Detection of trapping of He3 impurities in He4 crystals

NMR measurements of the diffusion coefficient D of He3 impurities in solid He4 containing 2−4% He3 were made. It is shown that in the region of the low-temperature plateau the diffusion coefficient decreases sharply with increase in concentration down to 2 · 10−11 cm2 sec−1, which indicates strong trapping of impurities in hep He4. Under these conditions there is a power-law increase in D with increase in temperature, which is consistent with Kagan’s theory of phonon stimulated coherent quantum diffusion. The contribution of vacancy diffusion in the presence of He3 trapping in He3 crystals is discussed.

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