Assessment of gamma radiation from a limited area of forest floor using a cumulative personal dosimeter. (August 2019)

• Record Type: Journal Article
• Authors: Yoshihara, Toshihiro; Kurita, Keisuke; Matsumura, Hideyuki; Yoschenko, Vasyl; Kawachi, Naoki; Hashida, Shin-Nosuke; Konoplev, Alexei; Yoshida, Hirohisa
• Is Part Of: Journal of environmental radioactivity. Volume 204(2019)
• Page Start: 95
• Page End: 103
• Publication Date: 2019-08
• Subjects: Forest floor -- Soil surface -- Ground -- Radiocesium -- Fukushima -- D-shuttle; FDNPP Fukushima Dai-ichi Nuclear Power Plant; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2019.03.023
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: To elucidate long term changes in gamma radiation from a limited region of interest of the forest floor, a simple monitoring procedure using a cumulative personal dosimeter (D-shuttle) was examined from 2016 to 2017. The test site was in a small forest in Abiko, Japan, where the initial radiocesium contamination from the Fukushima Dai-ichi Nuclear Power Plant was 60–100 kBq m −2 . Three experimental plots basically containing a set of two 5 × 5 m 2 observation areas were arranged at the site. The litterfall and decomposing organic layer of one area (D: decontaminated) were fully eliminated before the monitoring, whereas the other area (N: natural) was left unchanged. Five D-shuttle sets (i.e., D-shuttle, lead shield, and holder) per area were set up. One D-shuttle set could monitor the specific gamma radiation from radiocesium distributed within a limited area of ground (0.5 m radius of circle = ca. 0.8 m 2 area of flat ground). The results indicated significant differences in the accumulated doses among each of the plots and areas, reflecting their soil radiocesium inventories. Interestingly, every index decreased with time, but the decreases were slower than the theoretical decay of radiocesium ( 134 Cs and 137 Cs). In addition, the accumulated dose decreased during heavy rainfall events. One possible explanation for these changes of the accumulated dose is a combination of meteorological and tree phenological phenomena, such as radiocesium from the forest canopy being newly added to the floor primarily by litterfall and soil moisture content disturbing radiation emitted from soils. This simple procedure enables long-term observation of gamma radiation from a limited area of forest floor non-invasively and semi-quantitatively. Highlights: The D-shuttle set detected the specific gamma radiation from an interested area. The monitoring distinguished differences in radiation both of set up positions and entire observed areas. The monitoring results reflected specific radiocesium distributions under the D-shuttle sets. A long-term monitoring demonstrated a change in a trend of decontamination effect.