Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
J Environ Radioact. 2012 Feb;104:75-80. doi: 10.1016/j.jenvrad.2011.09.007. Epub 2011 Oct 6.
We collected 14 water column seawater samples in the southwestern Okhotsk Sea and 7 surface samples around the northern area of Hokkaido Island, Northern Japan, and employed low-background γ-spectrometry with convenient minimal radiochemical processing to determine the activities of (226)Ra (half-life t(1/2)=1600 y), (228)Ra (5.75 y), (137)Cs (30.2 y), and (228)Th (1.91 y) in the samples. Activities of (226)Ra (2.3 mBq/L), (228)Ra (0.7 mBq/L), and (137)Cs (1 mBq/L) of surface waters on the Okhotsk Sea side show notable differences from those on the Japan Sea side (Soya Warm Current Water; SWCW) (1.5 mBq/L; 1.5-2 mBq/L; 1.4-1.6 mBq/L), indicating their different origins and lateral mixing patterns. All of these nuclides exhibit unique vertical profiles; activities of soluble (226)Ra, (228)Ra, (137)Cs, and reactive (228)Th exhibit small variations from 50 to 500 m depth ((226)Ra, ~2.2 mBq/L; (228)Ra, ~0.4 mBq/L; (137)Cs, ~1 mBq/L; (228)Th, ~0.13 mBq/L). These profiles can be explained by the convective mixing of surface water such as the East Sakhalin Current Water (ESCW) to this layer.
我们在日本北海道北部周围收集了 14 个西南鄂霍次克海水柱海水样本和 7 个表层样本，并采用简便的最小放射性化学处理方法的低本底γ谱仪来测定样品中的（226）Ra（半衰期 t(1/2)=1600 年）、（228）Ra（5.75 年）、（137）Cs（30.2 年）和（228）Th（1.91 年）的活度。鄂霍次克海一侧表层水的（226）Ra（2.3 mBq/L）、（228）Ra（0.7 mBq/L）和（137）Cs（1 mBq/L）活度与日本海一侧（宗谷暖流海水；SWCW）（1.5 mBq/L；1.5-2 mBq/L；1.4-1.6 mBq/L）有明显差异，表明它们的来源和侧向混合模式不同。所有这些核素都呈现出独特的垂直分布特征；可溶的（226）Ra、（228）Ra、（137）Cs 和反应性（228）Th 的活度在 50-500 米深度范围内变化很小（（226）Ra，2.2 mBq/L；（228）Ra，0.4 mBq/L；（137）Cs，1 mBq/L；（228）Th，0.13 mBq/L）。这些分布特征可以通过表面水的对流混合来解释，例如东萨哈林海流（ESCW）到这一层。
