Polonium isomers

Hulubei s reported stable or long-lived isotope, if actually polonium, might be a nuclear isomer of a species which is already known. 

Actinium — (Gr. aktis, aktinos, beam or ray), Ac at. wt. (227) at. no. 89 m.p. 1050°C, b.p. 3198°C sp. gr. 10.07 (calc.). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Thirty-four isotopes and isomers are now recognized. All are radioactive. Actinium-227, a decay product of uranium-235, is an alpha and beta emitter with a 21.77-year half-life. Its principal decay products are thorium-227 (18.72-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300°C. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.77-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. Actinium-225, with a purity of 99%, is available from the Oak Ridge National... 

Radioactive elements have no stable isotopes. Among the natural elements, polonium (atomic number 84) and heavier ones are radioactive. Technetium with its atomic number 43 is the lightest of all elements having no stable isotopes. Another light such dementis 61 promethium. Technetium has 26 unstable and 11 metastable (isomer) isotopes, all radioactive [28.9]. Details of the three most long-lived isotopes and two metastable (m) isotopes, important for tracer work, are collected in Table 28.3. 

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