Neutron excitations in even mass Sn nuclei

Abstract High-spin neutron quasi-particle excitations in the even-mass 110–118 Sn nuclei have been investigated using Cd(α, 2nγ)Sn reactions. The experiments included γ-ray excitation function, γ-γ coincidence, lifetime, γ-ray angular distribution, γ-ray linear polarization and conversion electron measurements. Four new isomeric states were identified, i.e. the J π = 6 + state at 2480 keV in 110 Sn(T 1 2 = 8.3±0.4 ns ) , the J π = 8 − state at 3440 keV in 112 Sn(T 1 2 = 0.58±0.06 ns ) , the J π = 8 − state at 3190 keV in 114 Sn (T 1 2 = 0.35±0.20 ns ) and the J π = 7 − state at 2909 keV in 116 Sn (T 1 2 = 0.5±0.3 ns ) . These isomers and in addition several new levels observed in 110–114 Sn can be related to neutron quasi-particle excitations. Spin and parity assignments to known levels are firmly established. The data are interpreted within the framework of the broken-pair model, including proton 1p-1h excitations. Excitation energies and static moments are well accounted for by this model. Experimental transitions rates however, are not always well reproduced by the calculations, especially for E λ decays between excited states of the type J → J - λ . It is argued that in such cases collective two-broken-pair admixtures dominate the transitions.