The atoms and molecules in the path of radiation can be altered, and a chain of events begins that can destroy cells or make them function abnormally, This creates a health hazard if the cell becomes cancerous. However, the radiation may kill only the cell, which is what happens naturally to millions of cells every day. Alpha radiation often can be simply washed off the skin. It can be blocked by a sheet of paper. It enters the body through cuts, breathing or food or water.
Beta radiation consists of electrons.
More penetrating than the alpha radiation, the beta electrons can pass through several millimeters of skin. A sheet of aluminum a minute fraction of an inch thick will stop beta radiation. Gamma rays are a form of electromagnetic radiation, similar to x-rays, light and radiowaves and are very penetrating. X-rays are a more familar form of electromagnetic radiation, usually with a limited penetrating power. Typically, they are used in medical or dental examinations.