MCNP: Integral flux crossing the spherical surface of a spherical cap

[xisco]

TL;DR Summary

I want to calculate the integral flux crossing the spherical surface of a spherical cap, which I have defined using a spherical surface and a plane. What tally should I use?

c *************** BLOCK 2: SURFACE CARDS **************
10 PZ 100
110 SO 110

 

[xisco]

c ---- TALLIES-------------------------------------
F1:n 10

 

[Alex A]

I'm not that familiar with surface tallies, so I've checked a few things in the manual. If what you want is an integral of the *scalar* flux in particles (per source particle) then what I think you want is,

F1:n 110
FS1 10

So that is a tally through the sphere, with the sphere split by surface 10. That should give two values, the integrated flux through the sphere in the region where Z is larger than 100, since the sense is positive in the FS card, and all other flux. All other flux in this simple example is the sphere with Z<100. If you want it the other way around use -10 instead.

 

[xisco]

Thanks for your reply. Maybe I didn't quite understand what the question was.

 

[Alex A]

If you have two cells A and B, and a neutron crosses the surface from A to B the flux is now 1 neutron. Say this neutron scatters from something in B, back to A. The scalar flux, as I understand it, is now 2 neutrons. They don't cancel, they don't vector sum, they add like simple scalars. It's the usual meaning of flux, I'm sorry if I made it sound weird. Does that help?