Coulomb excitation of vibrational states in deformed even nuclei

Abstract

Low-lying states in deformed even rare-earth nuclei have been studied by Coulomb excitation with 43.5 MeV oxygen ions. Gamma rays from thin oxide targets (≈0.3 mg/cm 2) or thin metal targets (0.5–1.2 mg/cm 2) were observed in coincidence with back-scattered ions. The yields were normalized on the intensity of the scattered particles. Double groups of gamma rays ascribed to the 2 +′ → 0 + and the 2 +′ → 2 + transitions from K = 2 states were observed in Nd 150(1.07 MeV), Sm 152(1.09 MeV), Sm 154(1.44 MeV), Gd 156, Gd 158, Gd 160(1.02 MeV), Dy 160, Dy 162(0.89 MeV), Dy 164(0.77 MeV), Er 164(0.86 MeV), Er 166, Er 168, Er 170(0.93 MeV) and Yb 176(1.27 MeV), where the energies in the parentheses are given for 2 +′ states not observed earlier. Gamma rays ascribed to the 0 +″ → 2 +, 2 +″ → 0 + and 2 +″ → 2 + transitions from K = 0 states were observed in Nd 150(0.69 MeV), Sm 152, and Gd 154(0.68 MeV), where the energies are for the 0 +″ states. Gamma rays in Sm 154 and Gd 156 suggest K = 0 states at 1.10 and 1.06 MeV, respectively. The B(E2 values determined from the yields range from 2 to 8 single-particle units, being roughly inversely proportional to the excitation energies for the levels. The theory of multiple Coulomb excitation for the different bands was in qualitative agreement with the experimental observations.