Radioactive mineral sources can be examined.
Alpha particles have a range in air of about 2 or 3 cm; you must place the source close to the Radiation Monitor to observe the alphas. Inserting a piece of paper in the alpha beam stops them! Beta particles have a longer range in air, and are mostly unaffected by passing through a piece of paper. A thin lead sheet stops the betas, but some counting may remain due to the presence of a some gammas in the beta source. Gammas are unaffected by the paper or the thin lead sheet, but can be stopped by a lead brick