Created attachment 414 [details] Diff file containing fixes While comparing results of Geant4, STARucn(https://sourceforge.net/projects/starucn/), and my own simulation tool PENTrack (https://github.com/wschreyer/PENTrack) for ultra-cold neutrons I found several bugs in reflection and transmission processes for ultra-cold neutrons. I applied the fixes to my own fork of Geant4's Github repository, see here: https://github.com/Geant4/geant4/compare/geant4-10.2-release...wschreyer:geant4-10.2-release
Wolfgang, thank you for your corrections and fixes. I shall incorporate all of your suggestions for the next public release (10.3) Peter P.S. Dennis, can you please change the status of this bug report to resolved/fixed.