Assessment of the Second-Ionization Potential of Lawrencium: Investigating the End of the Actinide Series with a One-Atom-at-a-Time Gas-Phase Ion Chemistry Technique.

Experiments were performed at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron facility to investigate the electron-transfer reduction reaction of dipositive Lr ( = 103) with O gas. Ions of Lr were produced in the fusion-evaporation reaction Bi(Ca,2n) Lr and were studied with a novel gas-phase ion chemistry technique. The produced Lr ions were trapped and O gas was introduced, such that the charge-exchange reaction to reduce Lr to Lr was observed and the reaction rate constant was determined to be = 1.

First Direct Measurements of Superheavy-Element Mass Numbers.

An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two α-decay chains, produced via the ^{243}Am(^{48}Ca,xn)^{291-x}Mc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus.

Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in ^{254}Rf.

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus.

48Ca+249Bk fusion reaction leading to element Z = 117: long-lived α-decaying 270Db and discovery of 266Lr.

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the (48)Ca+(249)Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope (294)117 and its decay products.

Superheavy element flerovium (element 114) is a volatile metal.

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z.

Spectroscopy of element 115 decay chains.

A high-resolution α, x-ray, and γ-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated α-decay chains were detected following the fusion-evaporation reaction 48Ca + 243Am. The observations are consistent with previous assignments of similar decay chains to originate from element Z=115.

New superheavy element isotopes: ²⁴²Pu(⁴⁸Ca,5n) ²⁸⁵114.

The new, neutron-deficient, superheavy element isotope ²⁸⁵114 was produced in ⁴⁸Ca irradiations of ²⁴²Pu targets at a center-of-target beam energy of 256 MeV (E*=50  MeV). The α decay of ²⁸⁵114was followed by the sequential α decay of four daughter nuclides, 281Cn, 277Ds, 273Hs, and 269Sg. 265Rf was observed to decay by spontaneous fission.

Production and decay of element 114: high cross sections and the new nucleus 277Hs.

The fusion-evaporation reaction 244Pu(48Ca,3-4n){288,289}114 was studied at the new gas-filled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of {288,289}114. At a compound nucleus excitation energy of E{*}=39.

Independent verification of element 114 Production in the ;{48}Ca + ;{242}Pu reaction.

Independent verification of the production of element 114 in the reaction of 244-MeV ;{48}Ca with ;{242}Pu is presented. Two chains of time- and position-correlated decays have been assigned to ;{286}114 and ;{287}114. The observed decay modes, half-lives, and decay energies agree with published results.

Lightest isotope of Bh produced via the 209Bi(52Cr,n)260Bh reaction.

The lightest isotope of Bh was produced in the new 209Bi(52Cr,n)260Bh reaction at the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Positive identification was made by observation of eight correlated alpha particle decay chains in the focal plane detector of the Berkeley Gas-Filled Separator. 260Bh decays with a 35(-9)(+19) ms half-life by alpha particle emission mainly by a group at 10.

Development of an odd-Z-projectile reaction for heavy element synthesis: 208Pb(64Ni,n)271Ds and 208Pb(65Cu,n)(272)111.

Seven 271Ds decay chains were identified in the bombardment of 208Pb targets with 311.5 and 314.3 MeV 64Ni projectiles using the Berkeley Gas-filled Separator.

Chemical investigation of hassium (element 108).

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table.

Chemical characterization of bohrium (element 107).

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties.

Evidence for new isotopes of element 107: 266Bh and 267Bh.

New neutron rich isotopes 267107Bh and 266107Bh were produced in bombardments of a 249Bk target with 117-MeV and 123-MeV 22Ne ions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Identification was made by observation of correlated alpha-particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. 267Bh was produced with a cross section of approximately 70 pb and decays with a 17(+14)(-6) s half life by emission of alpha particles with an average energy of 8.

First Measurement of a Thermochemical Property of a Seaborgium Compound.

With only a few atoms of seaborgium (Sg, element 106), in the form of volatile SgO(2)Cl(2), it was possible to determine the sublimation enthalpy of this compound using gas chromatography. Furthermore, it was demonstrated that in Group 6 Sg is chemically more similar to W than to Mo.