Nuclear Relaxation of Solid Helium-3 in the bcc Phase

We have carried out measurements of the nuclear transverse and longitudinal relaxation times $T_2$ and $T_1$ in solid helium-3 between 0.35 and 2°K. Measurements over the whole density range in the bcc phase and for several frequencies between 0.3 and 8.2 Mc/sec are presented. The value of the nuclear exchange parameter $J$ is determined from the $T_2$ measurements using the theory of exchange narrowing first proposed by Anderson and Weiss. The parameter $J$ is also obtained from the longitudinal relaxation time, which is equal to the relaxation time between Zeeman and the exchange bath over the temperature range where $T_1$ is temperature-independent. A third determination of $J$ comes from the temperature-dependent $T_1$ below about 0.6°K, which is interpreted as the exchange lattice relaxation. The values of $J$ from the three different methods are found to agree within experimental error for all the densities investigated. The results are compared with those of the IBM and Oxford workers. A study of the linewidth as a function of frequency shows the expected narrowing as the frequency is increased. To our knowledge, this is the first systematic investigation of the $T_2$ variation in strongly exchange-narrowed lines that is being reported.