Factors and strategies in selection of instruments for radiation surveys around medical X-ray installations

The selection of an instrument for surveying the radiation transmitted through the barriers surrounding a diagnostic X-ray room should be based on considerations including maximum permissible exposure per week, weekly workload, precision required, sensitivity of the instrument, least count of the instrument scale, response time of the instrument (if it is rate-indicating), and the limitations of the X-ray tube as to heat loading. The inter-relationships of these factors are discussed, and a systematic procedure is presented. Numerical examples are presented showing the conditions, for particular instruments and for a tube with particular heat rating characteristics, under which a survey can be performed with adequate precision, minimal exposure to the surveyor, and heat loading within the allowed limits. This discussion focuses particularly upon diagnostic radiographic X-ray rooms, but the conclusions are applicable to fluoroscopic and therapeutic installations, for which the problems are much simpler. (author)