THE SURFACE DEGRADATION OF GLASS WITHIN RPL DOSIMETERS

Phosphate glass within radiophotoluminescent dosemeters can suffer fro m a brown discoloration. Typical RPL signal fading is normally 3-4% pe r year but brown glasses have shown an average loss of 9.24 +/- 0.84% per year which can be reduced to 3.96 +/- 0.36% by acid cleaning. Simi lar cleaning of glasses stored in a desiccator raised the signal loss to 4.2 +/- 0.6% from 3.12 +/- 0.24% per year. Rutherford back scatteri ng (RES) has shown that the front surface had a 100 to 200 nm film ric h in silver while, across the rear face, silver appeared to migrate lo cally. In contrast, surfaces of glasses stored in a desiccator were al l of the same composition. Scanning electron microscopy has shown that the front surface of brown glass is partly covered with small pits, a pproximately 2 mu m in diameter. On the rear surface pitting is confin ed to areas near to a silver rich dendritic growth.