-decay properties of new neutron-deficient isotope ²⁰³Ac

A new isotope Ac-203 was produced in the reaction Ca-40 + Tm-169 at beam energy of 226 MeV. One correlated alpha-decay chain was attributed to Ac-203. The alpha-particle energy and half-life were determined to be 8217(16) keV and 56(-26)(+269) mu s, respectively. The reduced alpha-decay width (delta(2)) of Ac-203 was deduced to be 1096(-906)(+921) keV, which indicates a favored alpha decay. The systematics of delta(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 Ac-203 was extracted as -1214(22) keV and the systematics of S-p for odd-A isotopes beyond proton drip line were discussed.