THE AMORPHIZATION PROCESS OF NEUTRON-IRRADIATED CRYSTALLINE QUARTZ STUDIED BY BRILLOUIN-SCATTERING

Brillouin scattering has been used to measure the acoustic velocity and attenuation of hypersonic wave for neutron-irradiated quartz crystals. Velocity and attenuation show a maximum value as a function of neutron dose. This maximum is interpreted as a transition between two regions. For neutron doses below this maximum, irradiated quartz remains essentially crystalline, while the amorphous character is dominant above the maximum. This picture is in accord with older results derived from annealing studies. A phenomenological description of the amorphization process based upon the behaviour of the acoustic properties, taking into account competition between crystalline and amorphous character, thermally activated structural relaxation and change of symmetry of the crystalline part during irradiation, is given.