Ion mobility in liquid He[superscript 3] below 1°K

The low field mobility of positive and negative ions in liquid He 3 was measured for temperatures between 0.03°K and 10K and pressures of 27.9 atm, 7.5 atm, and less than 0.35 atm. Ions in the liquid were produced by a radioactive tritiated titanium source and their mobility was obtained by directly measuring their drift velocity using a time of flight technique which involved a multigrid system of electrodes. Details of the experimental procedures as well as of the experimental apparatus and its construction are given. The positive ion mobility, ~+, was found to be larger than the negative, ~_, except at 27.9 atm above 0.3°K, where both are ~ 0.036 2 cm Iv sec. By increasing the pressure, ~ was observed to increase while ~+ decreased. Furthermore, ~_ was found to be a continuous function of the temperature, reproducible within 1% throughout the entire temperature range of the measurements, while ~+ presented hysteresis in a temperature range that depended on the pressure. The experimental results are presented in both,graph and table forms.The systematic error involved in the absolute value of the mobility is less than 10%. The "cluster" model for the positive ion and the "bubble" model for the negative ion in liquid helium are discussed in some detail and 3 applied for liquid He. The temperature and pressure dependence of ll_ between 0.03°K and 0.07°K is in agreement with the theoretical prediction for the mobility of an electron localized in a bubble that undergoes Brownian motion in a Fermi gas. No theoretical calculation available predicts ll_ between 0.07°i< and 10K or ll+ correctly.U of I OnlyThesi