Inoue M, Yoshida K, Minakawa M, Kofuji H, Nagao S, Hamajima Y, Yamamoto M. Spatial variations of 226Ra, 228Ra, 137Cs, and 228Th activities in the southwestern Okhotsk Sea.
JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2012;
104:75-80. [PMID:
21982392 DOI:
10.1016/j.jenvrad.2011.09.007]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 09/07/2011] [Accepted: 09/08/2011] [Indexed: 05/25/2023]
Abstract
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.
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