Charge radii of radium isotopes

We present a combined analysis of the available isotope-shift data from the optical spectra of Ra atoms and Ra+ ions. Atomic structure calculations of the field-shift and specific mass-shift constants of the low-lying levels in Ra+ are used. The nuclear radial differences delta for the radium isotopes are derived and compared to previous analyses and nuclear models. We discuss the relevance of our results to measurements of atomic parity violation in a chain of Ra+ isotopes.