Problem with versions 11.3+ for neutron transport

Physics Processes, Models and Cross Sections
1

Hello everyone,

I have an eigenvalue code for neutrons implemented with Geant4 that works when I use version 11.2.1. Indeed, I run the benchmark problem of this paper: Kreutle et. al. and find similar results.

However, with version 11.3.2, I find keff values of 0.93, far away from the expected value of 1.

I checked for all these versions:
11.2.1 → 1.002
11.2.2 → 1.002
11.3.0 → 0.93
11.3.2 → 0.93
11.4.0beta → 0.93

I use the “Shielding” physics list. My code can be found on thisgit repo . Did something major changed between version 11.2 and 11.3 in the way low energy neutrons are treated ?

Thanks,
Paul

_Geant4 Version:_11.3.2
_Operating System:_MacOS
Compiler/Version: Clang 16.0.6
_CMake Version:_3.28.3