Chemical Properties of Element 105 in Aqueous Solution: Cation Exchange Separations with α-Hydroxyisobutyric Acid

Abstract

Studies of the complexation of element 105 by unbuffered a-hydroxyisobutyric acid (a-HiB) and its elution from strongly acidic cation exchange resin were performed on a mixture of 34-s ²⁶²Ha and 27-s ²⁶³Ha produced in the ²⁴⁹Bk(¹⁸O,5n) and ²⁴⁹Bk(¹⁸O,4n) 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 ²⁵⁸Lr, and 6-s ²⁵⁹Lr. 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 liquid chromatography system ARCA II. In 0.05 M a-HiB, element 105 was found to be eluted within 4 s from 1.6 ×8 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^,263Ha was also used, for the first time, to demonstrate that their a- and spontaneous fission decays can be registered from a ≈ 23 pm thin aqueous layer in contact with a large-area passivated ion-implanted planar silicon detector. In addition, the a-HiB separations were instrumental in the successful identification of the hitherto undiscovered isotope ²⁶³Ha produced at an ¹⁸O beam energy of 93 MeV.