Hello I mentioned my problem (see below) at the hadron processes forum and JP Wellisch replied that it might belong to electromagnetic physics, and he knows about a bug under investigation in hEnergyLoss, concerning tritons. Hope here 's the right place: Yet I run geant4.3.1 on a linux-pc. I try to simulate the reactions of high energetic particles (protons) injected into a stratified atmosphere. More or less the physics from exampleN04 are adapted: mainly multiple scattering, ionisations, hadron interactions, elastic/ inelastic processes. e.g. I'm playing with 256 MeV protons (yet quite low in energy range) and "run/beamOn 500" straight down from top of atmopshere. It looks like working fine for a while, giving all kinds of secondaries, using all kind of physics (including deuterons, tritons, neutron, hionisation). Then an i-th primary yields a secondary which doesn't stop. I.e. a deuteron, triton or neutron keeps running and running hIonisations till the program is crudely quit. I've to confess that I don't understand, why this happens and how to stop it, better how to avoid it. I would be glad if anybody could give a hint. Regards, Edwina Wolff