I have lists of partial mass attenuation coefficients (photo-e, scattering, pp) from a mixture of substance (elements). How can I calculate for the probability of the interactions?
You need two things:
- The density $\rho$ of the material, and
- The length $\ell$ of the material.
Then, for mass attenuation coefficient $k$ (which has units of area over mass), the probability of interaction is
As you can see, the interaction probability approaches zero as the length goes to zero, and it approaches 1 as the length goes to infinity.