Cross section measurements of fissile nuclei for slow neutrons

It presents the experimental measurements of cross section of fissile nuclei for slow neutrons to improve the understanding of some heavy nuclei of great importance in the study of nuclear reactors. The different experiments are divided in three categories. In the first part, it studied the variation with energy of the cross sections of natural uranium, 233U, 235U and 239Pu. Two measurement techniques are used: the time-of-flight spectrometer and the crystal spectrometer. In a second part, the fission cross sections of 233U and 239Pu for thermal neutrons are compared using a neutron flux from EL-2 going through a double fission chamber. The matter quantity contained in each source is measured by counting the α activity with a solid angle counter. Finally, the average cross section of 236U for a spectra of neutrons from the reactor is measured by studying the β activity of 237U formed by the reaction 236U (n, γ) 237U in a sample of 236U irradiated in the Saclay reactor (EL-2). (M.P.)