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A new proton-unbound isotope 204Ac 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 204Ac 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 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 Eα = 7883(15) keV and T1/2 = 7.7−1.6+2.7 ms were obtained for 205Ac.

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]

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. [ABSTRACT FROM AUTHOR]