I am currently investigating the cross sections for the production of a radionuclide in its metastable state using FLUKA. Specifically, I would like to determine whether FLUKA is capable of simulating the cross sections for both the metastable and ground states of a radionuclide individually.
If such simulations are supported, I would appreciate guidance on the following points:
Which cards or options should be utilized to extract the cross sections for metastable and ground states separately?
Are there any specific settings, scoring methods, or post-processing techniques required to distinguish the contributions of these states in the simulation output?
The motivation for this inquiry stems from the fact that the calculated cross sections for the metastable state in my study are significantly higher than the experimental data reported in EXFOR. Therefore, I aim to validate and refine the modeling approach to improve agreement with the experimental results.
Your insights and suggestions on this matter would be highly valuable.
FLUKA can score the production of radionuclides in their ground state vs isomeric level(s), but only in a decay run (be it in semi-analogue mode or in activation mode), not in a prompt run. Incidentally, nuclear reactions proceed to the ground state in any case; in a decay run, at the moment of scoring, the residual is scored in the ground state or in an isomer level on an equiprobable basis.
From your post I surmise you are scoring the production of metastable/isomeric vs ground-state radionuclides in a “prompt” run instead, i.e., at production straight after the nuclear reaction, without RADDECAY cards, irradiation/cooling profiles, etc (let us know if that’s not the case). While such a scoring is not possible with FLUKA v4-4.1, it is an active topic of development: upcoming FLUKA versions will allow you to do this, and will additionally provide a refined model for the sharing among ground state and isomer level(s).
For now, in a prompt run you are de facto scoring the production of radionuclides, summing over ground state and any isomer level(s), without distinguishing among them. This should explain the higher-than-expected value you are obtaining.
If you have an a-posteriori recipe or experimental hint of what’s the ratio between ground state and isomer, for now you can use this information to scale the cross section you seem to already score in order to obtain the ground state or the isomer yields accordingly.
Thank you very much for your detailed and helpful response to my query. I greatly appreciate your insights and the clarification regarding FLUKA’s current capabilities and limitations for scoring radionuclides in ground and isomeric states.
To clarify, we are not using RADDECAY cards, irradiation, or cooling profiles. Instead, we are employing the USRYIELD card in conjunction with the AUXSCORE card. In the AUXSCORE card, there is an option to specify the isomeric state. Could you please advise on the appropriate value to use for scoring metastable state?
I don’t think the approach you propose will work: the isomer flag can be set in the AUXSCORE, but it will be ineffective, since no isomer production is attempted in a prompt run.
At present, the path ahead i see is what was suggested at the end of the first reply (the rest of it still holds).
