma
G4WT0 > trackID: 6

G4WT0 > PreVol: Crystal | CopyNo: 0
G4WT0 > PrePointKinEn: 231.16 keV
G4WT0 > PostVol: Crystal | CopyNo: 0
G4WT0 > PostPointKinEn: 0 eV
G4WT0 > EdepSD: 347.26 eV
G4WT0 > ParName: gamma
G4WT0 > trackID: 5

Am I thinking wrong or doing something wrong?

Thanks,
Onur

[maire]

Here a macro for example TestEm14, and the resulting plot.

anniAtRest.mac.txt (350 Bytes)

[maire]

if the positron in not at rest (for example 1 eV) the result is different.
anniNotAtRest.mac.txt (353 Bytes)

[onrptk]

Dear maire,

Thanks for your reply. Now I’m using QBBC, G4EmStandardPhysics_option4 and G4RadioactiveDecayPhysics for physicslist. Should I change the physicslist because I looked at the TestEm14 example that you said and there is different physicslist. Do you think the differences about energies is because of the physicslist?

Thanks,
Onur

[maire]

Your PhysicsList seems OK.
It could happen, not frequently, that positron annihilates before to go at rest.

What is your material ?

[onrptk]

I tried with aluminium, LaBr3 and wolframium but no one gives 511 keV

[onrptk]

I was trying from the SensitiveDetector class but when I wrote it to SteppingAction it’s solved

Thanks,
Onur