The Effect of Intrinsic Radiation from a 3 × 3-in. LaBr_3(Ce) Scintillation Detector on In Situ Artificial Radiation Measurements

摘要

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 x 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 Eu-152 (121.78 keV), Ba-133 (356 keV), Cs-137 (661.7 keV), and Co-60 (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.