Abstract
Measurements of rotational relaxation times in mixtures of normal deuterium and neon gas at temperatures of 290K, 480K, 700K and 900K are described. Using an ultrasonic frequency of 1MHz, acoustic absorptions and velocity dispersions were observed over a range of frequency upon pressure ratios of from 1MHz per atmosphere up to 100MHz per atmosphere. The equipment and its use is described, and its inherent limitations and sources of error are discussed. A variable path length technique was employed, using short bursts of tone. The received signal was phase sensitive demodulated with reference to the phase of the transmitted signal, and then it was time gated and averaged in the region of interest. The variation of this waveform with the ultrasonic path length was used to obtain both the absorption and the velocity of the ultrasound in the gas. Diffraction corrections for the radiation coupling from a disc to a disc were applied to the data. A new method of calculating these corrections is described, that could generate corrections for non piston-like transmitting and receiving discs in an absorbing medium. The analysis of the data is described in detail, showing how the various sources of experimental error were corrected. The results of calibration runs in neon gas are discussed, and then the results for pure deuterium, and for deuterium-neon mixtures are presented. These are put in the context of the results of other workers in this field, and then compared with available theoretical predictions.