New short-lived isotope 223Np and the absence of the Z = 92 subshell closure near N = 126

Abstract

The N=130 short-lived isotope Np-223 was produced as evaporation residue (ER) in the fusion reaction Ar-40 + Re-187 at the gas-filled recoil separator Spectrometer for Heavy Atom and Nuclear Structure (SHANS). It was identified through temporal and spatial correlations with alpha decays of Ac-215 and/or Fr-211, the third and fourth members of the a-decay chain starting from Np-223. The pileup signals of ER(Np-223)-alpha(Np-223)-alpha(Pa-219) were resolved by using the digital pulse processing technique. An alpha decay with half-life of T-1/2=2.15((100)(52)) mu s and energy of E-alpha=9477(44) keVwas attributed to Np-223. Spin and parity of 9/2(-) were tentatively proposed for the ground state of Np-223 by combining the reduced alpha-decay width and large-scale shell-model calculations. This assignment together with the proton separation energy disprove the existence of a Z=92subshell closure. (C) 2017 The Author(s). Published by Elsevier B.V.