Behavior of radioactive cesium concentration for 13 years after FDNPP accident at Koriyama campus of Nihon University, Fukushima, Japan.

This article focuses on the 13-year monitoring of radioactive cesium isotopes (^134Cs and ^137Cs) in soils and atmospheric fallouts at the Koriyama campus of Nihon University following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in 2011. The study found that cesium concentrations decreased rapidly due to decontamination efforts and environmental weathering, with environmental half-lives significantly shorter than their physical half-lives—approximately 1.21 to 2.82 years in soils and 1.58 to 2.08 years in atmospheric fallouts. Variations in cesium levels were influenced by factors such as incomplete decontamination in wooded areas and re-release of cesium by trees. Additionally, localized high-dose areas were identified near the campus, particularly in paddy fields and a wooded area affected by construction and embankment repair, highlighting the heterogeneous distribution of residual radiation.