Discovery of the alpha decay of 109I

Alpha emission is a rich source for nuclear-structure information [1]. The alpha-particle energies E$_{\alpha}$, corrected for the recoil effect, yield the difference between the ground-state masses of parent and daughter nuclides (Q$_\alpha$). Far from stability the determination of Q$_\alpha$ often represents the only way to determine the masses of ground and isomeric states. The evolution of Q$_\alpha$ values along an alpha-decay chain are also a probe for shell effects. In the region above $^{100}$Sn an alpha-decay island occurs, its presence is related to the strong Z=50, N=50 double shell-closure. In an experiment performed at the Recoil Mass Separator of the HRIBF at Oak Ridge National Laboratory, the first evidence for the alpha-decay branch of the proton-emitter $^{109}$I was obtained. The results and the consequences for nuclear masses in this region will be discussed. \newline [1] E. Roeckl, Alpha decay, in: {\it Nuclear Decay Modes}, ed. D.N. Poenaru, IoP Publishing, 1996, p. 237.