TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 52, 2018

Applying an improved method to measure 134Cs, 135Cs, and 137Cs activities and their atom ratios in marine sediments collected close to the Fukushima Daiichi Nuclear Power Plant


1Department of Radiation Chemistry, Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Hon-cho, Hirosaki, Aomori 036-8564, Japan
2Division of Nuclear Technology and Applications, Institute of High Energy Physics, Chinese Academy of Sciences; Beijing Engineering Research Center of Radiographic Techniques and Equipment, Beijing 100049, China
3School of Marine Science and Technology, Tokai University, Orido 3-20-1, Shimizu, Shizuoka 424-8610, Japan

(Received February 6, 2017; Accepted April 26, 2017)

Abstract: The 135Cs/137Cs atom ratio has been proved to be a reliable tracer for radiocesium source identification in the studies on the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. However, due to the technical challenge to measure 135Cs, no 135Cs data are available for Japanese river or ocean sediments. In the present study, the vertical distributions of 134Cs and 137Cs activities and their ratios in two marine sediment cores, collected offshore from the FDNPP site immediately after the accident, were measured by γ spectrometry. A conventional introduction system was replaced by an APEX-Q system, by which it was possible to get 6.5 times higher Cs intensities and then 135Cs was analyzed by triple-quadrupole inductively coupled plasma-mass spectrometry. From the vertical distributions, it was seen that the deposition of 134Cs and 137Cs presented an increasing trend, which indicated continuous radiocesium input into the ocean and deposition from sea water onto the sea floor up to the collection date. Therefore, the 134Cs/137Cs activity ratios (0.866-1.16) and 135Cs/137Cs atom ratios (0.249-0.343) (all decay-corrected to March 11, 2011) in marine sediment core samples showed the fingerprints of radiocesium in the oceanic environment were mainly derived from the FDNPP.
Key words: 135Cs/137Cs atom ratio, 134Cs/137Cs activity ratio, Fukushima Daiichi Nuclear Power Plant accident, marine sediment, triple-quadrupole inductively coupled plasma-mass spectrometry

*Corresponding author E-mail: myamada@hirosaki-u.ac.jp

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