EXPERIMENTAL ASPECTS OF THE STATISTICAL-THEORY OF NUCLEAR SPECTRA FLUCTUATIONS

A measurement of neutron resonance parameters of 156Gd was performed, up to a neutron energy of 2240 eV, in an attempt to realize favourable conditions for testing statistical theories of spectra fluctuations. The experiment was carried out at the electron linear accelerator of Geel (Euratom). The comparison between the measured resonances and the predictions of the random-matrix theory was faced by analysing also the set of gΓn values and by including in the theoretical model the effects of the finite observability threshold and of the presence of resonances excited by p-wave neutrons. The average spacing, D = 35.5 ± 2 eV, the s- and p-wave strength functions, 104S0 = 1.83±0.34 and 104S1 = 2.1±0.5, were determined without assigning the parity of the resonances. The statistical properties of the sequence of the measured resonance parameters were found to be in agreement with the predictions of the Gaussian orthogonal ensemble. The purity" of a sequence of resonances was found to be better determined by measuring their gΓn values than by the use of purity tests based on their energies. The limitations to the detectability of possible deviations from the theory are discussed. © 1979."