The role of dislocation as sinks for H centers in LiF

The effect of γ-irradiation at liquid nitrogen temperature on the low temperature internal friction of compressed LiF crystals was studied by the ultrasonic pulse method at a frequency of 10 MHz. The internal friction is increased substantially in compressed LiF after a 5.8×10 6 rdosage of γ-rays at liquid nitrogen temperature. It was noted that this enhanced internal friction decreases during isochronal annealing at a low linear rate between 83 K to 110 K. The kinetics of this annealing process is analyzed. It is concluded that a fraction of the H centers introduced in LiF by the γ-irradiation diffuse to dislocations with a migration activation energy of 0.138±0.004 eV. The H center appears to pin the dislocation in the temperature region between 83 K and 110 K.