Extinction Effects in Neutron Transmission of Polycrystalline Media

Abstract

The effects of primary and secondary extinction are considered for neutron transmission work in the energy region where diffraction is important. It is shown that in typical studies the grain size is the most important parameter affecting extinction, with the mosaic block size and the angular spread of the mosaic blocks of secondary importance. Experiments were performed to corroborate the theory, and criteria are set up to avoid extinction effects. It is shown how to determine the mosaic block size and the angular spread of the mosaic blocks in substances with large grain size by using fine resolution near the last crystalline cutoff, where the breadth of the Bragg peak becomes large compared to the angular misalignment of the mosaic blocks.