Isotope shifts of the neutron-deficient bismuth isotopes: charge radii systematics across the Z = 82 shell closure

The isotope shifts (IS) of 202,203,204Bi have been measured on the 306.7 nm line using an extremely sensitive gas cell technique of laser spectroscopy. A King plot analysis of this data with other IS measurements in neighbouring isotope chains reveals that the known behaviour of relative changes in mean square nuclear charge radius is only strictly observed above the Z = 82 shell closure.