Lecture series on heavy and super heavy elements (3/3)

Studies on the chemical properties of the heaviest elements offer unique opportunities to obtain information about trends in the periodic table of the elements at the limits of nuclear stability, and to assess the magnitude of the influence of relativistic effects on chemical properties. From the calculations of electron configurations of heavier elements, it is predicted that sudden changes in the structure of electron shells may appear due to relativistic effects which originate from the increasingly strong Coulomb field of the highly charged atomic nucleus. Thus, it is expected that heavier elements show a drastic rearrangement of electrons in their atomic ground states, and, as electron configurations are responsible for chemical behavior of elements, such relativistic effects can lead to surprising chemical properties. Increasing deviations from the periodicity of chemical properties based on extrapolation from lighter homologues in the periodic table are consequently predicted.

The heaviest elements must be produced at an accelerator using reactions of heavy-ion beams with heavy target materials and must be identified by measurement of their decay or that of their known daughter nuclei with unambiguous detection techniques. Both half-lives and production rates of nuclides of heavier elements are rapidly decreasing, and so each atom produced decays before a new atom is synthesized. This means any chemistry to be performed must be done on an "atom-at-a-time" basis.

To verify experimentally the influence of relativistic effects of electron shell structure, we are studying chemical properties of the heaviest elements, rutherfordium (Rf: element 104), ²⁶¹Rf (T_1/2 = 68 s) and dubnium (Db: element 105), ²⁶²Db (T_1/2 = 34 s) that were produced via the reactions of ²⁴⁸Cm(¹⁸O, 5n) and ²⁴⁸Cm(¹⁹F, 5n), respectively, using the JAEA tandem accelerator. In the seminar, chemical studies of Rf and Db at JAEA are reviewed. Then, we briefly introduce recent electrochemical studies of the heaviest elements on an atom-at-a-time scale.