In the long-term uninterrupted work of the real-time on-line monitoring system of water radioactivity, the spectrum drift, line broadening and shift of peak position are caused by the temperature change of the detector and various electronic components and the aging of components, which leads to the difficulty of spectral line analysis and the error of analytical results.

This study aims to develop a calibration device for real-time on-line monitoring system of water radioactivity based on cerium bromide detector.

The device was designed to consists of ¹³⁷Cs standard source (exemption source), lead block, lead chamber with calibration hole and linear motor. The optimum opening radius of the calibration hole and the optimum thickness of the lead block were obtained by Monte Carlo simulation. The standard ¹³⁷Cs source was used as the standard reference peak, and the calibration of peak position and peak area, the peak position drift and peak area of ¹³⁷Cs full-energy peak was analyzed by software with real-time gain calculation and parameters adjustment. Finally, the device was applied to the field application verification.

Results of Monte Carlo simulation indicate that the optimum radius of the calibration hole is 2.2 cm and the optimum thickness of the lead block is 5 cm. The verification results shows that the device can limit the change of peak position and peak area to ±1% and ±5%, respectively.