The Effect of Intrinsic Radiation from a 3 × 3-in. LaBr₃(Ce) Scintillation Detector on In Situ Artificial Radiation Measurements

In situ radiation measurements are commonly used to detect radioactive material in luggage; at border control checkpoints; for in-field monitoring; during the illicit transfer of nuclear material; and at radioactive contamination sites, e.g., the Fukushima nuclear accident site. In considering the high brightness, fast decay time, and good energy resolution of cerium-doped lanthanum bromide [LaBr₃(Ce)] scintillation detectors, this work conducted an experimental analysis aimed at evaluating the potential for applying LaBr₃(Ce) detectors to in situ artificial radiation measurements. The effect of the intrinsic radiation of the LaBr₃(Ce) detector was investigated. In addition, the intrinsic radiation contribution to the background radiation of the region of interest (ROI) under full-energy peaks for several artificial point sources and the minimum detectable activity (MDA) values of a 3 × 3-in. LaBr₃(Ce) detector for several artificial radioactive point sources under unshielded (in the natural background) and well-shielded (in a low background chamber) conditions were calculated. The results indicate that the intrinsic radiation has a significant effect on the background radiation of the ROI especially when the full-energy peaks of several artificial point sources are located in the low-energy region or near 789 and 1400 keV. In addition, the MDAs (the measured time is 300 s) of the LaBr₃(Ce) detector for ¹⁵²Eu (121.78 keV), ¹³³Ba (356 keV), ¹³⁷Cs (661.7 keV), and ⁶⁰Co (1332.5 keV) were 218.2, 63.6, 61.3, and 59.6 Bq, respectively, under unshielded conditions and 111.4, 39.1, 46.1, and 38.6 Bq, respectively, under well-shielded conditions. The intrinsic radiation also has some effects on the MDA of the LaBr₃(Ce) detector, especially in the low-energy region. Thus, the drawback of its intrinsic radiation limits its application to in situ weak artificial radiation measurements, but LaBr₃(Ce) detectors have the potential for use in medium- and high-radiation measurements due to the better energy resolution of these detectors than NaI(Tl) detectors.