Experimental identification of spin-parities and single-particle configurations in 257No and its α-decay daughter 253Fm -: art. no. 102502

alpha-gamma and alpha-electron coincidence spectroscopy for a short-lived heavy actinide nucleus No-257 (T-1/2=24.5 s) has been performed using a gas-jet transport system and an on-line isotope separator. Spin-parities of excited states in Fm-253 fed by the alpha decay of No-257 have been identified on the basis of the measured internal conversion coefficients. The nu 3/2(+)[622] configuration has been assigned to the ground state of No-257 as well as to the 124.1 keV level in Fm-253. It was found that the ground-state configuration of No-257 is different from that of lighter N=155 isotones.