Spectroscopy of 253No and its daughters

Abstract New high-statistics data have been obtained on the decay properties of 253 No and its daughters using the reaction 207 Pb( 48 Ca, 2n) 253 No. 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 253 No and 249 Fm have been revisited. The known level scheme of 249 Fm has been confirmed, including a new level at 669 keV excitation energy. The observation of L X-rays in coincidence with the α decay of 249 Fm gives additional support to the ground-state configuration of 1 / 2 + [ 631 ] instead of 5 / 2 + [ 622 ] for 245 Cf. In both…