Plastic, metal and paper, late 20th century.
© Science Museum / Science & Society Picture Library
All of these materials will stop various kinds of radiation. Alpha radiation is the weakest kind and can be stopped by a thin sheet of paper. Beta radiation, when the isotope loses electrons, cannot be stopped by paper, but can be stopped by a thin sheet of metal, such as tin foil. Gamma radiation is the strongest kind which can only eventually be stopped by large thicknesses of metal. This is the most dangerous kind of radiation.