1. The problem statement, all variables and given/known data Which, of an electron and a proton (of a few Mev), is more likely to penetrate further into matter if they both have: a) The same energy b) The same speed 2. Relevant equations Bethe-Bloch formula. Total stopping power = collision loss + radiation loss (de/dx)t = (de/dx)c + (de/dx)r 3. The attempt at a solution a) Electron will penetrate further. If both have the same energy, collision loss is less for electrons as (de/dx)c = 1/v2 b) Both will penetrate the same distance. If both have the same speed, collision loss is the same for both electrons and protons. Radiation loss is minimal as this only comes into effect for higher energies (many Mev).