Spectroscopy of No-253 and its daughters

New high-statistics data have been obtained on the decay properties of No-253 and its daughters using the reaction Pb-207(Ca-48, 2n)No-253. This was made possible thanks to an improved transmission of fusion evaporation residues through the VASSILISSA recoil separator and an increased efficiency of the GABRIELA detector setup. The decay schemes of No-253 and Fm-249 have been revisited. The known level scheme of Fm-249 has been confirmed, including a new level at 669 keV excitation energy. The observation of L X-rays in coincidence with the a decay of Fm-249 gives additional support to the ground-state configuration of 1/2(+)[631] instead of 5/2(+)[622] for Cf-245. In both Fm-249 and Cf-245, the interpretation of the data has been checked by comparing experimental a-particle and gamma-ray spectra with realistic simulations of the decay cascades and of the interaction of particles and photons in the detectors of GABRIELA. The population of a 0.7 ms isomeric state attributed to No-253 is confirmed by an a-tagged calorimetric measurement and the corresponding gamma and electron decay spectra are presented. Possible evidence for more than one isomer is given and a tentative partial decay scheme is discussed in the light of the available experimental data, systematics and theoretical expectations. (C) 2011 Elsevier B.V. All rights reserved.