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Entropy in hot 161,162Dy and 171,172Yb nuclei

M. Guttormsen, A. Bjerve, M. Hjorth-Jensen, E. Melby, J. Rekstad, A. Schiller, S. Siem, A. Belic

nucl-exarXiv:nucl-ex/9911011

Abstract

The density of accessible levels at low spin in the (3He,αγ) reaction has been extracted for the 161,162Dy and 171,172Yb nuclei. The entropy of the even-odd and even-even nuclei has been deduced as a function of excitation energy, and found to reach a maximum of 15 kB before neutron evaporation. The entropy of one quasi-particle outside an even-even core is found to be 1.70(15) kB. This quasi-particle picture of hot nuclei is well accounted for within a simple pairing model. The onset of two, four and six quasi-particle excitations in the 162Dy and 172Yb nuclei is discussed and compared to theory. The number of quasi-particles excited per excitation energy is a measure for the ratio of the level energy spacing and the pairing strength.

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