The effective period

Effective period is the period of time during which the radioactivity of the organism caused by penetrating radioactive substances is reduced by half. Reduction of radioactivity occurs due to physical decay of a radioactive substance (see Radioactivity) and biological its removal from the body. Radioactive substances are not fixed selectively in any bodies, such as radioactive sodium, quickly eliminated from the body, causing short-effective period calculated by days. When depositing in the long-living radioactive substances duration of the effective period of several years. For example, the effective period of radium, deponirovano in the bones, is 16 000 days.