<x content-type="symbol">α</x> decay studies of the neutron-deficient uranium isotopes <sup>215<x content-type="symbol">-</x>217</sup>U

Abstract

The α -decay study is an important tool for obtaining information on the nuclear structure of heavy neutron-deficient nuclei. For the N =126 and 124 isotones with even proton number, an intruder state ( π h 9/2 π f 7/2)8+ based on the attractive interaction of f 7/2 protons and f 5/2 neutrons was observed, which increases the binding energy of this configuration with increasing proton number. Additionally, taking into account the octupole correlations, a large-scale shell model calculations predict that the ( π h 9/2 π f 7/2)8+ state lies close or below the ( π h 9 / 2 2 ) 6+ state in the 216Th and 218U. To extend the systematic of the I π =8+ isomeric state in N =124 isotones and search for the most neutron-deficient uranium isotopes, an experiment for the α -decay studies of 215 - 217U was performed at the gas-filled recoil separator SHANS at the Heavy Ion Research Facility in Lanzhou (HIRFL). Heavy ion induced fusion evaporation reactions of the 180W(40Ar, x n)220 - x U ( x =3 - 5) were used to synthesize these neutron-deficient uranium isotopes. The 40Ar beam was delivered by the sector focusing cyclotron of the HIRFL. The evaporation residues recoiled from the thin target were separated in-flight from the primary beam particles by the gas-filled recoil separator SHANS. After passing through two multi-wire proportional counters, the residues were planted into a focal plane detection system. Based on the energy-position-time correlation measurement, the isotopes 215 - 217U were identified. At a beam energy of 187.2 MeV, two α -decaying states were observed in 216U with E α =8.384(30) MeV, T 1/2=