We have been having some issues producing neutrons from the photodisintegration of naturally occurring deuterons in a hydrocarbon fluid in Geant4 (a small part of a larger simulation).
Using Geant188.8.131.52 I tried a simple test modifying the extended example Hadr03. First 20 MeV gammas fired at a 100m cube of deuterons. Then 4 MeV gammas at the same cube. With the 20 MeV gammas, you get 2H(g,n)p with a Q = -2.2244 MeV. For the run using 4 MeV gammas you only see gamma + H2 → N gamma or e- + deuteron reactions listed. You’re above threshold but you don’t get any neutrons. I didn’t modify anything else in the example files.
Would one have to explicitly include G4EmExtraPhysics in the physics list in addition to what is included in the GammaNuclearPhysics.cc file? Or did I miss something else in setting up the problem?