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Comparison of Depth Profiles of 129I and 14C Concentration in the Surface Layer of Soils Collected from Northeastern Japan

Published online by Cambridge University Press:  18 July 2016

Hiroyuki Matsuzaki ,
Yoko Sunohara Tsuchiya ,
Yasuyuki Muramatsu ,
Yuji Maejima ,
Yosuke Miyairi  and
Kazuhiro Kato
Hiroyuki Matsuzaki*
Affiliation:
Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyoku, Tokyo 113-8656, Japan
Yoko Sunohara Tsuchiya
Affiliation:
Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyoku, Tokyo 113-8656, Japan
Yasuyuki Muramatsu
Affiliation:
Department of Chemistry, Gakushuin University, Tokyo, Japan
Yuji Maejima
Affiliation:
National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Japan
Yosuke Miyairi
Affiliation:
Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyoku, Tokyo 113-8656, Japan
Kazuhiro Kato
Affiliation:
National Institute for Environment Studies, 16-2 Onogawa, Tsukuba-City, Ibaraki 305-8506 Japan
*
Corresponding author: Email address: hmatsu@n.t.u-tokyo.ac.jp.
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Abstract

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129I/127I and 14C/12C depth profiles were compared for the surface 30-cm layer of soil samples (Andisols) collected from Shimokita Peninsula, northeastern Japan, in November 2005. The 129I/127I and 14C/12C profiles have a clear correlation, even taking into account that the data include samples collected from different sites with different surface histories. These results, and considering that 14C/12C can be regarded as a proxy of the original depth in stable soil, show the diversity of the 129I/127I ratio at the surface among the sites, indicating variations in the thicknesses of the layers recently removed. At one of the sampling sites (P003-1), the Δ14C value measures ∼110‰ near the surface, which is indicative of anthropogenic 14C produced by atmospheric testing of nuclear weapons during the late 1950s and early 1960s. This site has experienced no disturbances for at least the past 50 yr. The relatively high activity of 129I (0.8 mBq/kg) and the 129I/127I ratio (7 x 10–9) observed at the top layer of this site can be considered a “representative value” when considering the anthropogenic iodine transfer from the atmosphere to the ground. The observations also support 2 separate modes of 129I migration in the soil: i.e. “topmost quick diffusion” and “subsurface relatively slow migration process.” Even in the “subsurface relatively slow migration zone,” the 129I/127I ratio was still orders higher than the pre-anthropogenic natural level.

Type
Soils and Sediments
Information
Radiocarbon , Volume 52 , Issue 3: 20th Int. Radiocarbon Conference Proceedings , 2010 , pp. 1487 - 1497
Copyright
Copyright © 2010 by the Arizona Board of Regents on behalf of the University of Arizona 

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