Hi, I have 662 keV photons from a distant point source, incident on a NaI probe. The probe is made with coaxial cylinders of different materials. The core material is NaI. I record the deposited energy inside NaI and make deposited energy spectra. I use G4Penelope modules for the whole electromagnetic processes. The problem : As long as production cut is above 1 ľm (all particles) it is ok -> the photopeak appears at 662 keV as expected. It is very sharp since it is only within one channel, roughly 3 keV width. BUT, when cut values go below and equal to 1 ľm, the photopeak shifts to higher energies, and becomes gaussian shaped ! At 1ľm, the photopeak is at 720 keV. At 0.1 ľm the photopeak is at 805 keV.... The lower the threshold is, the higher is the peak. 1 ľm in NaI material gives an energy cut of around 1keV 0.1 ľm is below 100 eV. The lower limit of energy cut-off calculation is set to 100 eV. I have no explanation for this strange behaviour. Thank you for any comments, Alain Remarks : Please remember that this happens only with G4Penelope
The problem report is assigned to the Geant4 developer expert in Penelope processes.
Dear Alain, thank you for your report. The bug, which had effect only with very small cuts, was indentified and fixed. The corrected code will be available in the next public release. Thank you again for your report. Luciano Pandola
