Spectral statistics and the fine structure of the electric pygmy dipole resonance in N=82 nuclei

We study the statistical properties of the electric pygmy dipole resonance in four different isotones with neutron number N = 82. These nuclei are Ba-138(56), Ce-140(58), Nd-142(60), (144)(62)sm. The data set comprises levels with spin and parity J(pi) = 1(-) and their ground state B(E1) transition strengths. The statistics are found to be mixed, i.e., in between the predictions of random matrix theory for correlated and uncorrelated spectra. Moreover, we calculate spectra and transition strengths in the quasiparticle phonon model (QPM). We compare experimental and theoretical findings. The incompleteness of the data sets and its impact on the results is discussed. A consistent picture emerges which yields an improved understanding of the statistical properties of the pygmy resonance. (C) 2004 Elsevier B.V. All rights reserved.