Equivalent to FLUKA materials VACUUM & BLACKHOLE

Hello Geant4 users and experts,

I’m trying to find a proper way to define these two materials in Geant4.
VACUUM: Perfect vacuum, 0 density
BLACKHOLE: Perfect absorber.

I understand that it is not possible to define a material with zero density in G4,
and the equivalent and predefined material would be ‘G4_Galactic’, but it is still not a perfect vacuum…

I think it is easy to deal with the blackhole case just defining a material ‘blackhole’ (with random parameters…), and in the UserSteppingAction I could kill the particles entering in a region with this material, but I still do not find a similar solution for vacuum.

Could be possible to ‘turn off’ all the physics processes to all the regions with a ‘vacuum’ material?
(or maybe just force the transport of the particle)

I hope the question is clear. Also, any other idea is welcomed.



all these variants are possible.

You may define density as a very small value a bit above DBL_MIN, which will be numerically equivalent to zero. Another material with very high density but below DBL_MAX.

Alternatively, you may implement physics process(es) using G4FastSimulationManagerProcess as a base. For kill of particles it is possible to use one of “killer” processes available in Geant4 or create a custom one.


Dear Vladimir,

Perfect, I will try with that.
Thanks for your help