Physics : why do different radioactive sources (gama, alpha, beta) go through different materials.?

Alpha particles ( helium nuclei) are stopped by tissue paper, and Beta particles (electrons) are stopped by a few millimetres of perspex --because their size and energies mean they will hit a nucleus or electron in the shielding material ,relatively quickly.Gamma radiation , however, consists of electro magnetic radiation or photons . These are so small and energetic , that it takes a large thickness of even a dense material such as lead , having a large nucleus and a high electron density , to slow / stop them.