Bug #13328

Neutron capture not visible in LArG4 (on behalf of Ivan Lepetic)

Added by Gianluca Petrillo over 4 years ago. Updated over 4 years ago.

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From a mail thread by Ivan Lepetic:

I am now trying to produce neutrons, which are supposed to capture in stainless steel (which I placed in the GDML files) and subsequently produce a photon. When I do this, in over 99% of cases, LArSoft again does not produce any particles besides the initial neutron. I didn't have this problem in version 4.35.00, but I do in 5.12.01.
I tried simulating 400 MeV neutrons, and that produced plenty of particles. In version 4.35.00, I simulated 300 eV neutrons, and they produced photons via neutron capture of energy 1-10 MeV, as expected.
I'm using the generic 5.12.01 code. I've created a feature branch lepetic_sourceCalib. The changes I've made are to the prodsingle_sbnd.fcl file, and to GDML files to include the metal cylinders used in neutron capture.
I simulated 1000 neutrons of momentum 4 MeV at x=100, y=0 and z=250. This was the center of an acrylic cylinder of radius 1 inch, surrounded by a stainless steel cylinder of radius 3 inches (7.62 cm). The idea being that the neutrons would capture in the metal and produce photons.
In the past, I used momenta lower than 4 MeV. Although lower momentum neutrons do produce daughter particles, it doesn't appear that photons are produced, as they were before. Beyond that, it appears that 4 MeV neutrons do capture within the radius of the cylinder (7.62 cm), but they don't produce anything.


#1 Updated by Gianluca Petrillo over 4 years ago

  • Subject changed from (on behalf of Ivan Lepetic) to Neutron capture not visible in LArG4 (on behalf of Ivan Lepetic)

Originally I had thought it was a general problem, but from the latest report it is specific to neutron capture.
It might very well be about Geant4 physics lists. I'll ask some Geant4 expert about that.

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