Nuclear structure and reaction studies near doubly magic ²⁷⁰Hs

Abstract

Fast on-line gas chemical separations of Hs (hassium, element 108) in the form of HsO₄ were applied to investigate the reactions ²⁶Mg + ²⁴⁸Cm and ³⁶S + ²³⁸U. In an experiment at the gas-filled separator DGFRS the reaction ⁴⁸Ca + ²²⁶Ra was studied. In all cases the product of complete nuclear fusion is ²⁷⁴Hs^*. For the first time, the new nuclide ²⁷⁰Hs was produced in the 4n evaporation channel and its decay properties investigated. The nuclide ²⁷⁰Hs 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 ²⁶⁹Hs and its daughters, which led to a new assignment of decay properties of the daughter nuclides ²⁶⁵Sg and ²⁶¹Rf. There is evidence fo r isomeric states in ²⁶⁵Sg and ²⁶¹Rf, while ²⁶⁶Sg 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 ²⁶Mg + ²⁴⁸Cm led to the discovery of the nucleus ²⁷¹Hs 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 ⁴⁸Ca largely compensates for the lower fusion probability compared to more asymmetric reactions, while ³⁶S is not as promising as a projectile.