Why is the gamma-ray yield of the thorium decay chain not matching?

Physics Lists
1

I simulated U, Th decay series and other natural radionuclides with Geant4 example ; examples/extended/radioactivedecay/rdecay01.
In the case of the U decay chain, the gamma-ray yield values match well with the BIPM table of nuclides, but notably, the yield values for the thorium decay chain appear to be consistently lower. For instance, in the case of Pb-212, one of daughter isotopes of Th-232, which should have a 238.632 keV gamma-ray yield of around 43.6%, it is instead approximately 34.48%. It appears that in other Monte Carlo codes, the simulations work as expected, but in Geant4, the results are consistently underestimated for Th decay chain. Please explain why this is the case…

_Geant4 Version:11.1.2
_Operating System:Window 10 OS

2

Sometime in the past, a “maximum allowed” decay time has been introduced in Geant4 (for obscur reason …), above which ions are treated as stable.
By default, this maximum is ~ 1e+10 years, which is the same order of magnitude of Th-232 mean life.
In this situation, you can see on attached printout lee1.out.txt that only 7943 Thorium decay instead of 10000.
You must increase the maximum allowed decay time with the command :
/process/had/rdm/thresholdForVeryLongDecayTime
Then, everything goes right … see lee2.out.txt

lee.mac.txt (351 Bytes)
lee1.out.txt (2.8 KB)
lee2.out.txt (2.9 KB)

lee
lee698×475 25.1 KB