Created attachment 668 [details] Photoneutron spectra obtained after simulating 10^9 decay events of 124-Sb with BeO cylinder as the target. I have modified the G4 example- NeutronSource (https://gitlab.physik.uni-kiel.de/geant4/geant4/tree/a7fdc52004deb7778a619323a020cfe8f887b648/examples/extended/hadronic/NeutronSource). The target is Beryllium Oxide (BeO) and the source of gamma is 124-Sb. I have used the G4LENDorBERTModel for the photoneutron process. While the expected energy of the photoneutron is around 24 keV, I obtain two peaks at around 10 keV and 100 keV respectively as shown in the attachment. Hitting the target directly with gammas of any other energy too gives a result deviant from the expectation. I wonder if the problem is with the LEND model for 9Be?
The LEND model is based on the GND nuclear database, which has gamma interactions but does not cover all incident gamma energies. In your case, the GND files for the gamma + 9Be reaction only contain data for incident gamma energies above 1.57 MeV for the n + 2alpha final state, above 18.9 MeV for the n p Li7 gamma final state, and above 20.6 MeV for the 2n + Be7 final state. So, for the gamma energies you are interested in, the GND and therefore LEND model have no data. When this happens the G4LENDorBERTModel defaults to the Bertini model, which does not calculate discrete energy levels. It will do the best it can to get energy conservation right, but the final state will only be correct in some average sense. Note that the GND is relatively new and therefore does not have all gamma data yet. This is a work in progress.
Has there been any progress with respect to updating the GND (LEND model) for gammas in the 1.6 MeV range?
