I am encountering some issues while simulating the irradiation of a gadolinium (Gd)-doped radiation shielding material with thermal neutrons (0.0253 eV) and would appreciate your guidance:
Tracking Unreacted Gd Density: How can I calculate the atomic density of unreacted Gd within a specific region after different irradiation times? I have attempted to use the RESNUCLEI card for this purpose. However, it appears RESNUCLEI only provides the densities of the new nuclides produced by reactions, and does not seem to reflect the reduction trend of the original Gd atoms due to neutron capture/transmutation over time.
Shielding Degradation: How can I calculate the leaked neutron flux outside the shielding as a function of irradiation time, as the Gd atomic density decreases? I used the DCYSCORE and USRBDX cards for this issue, but no valid results were enerated.
As you correctly observed, FLUKA doesn’t track the changes of the material. You may could calculate the amount of the “burned up” Gadolinium by summing the daugther isotopes from the Gd (n,x) X interactions, but that could be messy if thes isotopes are also produced from other mother isotopes.
To see the effect of the changing material you need to use an interative approach with FLUKA. You need to run a separate simulation for each timestep (of you choosing), Calculate the material change, and feed the updated material into the input of the next timestep.
Thank you for your prompt and insightful response. ​Your suggestion makes excellent sense to me.​​ I will run an iterative simulation at each timestep, manually updating material compositions between runs to evaluate shielding degradation effects. I truly appreciate your expertise and time.
Thank you for your contributions to the FLUKA community.