Inoue M, Tanaka K, Watanabe S, Kofuji H, Yamamoto M, Komura K
Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
J Environ Radioact. 2006;89(2):138-49. doi: 10.1016/j.jenvrad.2006.04.001. Epub 2006 Jun 8.
In this study, low-background gamma-spectrometry was used to determine the (228)Ra/(226)Ra ratio of 131 coastal water samples from various environments around Honshu Island, Japan (mainly around Noto Peninsula) at 1-3 month intervals from April 2003 until September 2005. Spatial variation in (228)Ra/(226)Ra ratios was also assessed by analyzing 34 coastal water samples from five areas within the Sea of Japan during May and June 2004. The (228)Ra/(226)Ra ratio of coastal water from all sites around Noto Peninsula shows seasonal variation, with minimum values during summer ((228)Ra/(226)Ra=0.7) and maximum values during autumn-winter ((228)Ra/(226)Ra=1.7-2). This seasonal variation is similar to that recorded for coastal water between Tsushima Strait and Noto Peninsula. The measured lateral variation in (228)Ra/(226)Ra ratios within coastal water between Tsushima Strait and Noto Peninsula is only minor (0.5-0.7; May-June 2004). Coastal waters from two other sites (Pacific shore and Tsugaru Strait, north Honshu) show no clear seasonal variation in (228)Ra/(226)Ra ratio. These measured variations in (228)Ra/(226)Ra ratio, especially the temporal variations, have important implications for seasonal changes in patterns of coastal water circulation within the Sea of Japan.
在本研究中，采用低本底伽马能谱法，于2003年4月至2005年9月期间，每隔1 - 3个月测定了日本本州岛周围（主要是能登半岛周围）不同环境的131个沿海水样的镭-228/镭-226比值。2004年5月和6月，通过分析日本海五个区域的34个沿海水样，还评估了镭-228/镭-226比值的空间变化。能登半岛周围所有站点的沿海水样中镭-228/镭-226比值呈现季节性变化，夏季时最低（镭-228/镭-226 = 0.7），秋冬季节时最高（镭-228/镭-226 = 1.7 - 2）。这种季节性变化与对津轻海峡和能登半岛之间沿海水域记录的变化相似。在津轻海峡和能登半岛之间的沿海水域内，所测得的镭-228/镭-226比值的横向变化很小（0.5 - 0.7；2004年5 - 6月）。另外两个站点（本州北部的太平洋海岸和津轻海峡）的沿海水样中，镭-228/镭-226比值没有明显的季节性变化。所测得的镭-228/镭-226比值的这些变化，尤其是时间变化，对日本海内沿海水流循环模式的季节性变化具有重要意义。
