High-spin levels in138Ce and140Nd Observed in the (?, 4n ?) reactions

Abstract

Levels of138Ce and140Nd have been studied using the138Ba(α,4nγ)138Ce and140Ce(α, 4nγ)140Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7−, 5−, 6− and 10+ can be explained by two-quasiparticle neutron configurations of the types (h 11/2 −1 ,d 3/2 −1 ) 7− , (h 11/2 −1 ,S 1/2 −1 ) 5−, 6− and (h 11/2 −2 ) 10+. Several high-spin states observed in138Ce and140Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3− state at an energy of 2,137.4 keV is observed in138Ce. The evidence for the existence of the low-lying 3− states in140Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7−) isomeric state in138Ce another state at 3,538.5keV (10+) with a half life of about 200 ns has been observed. The observed levels in the138Ce and140Nd nuclei are compared with theoretical predictions using delta force interaction.