HIGHLY SENSITIVE MEASUREMENTS OF RN-222 PERMEABILITY IN AU

The permeation rate of Rn-222(N-Rn) through the high purity annealed a nd cold worked Au was measured at 30-150 degrees C on atomic scale by means of a modified highly sensitive alpha-spectroscopic method. Virgi n annealed Au was impermeable to Rn-222 upto 150 degrees C, but it bec ame permeable after being subjected to a thermal cycle of negative mag nitude, whereas virgin cold worked Au was highly permeable at room tem perature. Prolonged isothermal holding resulted in permeation plateaux in annealed Au, and fairly well defined permeation peaks in cold work ed Au. The activation energy of permeation in cold worked Au (18.0 to 22.5 kJ/mol) was appreciably smaller than that in annealed Au (33.2 to 35.4 kJ/mol), while in the former N-Rn was about two orders of magnit ude higher. The observations have been interpreted in terms of capture of vacancies by diffusing Rn-222 atoms and structural changes in diff usion paths (e.g., grain boundaries) by deformation induced defects.