Problems in high dose measurement

Many accelerators and large sources of 60Co are now being operated as a result of the growing use of radiation for food preservation, sterilization and industrial application. The measurement errors of absorbed dose required in high dose irradiation are +- 10% for food irradiation and sterilization and less than +- 5% for chemical irradiation because of industrial production control and economy. On the other hand, measuring instruments include chemical, glass and film dosimeters, and ion chambers and calorimeters for calibration. Any of these measuring methods depends upon radiation energy, quality, dose, and dose-rate, and their dependence on high dose and dose-rate is not yet completely investigated. Measured results are also discrepant according to persons and measuring organizations. Here the typical problems arising in the absorbed dose measurement in high dose irradiation already in practical use are taken up, and their present status and future requirements are described. They are: lack of experimental data and theoretical formulas on the behavior of low energy electron beam, inaccuracy of the representation of 60Co dose, no establishment of high reliability measuring method, and standardization of methods and instruments. (Wakatsuki, Y.)