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Early transuranium elements. After the discovery of the neutron by Chadwick in 1932, the group led by Fermi in Rome. began bombarding different elements with neutrons to study the radioactivity induced through. (n,() reactions. The decay characteristics of the radioactivity in neutron-irradiated uranium was. interpreted to indicate that some of the products were probably transuranium elements. Similar. conclusions were reached by other research groups; for example in 1937 Meitner, Hahn and.
The periodic table had two vacant slots below manganese and finding these missing elements, technetium and rhenium, proved difficult. Rhenium was the lower one and indeed it was the last stable, non-radioactive, naturally-occurring element to be discovered. In 1905, Masataka Ogawa found it in the mineral thorianite from Sri Lanka.