Hi everyone, I am simulating a helium-3 detector and want to calculate it’s efficiency with a point source of neutrons. In this case I’m calculating efficiency as:
\varepsilon = \frac{\mathrm{neutron\ absorption\ events}}{\mathrm{neutrons\ passing\ through\ active\ detector\ volume}}
My numerator is easy to calculate from OpenMC – it’s just the ‘absorption’ tally with a cell filter times my source strength, which gives n/s. The denominator is what’s confusing me. Flux is given in n-cm/s from OpenMC, so how does one normalize the flux to n/s through the detector volume?
In addition, for a real-life experiment equivalent, how would one calculate the efficiency? If I know the source activity and the distance from the source to the detector, and I’ve measured counts (and assumed they’re equal to absorption events, ignoring losses in the electronics), what is the appropriate method of calculating flux?