Positron-lifetime measurements were performed in order to determine how the positron-trapping efficiency of dislocations in 6N-purity material changed during isochronal annealing after deformation at room temperature. It was shown that the positron-trapping efficiency continued to increase during annealing, while the lifetime of trapped positrons first decreased but then assumed a constant value of about 210ps. The highest observed value of the positron-trapping efficiency of dislocations was equal to about 0.00045m2/s. This was much larger than the previous reported values of 6.6 x 10-6 to 2 x 10-4m2/s. After heating to higher temperatures, it was also found that a small applied stress could cause a marked decrease in the positron-trapping efficiency of dislocations, without any significant change occurring in the lifetime of trapped positrons. The results suggested that the positron-trapping efficiency of dislocations depended strongly upon the dislocation configuration. Its increase during annealing was attributed to the development of long straight dislocation line segments.

M.Iwami, E.Hashimoto, Y.Ueda: Journal of Physics - Condensed Matter, 1995, 7[50], 9935-42