Levels and γ-ray transitions in ¹⁹⁰Os, a perturbed O(6) nucleus

Levels up to 2.5 MeV in ¹⁹⁰Os have been studied with the (n, γ) and (n, e^-) reactions at thermal and resonance energies. Transition multipolarities were deduced from the measured conversion coefficients and from L- and M-subshell ratios. Due to the nature of the (n, γ) reaction, the level scheme developed stresses low spin states and is complementary to those already existing based on the (α, xn) reaction and on β-decay from high spin parent states. The level populations are shown to lead to a new use of population systematics to extract nuclear structure information. The remarkable decay characteristics of the excited 0⁺ states are also studied and explained as a natural consequence of the interacting boson approximation model of Arima and Iachello. The full set of positive purity levels below the pairing gap is interpreted in terms of this model, specifically, in terms of the transition from the O(6) limit characterizing ¹⁹⁶Pt toward the deformed symmetric rotor limit.