Simulating neutron absorption

Hi all,

I am trying to simulate the energy deposition of the resultants from a neutron capturing onto boron-10, but am wondering if there’s a simpler approach to take. I have a 3D map of where in the material this capture occurs, so all I really need to do is simulate the kinematics of the alpha, lithium, and gamma produced by this. My thought is that rather than randomly generating a momentum for one particle and then generating the other particles’ momenta from conservation laws, this could be done by simple using a neutron capture physics process which produces the output particles with the correct kinematics.

But I was wondering if someone could clarify a few things.

  • In Geant4, when an unstable particle is generated at rest, it immediately decays. If a neutron is placed at rest in an absorbing material, is it similarly immediately absorbed?

  • What physics list is most appropriate for this?

Thank you!

No. The hadronic interactions are all discrete (“PostStepDoIt”) processes, not AtRest processes. A neutron at rest will decay, and the time stamp of the daughters will be set by throwing randomly based on the neutron lifetime.

you can shoot neutron at meV energies.
Here, a run of example Hadr03, with QGSP_BIC_HP selected (see

nicconflo.mac.txt (443 Bytes)
nicconflo.out.txt (1.9 KB)

This works, but the energies do not seem correct. They seem to vary by a few keV between runs instead of being constant as they should. Why is that?

Edit: the issue may be related to this thread, where the variation came from disagreeing values for mass in different G4 data files.