Excited states in 146Sm and 147Sm

Abstract

The 144, 146Nd(α, χn) and 146,148Nd( 3He, χn) reactions with E α = 20–43 MeV and E 3He , = 19–27 MeV are used to investigate excited states in the isotopes 146Sm and 147Sm. The experiments involve measurements of singles γ-ray spectra and conversion electron spectra, γ-ray angular distributions and three-parameter ( E γ - E γ -time) coincidences. From these experiments information is obtained for states with spin up to I = 13 + and I = 27 2 − , respectively. These states are interpreted within the framework of the cluster-vibration model (CVM) as well as the shell model. In the latter approach, the energies of several well established states, in both isotopes, are calculated using empirical singleparticle energies, empirical two-particle interaction matrix elements and angular momentum algebra. The average deviation between the calculated and the experimental energies is less than 100 keV. The CVM calculations involve the coupling of a three-particle neutron cluster to the quadrupole vibration of the core. For 147Sm, these calculations reproduce the observed sequence of states based on the I π = 7 2 − ground state, as well as the sequence of states based on the I π = 13 2 + excited state. The CVM calculations also reproduce the ground band in 146Sm, while for the negative parity states based on the cluster (f 7 2 i 13 2 ) 3 − −10 − an additional shift in energy is expected due to the mixing with octupole phonons.