Gamma-ray studies of the γ-vibrational band of 166Er

Abstract

Improved energy and intensity values have been obtained for the γ-radiation emitted in the decay of 1200 y 166Ho, 27 h 166Ho and 7.7 h 166Tm. These data have been used to investigate the mixing between the ground state band and the γ-vibrational band of 166Er. The effect of this mixing on the interband E2 transition probabilities is discussed from the points of view of the conventional ΔK = 2 band-mixing picture and of the generalized approach of Mikhailov. The former picture has been extended to treat the situation in which the intrinsic quadrupole moments of the two bands are unequal, and the resultant expressions are presented. The analysis yields a value of 0.041 ± 0.002 for the band-mixing parameter z γ and indicates that, contrary to the conclusions of some previous analyses, the intrinsic quadrupole moments of these two bands in 166Er are equal. An odd-even shift in the energies of the members of the γ-vibrational band is observed and is found to be well described by a term of the form (−)′ A 4( I−1) I( I+1)( I+2) with A 4 = + (0.079 ± 0.007) eV. This value is roughly an order of magnitude smaller than that expected based on the results of the band-mixing analysis of the interband y-ray transition probabilities. Evidence for the existence of M1 transitions within the γ-vibrational band of 166Er is presented. These data suggest that | g K- g R| is constant within the band and has the value ≈ 0.11. A hindrance factor of ≈ 400 with respect to the single-particle estimate is inferred for these M1 transition probabilities.