Cobalt Glass Dosimetry

The fading of radiation-induced absorbancy of cobalt glass as a function of exposure rate and time was investigated. A linear accelerator (Linac) and a 600 curie cobalt-60 source were used. The fading of the absorbancy was found to obey an empirical relationship over four orders of magnitude of the form A(t) = A(to) - n In t/to where A(to) is the absorbancy at time to. The slopes of the fading curves (n) were found to depend upon the initial absorbancy A(to) and wavelength. The difficulties of using a calibration curve determined with a low-exposure rate source for Linac dosimetry are briefly discussed.