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Yamada, Susumu; Machida, Masahiko; Tanimura, Naoki*
EPJ Web of Conferences, 302, p.16004_1 - 16004_10, 2024/10
When we decommission a reactor building, it is desirable to identify the radiation source distribution for safety. It has been reported that the source distribution can be estimated from the measured air dose rates at appropriate observation points by minimizing an evaluation function using the Least Absolute Shrinkage and Selection Operator (LASSO). However, it is difficult to decide on suitable points in advance. Therefore, we estimate the posterior distribution from the prior distribution of the source amounts, which are calculated by the standard LASSO, using the Bayesian LASSO, and evaluate the predictive distribution of the evaluated air dose rates at the candidate observation points from the posterior distribution. We select the additional observation point based on the variances of the predictive distributions. We confirmed that the method can estimate the source distribution with fewer additional observation points than when adding ones randomly in most cases.
Li, H.; Maekawa, Masaki; Kawasuso, Atsuo; Tanimura, Naoki*
Journal of Physics; Condensed Matter, 27(24), p.246001_1 - 246001_5, 2015/06
Times Cited Count:7 Percentile:30.61(Physics, Condensed Matter)Liu, X.; Machida, Masahiko; Saito, Kimiaki; Tanimura, Naoki*
no journal, ,
Ecological half-life has been widely used to describe the long-term decrease of ambient dose rates in addition to radioactive decay. In the present work, we introduce a new, robust, and efficient numerical method to extract space dependent ecological half-lives from car-borne survey data. Numerical results indicate complexed ecological half-life profiles, which are originated from their spatial patterns.
Machida, Masahiko; Uno, Shumpei*; Tanimura, Naoki*; Saito, Kimiaki; Yoshimura, Kazuya
no journal, ,
Air dose rates in urban areas decrease faster in residential areas than in evacuation zones. This suggests that human activities facilitate the reduction. However, since human activities include various factors such as decontamination and road wear caused by traffic, it is difficult to evaluate the effect of human activities by conventional analysis using monitoring data, except for the effect of decontamination. Then, this series of studies aim to evaluate the effects of human activities on the reduction. Among the series presentations, this one focuses on correlations between population dynamics characterized by mobile phone GPS information and ecological half life decays of air dose rates measured by KURAMA over a wide area with long-term monitoring using LASSO scheme.
Yamazaki, Takumi; Takada, Chie; Nakamura, Keisuke; Sagawa, Naoki; Hoshi, Katsuya; Nakagawa, Takahiro; Takimoto, Misaki; Tanimura, Yoshihiko*; Takahashi, Fumiaki; Momose, Takumaro; et al.
no journal, ,
no abstracts in English
Machida, Masahiko; Liu, X.*; Tanimura, Naoki*; Saito, Kimiaki
no journal, ,
no abstracts in English
Machida, Masahiko; Murakami, Masashi; Yoshida, Yukihiko; Sasaki, Toshiki; Tanimura, Naoki*
no journal, ,
no abstracts in English
Liu, X.; Machida, Masahiko; Saito, Kimiaki; Tanimura, Naoki*
no journal, ,
To extract the space dependent ecological half-lives from car-borne survey data, a linear sparse model with LASSO regularization and Bayesian background has been developed. The model has been applied to analysis the KURAMA data in Fukushima Prefecture in 2011-2016. The fitting results are in reasonably good agreement with previous works, and could be studied other space dependent factors.