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We report on a set of in-beam studies of excited states in 250 Fm. 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. 250 Fm nuclei were produced through the 204 Hg( 48 Ca,2n) 250 Fm 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 β 2 = 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 250 Fm is measured to be 30.4 ± 1.5 min.predict it at Z = 126, N = 184 [11,12]. However, in a number of parametrizations no double shell closure is seen and a large proton gap appears at Z = 120. In relativistic mean-field (RMF) models, a double shell closure at Z = 120, N = 172, is favored [11][12][13][14][15].Nuclei close to this region have been successfully produced, albeit at the level of a few atoms. At GSI (Gesellschaft für Schwerionenforschung), the elements up to Z = 112 have been produced and unambigously identified by means of α-decay chains ending in well-known lighter isotopes [16]. At Dubna several isotopes of elements 114 [17], 115 [18], and 116 [19] have been reported, and recently element 113 was reported from RIKEN [20]. Although proton number 116 has thus been reached, the isotopes produced were still rather neutron deficient compared with the most stable neutron configuration with N = 184 predicted by the macroscopic-microscopic method. A further means of studying the evolution of single-particle states in this region is the study of the α decays of odd-mass nuclei. These decays populate excited states in the daughter nuclei. Because

The spectrum of prompt conversion electrons emitted by excited 254No nuclei has been measured, revealing discrete lines arising from transitions within the ground state band. A striking feature is a broad distribution that peaks near 100 keV and comprises high multiplicity electron cascades, probably originating from M1 transitions within rotational bands built on high K states.

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