in the case, for the neutron with energy of 2.53E-11GeV, almost every neutron produce one gold 198, so the total produced gold 198 is: 3606.25E+11(ignoring decay of gold 198), so after irradiation, the activity of gold 198 should be: ln(2)/2.695/24/3600 360*6.25E+11, the result shold be: 6.69785E+08Bq.
but the result from Fluka is: 3.9127E+08Bq.

and the result from Phits and Dchain is: 6.4645E+08(considering decay of gold 198).

Recently, I led a team using the FLUKA to study the low energy neutron (<20MeV) irradiation induced activity. The results were comparing with other radionuclei inventory code, e.g. FISPACT-II, which also showed the similar discrepancy, even we have made the geometry correction to benchmark such 0-dimension Bateman equation solution.

We have try the different scoring card of RESNUCLES and USBIN-ACTOMASS associating to the DECSCORE card to calculate the specific activity (Bq/kg). But the results still have a three times higher than the FISPACT-II results, for the natural Iron case.

I guess the problem might come from the FLUKA code itself, or we have a misunderstanding on the problem setting, especially for the unit, e.g.

@101013211 , thanks for replying my question,
as my opinion, “per primary” means the results by one source particle.
the unit of the result in my case uploaded should be Bq, it can be found from the comment about RADDECAY card of the manual of Fluka, see notes 7 of RADDECAY card.
The probability of producing gold 198 by thermal neutron was checked using Fluka, it is almostly 100%.
so maybe the half-life of gold 198 is wrong in Fluka.

We will use the RESNUCLE scoring card without associating to the DCYSCORE, to obtain the number of each residual nuclei. Then manually multiply by the decay constant of nuclei to examine the results with other code.

so for isotope gold 198, the half-life is longer than 2.695 days
and for isomer gold 198, the half-life is 2.272 days, it seems right.

by the way, for gold foil activation experiments, little special gamma energy from isomer gold 198 was found, the classical gamma pulse amplitude spectrum is:

Both the 198Au half-lives, of the ground state and the 812 keV level, are correct in FLUKA.
For the residual activity calculation, the 198Au direct production by neutron capture is presently split by construction on either level at 50% (hence the apparent activity underestimation you started from).
The fact that for the ground state you see at its half-life significantly more than half of its initial activity is simply due to the re-population by the isomer.

You can get it from ENSDF.
Note, however, that the aforementioned 50% split between the 812 keV level and the ground state as a result of neutron capture is merely an arbitrary assumption.

@ceruttif , Maybe the assumption is not reasonable because little special gamma ray for the 812 keV level was observed from the gold activation foil in the experiment.