A new apparatus for on-site calibration of gamma dose rate monitors

In order to carry out on-site calibrations of environmental gamma dose rate monitors, a new irradiation apparatus was developed in this study. The apparatus mainly consists of a piece of ¹³⁷Cs source, a set of beam attenuators, and 3 built-in laser rangefinders, and it can be remotely controlled by using a laptop through WiFi network. With an activity of 4.6 × 10⁸ Bq of ¹³⁷Cs source, the reference air kerma rate could be adjusted from 0.26 μGy h^-1 to 140 μGy h^-1 by changing the calibration distance from 0.5 m to 5 m and using different beam attenuators (or none), and both the reproducibility and the homogeneity of reference radiation were better than 97%. The overall uncertainty of the calibration was estimated to be 6.5% (k = 2). Both the laboratory and field experiments confirmed that the calibration method met the requirements of ISO 4037-1. As the advantages of portability and simplicity, it is considered that the new irradiation apparatus is applicable to stationary gamma radiation monitors for on-site calibration.