Nuclear charge radii and electric monopole transitions in the interacting boson model

The interacting boson model (IBM) of Arima and Iachello is applied to calculate nuclear charge radii and electric monopole transitions of even-even nuclei in the rare-earth region. Consistent operators are used for the two observables. A relation between summed M1 strength and $\rho (\mathrm{E}0)$ values is pointed out.