U 器Kr 盈U t锡Ba 墨Kr U on U Kr U U U 锡Ba U Ba n U 器Kr U Ba U U12.4 The Manhattan Project (1942) • In 1938, the German physicist Otto Hahn (1879–1968) found that the atom could be split. As a result, a pound of the fissionable isotope (同位素) of uranium, U–235, was estimated to be the equivalent of 15,000 tons of TNT (黄 色炸药)