Elsevier

Nuclear Physics A

Volume 449, Issue 3, 24 February 1986, Pages 579-602
Nuclear Physics A

High-spin neutron excitations in neutron-deficient even-mass Pb isotopes

https://doi.org/10.1016/0375-9474(86)90235-6Get rights and content

Abstract

High-spin states in 194, 196pb have been investigated using the 188Os(12C, χn)194, 196Pb and the 198Hg(α, 6n)196Pb reactions. The experiments included γ-ray excitation function, γ-γ coincidence, γ-∑γ coincidence, γ-ray angular distribution, lifetime and conversion electron measurements. The level schemes of 194Pb and 196Pb have been extended up to states with Jπ = 15 (E = 3955 keV) and Jπ = 20+ (E = 5444 keV), respectively. All levels except two new isomers which have most likely spin and parity Jπ = 10 (194Pb) and Jπ = 11 (196Pb) can be interpreted as neutron excitations. The excitation energies of levels with spin J ⩽ 12 are well accounted for by the one-broken-pair model including 1p1h excitations. The B(E2, 12+ −10+) values reflect the systematic trend for a pure (i132)2 configuration. Levels with spin 12 < J < 20 can be described as two-broken-pair model configurations. The excitation energies of these states can be reproduced quite well in a phenomenological approach in which two i132 neutron holes are coupled to core excitations in the A + 2 nucleus and also by calculations performed within the two-broken-pair model. Within this framework the Jπ = 20+ state observed in 196Pb has a pure (i132)4 configuration.

The two new isomers have most likely a proton 2p2h structure. The excitation energy of the Jπ = 11 isomer in 196Pb agrees with that predicted for a deformed 12+[404]292[514]132+[606]11 state.

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    Present address: Institute for Nuclear Studies, Swierk, Poland.

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