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

• Received 16 May 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.082501