<Tr> <Th> Excess energy </Th> <Td> 971 keV </Td> </Tr> <Tr> <Td_colspan="2"> Complete table of nuclides </Td> </Tr> <P> Iodine - 131 (I) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley . It has a radioactive decay half - life of about eight days . It is associated with nuclear energy, medical diagnostic and treatment procedures, and natural gas production . It also plays a major role as a radioactive isotope present in nuclear fission products, and was a significant contributor to the health hazards from open - air atomic bomb testing in the 1950s, and from the Chernobyl disaster, as well as being a large fraction of the contamination hazard in the first weeks in the Fukushima nuclear crisis . This is because I - 131 is a major fission product of uranium and plutonium, comprising nearly 3% of the total products of fission (by weight). See fission product yield for a comparison with other radioactive fission products . I - 131 is also a major fission product of uranium - 233, produced from thorium . </P> <P> Due to its mode of beta decay, iodine - 131 is notable for causing mutation and death in cells that it penetrates, and other cells up to several millimeters away . For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation . For example, children treated with moderate dose of I - 131 for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not . Likewise, most studies of very - high - dose I - 131 for treatment of Graves disease have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with I - 131 absorption at moderate doses . Thus, iodine - 131 is increasingly less employed in small doses in medical use (especially in children), but increasingly is used only in large and maximal treatment doses, as a way of killing targeted tissues . This is known as "therapeutic use". </P>

Which is the correct way to write iodine (i) with an atomic mass of 131
find me the text answering this question