Tunneling states in neutron-irradiated quartz: Measurements of the ultrasonic attenuation and velocity change.

Abstract

We report the results of a systematic investigation of the tunneling states (TS's) in neutron-irradiated quartz. Measurements of the acoustic absorption and the variation of the velocity of sound were carried out as a function of temperature (0.3--300 K) and in the ultrasonic frequency range 200--700 MHz, on quartz specimens exposed to different neutron doses. From numerical fits of the data with the tunneling model, including Raman processes, the density of states P\ifmmode\bar\else\textasciimacron\fi{} and the coupling parameter ${\ensuremath{\gamma}}_{\mathit{l}}$ were determined independently. A comparison of the TS parameters obtained from both attenuation and velocity measurements with each other and with our previous ultrasonic-attenuation studies and with thermal-conductivity and vibrating-reed experiments shows that the results are qualitatively in agreement with each other, but indicates some shortcomings of the tunneling model, also observed in glasses. TS parameters deduced from experiments which probe TS's of different parts of the distribution function are systematically found to be slightly different. The results are further related to studies of the damage induced by neutron irradiation in quartz. The differences in dose units, used by different authors, are considered more closely, which leads to a consistent picture of the damage-related parameters and allows a more reliable comparison between the TS and the damage.