X-ray diffraction profiles fron neutron-irradiated LiF single crystals

The detailed measurement of the Bragg line profiles of several X-ray reflections from six single-crystal samples of LiF irradiated under different and well defined conditions in the core of a swimming-pool type nuclear reactor are reported. The crystals were irradiated with three different spectra: (a) total neutron spectrum plus the γ background radiation, (b) same as (a) without thermal neutrons, the crystal being wrapped in a cadmium foil, and (c) the background γ radiation alone. The experimental results presented display the changes in the profiles due to the different radiation spectra used and to the change in irradiation temperature within the interval from 113 to about 173°C. That peak intensities decrease while integrated intensities increase with irradiation is a well known result amply confirmed here. Integrated intensities in these experiments increase from 4 to 14 times with respect to the unirradiated crystal. The strongest reflections (111, 200 and 220) experienced the highest increases. The influence of the temperature of irradiation has been verified through measurements of reflections 111, 200 and 220 from crystals irradiated at temperatures of 113, 148 and 173°C. As the irradiation temperature rises the peak intensities clearly tend to those of the unirradiated crystal while integrated intensities attain a maximum at about 150°C. The results also indicate that at least under the conditions prevailing in the present experiments the highest amount of damage is due to thermal neutrons (E ≤ 0.45 eV).