Problems in the Design of a Fluorescence Meter for Interstitial Therapy, and a Practical Design of Instrument

Details are given of a robust and portable fluorescence dosemeter for the direct measurement of radium and radon dose-rates from 1 to 100 r/hr., with a probe 6 mm in diameter and 20 cm long. Experimental data are presented concerning the sensitivity, stability and proportionality to dose-rate of such dosemeters. Particular study has been made of the magnitude of the errors arising from fluorescence in Perspex light-guides and from direct effects of the γ radiation on the photomultiplier. An optical shutter is described which eliminates the latter effects, making the meter reading directly proportional to the dose-rate at the phosphor, without the application of any corrections.