The Hong Kong Observatory (HKO) regularly carries out sampling and measurement works to monitor the ambient radiation levels in Hong Kong. Part of the measurement work is performed by the radiation Contamination Monitoring System (CMS).

CMS hardware includes a sodium-iodide detector, lead shield (to remove background radiation) and multiple channel analyzer. The associated software will perform gamma-ray spectrum analysis and can quickly detect the presence of artificial radionuclides in water and food, focusing in particular on caesium-134, caesium-137 and iodine-131. If the measured activity exceeds pre-set thresholds, further analyses will be conducted in the laboratory.

The CMS needs to be calibrated annually to ensure accuracy in the measurement results. The CMS will measure the calibration sources, and based on the input data and measurement results, the analysis software will update the efficiency curve of the detector.