Discovery of Xe109 and Te105: Superallowed α decay near doubly magic Sn100

Two new α emitters Xe109 and Te105 were identified through the observation of the Xe109→Te105→Sn101 α-decay chain. The Xe109 nuclei were produced in the fusion-evaporation reaction Fe54(Ni58,3n)Xe109 and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at Eα=4062±7keV and Eα= 3918±9keV were interpreted as the l=2 and l=0 transitions from the 7/2+ ground state in Xe109 (T1/2=13±2ms) to the 5/2+ ground state and a 7/2+ excited state, located at 150±13keV in Te105. The observation of the subsequent decay of Te105 marks the discovery of the lightest known α-decaying nucleus. The measured transition energy Eα= 4703±5keV and half-life T1/2=620±70ns were used to determine the reduced α-decay width δ2. The ratio δTe1052/δPo2132 of ∼3 indicates a superallowed character of the α emission from Te105.