Absorbed dose rate assessment for the Japanese cedar stand affected after the Fukushima NPP accident.

The nuclear disaster from the FNPP accident resulted in the major contamination of forest ecosystem of Eastern Japan. Forests are the most susceptible to ionizing radiation exposure, especially conifers due to their high radiosensitivity and pollutant interception abilities. A high concentration of radionuclides in forest ecosystems caused an increase in the dose rate. Japanese cedar belongs to Japan's endemic species; therefore, the current study was aimed at the absorbed dose rate assessment of the C. japonica forest stand in the Yamakiya district. To estimate the absorbed dose rates to the Japanese cedar trees, we used the ^134,137Cs concentrations in different forest ecosystems’ compartments. The calculations include data from 2011 to 2017. The dose rate assessments were performed at different heights of the forest ecosystem (canopy, trunk, understory). The average dose rates decreased from 40 µGy/day in 2011 to 13 µGy/day in 2017. The assessment results comply with the ambient dose rate measured from 2011 to 2015. The assessment showed that the water content in the litter and topsoil layers significantly influence the formation of the dose rate. Via the model, we simulated the dose rates for 20% and 80% of the litter water content. The results showed that the average measured dose rates lie within the estimated results. Due to the lack of data on litter and soil moisture during sampling, now we are trying to calculate the ground layers’ water content using the available information on precipitation rate.