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

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