Questions about CAVSPHnrc "Cavity Zones" and "Material" and "Source" Input

[karenrex1023]

Hello, I am trying to get a Kwall correction factor for a spherical ion chamber that I've modelled as concentric spheres (innermost sphere = C552 material to represent collector, middle sphere = air, outer sphere = wall). I was confused about the cavity zones input. When I change that input from 2 to 3, I get a different value for Kwall. I was wondering if you could clarify how I should specify this parameter.
I also had a question on whether the transport medium before the spherical chamber geometry would be automatically set to air or vacuum in the simulation?

Finally, is there a way to specify the source in CAVSPHnrc as an isotropic cylindrical source rather than just a point source or a parallel beam?
 
This is what I have as my input:
:start geometrical inputs:

NUMBER OF CONES= 0

NUMBER OF SPHERES= 2

RADII= 0.2224, 0.945, 1.196

CAVITY ZONES= 3

######## Material Input

MEDIA= c552_512icru,
air512icru
MEDNUM= 1, 2, 1
START REGION= 2, 3, 4
STOP REGION= 2, 3, 4

:stop geometrical inputs: