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Journal Articles

Selection method for observation points using Bayesian LASSO at estimating radiation source distribution from air dose rates

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.

Journal Articles

Effect of magnetic field on positron lifetimes of Fe, Co and Ni

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)

Oral presentation

Investigation on distribution of radioactive substances in Fukushima, 4; Study on the ecological half-lives of ambient dose rates using car-borne survey data with fused LASSO

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.

Oral presentation

Anthropogenic impacts on temporal decrease in air dose rate in urban areas, 3; Correlation between population dynamics and ecological half-life decay estimated by using LASSO

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.

Oral presentation

Investigations of personal dose characteristics involved Fukushima Daiichi reactor accident, 4; Field test, 2; Response of the personal dosemeter on the phantoms and result of a measurement of the ambient dose and the energy spectrum of $$gamma$$ rays

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

Oral presentation

Investigation on distribution of radioactive substances in Fukushima, 16; Development of air dose rate temporal change model employing machine learning

Machida, Masahiko; Liu, X.*; Tanimura, Naoki*; Saito, Kimiaki

no journal, , 

no abstracts in English

Oral presentation

Studies of machine learning techniques toward rapid analysis of X-ray fluorescence spectra

Machida, Masahiko; Murakami, Masashi; Yoshida, Yukihiko; Sasaki, Toshiki; Tanimura, Naoki*

no journal, , 

no abstracts in English

Oral presentation

A Study of KURAMA measurement data by sparse modeling

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.

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