Discovery of the new isotopes ²⁴⁰Es and ²³⁶Bk and in-beam spectroscopic studies of ²⁴⁴Cf

Abstract

The hitherto unknown neutron-deficient nuclei 240Es and 236Bk were synthesised using the fusion-evaporation reaction 209Bi(34S,3n)240Es. The ritu gas-filled recoil separator and the great spectrometer were used in this decay spectroscopic study. The measured electron-capture delayed fission (ECDF) branches in both of the new isotopes complement the experimental data available in the heavier odd-odd Es and Bk isotopes. Furthermore, the ECDF branches show a continuation in the exponential increase of the ECDF probabilities as a function of QEC − Bsf when approaching the proton dripline. In addition, an in-beam γ-ray spectroscopic study of the neutron-deficient isotope 244Cf was made using the fusion-evaporation reaction 198Pt(48Ca,2n)244Cf. The jurogamii array coupled to ritu and great was used to detect the prompt γ rays emitted at the target position. The excited states in 244Cf were studied for the first time using the recoil-decay tagging method. The ground-state rotational band of 244Cf was measured up to a tentative spin and parity of Iπ = 20+. The behaviour of the moments of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high- j orbitals starting at a rotational frequency of about ~ω = 0.2 MeV. The results were compared to the systematic behaviour of the heavy even-even N = 146 isotones as well as to theoretical calculations where available.