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A new proton-unbound isotope $^{204}$Ac was produced in the fusion-evaporation reaction Tm(40169Ca,5n)204Ac and identified via the recoil-α correlation at the gas-filled recoiled separators SHANS2 and SHANS. The excitation function for producing $^{204}$Ac was measured and the optimal beam energy was evaluated to be 212 MeV. Nineteen ER - α1 - α2 - α3 decay chains were observed for this isotope. Based on these chains, the α-particle energy and half-life of $^{204}$Ac 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 $^{204}$Ac. In addition, more precise decay properties of Eα = 7883(15) keV and T1/2 = 7.7−1.6+2.7 ms were obtained for $^{205}$Ac.

The decay of $^{218}$Pa was investigated by means of α and γ spectroscopy. The nucleus was produced in the fusion reaction $^{40}$Ar+$^{182}$W and separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The known α decays of $^{218}$Pa 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 $^{218}$Pa 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.

The semi-magic nucleus $^{219}$Np was produced in the fusion reaction $^{187}$Re($^{36}$Ar, 4n)$^{219}$Np at the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). A fast electronics system based on waveform digitizers was used in the data acquisition and the sampled pulses were processed by digital algorithms. The reaction products were identified using spatial and time correlations between the implants and subsequent α decays. According to the observed α-decay chain, an energy of Eα=9039(40) keV and a half-life of T1/2=0.15−0.07+0.72 ms were determined for $^{219}$Np. The deduced proton binding energy of $^{219}$Np fits well into the systematics, which gives another evidence of that there is no sub-shell closure at Z=92. The influence of the N=126 shell closure on the stability of Np isotopes is discussed within the framework of α-decay reduced widths.