Darleane C. Hoffman

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. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes 269Hs (refs 8, 9) and 270Hs (ref. 10) in the fusion reaction between 26Mg and 248Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO4, for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO4. These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

Spontaneous fission half-lives for ground-state nuclide (Technical report)

Measurements of the spontaneous fission half-lives of nuclides of elements Z = 82 through 109 have been compiled (cutoff date of April 1998) and evaluated. Recommended values are tabulated along with total half-lives.

ION-EXCHANGE SEPARATIONS OF THE LANTHANIDES AND ACTINIDES BY ELUTION WITH AMMONIUM ALPHA-HYDROXY-ISOBUTYRATE

Abstract Lanthanide and actinide separations by means of elution with ammonium α-hydroxy-isobutyrate solutions at room temperature from Dowex 50-X4 resin columns were investigated. Separations comparable to those reported1, 2 for elution from Dowex 50-X12 resin columns with hot ammonium α-hydroxy-isobutyrate were obtained. The simplicity and convenience of the method recommend it for use on the tracer scale.

Chemical properties of element 106 (seaborgium)

The synthesis, via nuclear fusion reactions, of elements heavier than the actinides, allows one to probe the limits of the periodic table as a means of classifying the elements. In particular, deviations in the periodicity of chemical properties for the heaviest elements are predicted as a consequence of increasingly strong relativistic effects on the electronic shell structure. The transactinide elements have now been extended up to element 112 (ref. 8), but the chemical properties have been investigated only for the first two of the transactinide elements, 104 and 105 (refs 9,10,11,12,13,14,15,16,17,18,19). Those studies showed that relativistic effect render these two elements chemically different from their lighter homologues in the same columns of the periodic table (Fig. 1). Here we report the chemical separation of element 106 (seaborgium, Sg) and investigations of its chemical behaviour in the gas phase and in aqueous solution. The methods that we use are able to probe the reactivity of individual atoms, and based on the detection of just seven atoms of seaborgium we find that it exhibits properties characteristic of the group 6 homologues molybdenum and tungsten. Thus seaborgium appears to restore the trends of the periodic table disrupted by relativistic effects in elements 104 and 105.

Some short-lived isotopes of cerium and praseodymium☆

Abstract The following new β-decay chains of cerium and praseodymium were identified in the fission products of 235U: 147Ce(65 ± 6 sec)-147Pr(12·0 ± 0.5 min) and 148Ce(43 ± 10 sec)-148Pr(1·98 ± 0·10 min). The cerium half-lives were determined by measuring the relative amounts of the praseodymium daughter activities in samples milked from fission product cerium at suitable intervals. The praseodymium half-lives were obtained by direct observation of the decay of the milked samples. Studies of the radiations of 147Pr and 148Pr with β- and γ-scintillation spectrometers indicated total β-decay energies of 2·7 ± 0·2 MeV and 4·5 ± 0·4 MeV, respectively. A partial decay scheme for 147Pr has been proposed. The mass assignments of 5·98 hr 145Pr and the 12 min 147Pr were substantiated by (γ, p) reactions on enriched 146Nd and 148Nd. Similar irradiations of 150Nd produced some evidence for an ≈ 2·3 min activity attributable to 149Pr.

Half-lives of some rare earth nuclides☆

Measurements were made of the half lives of Y/sup 91/, Pr/sup 143/, , Tb/ sup 160/, Tb/sup 161/, Dy/sup 159/, Dy/sup 166/, and Ho/sup 166/. (auth)

First Aqueous Chemistry with Seaborgium (Element 106)

For the first time, chemical separations of element 106 (Seaborgium, Sg) were performed in aqueous solutions. The isotopes Sg and Sg were produced in the Cm + Ne reaction at a beam energy of 121 MeV. The reaction products were continuously transported by a He(KCl)-jet to the computer-controlled liquid chromatography system ARCA. In 0.1 M HNO3/5 X ΙΟ -4 M HF, Sg was found to be eluted within 10 s from 1.6X8 mm cation-exchange columns (Aminex A6, 17.5±2 μπι) together with the hexavalent Moand W-ions, while hexavalent U-ions and tetravalent Zr-, Hf-, and element 104 ions were strongly retained on the column. Element 106 was detected by measuring correlated α-decays of the daughter isotopes 78-s 104 and 26-s 102. For the isotope Sg, we have evidence for a spontaneous fission branch. It yields a partial spontaneousfission half-life which is in agreement with recent theoretical predictions. The chemical results show that the most stable oxidation state of Sg in aqueous solution is +6, and that like its homologs Mo and W, Sg forms neutral or anionic oxoor oxohalide-compounds under the present condition. In these first experiments, Sg exhibits properties very characteristic of group 6 elements, and does not show U-like properties.

Evidence for the possible synthesis of element 110 produced by the {sup 59}Co+{sup 209}Bi reaction

An experiment to synthesize element 110 by the {sup 59}Co+{sup 209}Bi reaction has been performed at the SuperHILAC at the Lawrence Berkeley Laboratory. One event with many of the expected characteristics of a successful synthesis of {sup 267}110 was observed. This event corresponds to a production cross section of about one picobarn.

Chemical Properties of Element 105 in Aqueous Solution: Back Extraction from Triisooctyl Amine into 0.5 M HCl

Previous studies of the halide complex formation of element 105 and its anion exchange with triisooctyl amine (TIOA) were continued. The experiments were performed on a one-minute time scale with the computer-controlled liquid chromatography system ARCA II on a mixture of 34-s 2 6 2 Ha and 27-s 2 6 3 Ha produced in the 2 4 Bk( 0,5n) and 2 4 Bk( 0,4n) reactions at a beam energy of 99 MeV. The Ha isotopes were detected by measuring the spontaneous fission and α-activities associated with their decay, and the α-decays of their daughters, 4-s Lr, and 6-s Lr. Time-correlated pairs of parent and daughter α-particles were also registered. 2 6 2 , 2 6 3 Ha was absorbed on the TIOA columns from either 12 M HCl/0.01 M HF or 10 M HCl, and was subsequently eluted in 0.5 M HCl/0.01 M H F like its homolog niobium, and the pseudohomolog protactinium, and unlike the closest homolog, tantalum, which remains in the amine phase under these conditions. The effluent was divided into an early Pa fraction and a subsequent Nb fraction. By varying the cut between the Pa fraction and the Nb fraction in rough steps, it was shown that the elution of element 105 occurs closer to the Pa elution position, i.e., earlier than the elution of Nb. These results confirm the non-tantalum like behavior of element 105 in 0.5 M HCl/0.01 M HF, and corroborate previously suggested structural differences between the halide complexes of element 105, niobium, and protactinium, on the one hand, and those of tantalum on the other hand.

Spontaneous fission half-lives for ground state nuclides

Measurements of the spontaneous fission half-lives of nuclides of elements Z = 90 to 107 have been compiled and evaluated. Recommended values are presented. 126 refs., 96 tabs.