Dear G4 experts,
I am experiencing a weird behavior in a simple application I have developed to test energy deposition in a Gold/Bismuth thin absorber. I am generating monoenergetic photon beams at different energies, and in the deposited energy spectrum a weird line at 2.734 keV appears. I am able to identify all of the other lines in the absorption spectrum as fluorescences or escape peaks, but this one has no explaination at all.
This energy roughly corresponds to one of the M absorption edges for Gold, and it was also identified as such in this reference (https://iopscience.iop.org/article/10.1088/1742-6596/718/6/062051/pdf, you can just search for “2.734” string in the pdf).
But the other edges are not present, and as you can see in the following table obtained from NIST database, the cross section for photoelectric absorption for that edge is not dramatically different from the others close absorption edges (not as much as to create such a prominent line with hundreds of counts in a 0.1 eV binned histogram anyway)
Moreover, this is not how absorption edges are supposed to work according to my understanding: if I sent a flat spectrum I should see a line corresponding to increased absorption probability at that energy, but in this case I am sending monoenergetic 5 keV photons.
I went looking into the raw SD output file for some of these events, and I became even more puzzled: as you can see below, the events are all slightly different, but the deposited energy always sums up to 2.734
Event 1:
| EvtID | Particle ID | Parent Particle ID | Eprestep (MeV) | Edep (MeV) | Epoststep (MeV) | Evertex (MeV) | PXL# |
|---|---|---|---|---|---|---|---|
| 88647 | 1 | 0 | 0.005 | 0.00015874 | 0 | 0.005 | 497 |
| 88647 | 4 | 1 | 0.00220333 | 0.00033505 | 0 | 0.00220333 | 497 |
| 88647 | 5 | 4 | 0.00186828 | 0.0012053 | 0.000393878 | 0.00186828 | 497 |
| 88647 | 5 | 4 | 0.000393878 | 0.000393878 | 0 | 0.00186828 | 497 |
| 88647 | 6 | 5 | 0.000269102 | 0.000269102 | 0 | 0.000269102 | 497 |
| 88647 | 3 | 1 | 0.00037193 | 0.00037193 | 0 | 0.00037193 | 497 |
Event2:
| EvtID | Particle ID | Parent Particle ID | Eprestep (MeV) | Edep (MeV) | Epoststep (MeV) | Evertex (MeV) | PXL# |
|---|---|---|---|---|---|---|---|
| 41481 | 1 | 0 | 0.005 | 0.00054367 | 0 | 0.005 | 175 |
| 41481 | 4 | 1 | 0.00176192 | 6.32462e-05 | 0.00133479 | 0.00176192 | 175 |
| 41481 | 4 | 1 | 0.00133479 | 0.000919869 | 0.000414922 | 0.00176192 | 175 |
| 41481 | 4 | 1 | 0.000414922 | 2.48064e-05 | 0.000390116 | 0.00176192 | 175 |
| 41481 | 5 | 4 | 0.000363883 | 0.000363883 | 0 | 0.000363883 | 175 |
| 41481 | 3 | 1 | 0.00042841 | 0.00042841 | 0 | 0.00042841 | 175 |
| 41481 | 2 | 1 | 0.002266 | 0.000390337 | 0.00187566 | 0.002266 | 175 |
Event 3:
| EvtID | Particle ID | Parent Particle ID | Eprestep (MeV) | Edep (MeV) | Epoststep (MeV) | Evertex (MeV) | PXL# |
|---|---|---|---|---|---|---|---|
| 114435 | 1 | 0 | 0.005 | 0.00029461 | 0 | 0.005 | 165 |
| 114435 | 5 | 1 | 0.00022722 | 0.00022722 | 0 | 0.00022722 | 165 |
| 114435 | 4 | 1 | 0.00178376 | 0.000676115 | 0.000901289 | 0.00178376 | 165 |
| 114435 | 4 | 1 | 0.000901289 | 0.000901289 | 0 | 0.00178376 | 165 |
| 114435 | 6 | 4 | 0.000206356 | 0.000206356 | 0 | 0.000206356 | 165 |
| 114435 | 3 | 1 | 0.00042841 | 0.00042841 | 0 | 0.00042841 | 165 |
So I am literally lost and havo no clue if this is a physical process or a bug. Can someone more expert than me help me figure out what is happening?
Thanks a lot in advance
