Online measurement system for natural water radioactivity with array CeBr3 detector

Abstract

With the development of power and non-power-related nuclear technologies, measurements of radioactivity levels in natural water have become an important part of environmental radioactivity monitoring. To improve the ability to monitor radioactivity levels in water and provide rapid warning for nuclear accidents, an online water radioactivity measurement system has been developed. The system is a gamma-ray detector array composed of three 45 mm × 50 mm CeBr₃ crystals coupled each to a photomultiplier tube (PMT). The detection efficiency and the minimum measurement time of the system were determined by numerical simulation, and ²⁴¹Am automatic spectrum stabilization technology was established to eliminate peak drift during long-term monitoring. The minimum detectable activity concentration (MDAC) of the system for the common artificial radionuclides ¹³¹I, ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir and ¹⁵²Eu can reduce to 0.0161 Bq/L, 0.0149 Bq/L, 0.0142 Bq/L, 0.0458 Bq/L and 0.1067 Bq/L, respectively, for 12 h measurement time, within which the peak drift is less than ±1 channel. The measurement accuracy of the system was verified by a low-background gas-flow proportional counter, and the results show that the online measurement and laboratory analysis are found to be in very good agreement within uncertainties. The system was evaluated through the continuous measurement of the Qingyi River in Sichuan Province, the measurement results show that radionuclides in the Qingyi River included ⁴⁰K, ²¹⁴Bi, ²⁰⁸Tl, ²¹⁴Pb, ²²⁴Ra and ²²⁶Ra, which ranged from 0.0024 to 0.21 Bq/L, and the gross α/β⁻ activity concentration remains around 0.0145 Bq/L and 0.22 Bq/L, respectively.