Hi Lorenzo,
My original question above was specifically about how to create these specific histrograms of the secondary particles.
Also, speaking of introductory courses, when and where are these offered? Can they be accessed remotely, or better yet, taken online right now? I have been trying to learn GEANT4 by myself with the help of the Getting Started page, Guide for Application Developers page, and this forum. An introductory course, even if self-paced, would definitely help.