UNIFORMITY OF HIGH-ENERGY ELECTRON-BEAM CALIBRATIONS

A survey is made of the first year of operation of a new service offered by the National Bureau of Standards (NBS). Dosemeter units, consisting of polystyrene blocks holding stoppered quartz spectrophotometer cells filled with Fricke solution, are being shipped periodically to groups requesting assistance with absorbed-dose measurements in high-energy electron beams. As a check on their stability, all dosemeters are pre-exposed to 60Co γ-rays. The participants irradiate a portion of the dosemeters with electrons, using energies between about 5 and 50 Mev, and doses between 4000 and 8000 rads in water. The exposed dosemeters are returned to NBS for evaluation. During the first year of operation, slightly more than one-half of the doses reported by the participants were within ±5% of the NBS dose interpretation, but some differed by as much as 30% or more. Little correlation was found between a participant's method of beam calibration and agreement with NBS dose interpretation.