What do scientists mean by a half life?
This odd expression sounds as though it belongs in biology, the science of living things. You might suspect that a half life has something to do with the age of a plant or animal. But no. The term half life belongs in physics, the dynamic science of nonliving matter and energy. The term half life belongs in the field of radioactivity. It is used by atomic scientists and nuclear physicists. Experts who use or experiment with radioactive substances must know something about the half life. It tells how long they can depend upon this or that radioactive material. A half life is a period of time sometimes a split second, sometimes several billion years. It cannot be speeded up or slowed down and it works constantly in every sample of radioactive material. When a half life period of time is up, exactly half of the sample will have become a different substance. A big hospital keeps a supply of radioactive radium. Day and night, at a fixed rate, a definite number of atoms in this supply break
