Fine structure in the alpha decay of even-even nuclei as an experimental proof for the stability of the Z=82 magic shell at the very neutron-deficient side

Fine structure has been observed in the α decay of ${}_{}{}^{202}{}_{}{}^{}\mathrm{Rn}$, ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Po}$, ${}_{}{}^{186,188}{}_{}{}^{}\mathrm{Pb}$, and ${}_{}{}^{180,182,184}{}_{}{}^{}\mathrm{Hg}$ and has led to the identification of low-lying $0^{+}$ states in ${}_{}{}^{198}{}_{}{}^{}\mathrm{Po}$, ${}_{}{}^{190,192,194}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{182,184}{}_{}{}^{}\mathrm{Hg}$, and ${}_{}{}^{176,178,180}{}_{}{}^{}\mathrm{Pt}$. The large variation in the hindrance factors of the α decay to the exicted $0^{+}$ state is a proof for the persistence of the Z=82 shell closure at the neutron-deficient side. Comparing the reduced widths of the α decays to the ground and excited states offers a unique way to probe the proton particle-hole character of the $0^{+}$ states in this region.