ULTRASONIC STUDY OF THE TUNNELING STATES IN QUARTZ AMORPHIZED BY NEUTRON-IRRADIATION

The ultrasonic absorption and velocity change is measured in neutron irradiated quartz, for a dose of 1 x 10(20) n/CM2. These experiments are carried out as a function of temperature at two different frequencies. The results are analysed using the tunneling model and the TS-parameters PBAR and gamma1 are derived from numerical fits. A comparison with previous measurements reveals that the increase of PBAR with the dose, observed so far, is no longer continued; instead a remarkable drop of the density of states is found in this highly irradiated sample. This confirms that a considerable part of the TS in samples that are only slightly damaged by irradiation must be attributed to the defective crystalline regions rather than to the radiation induced amorphous regions.