Resonance overlap: effect of neighbouring resonances

The neutron flux in the region of, and beJow a resonance is considered. The results of Goldstein which give an asymétrie flux shape in the region of a resonanceqre adjusted to allow for neutron absorption in the resonance, and gives reasonable agreement with the computed results. A simple form.ula for the calculation of the absorption in a resonance is developed, and it is found that it satisfactorily expresses the dependence of absorption On the total scattering cross section, and the energy of resonance, but gives a greater variation with temperature than is so. The approximation is found to be suitable for estimating the flux perturbation effects caused by neutron absorption. Maximum flux depression occurs at about .9 of a moderator collision range above the resonance lethargy. Flux perturbations from a resonance cause slight variations in the absorption by a lower resonance, when the separation lethargy is about one moderator lethargy interval. This effect is estimated and compared with calculated values. A value of about 1 per cent increase in the reduction of absorption is found to occur for predominantly absorbing resonances.