Drastic neutron capture gamma changes in version 11.3.2

Physics Processes, Models and Cross Sections
1

I am running a simulation where fission neutrons are emitted inside a plastic sphere. After upgrading to version 11.3.2, I noticed some unusual behavior in the energies of gammas emitted following neutron capture. Please see the histogram below of gamma energies from neutron capture on hydrogen-1. The only change between the two plots is which installation I built against.

In version 11.2.0, gamma emission occurs only at 2223 keV, as expected. However, in version 11.3.2, the result is a continuum spectrum with an endpoint at 2223 keV. This version appears to emit many (10-50) gammas per single neutron capture, with the total energy summing to 2223 keV.

This appears to be a bug in version 11.3.2. To the best of my knowledge, it has not yet been addressed.

n_capture_hist
n_capture_hist1834×1414 157 KB

Geant4 Version:11.2.0 and 11.3.2
Operating System: Macos 15.5
Compiler/Version: Apple clang version 17.0.0
CMake Version:4.0.1

1 Like
2

Hello,

thank you very much for this report. It seems to be a bug. Can you , please, post this report in Geant4 bug report system bugzilla. this text and plot is enough, you should not add extra information - the problem is clear.

VI