To monitor radioactivity levels in seawater Korea Institute of Nuclear Safety has installed and been operating 18 NaI(Tl)-based gamma detectors around the Korean peninsula. This study was conducted to estimate the detector efficiency and MDA of 137Cs in seawater for measurement situations. For this purpose, experiments in the air and a water tank, and Monte Carlo simulations were performed using a seawater radioactivity monitor system with 3 in. × 3 in. NaI(Tl) scintillation detector. In the geometry reliability assessment using certified reference materials in a disc source, the validity of simulations was obtained by comparing measurement and Monte Carlo simulation results. The FWHM of the seawater radioactivity monitor were obtained from the results of the water tank measurement for applying a Gaussian Energy Broadening (GEB) option to Monte Carlo N-Particle (MCNP) radiation transport code. In addition, the detection efficiency of 40K in the water tank was measured and compared with the Monte Carlo simulation results in order to estimate the MDA and the detection efficiency of the seawater radioactivity monitoring system. For the based condition of water tank, 40K concentration in water tank was controlled to 10.13±0.18 Bq/L, similar to that of real marine. In laboratory water tank experiments, the detection efficiency of the radioactivity monitor for 40K was measured at 0.184±0.005 cps/(Bq/L), the Monte Carlo simulations showed the similar result of 0.182±0.002 cps/(Bq/L), and the detection efficiency of 137Cs was estimated to be 0.224±0.009 cps/(Bq/L) from the simulations. For 3h measurement in the water tank based condition, the MDA of 137Cs was estimated to be 0.077±0.003 Bq/L. Future research will include detailed studies for detector sizes and seawater salinities.

中文翻译：

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基于NaI（Tl）的海水监测系统的检测效率和最小可检测活性估计的初步研究。

为了监测海水中的放射性水平，韩国核安全研究所已在朝鲜半岛附近安装并运行了18个基于NaI（Tl）的伽马探测器。进行这项研究以估计用于测量情况的海水中137 Cs的探测器效率和MDA。为此，使用带有3英寸×3英寸NaI（Tl）闪烁探测器的海水放射性监测系统在空气和水箱中进行了实验，并进行了蒙特卡洛模拟。在使用经认证的参考材料在磁盘中进行几何形状可靠性评估时，通过比较测量结果和蒙特卡洛模拟结果来获得模拟的有效性。海水放射性监测仪的FWHM是从水箱测量结果中获得的，该测量结果将高斯能量扩展（GEB）选项应用于蒙特卡洛N粒子（MCNP）辐射传输代码。另外，测量了水箱中40K的探测效率，并将其与蒙特卡洛模拟结果进行比较，以估算MDA和海水放射性监测系统的探测效率。对于水箱的基础条件，将水箱中的40K浓度控制在10.13±0.18 Bq / L，与真实的海洋相似。在实验室水箱实验中，放射性监测仪对40K的检测效率为0.184±0.005 cps /（Bq / L），蒙特卡洛模拟结果相似，为0.182±0.002 cps /（Bq / L），从模拟结果估计137Cs的检测效率为0.224±0.009 cps /（Bq / L）。在基于水箱的条件下进行3h测量时，估计137Cs的MDA为0.077±0.003 Bq / L。未来的研究将包括对探测器尺寸和海水盐度的详细研究。