In 1940, shortly after the discovery of fission, McMillan and Abelson studied the recoil range of fission products induced by neutrons incident on a thin uranium foil (McMillan, 1939; McMillan and Abelson, 1940). While fission products were mostly ejected from the foil, two activities were significantly retained, one with a half-life of 23 min and the other with a half-life of 2.3 days. The shorter activity was known (Meitner et al., 1937) to belong to 239U, produced by neutron capture in 238U; the longer-lived activity was demonstrated to be the beta-decay daughter of 239U, an isotope of the new element neptunium, which had an atomic number of 93. By analogy, just as the beta decay of 239U produces 239Np, the subsequent beta decay of 239Np must also produce an isotope of a new element with atomic number 94 (plutonium), which was not observable in earlier experiments because of a lack of sensitivity for the detection of radioactive species with long half-lives.

MOODY Kenton J.;  SHAUGHNESSY Dawn A.;  CASTELEYN Karin;  OTTMAR H.;  LUETZENKIRCHEN Klaus;  WALLENIUS Maria;  WISS Thierry; 

2010-12-15

Springer

JRC62368

978-90-481-3146-4,   

http://www.springer.com/chemistry/inorganic,    chemistry/book/978-90-481-3146-4,    https://publications.jrc.ec.europa.eu/repository/handle/JRC62368,