Double giant resonances in atomic nuclei

Giant resonances are collective excitations of the nucleus in which a large fraction of the component nucleons are set into coherent modes of vibration. Double giant resonances, in which vibration is excited in a nucleus already undergoing a giant resonance, were predicted thirty years ago, but have only recently been observed experimentally. Their properties confirm broad aspects of nuclear structure theory, but show some anomalies that have yet to be explained.