Alpha-gamma decay studies of 251,253No and their daughter products 247,249Fm

The isotopes No-251 and No-253 were produced in nuclear reactions Pb-206 (Ca-48,3n)No-251 and Pb-207(Ca-48,2n)No-253. Radioactive decay of these isotopes and their daughter products has been investigated by means of alpha- and, alpha-gamma- spectroscopy. An isomeric state No-251m, having a half-life of T-1/2 = (0.93 +/- 0.06) s and decaying by emission of a particles of E-alpha = (8665 8) keV was identified. The measured decay data allowed for the construction of partial level schemes for No-251, Fm-247,Fm-249 and Cf-243,Cf-245 and an extrapolation of energy systematics of single particle levels of N = 145, 147 and 1.49 isotones with even Z towards higher atomic numbers up to Z = 102.