Nuclear structure and reaction studies near doubly magic ²⁷⁰Hs

Abstract

Superheavy elements / Hassium / Nuclear structure / Reaction studiesSummary. Fast on-line gas chemical separations of Hs (hassium, element 108) in the form of HsO 4 were applied to investigate the reactions 26 Mg + 248 Cm and 36 S + 238 U. In an experiment at the gas-filled separator DGFRS the reaction 48 Ca + 226 Ra was studied. In all cases the product of complete nuclear fusion is 274 Hs * . For the first time, the new nuclide 270 Hs was produced in the 4n evaporation channel and its decay properties investigated. The nuclide 270 Hs was predicted by microscopic-macroscopic calculations to be a deformed doubly magic nucleus and its decay properties are therefore of special interest to theory. Also, much more detailed information was gained on the decay of 269 Hs and its daughters, which led to a new assignment of decay properties of the daughter nuclides 265 Sg and 261 Rf . There is evidence for isomeric states in 265 Sg and 261 Rf , while 266 Sg is not an alpha-particle emitter as believed previously, but decays by spontaneous fission (SF) with a rather short half-life. Also, interesting features of the used reaction 26 Mg + 248 Cm led to the discovery of the nucleus 271 Hs in the same experiments. An investigation of the influence of the Q-value on the fusion reaction in relation to the location of the fusion barrier showed, that the high binding energy of 48 Ca largely compensates for the lower fusion probability compared to more asymmetric reactions, while 36 S is not as promising as a projectile.

Alpha-decay and spontaneous fission half-lives of super-heavy nuclei around the doubly magic nucleus270Hs

“…4 we may conclude that the SHN from unstable configurations undergo spontaneous α-decay or SF until the nuclear stability is reached. Our results for the decay properties of SHN around 270 Ds are in good agreement with existing data [1][2][3][4][5][6][7][8][9][10][11][12][13]. In general, the calculated α-decay half-lives are greater than the estimates based on previous predicted Q α -values of models developed in Refs.…”

“…The quantity and quality of experimental data on the production and decay of the SHN have increased considerably in the last two decades [1][2][3][4][5][6][7][8][9][10][11][12][13]. Systematic studies of the existing data are revealing new reaction mechanisms, a rich diversity of nuclear structures involving weakly bound states coupled to an environment of scattering states and new competing decay modes that are challenging our understanding of the nucleus at its limits of stability.…”

Chemistry of superheavy elements

“…Consequently, three to five neutrons are emitted before the compound nucleus has cooled. Still, because of the neutron-richness of actinides targets, these reactions yield the more neutron-rich, rela- tively long-lived isotopes used in chemical investigations of SHE; see Table 2 for used nuclides and [25,32,37,38,60,78,79] for more details.…”

“…Like its lighter homologs Ru and Os, it is expected to show a property which is unique among all transition metals: formation of a highly volatile tetroxide MO 4 (M = Hs, Os, Ru) while exploiting the highest possible oxidation state (8+). All successful Hs chemistry experiments used HsO 4 , explored its volatility [81] and reactivity [155], and exploited its volatility in nuclear synthesis and decay studies [78,227] with unprecedented sensitivities. This gave access to new and interesting Hs isotopes -doubly-magic, deformed 270 Hs [72] and 271 Hs [80] formed in a 3n-evaporation channel -and their Sg and Rf daughter nuclides [78,215].…”

“…All successful Hs chemistry experiments used HsO 4 , explored its volatility [81] and reactivity [155], and exploited its volatility in nuclear synthesis and decay studies [78,227] with unprecedented sensitivities. This gave access to new and interesting Hs isotopes -doubly-magic, deformed 270 Hs [72] and 271 Hs [80] formed in a 3n-evaporation channel -and their Sg and Rf daughter nuclides [78,215]. In addition, these experiments confirmed the discovery of element 112 by measuring concordant decay properties in α-decay chains starting from chemically separated Hs fractions [78].…”