Structural Behaviour of Neutron Irradiated Quartz

X-ray and density studies have been made on single crystals of quartz irradiated with fast pile neutrons at approximately 100 deg C. The structural effects of the irradiation follow at least two processes with doses up to 1.2 x 10/sup 20/ neutrons/cm/sup 2/. Crystals irradiated with less than 3 x 10/sup 19/ neutrons/cm/sup 2/ expand anisotropically in a manner that is similar to the thermal expansion of unirradiated quartz. In this dosage range the volume increase is the same, as determined by x-ray and hydrostatic methods, and littie or no distortion is observed in x-ray diffraction patterns. The model which seems to fit these results best consists of point defects and slightly disordered regions which result in an elastic distention of the lattice. After doses in excess of 3 x 10/sup 19/ neutrons/cm/sup 2/ the damaging process is more complex since the volume change indicated by x-ray measurements of the host lattice becomes larger than the bulk volume change determined hydrostatically. After irradiation with 8 x 10/sup 19/ neutrons/cm/sup 2/ an inhomogeneous shear strain is observed in the extreme skewing of the (22.0) reflection which is interpreted as being due to the crowding of oxygen ion interstitials into the open c-axis channels. Amorphous regions enmeshed in the host lattice are identified in crystals that still possess long range order after irradiation with 7 x 10/sup 19/ neutrons/cm/sup 2/. The diffuse x-ray scattering halo associated with the amorphous material changes peak position, shape, and intensity with increasing dosages of irradiation. It is suggested that these changes result from a reorientation of disordered regions which is assisted by the increased expansion of the lattice and the presence of ruptured silicon--oxygen bonds. A second kind of diffuse scattering appears at these high doses which cannot be accounted for on the basis of a thermal origin but is probably related to scattering resulting from imhomogeneous lattice strains. In a complementary study it was found that coesite, a high density crystalline silica remained stable under neutron irradiation dosages which completely disorder quartz. These results indicate that the rate of damage in silica solids is structure dependent. (auth)