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:

[rtownson]

You could consider switching to cavity or egs_chamber for more geometry and source flexibility.

The cavity zones are all the regions that comprise the cavity sensitive volume. See the region numbering scheme in section 7.2.1. The region outside the sphere is region 1, so you can set its material just like any other region.