Fine Structure in the Alpha-Decay of the Neutron-Deficient ¹⁹¹Po and ¹⁹¹Bi Isotopes

摘要

The α-decay properties of the neutron-deficient ¹⁹¹Po and ¹⁹¹Bi nuclei have been investigated at the RITU gas-filled separator using the 5n and p4n evaporation channels of the ³⁶Ar+¹⁶⁰Dy→¹⁹⁶Po^? reaction. In contrast to previous studies two α-decaying isomeric states were observed in the decay of ¹⁹¹Po. Evidence was found for α-decay to excited levels in the ¹⁸⁷Pb daughter nucleus. The tentative interpretation of these levels could be a weak coupling of the odd neutron to an intruder 2p–2h deformed 0⁺ state in the even-even core. The difference in the reduced α widths of the α transitions towards the ground state and excited state points to a deformed 13/2⁺ isomeric state in ¹⁹¹Po. Branching ratios of b_α(^187mPb)=12(2)% and b_α(^187gPb)=7(2)% have been experimentally measured. For ¹⁹¹Bi two new alpha-lines have been observed. A more precise half-life value of T_1∕2 = 115(10)ms was determined for ^191mBi.