Primary particle generation from within the volume of a cylinder

Hi G4 experts,
I have made a volume of copper tubes using the G4Tubs that has a radius of 2m and height of 2m, and then I made another volume of argon using G4Tubs again that has a radius of 1.9m and height of 1.9 m. Now I place the argon volume inside the copper volume (so that copper is the mother volume of argon volume) without any translation and rotation. Now during simulation, I use a macro that has " /gps/confine <name_of_physical_volume_of_copper_tubes>" expecting to simulate the neutrons from the volume of copper tubes only(neutrons should start from within a radius of 1.9m to 2m only). But, neutrons are starting from radius=0m to radius=2m which I don’t want. Could you please hint me a solution to this problem?

how about this? provide the pMinR=1.9*m as parameter for the copper tubs and place both cylinders into the world.

Thanks for the reply @weller. I have very complicated geometry in my original setup. I shortened the things in my question. yes, you are right I can certainly do that and I have done that as well and it works fine for the setup you suggested. But I am looking for some /gps/ command that could do the job.

for more complicated volumes, maybe a G4SubtractionSolid? I doubt that there is such a /gps/ command, at least I did not notice any of this kind…