Shape polarization in the tin isotopes near N = 60 from precision g-factor measurements on short-lived 11/2⁻ isomers

The g factors of 11/2⁻ isomers in semimagic ¹⁰⁹Sn and ¹¹¹Sn (isomeric lifetimes τ=2.9(3) ns and τ=14.4(7) ns, respectively) were measured by an extension of the Time Differential Perturbed Angular Distribution technique, which uses LaBr₃ detectors and the hyperfine fields of a gadolinium host to achieve precise measurements in a new regime of short-lived isomers. The results, g(11/2⁻;¹⁰⁹Sn)=−0.186(8) and g(11/2⁻;¹¹¹Sn)=−0.214(4), are significantly lower in magnitude than those of the 11/2⁻ isomers in the heavier isotopes and depart from the value expected for a near pure neutron h_11/2 configuration. Broken-symmetry density functional theory calculations applied to the sequence of 11/2⁻ states reproduce the magnitude and location of this deviation. The g(11/2⁻) values are affected by shape core polarization; the odd 0h_11/2 neutron couples to J^π=2⁺,4⁺,6⁺.. configurations in the weakly-deformed effective core, causing a decrease in the g-factor magnitudes.