Production of Terbium-149: 141Pr(12C,4n)149Tb reaction didn't happen

Dear Fluka experts,

I’m bombaring 141Pr with 12C to produce 149Tb, the reaction channel is 141Pr(12C,4n)149Tb. As in the experimental results described in the literature, I calculated the reaction cross-section of 12C with 141Pr at 65MeV and the activity of 149Tb produced by irradiation.

There is no 149Tb in the residual nuclei, but I followed the methodology based on the following topic: Production cross section of 67Ga and 68Ga from interaction of Li7 beam on Cu target - Scoring - FLUKA User Forum (, the cross section is 9.4420305E-03/1.3350E-05=707mb,this result is far from the experimental data. Why are the results of RESNUCLEI and USRYIELD different?

Here is my input file.
65MeV-141Pr.inp (10.4 KB)

Your calculation is correct, as indicated by the following figure:

Note that the yellow data, you seem to compare with, refer to the production of 149Tb in its ground state, while the FLUKA results (and the other blue dataset) include also the production of the metastable state, which cannot be properly disentangled at this stage.

As for RESNUCLEi, it accounts for the nuclides stopping in the scoring region, and not the ones leaving it.

Dear @ceruttif
Thank for your reply!

I have understood the explanation about the cross section, but regarding the calculation of yield, I understand that you mean 149Tb was emitted from the target, so I increased the target thickness and recalculated. However, there is still no 149Tb. The SRIM calculation of the range of 65MeV 12C in 141Pr is 60μm, and I set the target thickness to 6mm, yet there is still no remaining 149Tb nuclei in the target. Could you tell me how to calculate the yield of 149Tb?

You need to properly set the Max Z value in the RESNUCLEi card, since the default value is based on the atomic number of the element(s) of the material assigned to the scoring region (see the manual), and is not automatically adjusted according to the projectile nucleus charge.

Thank you very much for your reply.
I have solved the problem. I wish you a pleasant life.