DETECT discrepancies

Dear FLUKA experts,
I ran a simulation in which I scored the scintillator output using two DETECT cards. The first one goes from 100keV to 2.3MeV, the other one from 400keV to 600keV (this is the region I’m interested in). Here you can see the input and the results of both cards:


FIRST card:


If I crop the first card’s energy interval to the 400 - 600 keV region, I get different results than with the second card.

FIRST card cropped
detect large bins crop

In particular, the step centered at 487 keV is one order of magnitude higher in the first card, and I think that’s due to the width of the channels: both cards have 1024 channels, but the width are 2.2keV and 0.2 keV respectively. Since there’s a factor 11, I expect that 11 times more events would fall inside the larger bin, thus the higher counts in the first card.
However, this seems not to be the case with the peak at 511keV.

Is my reasoning correct? Do you have any idea why the 511 behaves differently?

Thank you in advance,

no PCB vacuum collimator.flair (6.9 KB)

Correct. The 478 keV bump reflects the Doppler broadening earlier pointed out by Vasilis, due to the motion of the emitting 7Li nucleus that is altering the actual gamma energy, thereby its height is sensitive to the scoring resolution, separating or not separating different energies. This is not the case for the sharp positron annihilation line, which is physically not subject to such a broadening.