There are three basic products of radioactive decay: alpha particles, beta particles, and gamma radiation. Alpha particles are basically helium nuclei emitted via the alpha decay of a radioactive element like uranium. They can be blocked with something as simple as a sheet of paper. Beta particles are high speed electrons produced via the beta decay of radioactive nuclei like potassium-40. They can be blocked with aluminum foil. Gamma rays are not particles but very high energy eletromagnetic waves that require much heavier shielding than the other two. Alpha and beta particles can be blocked with protective clothing but gamma rays require things like lead and concrete which cannot be incorporated into clothing. As a result, gamma rays require the use of remote handling equipment.