First Direct Mass Measurements of Nuclides around Z=100 with a Multireflection Time-of-Flight Mass Spectrograph

Abstract

The masses of Es246, Fm251, and the transfermium nuclei Md249-252 and No254, produced by hot- and cold-fusion reactions, in the vicinity of the deformed N=152 neutron shell closure, have been directly measured using a multireflection time-of-flight mass spectrograph. The masses of Es246 and Md249,250,252 were measured for the first time. Using the masses of Md249,250 as anchor points for α decay chains, the masses of heavier nuclei, up to Bh261 and Mt266, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter δ2n derived from three isotopic masses was updated with the new masses and corroborates the existence of the deformed N=152 neutron shell closure for Md and Lr.