Define primary Particle

Particles, Track, Event, Run and Biasing
1

Hi Dear Geant4 member user !
I have some problem to define my soil sample source at a primary particle.
I already construct it like a geometry, and now I want to define it at the primary particle.
can someone have any idea ?

2

Check Check examples/basic/B1/include B1PrimaryGeneratorAction.hh
And
examples/basic/B1/src/B1PrimaryGeneratorAction.cc