Search

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 (δ2) of 203Ac was deduced to be 1096−906+921 keV, which indicates a favored α decay. The systematics of δ2 and single-particle energy levels indicate that the new state probably arises from the intruder s1/2 configuration, which shows an onset of deformation in Ac isotopes. The proton separation energy Sp of 203Ac was extracted as −1214(22) keV and the systematics of Sp for odd-A isotopes beyond proton drip line were discussed.

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.