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Level Statistics of Near-Yrast States in Rapidly Rotating Nuclei

M. Matsuo·T. Døssing·E. Vigezzi·S. Åberg
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Abstract

The nearest neighbour level spacing distribution and the $Δ_3$ statistics of level fluctuations associated with very high spin states ($I \gesim 30$) in rare-earth deformed nuclei are analysed by means of a cranked shell model. The many particle-many hole configurations created in the rotating Nilsson potential are mixed by the surface-delta two-body residual interaction. The levels in the near-yrast region show a Poisson-like level spacing distribution. As the intrinsic excitation energy $U$ increases, the level statistics shows a gradual transition from order to chaos, reaching at $U \gesim 2$ MeV the Wigner distribution typical of the Gaussian orthogonal ensemble of random matrices. This transition is caused by the residual two-body interaction. On the other hand, the level spacings between the yrast and the first excited state show a peculiar behaviour, displaying a Wigner-like distribution instead of the Poisson-like distribution seen for the other near-yrast rotational states. The lowest spacings reflect the properties of the single-particle orbits in the mean-field, and are only weakly affected by the residual two-body interaction.

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M. Matsuo, T. Døssing, E. Vigezzi, S. Åberg. 1997-03-22. Level Statistics of Near-Yrast States in Rapidly Rotating Nuclei. https://doi.org/10.1016/s0375-9474(97)00170-x

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