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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.

Fine structure in the $\alpha$ decay of $^{223}$U was observed in the fusion-evaporation reaction $^{187}$Re($^{40}$Ar, p3n) by using fast digital pulse processing technique. Two $\alpha$-decay branches of $^{223}$U feeding the ground state and 244 keV excited state of $^{219}$Th were identified by establishing the decay chain $^{223}$U $\xrightarrow{\alpha_{1}}$ $^{219}$Th $\xrightarrow{\alpha_{2}}$ $^{215}$Ra $\xrightarrow{\alpha_{3}}$ $^{211}$Rn. The $\alpha$-particle energy for the ground-state to ground-state transition of $^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62$^{+14}_{-10}$ $\mu$s. Evolution of nuclear structure for $N$ = 131 even-$Z$ isotones from Po to U was discussed in the frameworks of nuclear mass and reduced $\alpha$-decay width, a weakening octupole deformation in the ground state of $^{223}$U relative to its lighter isotones $^{219}$Ra and $^{221}$Th was suggested., Comment: 6 pages, 6 figures

The decay of 218Pa was investigated by means of α and γ spectroscopy. The nucleus was produced in the fusion reaction 40Ar+182W and separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The known α decays of 218Pa were measured with improved precision and newly assigned to be originating from the ground state, which clarified the ambiguities in their previous assignments. In addition, a new isomeric state in 218Pa decaying with α-particle energies of 9691(15) keV, 9595(21) keV and a half-life of 135−32+62 μs was identified. The spins and parities of the involved states were tentatively assigned on the basis of the systematic α-decay properties of the odd-proton N=127 isotones and shell model calculations. Keywords: Odd-proton N=127 isotones, Isomeric state, α-particle energy, Half-life, Shell model calculation, Spin and parity