Influence of granulation of the diabase sample on the thermal neutron Σ Σ Σ Σ a measurement

The effective thermal neutron macroscopic absorption cross section Σ a of a heterogeneous material is lower than the cross section of the corresponding homogeneous material which contains the same components contributing in the same proportions. When rock materials are investigated the sample contains usually grains which create heterogeneity. The heterogeneity has to be considered in respect to the thermal neutron transport in the sample. The heterogeneity effect depends in this case on the mass contribution of highly- and low-absorbing centres, on the ratio of their absorption cross sections, and on their sizes. Final results of measurements can be perturbed by neglecting the heterogeneity effects. In the work, an influence of granulation of diabase sample on the result of the measurement of the cross section Σ a of diabase with Czubek's method has been experimentally investigated. The samples of two different granulations of diabase have been used, saturated with a few different fluid absorbers. The complex samples, being various combinations of these components, have allowed to interpret from the experiments an unperturbed value of the cross section Σ a of diabase and to establish the limit grain size for considering the medium as either homogeneous or heterogeneous. The results can be applied to other rock material of similar neutron properties.