I am attaching the relevant code lines and files below.
I am using the source_newgen.f subroutine with the following lines:
momentum_energy = sample_loghistogram_momentum_energy( “AmBe_Large.txt”, “MeV” )
energy_logical_flag = .true.
The direction of emission is isotropic.
The sample_loghistogram_momentum_energy function comes from the .f file provided by @horvathd in this post: D20 moderated Cf and source_newgen.f
“AmBe_Large.txt” is attached. The energy distribution is taken from ISO 8529-1:2021 and corresponds to the Am-Be large source. AmBe_Large.txt (2.0 KB)
As for the input file, it reproduces the whole irradiation facility with a very complex geometry, so I am attaching only the parts relevant to the scope of my question:
I am also attaching the .lis file obtained as output of the USRTRACK with the simulation (this is with 500 bins, but with 200 bins or 500 bins I get the same issue). To plot the spectrum in lethargy scale, I take the value in the third column, multiply it by dE = Emax - Emin, and then divide by ln(Emax/Emin). I was wondering whether the issue might be in this post-processing.
Irradiation_21_tab.lis (29.9 KB)