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A new isotope 203Ac was produced in the reaction 40Ca + 169Tm at beam energy of 226 MeV. One correlated α -decay chain was attributed to 203Ac. The α -particle energy and half-life were determined to be 8217(16) keV and 56 − 26 + 269 μs, respectively. The reduced α -decay width (δ 2) of 203Ac was deduced to be 1096 − 906 + 921 keV, which indicates a favored α decay. The systematics of δ 2 and single-particle energy levels indicate that the new state probably arises from the intruder s 1 / 2 configuration, which shows an onset of deformation in Ac isotopes. The proton separation energy S p of 203Ac was extracted as − 1214 (22) keV and the systematics of S p for odd- A isotopes beyond proton drip line were discussed. [ABSTRACT FROM AUTHOR]

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

A new proton-unbound isotope 204Ac was produced in the fusion-evaporation reaction Tm ( 40 169 Ca , 5n) 204 Ac and identified via the recoil- α correlation at the gas-filled recoiled separators SHANS2 and SHANS. The excitation function for producing 204Ac was measured and the optimal beam energy was evaluated to be 212 MeV. Nineteen ER - α 1 - α 2 - α 3 decay chains were observed for this isotope. Based on these chains, the α -particle energy and half-life of 204Ac were determined to be 7948(15) keV and 7.4 − 1.4 + 2.2 ms, respectively. Both are consistent with the theoretical prediction. The reduced α -decay width was deduced to be 49 − 15 + 10 keV, which indicates a favored α decay for 204Ac. In addition, more precise decay properties of E α = 7883(15) keV and T 1 / 2 = 7.7 − 1.6 + 2.7 ms were obtained for 205Ac. [ABSTRACT FROM AUTHOR]