Recoils in nuclear interactions

i want to calculate the pulse amplitude spectrum of neutron bombing Hydrogen, when using Pre-defined materials with fluka name HYDROGEN, everything work well.
the .inp file with name np.inp is uploaded.

but with the materials dedfined by myself, it seems no proton recoil in the results.
the .inp file with name uTPC.inp is uploaded and the source file source.f

when using the the materials dedfined by user, somethings else shauld be added to the .inp (1.1 KB)
uTPC.inp (1.6 KB)
source.f (9.4 KB)

when i calculate the nucleus recoil pulse amplitude spectrum by neutron, there are two peaks occurs, why?
the related files upload.uTPC.inp (1.7 KB)
source.f (9.4 KB)

Dear Lihua Li,

In the first input file you sent (np.inp above), you simply assign HYDROGEN to your target. Doing so while passing a DEFAULTS card with SDUM=PRECISIOn, you get point-wise low-energy neutron transport on 1-H (for neutron energies between ~3 eV and 20 MeV). In your DETECT card you
should then get a continuous spectrum (you have a continuum of proton recoils).

In the second input file you sent (uTPC.inp in your first post), you build a GAS compound from H, C, and He, naming the FLUKA materials as “H”, “C”, and “He”. You assign them group-wise cross sections from the FLUKA database, but in doing so the point-wise treatment on 1-H is lost.

You recover it by naming your hydrogen as “HYDROGEN” (actually it suffices for the name to contain “HYDR” I think), as you do in the uTPC.inp of your second post. The DETECT spectrum you show for this scenario exhibits a continuum (from the point-wise HYDROGEN recoil) and the two spikes you witness are kerma depositions in C and in He. This is an artifact of the group-wise treatment. In a point-wise treatment the spike would melt into a continuum of recoil energies and it would spread out in your DETECT spectrum.

Work is ongoing towards a more extended point-wise treatment for a future major release.



@ Francesc Salvat Pujolcesc,thanks!