Our own bodies - muscles, bones, and tissue - contain naturally occurring radioactive elements. Man has always been exposed to natural radiation arising from the earth as well as from outside the ...

Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper or a human hand. Gamma radiation is the most penetrating. It can penetrate air, paper or thin metal.

alpha particles are helium nuclei consisting of two protons and two neutrons emitted from unstable nuclei; alpha radiation is stopped by a few centimetres of air or a thin sheet of paper ...