~ 32 mended and adopted. Distribution of Radiotsotopes in the Sea The radioisotopes present in the sea are those that (1) occur naturally, (2) have been created by the detonation of atomic devices, or (3) have been disposed of as waste from the operation of atomic reactors or from research and clinical laboratories. The naturally occurring radioisotopes in sea water are listed in Table II. These isotopes have been and will continue to be present in the ocean at the level of abundance given in the table, and H’. with the exception of cl4 Carbon-14 is formed naturally in the atmosphere by a two-stage process which involves the shattering of a nitrogen atom by a high-energy proton from space. Most ci4 exists in the form of carbon dioxide for which the residence times are an average of five years in the atmosphere, five years in the surface layer of the ocean and 1,200 years in the deep waters. explosions also produce cht, However, thermonuclear Since the detonation ot the first thermonuclear device in 1952,a ton of C14 has been produced which equals about one per cent of the total