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

Fine structure has been observed in the \ensuremath{\alpha} 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 \ensuremath{\alpha} 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 \ensuremath{\alpha} 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.