Superallowed α Decay to Doubly Magic 100Sn

We report the first observation of the ¹⁰⁸Xe → ¹⁰⁴Te → ¹⁰⁰Sn α -decay chain. The α emitters, ¹⁰⁸Xe [E_α=4.4 (2 ) MeV , T_{1 /2}=5 8_-23⁺¹⁰⁶ μ s ] and ¹⁰⁴Te [E_α=4.9 (2 ) MeV , T_{1 /2}<18 ns ], decaying into doubly magic ¹⁰⁰Sn were produced using a fusion-evaporation reaction ⁵⁴Fe (⁵⁸Ni, 4 n ) ¹⁰⁸Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of ²¹²Po into doubly magic ²⁰⁸Pb. Enhanced proton-neutron interactions in the N =Z parent nuclei may result in superallowed α decays with reduced α -decay widths significantly greater than that for ²¹²Po. From the decay chain, we deduce that the α -reduced width for ¹⁰⁸Xe or ¹⁰⁴Te is more than a factor of 5 larger than that for ²¹²Po.