https://doi.org/10.1351/goldbook.09256
Number, \(N_{\rm{imp}}\), of energetic particles of a specified type incident on a solid within a surface area \(A\) and stopped within the solid divided by \(A\). \(D_{\rm{imp}} = N_{\rm{imp}}/A\).
Note: Particles that are not stopped within the solid are either backscattered or transmitted.