Almost 8 years after the Japanese Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for 236U and 236U/238U have mainly remained limited to only a few heavily contaminated samples. In the present study, activities of 236U, 134Cs, and 137Cs, along with 234U, 235U, 238U, in 15 river bank soil and 10 river sediment samples, were measured by ICP-MS/MS and γ spectrometry. The 134Cs activities and 134Cs/137Cs activity ratios (decay-corrected to March 11, 2011) in these 15 river bank soil samples were from 74.8 to 3.88 × 105 Bq kg-1 and from 0.944 to 1.02, respectively; and in these 10 river sediment samples were from 87.1 to 1.86 × 105 Bq kg-1 and from 0.904 to 0.990, respectively. The 236U activities and 236U/238U atom ratios in these soil samples were in the respective ranges of (0.139-17.6) × 10-5 Bq kg-1 and (0.259-3.83) × 10-8; and in these sediment samples were in the respective ranges of (0.884-27.0) × 10-5 Bq kg-1 and (1.12-5.04) × 10-8. For one river sediment core sample, 134Cs and 236U activities decreased with the depth indicating 134Cs and 236U accumulated in the river sediment with time. Unlike 134Cs, no clear evidence of FDNPP accident-derived 236U has been found in this study, although further monitoring is encouraged to establish the background database on 236U/238U for its potential application as a tracer in environmental studies.
Keywords: (134)Cs/(137)Cs; (236)U/(238)U; ICP-MS/MS; River system; Source identification.
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