ONLINE GAS-CHROMATOGRAPHIC STUDIES OF CHLORIDES OF RUTHERFORDIUM AND HOMOLOGS ZR AND HF

Gas-phase isothermal chromatography is a method by which volatile comp ounds of different chemical elements can be separated. The technique, coupled with theoretical modeling of the processes occurring in the ch romatography column, provides information about thermodynamic properti es (e.g., adsorption enthalpies) for compounds of elements, such as th e transactinides, which can only be produced on an atom-at-a-time basi s. In addition, the chemical selectivity of the isothermal chromatogra phy technique provides the decontamination from interfering activities necessary for determination of the nuclear decay properties of the is otopes of these elements. The Zr and Hf isotopes, 30.7-s Zr-98 and 38- s Hf-162 were produced via the U-235(n,f) and Sm-147(Ne-20,5n) reactio ns, respectively. The 65-s (261)Rf was produced via the Cm-248(O-18, 5 n) reaction. A new and more accurate half-life for (261)Rf of 78(-6)(11)-s has been measured. Measurements were performed on chloride speci es of Rf and its group 4 homologs, Zr and Hf and on Zr-bromides using the Heavy Element Volatility Instrument (HEVI). Adsorption enthalpies were calculated for all species using a Monte Carlo code simulation ba sed on a microscopic model for gas thermochromatography in open column s with laminar flow of the carrier gas and the following adsorption en thalpies for the group 4 chlorides were obtained for quartz surfaces: Zr(-74+/-5 kJ/mol), Hf (-96+/-5 kJ/mol) and Rf (-77+/-6 kJ/mol). These results indicate that Rf deviates from the trend expected based on ex trapolation of the Zr and Hf values. Further calculations are needed t o assess whether this is due to relativistic effects in the transactin ide region.