Paul Garrett, University of Guelph
Do nuclei vibrate?
Argonne Physics Division Seminar - 16 Nov 2009

One of the most fundamental excitation modes of nearly every macroscopic system, and many microscopic systems, are vibrational modes. From vibrating strings to vibrational molecular states, the importance of these excitations is without question. On the subatomic level, nuclei have long been considered to possess surface vibrational states, an idea that emerges naturally from the picture of the nucleus as a liquid drop. From the early 1950's onward with the development of the Bohr model, low-lying states in nuclei, especially spherical nuclei, are often interpreted as possessing vibrational, or multi-phonon, excitations. The stable cadmium nuclei have, for several decades, been suggested as some of best examples of vibrational states in nuclei, with some suggestions of excitations up to the 5'th or 6'th harmonic. Recent systematic and detailed spectroscopy of the Cd isotopes employing a variety of complementary techniques has revealed, however, serious departures from the expected properties of the multi-phonon states, leading us to conclude that vibrational motion breakdown at the 3-phonon level. Further, the detailed data now available suggests an alternative description of the low-lying states in the Cd isotopes; a description that could be tested in experiments at ATLAS that could result in a fundamental shift in our understanding of collectivity in nuclei.

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