Some natural elements are unstable.
When radiation passes through matter, it can cause that matter to become electrically charged or ionized In living tissue, the electrical ions produced by radiation can affect normal biological processes. Radioactive waste is categorised according to levels of radioactivity, heat content and potential hazard. The term half-life refers to the time a radionuclide takes to lose half of its radioactivity. So after 30 years, the strength of caesium-137 is reduced by half and in another 30 years, it is again reduced by half. Long-lived wastes do not decay to acceptable national levels during a period for which administrative control can be expected.