Width correlations and intermediate structure in the n-γ spectra of Au, Sb, I and Tb

Abstract

A search for non-statistical effects in the resonance neutron capture γ-ray spectra of Au, Sb, I and Tb is made through observation of the correlation between neutron and partial radiation widths, and through detection of intermediate structure in the intensity of high energy γ-rays, when plotted as a function of the neutron resonance energy. The integrated intensity method, which is used in the present measurements, is shown to be attractive for a faster mapping of width correlations. A high correlation of 0.96 for Tb and the zero values for Au and I are in agreement with the doorway state hypothesis of Lane. The 159Tb data show non-statistical behaviour, indicating the existence of a narrow intermediate structure with a width of about 40 eV, together with a high value for the correlation coefficient. No evidence for such structure is found in the earlier measurements of similar type on 115In and 187Re when the recently established run statistic is applied to the data. From several experimental facts it is concluded that the neutron capture decay process in Au is in complete agreement with the statistical model, in contrast to the earlier 2p-1h doorway hypothesis for this nucleus.