Professor of the Graduate School
email: hoffman@lbl.gov
office: LBL 70-319
phone: 510.486.4474
Research Interests
Nuclear Chemistry Actinide, Transactinides & Superheavy Elements
Heavy ion reactions with rare radioactive actinide targets are used to produce actinide and transactinide isotopes at the very limits of nuclear stability. Computer-controlled, automated fast chemical separation systems have been developed to perform these "atom-at-a-time" studies using liquid-liquid extractions, solid-phase chromatographic extractions, and gas-phase chromatographic separations. Both aqueous and gas-phase properties of the transactinide elements from rutherfordium (104) through seaborgium (106) have been studied and compared with predictions of their properties based on relativistic calculations. Although in general the observed properties allow their placement in the periodic table as the heaviest members of groups 4 through 6, their detailed behavior exhibits some surprising differences from trends predicted by simple extrapolation of the properties of their lighter homologues in these groups. These differences are a result of increasingly important relativistic effects that can now be rather well predicted by relativistic theoretical calculations. Studies of the gas-phase chemistry of the very short-lived elements 107 (bohrium) and 108 (hassium) have recently been performed as part of an international collaboration and, again, indicate that they should be placed as the heaviest members of groups 7 and 8. Further experiments to investigate their behavior in more detail are needed. Plans are underway for studies of the chemistry of element 109 (meitnerium), provided we can discover a new isotope with a longer half-life than that of the longest currently known isotope, which is only 0.04 seconds. Our group completed construction and testing of the Berkeley Gas-filled Separator (BGS) at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron in 1999. The BGS will be used to try to identify a new longer-lived isotope of element 109 and to continue our studies of the properties of other short-lived transactinide isotopes and their production cross sections and to try to produce new heavy elements. BGS was used recently for the first time as a pre-separator prior to chemical studies of Rf using an on-line, automated system for conducting liquid-liquid extractions on the seconds time-scale. This use will be increasingly important in future studies. The group also studies the unique nuclear decay properties of the heaviest elements, including spontaneous fission, delayed fission, and decay. Our studies of chemical and nuclear properties are complementary and proceed hand in hand.
Biography
Professor of the Graduate School, born 1926; B.S. and Ph.D. Physical (Nuclear) Chemistry, Iowa State University (1948, 1951); Oak Ridge National Laboratory (1952); Los Alamos National Laboratory (1953-84): Staff Member, Associate Group Leader, Division Leader of Chemistry and Nuclear Chemistry and Isotope and Nuclear Chemistry Divisions; Guggenheim Fellow (1978-79); Alumni Citation of Merit, Iowa State University (1978); ACS Award for Nuclear Chemistry (1983); ACS Garvan Medal (1990); Norwegian Academy of Science and Letters, 1990; University of California Berkeley Citation of Merit (1996); Natl. Medal of Science (1997); ACS Priestley Medal (2000); U. S. National Medal of Science, 1997; Fellow, American Academy of Arts and Sciences, 1998; Women in Technology International Hall of Fame, 2000; Honorary Doctorates: Clark University, 2000, University of Bern, Switzerland, 2000; Harry & Carol Mosher Award of the Santa Clara, California, Section of the American Chemical Society, 2001. Group leader 1984-2002, Heavy Element Nuclear & Radiochemistry Group, Faculty Senior Scientist, Nuclear Science Division, Lawrence Berkeley National Laboratory (1984-present); Director, Seaborg Institute for Transactinium Science (1991-96); Senior Advisor & Charter Director (1996-present). November, 2003: Sigma Xi Procter Award for Scientific Research