USRBDX interpretation of results

Hi experts
I wanted to check the number of interactions in NaI detector for 1.44 MeV photons. I wanted to check the effect of a shield on the detector. 3 detectors are placed as in geometry and one inside a shield. I couldnt intrepret the results may be my scoring card used is wrong one.
I wanted to check response of NaI detector. Please guide me.

Gamma NaI.flair (4.2 KB) Gamma NaI.inp (3.8 KB)

Thanks in advance

Dear Sunil,

First of all, given the location of the source at (0,0,-50) and the shielding orientation, I assume you are not trying to protect the detector from the source, but rather to estimate the background induced by the presence of the shielding. If it’s the former, then it is not surprising if there is no reduction, as can be seen in this plot of photon fluence.


Concerning the USRBDX scoring, what you are probably looking for are three one-way scorings from region VOID to regions sod1/2/3 with linear energy binning (therefore using the option: Φ1,LinE,LinΩ), with energy bins from 0.0 to 0.0015 GeV; setting 150 bins will give you 10 keV/bin which should be sufficient for now. It is also probably sufficient to have a single angular bin, since NaI detectors do not give you any angular information with which to compare. You can leave the corresponding field empty, at that point the result will be the energy spectrum of photons entering each detector, independent of the angle.

The scorings you defined as going from regions sod1/2/3 to region VOID would instead give you the spectrum of photons exiting the detectors, which is unlikely to be what you are looking for. So I think you could trim down the USRBDX cards to just the 3 descibed above.

Since the detectors are in vacuum, you would expect to get the source γ-peak in all detectors, plus some background produced by interactions in the shielding (affecting mostly the detector nearest to it) and in the other detectors.


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