2018 Volume 34 Issue 1 Pages 1-6
Sampling numbers that were necessary to get the mean air dose rate in the range ±10% with a 95% confidence interval were estimated with data of seven grasslands in Iwate Prefecture, Japan. Air dose rates of six grasslands were collected in 2011, and of a grassland were collected from 2011 to 2016. Mean air dose rates of five grasslands, located at central part of Iwate Prefecture, ranged from 0.070 to 0.103 μSv/h, and of two grasslands, located at southern part of Iwate Prefecture, ranged from 0.318 to 0.793 μSv/h. Sampling numbers necessary for estimating accurate mean air dose rate by bootstrapping ranged from 1.2 to 4.6 per hectare. This result shows that unbiased five samples per hectare are necessary to estimate accurate mean air dose rate of grasslands. Six years' data showed that sampling number could be reduced after the third year of the nuclear power plant accident.
