How I can declare a spherical neutron source to calculate the thermal neutron flux in a cell?

c Created on: Tuesday, September 05, 2023 at 11:26
1 1 -1.58 -1
2 0 -2 #1
3 0 -3 #1 #2
4 0 3

1 rpp -0.5 0.5 -0.5 0.5 0 0.1
2 so 10
3 so 15

mode n
m1 15000. 0.12951 $matrix
6000. 0.01731 12000. 0.00546 11000. 0.008
20000. 0.35857 13000. 0.002184 8000. 0.40146
16000. 0.0118 26000. 0.0026 14000. 0.0101
imp:n 1 1r 0 1 $ 1, 4
sdef cell=2 rad=d1 erg= 0.025 par=1
si1 0 10
f4:n 1
e4 1.01e-10 121i 0.025
nps 10000

A few things to think about,

The void cell is 4, so your imp line should be 1 1 1 0 not 1 1 0 1, right?

You have a point source at 0 0 0 (default source location) is this on the edge of two cells? It needs to not be on the edge. If you want to make cell 2 a homogeneous source, a sphere with a box cut out of it, that is tricky. A surface source might be easier from surface 2, but it depends a lot on what the problem is.

erg= has a space before 0.025

If you rename your input file to add .txt you can attach it to a post, or you can paste into BB code tags, then we can see the version with the correct formatting.

Thank you sir for your comments
Cell 1 is immersed in a thermal neutron source which is the cell 2