In-beam gamma ray and conversion electron study of Fm250

Abstract

We report on a set of in-beam studies of excited states in Fm250. We detected prompt γ rays by using the JUROSPHERE IV array and conversion electrons by using the SACRED spectrometer. Both devices were used in conjunction with the RITU gas-filled recoil separator located at the University of Jyväskylä. Fm250 nuclei were produced through the Hg204(Ca48,2n)Fm250 fusion-evaporation reaction. An experimental excitation function gave a maximum reaction cross section of (980 ± 160) nb at an energy of 209 MeV in the center of the target. Tagging techniques were employed, and a number of E2 transitions were observed that connected the ground-state band levels from spin 4+ up to 18+. The highly converted 4+→2+ transition is observed only by use of conversion electron spectroscopy. The observed ground-state band transitions indicate a rotational structure. We deduce a quadrupole deformation parameter of β2=0.28 ± 0.02. A low-energy background of apparent nuclear origin is observed in conversion electrons and postulated to arise from the decay of high-K bands. The half-life of Fm250 is measured to be 30.4 ± 1.5 min. Show more