Free Migration of Interstitials in Tungsten

The internal friction and dynamic modulus of W single crystals were measured after neutron irradiation near liquid-helium temperature. The results on dislocation pinning and the associated relaxation peaks suggest that in W the (110) split interstitials perform a free migration at 15 K (substage I&) and the -30-K stage (substage I&) is associated with detrapping of the (110) split interstitials from impurity atoms.