Trends in heavy nuclei
Changes in the mean square charge radius of nuclei derived from
laser measurements of isotope shifts as a function of neutron number for 11
different heavy elements. This plot shows that the charge radius tends to
increase as neutrons are added along the isotope chains. (Note that the spacing
between the chains shown here is only representative.) Naturally occurring
isotopes are shown as solid circles, and radioactive isotopes as hollow
circles. The fact that the gradient along the isotope chains is less than the
trend through the sequence of stable isotopes running from hafnium up to
bismuth (green line), implies that neutron-rich isotopes develop a neutron-rich
skin or mantle. The lighter isotopes of several elements show unusual shape
effects (notably gold) and a phenomenon known as size staggering (e.g. in lead
and thallium) is a common feature in most chains. A number of long-lived
excited nuclear states (isomers) have been measured and two of these results
are shown by stars.