The Effect of Crystal Orientation on the Scattering of Slow Neutrons

Abstract

A simple theory is developed for taking into account non-random orientations in microcrystalline material of the hexagonal system. The transmission of slow neutrons through extruded and through powdered graphite is measured experimentally and compared with the theory.

Porosity effects on the neutron total cross section of graphite

“…This effect has been studied in the early works of Refs. [6,7]. The present results show a smaller total cross section along the extrusion direction, in accordance with Ref.…”

“…1. Such differences have been reported on nuclear-grade graphites of different origins by several groups [6][7][8]5]. Whilst the difference between the first Bragg edge (at 0.0018 eV) and 0.03 eV can be ascribed to the crystallographic texture of the material, there is yet no satisfactory explanation for the cross section measured at energies below the first Bragg edge.…”

“…For the needle-coke graphite we used a cubic sample of 5 cm side. Previous works showed that the transmission of thermal neutrons through anisotropic materials depends on the neutron energy and the orientation of the sample [6,7,18].…”

“…The values of the calculated porosities (shown in Table 1) are in the range of variation observed on graphites (between 7% and 30% [16]). [6,8,5]) with calculation performed with the NJOY code.…”