Alpha particles have a positive electrical charge and are emitted from naturally occurring elements such as uranium and radium, as well as from some man-made elements. Because of their relatively large size, alpha particles collide readily with matter and lose their energy quickly. They therefore have little penetrating power and can be stopped by the first layer of skin or a sheet of paper. However, if they are taken into the body, for example by breathing or swallowing, alpha particles can affect the body's cells. Inside the body, because they give up their energy over a relatively short distance, alpha particles can inflict more biological damage than other radiations.
Beta particles are fast-moving electrons ejected from the nuclei of atoms.
These particles are much smaller than alpha particles and can penetrate up to 1 to 2 centimetres of water or human flesh. They can be stopped by a sheet of aluminium a few millimetres thick. Beta particles are emitted from many radioactive elements. Cosmic radiations consist of very energetic particles which bombard the earth from outer space. They are more intense at higher altitudes than at sea level where the earth's atmosphere is most dense and gives the greatest protection.