review FlexibleCollimator::isStopped() method in Classic
@kraus "The question is, where we should check whether a particle hits material at the center or at the end of a time step (ideally everywhere but too time consuming). It used to be at the end (before I implemented the configurable collimator) and I changed it to the middle. The extra argument could probably be removed."
See discussion on MR !269 (merged)