Changes in the distribution of radiocesium in the wood of Japanese cedar trees from 2011 to 2013

摘要

The changes in the distribution of Cs-137 in the wood of Japanese cedar (Cryptomeria japonica) trunks within three years after the Fukushima Dai-ichi Nuclear Power Plant (FDNP) accident in 2011 were investigated. Thirteen trees were felled to collect samples at 6 forests in 2 regions of the Fukushima prefecture. The radial distribution of Cs-137 in the wood was measured at different heights. Profiles of Cs-137 distribution in the wood changed considerably from 2011 to 2013, and the process of Cs-137 distribution change in the wood was clarified. From 2011 to 2012, the active transportation from sapwood to heartwood and the radial diffusion in heartwood proceeded quickly, and the radial Cs-137 distribution differed according to the vertical positon of trees. From 2012 to 2013, the vertical diffusion of Cs-137 from the treetop to the ground, probably caused by the gradient of Cs-137 concentration in the trunk, was observed. Eventually, the radial Cs-137 distributions were nearly identical at any vertical positions in 2013. Our results suggested that the active transportation from sapwood to heartwood and the vertical and radial diffusion in heartwood proceeded according to the vertical position of the tree and Cs-137 distribution in the wood approached the equilibrium state within three years after the accident. (C) 2016 Elsevier Ltd. All rights reserved.