Fine-structure in the alpha-decay of even-even nuclei - experimental-evidence for the stability of the z=82 magic shell

The fine structure in the alpha decay of even-even Po, Pb, Hg and Pt isotopes has been studied. Feeding towards low-lying 0+ states in the 196,198Po, 190,192,194Pb, 182,184Hg and 176,178,180Pt isotopes is observed. The energy systematics of the positive parity states in the light Po isotopes indicates the appearance of shape coexistence in these nuclei as well. The hindrance factors of the alpha decay towards the excited 0+ states has been interpreted in a two-level mixing calculation. It offers a probe for the identification of the proton particle-hole character of the 0+ states in this region and strongly supports the persistence of the Z = 82 shell closure in the light Pb isotopes.