Vertical ¹³⁷Cs distribution in the bark of Japanese cedar trees in 2012 after the Fukushima Dai-ichi Nuclear Power Plant Accident

Abstract

Vertical ¹³⁷Cs distribution in the barks of Japanese cedar (Cryptomeria japonica) trees in the initial phase after the Fukushima Dai-ichi Nuclear Power Plant accident was investigated in several forests in Fukushima prefecture in 2012. 12 trees that were felled in 7 forests were used in the present study. ¹³⁷Cs concentration in bark samples taken at various heights were determined using a NaI spectrometer. In order to compare the vertical ¹³⁷Cs distribution in the bark of each tree, ¹³⁷Cs concentration was normalized to that at the lowest height from the ground. An increase of ¹³⁷Cs concentration from the bottom to the tree top was clearly observed for 9 trees. The inner barks were almost constant at any vertical positions. Large part of the ¹³⁷Cs in the barks existed in the outer barks. These results indicated that the vertical distribution of the outer ¹³⁷Cs contamination on the barks in 2012 had a common ¹³⁷Cs concentration profiles against the tree top with the different contamination levels of the forests and different height of the tree.