Pm - Promethium
(Prometheus, who, according to mythology, stole fire from heaven) In 1902 Brannerpredicted the existence of an element between neodymium and samarium, and this wasconfirmed by Moseley in 1914. In 1941, workers at Ohio State University irradiatedneodymium and praseodymium with neutrons, deuterons, and alpha particles, and producedseveral new radioactivities, which most likely were those of element 61. Wu and Segre, andBethe, in 1942, confirmed the formation; however, chemical proof of the production ofelement 61 was lacking because of the difficulty in separating the rare earths from eachother at that time. In 1945, Marinsky, Glendenin, and Coryell made the first chemicalidentification by use of ion-exchange chromatography. Their work was doen by fission ofuranium and by neutron bombardment of neodymium.
Searches for the element on earth have been fruitless, and it now appears thatpromethium is completely missing from the earth's crust. Promethium, however, has beenidentified in the spectrum of the star HR465 in Andromeda. This element is being formedrecently near the star's surface, for no known isotope of promethium has a half-lifelonger than 17.7 years. Seventeen isotopes of promethium, with atomic masses from 134 to155 are now known. Promethium-147, with a half-life of 2.6 years, is the most generallyuseful. Promethium-145 is the longest lived, and has a specific activity of 940 Ci/g.