Measured magnetic moments of 2₁⁺ states in ^190-198Pt and interacting boson model description of M1 systematics in the platinum isotopes

The g-factor of the 2₁⁺ state in ¹⁹⁰Pt has been measured for the first time using the thin-foil transient-field technique with a target enriched (to 4.19%) in ¹⁹⁰Pt. Precessions for the 2₁⁺ states of ^{190,192,194,196,198}Pt were measured simultaneously. The Coulomb excitation cross section to the 2₁⁺ state in ¹⁹⁰Pt was also measured relative to the 0₁⁺ → 2₁⁺ excitations in ¹⁹⁴Pt and ¹⁹⁶Pt. The near constancy of g(2₁⁺) for the even ^190-198Pt isotopes is in marked contrast with the behaviour observed in neighbouring even ^182-186W and ^186-192Os nuclei and the predictions of the proton-neutron interacting boson model in the limit of F-spin symmetry. It is shown that the observed g-factor and M1 transition systematics in the Pt isotopes can be described by appropriate F-spin symmetry breaking, while maintaining satisfactory descriptions of the energy levels and E2 properties.