Basic B4 arrangement

I’m a master student who is focus on medical physics.
I changed the exampleB4 and got the measurement result with the GSO(Composition ratio Gd2SiO5:Cd) scintillator.
I have detected secondary particles that are emitted at any angle after hitting the target with incident particles, but I don’t know how to place the target in front of the detector.

Please help someone

If I understand correctly tour e-mail, what you should do is to create a target volume in your DetectorConstruction class.