The activity concentrations in naturally occurring radioactive material (NORM) samples are conventionally measured using a gamma-ray spectrometer with a single detector (mostly HPGe or NaI:Tl) enclosed in a lead shield. In this work, a passive water shield to reduce background radiation reaching the detectors was designed using GEANT4-toolkit Monte Carlo simulations and then constructed. This measurement system is portable and cost-effective for ex-situ measurements. IAEA-375 soil and beach sand each placed in Marinelli beakers were measured using two LaBr₃:Ce detectors in singles and coin-cidence modes. A novel method of background reduction by using photon time-of-flight was employed together with the measurement of the two photons energies. These samples were also measured in singles mode using a NaI:Tl detector inside the constructed water shield and HPGe detector shielded with lead to compare and validate the results of LaBr₃:Ce detectors measurement. Both the simulated and measured results show that the water shield (500 mm thick) attenuates 2614.5 keV gamma rays by 90 %. The minimum detectable activity (MDA) measured for 24 h using the NaI:Tl detector without shield and inside the water shield are; 546 Bq kg⁻¹ and 146 Bq kg⁻¹ at 1460.8 keV (⁴⁰K), 194 Bq kg⁻¹ and 15 Bq kg⁻¹ at 1764.5 keV (²³⁸U series), and 131 Bq kg⁻¹ and 15 Bq kg⁻¹ at 911.2 keV (²³²Th series), respectively. The measured activity concentrations of ²³⁸U and ²³²Th series and ⁴⁰K radionuclides inside IAEA-375 soil agree with certified values to within measurement uncertainties. The measured activity of ¹³⁸La in the LaBr₃:Ce detector crystal is 263.8 $\pm$ 26.8 Bq kg⁻¹. The internal activity of the LaBr₃:Ce detector increases the MDA at 1460.8 keV and 2614.5 keV, which limits the measurement of primordial radionuclides with low activity concentration in singles mode. The activity concentrations of ²³⁸U and ²³²Th series radionuclides in beach sand were measured using NaI:Tl and LaBr₃:Ce detectors. The results are consistent with those from HPGe measurement to within uncertainties.

常规地，使用伽马射线光谱仪来测量天然存在的放射性物质（NORM）样品中的活性浓度，该伽马射线光谱仪的铅屏蔽层中装有单个检测器（主要是HPGe或NaI：Tl）。在这项工作中，使用GEANT4-toolkit蒙特卡洛模拟设计了一个无源水屏蔽，以减少到达探测器的背景辐射，然后进行构造。该测量系统是便携式的，并且对于异地测量具有成本效益。使用两个LaBr ₃测量了分别放置在Marinelli烧杯中的IAEA-375土壤和海滩沙子：Ce探测器在单打和硬币探测模式下使用。通过使用光子飞行时间来减少背景光的新方法与两个光子能量的测量一起使用。还使用构造的水屏蔽罩内的NaI：Tl检测器和铅屏蔽的HPGe检测器以单次模式测量了这些样品，以比较和验证LaBr ₃：Ce检测器的测量结果。模拟结果和测量结果均表明，防水罩（500毫米厚）可将2614.5 keV伽马射线衰减90％。使用不带防护罩的NaI：Tl检测器在水防护罩内测量24小时的最小可检测活性（MDA）为；546公斤贝^-1和146公斤贝^-1在1460.8千电子伏（⁴⁰ K），194公斤贝^-1和15公斤贝^-1在1764.5千电子伏（²³⁸ U系列），和131公斤贝^-1和15公斤贝^-1在911.2千电子伏（²³²分别TH系列）。在IAEA-375土壤中测得的²³⁸ U和²³² Th系列放射性核素和⁴⁰ K放射性核素的活度浓度与标准值相符，在测量不确定性范围内。在LaBr ₃：Ce检测器晶体中测得的¹³⁸ La活度为263.8$\pm$26.8 Bq千克^-1。LaBr ₃：Ce检测器的内部活性会在1460.8 keV和2614.5 keV处增加MDA，这限制了在单峰模式下对低放射性浓度的原始放射性核素的测量。使用NaI：Tl和LaBr ₃：Ce检测器测量了海滩沙子中²³⁸ U和²³² Th系列放射性核素的活度浓度。结果与从HPGe测量到不确定性的结果一致。