Investigation of the Capture Gamma-Ray Spectra for Individual Resonances in the 169Tm(n, γ) Reaction

Abstract

Recent studies of the high energy gamma ray spectra resulting from resonance neutron capture by 169Tm have indicated the existence of non-statistical effects in the form of neutron width-radiation width correlations [1,2]. These experiments have investigated resonances up to 160 eV using both Ge(Li) and Nal detectors. In the light of current developments in this field, the results would be important if it were not for the limited range of experimental data and the possibility of false correlations. These could be the result of poor time of flight resolution [1] or incorrect spin assignments [1,2], The latter is particularly important in the present case, since the resonance spins for s-wave capture are 0 or 1, with the result that neutron widths and partial radiation widths of spin 0 resonances are substantially enhanced. The most reliable resonance spin measurements to date are those of the Brookhaven group [3]. These assignments have been made by comparing the ratios of certain low energy capture gamma rays below 200 keV. The present experiment was carried out to check and extend the spin assignments and obtain a set of partial radiation widths up to 160 eV with improved time of flight resolution.