Nearest-neighbour-spacing distribution of low-lying nuclear energy levels

The simple expression for the nearest-neighbour-spacing (NNS) distribution of energy levels of partially chaotic systems that has recently been proposed to interpolate between the Poisson and Wigner distributions is shown to provide a reasonable description of the level statistics of nuclei in the ground-state region and give a fast estimation of the fractional volume of the regular region of the corresponding classical phase space.