Discovery of 109Xe and 105Te:: Superallowed α decay near doubly magic 100Sn

Two new alpha emitters Xe-109 and Te-105 were identified through the observation of the Xe-109 -> Te-105 -> Sn-101 alpha-decay chain. The Xe-109 nuclei were produced in the fusion-evaporation reaction Fe-54(Ni-58,3n)Xe-109 and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at E-alpha=4062 +/- 7 keV and E-alpha=3918 +/- 9 keV were interpreted as the l=2 and l=0 transitions from the 7/2(+) ground state in Xe-109 (T-1/2=13 +/- 2 ms) to the 5/2(+) ground state and a 7/2(+) excited state, located at 150 +/- 13 keV in Te-105. The observation of the subsequent decay of Te-105 marks the discovery of the lightest known alpha-decaying nucleus. The measured transition energy E-alpha=4703 +/- 5 keV and half-life T-1/2=620 +/- 70 ns were used to determine the reduced alpha-decay width delta(2). The ratio delta Te-105(2)/delta Po-213(2) of similar to 3 indicates a superallowed character of the alpha emission from Te-105.