Measurement of cross-sections and resonance absorption integrals by the oscillation method

The authors used the oscillation method to measure reaction rates and to derive the cross-sections from them. To obtain maximum efficiency from the method they developed original applications designed to produce, depending on the nature of the material and cross-section to be investigated, measurement conditions which would permit the attainment of maximum accuracy and at the same time facilitate interpretation of the results in work with a fully known neutron spectrum. The phase oscillation method was used at ZOE to measure the thermal absorption cross-sections of materials with little capacity for capture but marked capacity for scattering, since it permits attenuation of the diffusion effect by a considerable factor with a measuring point located in the reflector, i.e. in a well-thermalized medium . The results obtained by this method for absorption cross-sections at 2200 m/s are given. The conventional amplitude oscillation method was used at the MINERVE reactor to measure the reaction rates produced by small samples. The measurements were made at the centre of the core, without a cadmium filter, in a spectrum with a great abundance of epithermal neutrons. By deducting the thermal part, the authors derived the resonance integral from the measured cross-section by calibration with reference to gold. The samples used were in the form of solutions or plates. To derive the values at infinite dilution or at zero thickness, they extrapolated the results obtained for different concentrations or thicknesses, adopting the self-shielding factors calculated according to the ZUT programme and checking to see that they confirmed the experimental results. The resonance integrals measured, not including the 1/V part, are given. For materials whose resonance parameters are known with sufficient accuracy, the measured values are compared with those calculated or measured by different authors. (author)