Thomas Nelson Ginter

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.

Performance of the Recoil Mass Spectrometer and its Detector Systems at the Holifield Radioactive Ion Beam Facility

The recently commissioned Recoil Mass Spectrometer (RMS) at the Holifield Radioactive Ion Beam Facility (HRIBF) is described. Consisting of a momentum separator followed by an E-D-E Rochester-type mass spectrometer, the RMS is the centerpiece of the nuclear structure endstation at the HRIBF. Designed to transport ions with rigidities near K = 100, the RMS has acceptances of +/- 10% in energy and +/- 4.9% in mass-to-charge ratio. Recent experimental results are used to illustrate the detection capabilities of the RMS, which is compatible with many detectors and devices

New cold and ultra hot binary and cold ternary spontaneous fission modes for 252Cf and new band structures with gammasphere

Abstract Prompt γ-γ-γ and x-γ-γ coincidence studies following the spontaneous fission of 252Cf were carried out first at Oak Ridge then at Gammasphere first with 36 and later with 72 Ge and two x-ray detectors and a long x-ray-γ coincidence experiment at Idaho. Many new cases of correlated pairs in cold (zero neutron emission) binary fission are observed and for the first time the heavier correlated pairs are identified in ternary fission where the third partners are α, 6He (or α2n), 10Be and, tentatively, 14C. Theoretical calculations were carried out of the relative yields of cold binary and ternary fission. There is reasonable agreement between the relative theoretical and experimental yields. New level structures and isotopes include new octupole deformations, identical bands and other structures. Stable octupole deformation is now observed in N=86, 140Xe, 142Ba and 144Ba and 143Ba, 148Ba and to higher spin in 144Ba. The 142–146Ba data provide the first evidence for the predicted disappearance of stable octupole deformation at high spins from band crossings. Identical yrast bands are observed with widely different neutron and proton numbers in 98,100Sr, 108,110Ru, 112,116Pd, 144,146Ba, 152,154,156Nd, 156Sm, 160Gd and a new type of shifted identical bands in 156,158,160Sm as well as the first identical octupole bands in 142,144Ba. Other new level structures are found. Yields and neutron multiplicities were measured directly for SrNd, ZrCe, MoBa, RuXe, and PdTe correlated pairs. A new ultra hot fission mode was discovered going via only 108Mo144Ba, 107Mo145Ba, and/or 106Mo146Ba pairs where one or more of 44,145,146Ba are hyperdeformed at scission with 3:1 axis ratio.

Octupole deformation in 142,143Ba and 144Ce: new band structures in neutron-rich Ba-isotopes

Abstract New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

Identification of 152Ce and unexpected variations in moments of inertia with neutron number and spin in 142-148Ba, 144-152Ce and 146-156Nd

Levels in 152Ce are identified for the first time along with new high spin states in 142-148Ba, 144-150Ce and 150-156Nd from X-X, gamma -X and gamma - gamma - gamma -ray coincidence measurement in spontaneous fission of 252Cf and 242Pu. The N=88, 90 Ba nuclei have very nearly identical J1 for the yrast bands (2+ to 10+) and for the octupole bands (3- to 15-). The N=92, 94 Nd nuclei have essentially identical yrast J1 (0+ to 16+).

Cold binary and ternary fragmentations in spontaneous fission of252Cf

SummaryThe phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

Identical and shifted identical bands

SummarySpontaneous fission of252Cm was studied with 72 large Compton suppressed Ge detectors in Gammasphere. New isotopes160Sm and162Gd were identified. Through X-ray-γ and γ-γ-γ coincidence measurements, level energies were established to spins 14+ to 20+ in152, 154, 15660Nd92, 94, 96156, 158, 16062Sm94, 96, 98 and160, 16264Gd96, 98. These nuclei exhibit a remarkable variety of identical bands and bands where the energies and moments of inertia are shifted by the same constant amounts for every spin state from 2+ to 12+ for various combinations of nuclei differing by 2n, 4n, 2p, 4p and α.

Towards new proton radioactivities with radioactive beams and digital signal processing

Abstract Particle radioactivity studies using the XIA DGF-4C digital signal processing units at the Recoil Mass Separator of Oak Ridge National Laboratory are presented. Proton emission signals were observed starting from 500 ns after recoil implantation. An energy threshold below 100 keV for particle detection was achieved. For the 145 Tm and 146 Tm decay, evidence for the fine structure in proton emission was obtained. An experiment to search for a new proton emitter 149 Lu is described as an example where the combination of a 56 Ni radioactive beam and digital signal processing is a major advantage.

A search for neutron single-particle states populated via proton emission from 146Tm

We studied the proton emission from 69145Tm77 and observed three new transitions. New transitions at 0.89 and 0.93 MeV have half-lives similar to that of the previously observed transition at 1.19 MeV, while a new transition at 1.02 MeV has a half-life similar to that of the previously observed transition at 1.12 MeV. These new transitions indicate the population of excited neutron single-particle states in 68145Er77.

Prospects for future proton studies at HRIBF

Great progress has been made in the last 20 years in the study of proton emission from unstable nuclei, but the prospects for additional strides in the next several years are bright. The present main limitations on the study of proton radioactivity are related to the inability to produce copious quantities of nuclides beyond the proton drip line, and the difficulty of measuring proton radioactivity of a mass-separated nucleus in the first few microseconds of its existence. At the Holifield Facility we will attack the second of these limitations by using new signal processing CAMAC modules DGF-4C. Digitizing of the preamplifier signals should enable the analysis of a proton decay occurring at times even less than 1 microsecond after an implant in a strip detector. In the same process, the threshold energy at which we can make measurements will be lowered. These two things will hopefully enable the measurement of lower-energy, but faster decays of isotopes in the 100Sn region and below. For the latter regio...