Element 105 / Chemicalproperties / Complexation with OL-hydroxyisobutyrate / Pentavalent oxidation State / Nuclear decay of^^^-^^^Ha AbstractStudies of the complexation of element 105 by unbuffered ahydroxyisobutyric acid (a-HiB) and its elution from strongly acidic cation exchange resin were performed on a mixture of 34-s ^"Ha and 27-s "'Ha produced in the and reactions at a beam energy of 99 MeV. The Ha isotopes were detected by measuring the spontaneous fission and a-activities associated with their decay, and the a-decays of their daughters, 4-s and 6-s ^"Lr. Time-correlated pairs of parent and daughter a-particles were also registered. The experiments were performed on a one-minute time scale with the computer-controlled hquid chromatography system ARCA II. In 0.05 M a-HiB, element 105 was found to be eluted within 4 s from 1.6x8 mm columns together with the pentavalent Nb-, Ta-, and Pa-ions, while tetravalent Zr-and trivalent Eu-ions were strongly retained on the columns. This is independent proof that the most stable oxidation State of element 105 in aqueous Solution is + 5. This very efficient Separation of 262,263^^2 was also used, for the first time, to demonstrate that their a-and spontaneous fission decays can be registered from a «23 um thin aqueous layer in contact with a large-area passivated ionimplanted planar Silicon detector. In addition, the a-HiB separations were instrumental in the successful Identification of the hitherto undiscovered isotope produced at an '®0 beam energy of 93 MeV.