Evert Jan Hengeveld

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

Abstract High-spin states in 194, 196 pb have been investigated using the 188 Os( 12 C, χn) 194, 196 Pb and the 198 Hg(α, 6n) 196 Pb 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 194 Pb and 196 Pb have been extended up to states with J π = 15 − ( E = 3955 keV) and J π = 20 + ( E = 5444 keV), respectively. All levels except two new isomers which have most likely spin and parity J π = 10 − ( 194 Pb ) and J π = 11 − ( 196 Pb ) 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 ( i 13 2 ) 2 configuration. Levels with spin 12 J i 13 2 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 J π = 20 + state observed in 196 Pb has a pure ( i 13 2 ) 4 configuration. The two new isomers have most likely a proton 2p2h structure. The excitation energy of the J π = 11 − isomer in 196 Pb agrees with that predicted for a deformed 1 2 + [404] − 29 2 − [514] 13 2 + [606] 11 − state.