Changing the half-life of a nuclide

Physics, Transport and Magnetic Fields
1

Dear FLUKA experts,
Due to research needs, I would like to change the half-life of nuclides. For example, uranium fission produces 99Mo and I want to introduce a pseudo-decay factor. Therefore the half-life of 99Mo needs to be modified. I read the input cards and user-defined files related to decay and didn’t find a solution. I would like to ask the experts, is there any way to realize this requirement in FLUKA?
Thank you very much for your help and answer! Looking forward to your reply. Wish you the best of luck in everything.
Lin

3

Hi Lin,

FLUKA does not allow users to modify or add any physics processes.
For your specific request, I see two possible approaches:

  1. Score the produced 99Mo at the time of production (e.g., via mgdraw.f, as described here: link). Once you obtain the 99Mo particle list, you can evaluate its population evolution using the Bateman equation, with the decay times you want.
  2. Manipulate the weight of the produced residual nuclei via usrrnc.f, as described here (slide 22): link. In principle, for a fixed decay time, introducing a pseudo-decay factor would effectively be equivalent to reducing or increasing the initial fission yield.

I would recommend the first approach, but the choice depends on the observables you aim to extract from the simulations.

Cheers,
Daniele

4

Dear @dcalzola ,
Thank you for your reply and help. I have some doubts about the first method. After using the mgdraw.f file to get the production information of 99Mo, then the Bateman equation is used to calculate the decay evolution. Can both steps be realized in the mgdraw.f file? Or does the Bateman equation calculation need to be done externally?
Because my calculation model is long time irradiation. So it contains both irradiation generation and decay reduction. So the irradiation generation cannot be considered if the decay calculation is done externally.
I have another question, is it possible to modify the half-life of 99Mo by modifying the FLUKA decay database?
Thanks for your help.
Lin

5

Dear @dcalzola ,
Is it possible to turn off the decay of a certain nuclide (e.g. 99Mo)? Thanks.
Linn

6

Hi Linn,

  1. The mgdraw.f is solely responsible for the scoring. Unfortunately, any further step shall be done externally.
  2. The database is encoded in the binaries, therefore it is not possible to modify the half-life of any isotope
  3. As above, you cannot alter the physics within FLUKA. However, if you want to exclude all decays from 99Mo in your results, you can use usrnnc.f routine to kill the residual nucleus of interest (I was doing this in slide 23: https://indico.cern.ch/event/1200922/contributions/5411837/attachments/2661810/4611453/08_User_routines_2023_Advanced_ANL.pdf)

Hope this helps you!
Cheers,
Daniele

7

Dear @dcalzola ,
Thank you very much for your advice, I will try further based on your suggestions. Thanks again.
Wish you all the best!
Lin