Sample_spectrum_momentum_energy()

Source Definition
1

Dear FLUKA Experts,

Could you please assist me with the following issue that I am encountering with my SOURCE routine? I am attempting to use source_newgen.f to load a spectrum that I have created using the SPENVIS tool to simulate the GCR radiation that is present within Low Earth Orbit. I have attached the proton spectrum I am using in the file 1_fluence.txt. Here is a figure showing the characteristics from SPENVIS:

spenvis-plot.pdf (23.5 KB)

When I compile my source routine, loading 1_fluence.txt using sample_spectrum_momentum_energy() and run the attached simple simulation of protons being born at the origin and passing through a sphere where I calculate their fluence using USRBDX, I obtain the following:

spenvis_test-0: USR-1D spenvis test 41.pdf (36.9 KB)

One notable difference between the two plots is that the SPENVIS spectrum peaks near 400 MeV, but the spectrum that I am calculating in the USRBDX peaks near 2 GeV. I have confirmed that the spectrum file was read correctly, walked through the energy binning, and duplicated the calculations performed in sample_spectrum_file() at lines 812-845 of source_library.inc, but I am unable to understand why this spectrum would be shifted in this manner when I run the FLUKA simulation. Thank you in advance your expertise.

John

spenvis_test.inp (1.2 KB)
spenvis_test.flair (1.1 KB)
source_spenvis.f (21.8 KB)
1_fluence.txt (1.8 KB)
spenvis_test_41_tab.lis (175.2 KB)
spenvis_test001.out (74.4 KB)

2

Dear John,

You need to set the energy_logical_flag variable to .true.. Otherwise, the source routine will assume your spectrum contains the particle momentum and not the kinetic energy.

Also, you are plotting your FLUKA results in lethargy units which can’t be compared to the differential fluence plot of your source.

Cheers,
David

3

David,
Thank you for your expertise in identifying this simple error - I think that I was assuming that when I set the units to GeV that it would read in energy.
Best,
John