A shipboard gamma-ray measurement system equipped with a 7.6 cmØ $\times$ 7.6 cm NaI(Tl) detector for remote real-time radioactivity monitoring of gamma-ray emitting radionuclides in surface seawater is presented. The full energy peak detection efficiency of the detector to convert measured gamma-ray counts to radioactivity concentration was estimated using Monte Carlo simulation with the MCNP code. The detection efficiency calibration was validated by sampling and laboratory analysis for ⁴⁰K in seawater from the site where the ship with the measurement system stayed. The minimum detectable activity of this measurement system for ¹³¹I, ¹³⁴Cs and ¹³⁷Cs in seawater with the varied spectrum accumulation time is discussed.

配备7.6厘米直径的舰载伽马射线测量系统 $\times$提出了7.6 cm NaI（Tl）检测器，用于对地表海水中的伽马射线发射放射性核素进行远程实时放射性监测。使用带有MCNP代码的蒙特卡洛模拟法估算了将测量的伽马射线计数转换为放射性浓度的探测器的全部能量峰值探测效率。通过对带有测量系统的船舶所在地点的海水中的⁴⁰ K进行采样和实验室分析，对检测效率校准进行了验证。讨论了该测量系统在海水中¹³¹ I，¹³⁴ Cs和¹³⁷ Cs随光谱累积时间变化的最小可检测活性。