VOID GROWTH AND THERMAL-DESORPTION OF DEUTERIUM FROM VOIDS IN TUNGSTEN

The growth of voids and the deuterium interaction with voids in tungsten have been studied with thermal desorption and positron annihilation techniques. Voids were created by 30 keV 1 x 10(20) D-2(+) m(-2) ion irradiation of single crystalline tungsten. The thermal annealing of the defects was monitored up to T-A = 1900 K. It was observed that vacancy clustering took place at similar to 650 K. Apparently clusters were formed from four to ten vacancies. Further cluster growth proceeded in two stages. At similar to 1050 K the initially formed clusters were breaking up and formed clusters with 11-16 vacancies. The V-11-16 clusters disappeared at around 1450 K in favor of clusters containing 40-60 vacancies. Finally these clusters were removed by annealing above 1700 K. The different cluster sizes were decorated with deuterium. Upon annealing, deuterium release took place at 800 K from the V-11-16 and at 600 K from the V-40-60 clusters. The release of all deuterium at T < 1000 K together with the stability of the microcavities, allowed deuterium to be used as a useful probe for microcavities.