Nuclear size isomers

Developing of methods of measuring the radii of nuclei in their highly excited states led to observation of those with dimensions enhanced and, probably, diminished in comparison with the corresponding ground states. Experimental data including very recent ones demonstrating that such "size isomers" belong to two groups: excited states having neutron halos (in C-13, Be-11 and Be-9) and some specific cluster states (in C-12, C-13 and B-11), are discussed.