GPS ion can not generate a proper spectrum

[baisong57]

I have a question, why is it that after setting the Co60 isotope correctly in the macro file and enabling the decay process in the physics list, the outgoing particles are all at 1MeV instead of the decay energy spectrum of Co60? Attached is my macro file and physics list, can you help me analyze where the problem is?
PrimaryGeneratorAction.cc (2.3 KB)

primary.mac:
#define incident particle
#/gps/verbose 2
/gps/particle ion
/gps/ion 27 60 0 0
##########################
######## type and distribution of beam
/gps/pos/type Plane
/gps/pos/shape Square
##########################
######## Setting position
/gps/pos/centre 0. 0. 56.065 um
/gps/pos/halfx 0.4 cm
/gps/pos/halfy 0.4 cm
######## Set direction
/gps/direction 0. 0. -1.
##########################

[jrellin]

If you are only setting the particle gun parameters here, than the default energy of whatever particle you use is 1 MeV. You need to explicitly set it to 0 so it can decay “at rest”. Otherwise you have to wait a half life and that is very long for co60 and so you will only detect its kinetic energy and not decay products (gammas) since the particle will leave your world volume before it decays.

/gps/energy 0. MeV

[baisong57]

Thank you for your answer. But if I modify it like this:
/gps/particle ion
/gps/ion 27 60 0 0
/gps/energy 0. MeV
Then all the energy of the particles is 0, which is very strange.

[jrellin]

Two possible issues:

1. There is no radioactive decay physics list. rdecay01 and rdecay02 (especially the latter) will have good lists to use.
2. The time threshold for decay is too short relative to the half life of co60

If 1 is set, than this command in the macro will cover 2:

/process/had/rdm/thresholdForVeryLongDecayTime 1.0e+60 year

This automatic threshold was changed at least twice between recent versions.

[baisong57]

Sorry for the late reply, I have solved the problem. Thank you very much!