Pre- and post-accident (129)I and (137)Cs levels, and (129)I/(137)Cs ratios in soil near the Fukushima Dai-ichi Nuclear Power Plant, Japan.
To evaluate the deposition density and extent of subsurface infiltration of (129)I and (137)Cs in the restricted area that was highly contaminated by the accident of Fukushima Dai-ichi Nuclear Power Plant, cumulative inventories of (129)I and (137)Cs, concentrations of (129)I and (137)Cs, and (129)I/(137)Cs ratio in 30-cm-long soil columns were compared with pre-accident levels from the same area. The cores were collected before and after the accident from locations of S-1 (4 km west of FDNPP) and S-2 (8 km west of FDNPP). Deposition densities of (129)I and (137)Cs in the soil following the accident were 0.90-2.33 Bq m(-2) and 0.80-4.04 MBq m(-2), respectively, which were 14-39 and 320-510 times larger than the pre-accident levels of (129)I (59.3-63.3 mBq m(-2)) and (137)Cs (2.51-7.88 kBq m(-2)), respectively. Approximately 90% of accident-derived (129)I and (137)Cs deposited in the 30-cm soil cores was concentrated in the surface layer from 0 to 44-95 kg m(-2) of mass depth (0-4.3-6.2 cm depth) and from 0 to 16-25 kg m(-2) of mass depth (0-1.0-3.1 cm depth), respectively. The relaxation mass depths (h0) of 10.8-11.2 kg m(-2) for (129)I estimated in the previous study were larger than those of 8.1-10.6 kg m(-2) for (137)Cs at both sites, owing to the larger infiltration depth of radioiodine mainly by the gravitational water penetration in the surface soil in our study sites. Approximately 7-9% of the accident-derived (129)I was present in the lower layer from 44 to 100 kg m(-2) (4.3-8.6 cm depth) at S-1, and from 95 to 160 kg m(-2) (6.2-10.2 cm depth) at S-2. Approximately 1% of (137)Cs seems to infiltrate deeper than (129)I in the lower layer at each site in contrast to the surface layer.
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan. Electronic address: matsunaka@tac.tsukuba.ac.jp.
Tetsuya
T
Matsunaka
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Kimikazu
K
Sasa
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Keisuke
K
Sueki
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Tsutomu
T
Takahashi
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Yukihiko
Y
Satou
Accelerator Mass Spectrometry Group, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
Masumi
M
Matsumura
Institute of Technology, Shimizu Corporation, 3-4-17 Etchujima, Koto-ku, Tokyo 135-8530, Japan.
Norikazu
N
Kinoshita
Radiation Science Center, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
Jun-Ichi
JI
Kitagawa
The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Hiroyuki
H
Matsuzaki
D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D007457:Iodine Radioisotopes / Q000032:analysis*; D007564:Japan; D055848:Nuclear Power Plants; D011834:Radiation Monitoring; D012621:Seasons; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
D002588:Cesium Radioisotopes; D007457:Iodine Radioisotopes; D012990:Soil Pollutants, Radioactive
Accelerator mass spectrometry; Behavioral response; Depth distribution; Fukushima accident; Radiocesium; Radioiodine