The amount of radioactivity is measured in curies. Nuclear wastes from all hospitals in the United States amount to less than one curie a year. Destructive energy of one curie of radiation depends on the substance. Neutrons and alpha particles of any energy may harm human cells and genes. Neutrons can penet rate deep in tissues and alpha particles, although limited in range, generate a great of heat.
Some radioactive wastes have long half-life .
Different radioactive elements have different half-lives. The danger of nuclear wastes decrease with time exponentially. Presumably, the wastes will be kept in leak-proof containers in underground mines dug into bed rocks. Waste containers do erode with time and may not outlast long-lived radiation matter. Therefore, waste should be placed in a manner which will facilitate recontainerization and make continued isolation from the environment possible in the future.