Neutron excitations in even mass Sn nuclei

Abstract

Abstract High-spin neutron quasi-particle excitations in the even-mass 110–118Sn 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 Jπ = 6+ state at 2480 keV in 110 Sn(T 1 2 = 8.3±0.4 ns ) , the Jπ = 8− state at 3440 keV in 112 Sn(T 1 2 = 0.58±0.06 ns ) , the Jπ = 8− state at 3190 keV in 114 Sn (T 1 2 = 0.35±0.20 ns ) and the Jπ = 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 110–114Sn 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 Eλ 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.