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