[1D05-08] Environmental Radioacitivty and Monitoring 1

[1D08] 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 algorithm

*Xudong Liu¹, Masahiko Machida¹, Kimiaki Saito¹, Naoki Tanimura² (1. JAEA, 2. Mizuho Information & Research Institute, Inc.)

Keywords:ecological half-life, ambient dose rate, car-borne survey, fused LASSO

Ecological half-life has been widely used to describe the long-term decrease of ambient dose rates in addition to radioactive decay. With large-scale car-borne survey, the over-all ecological half-lives have been evaluated using campaign averaged data. However, extracting space dependent information remains a challenging task, which requires fundamental developments in methodology. 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. The key components of our work include a linear sparse model for non-linear fitting, Bayesian treatment for background dose, and fused LASSO for spatial correlations. By combing depth first search approximation, Taut String solution, and back-tracking FISTA, our new algorithm could simultaneously fit space-time information with linear time complexity.