Our new article on CsMP dispersion in Fukushima has been published in the Journal of Hazardous Materials.

During the Fukushima Daiichi Nuclear Power Plant accident, tiny particles a few micrometers in diameter, known as highly radioactive cesium-rich microparticles (CsMPs), were released into the environment. Because these particles contain highly concentrated radioactive cesium, understanding their health impacts when inhaled and how they dispersed through the environment has been an important issue.

In this study, we analyzed soil samples collected from 100 locations across Fukushima Prefecture to investigate the abundance and distribution of CsMPs. The results showed that CsMP abundance varied greatly by region, and in some locations upto 60% of the total radioactivity in the soil was attributable to CsMPs.

By combining the measurements with atmospheric dispersion simulations, we further revealed that a large number of CsMPs were generated and released around 3:00 a.m. on 15 March 2011. A radioactive plume containing up to 4,700 CsMPs per cubic meter of air was transported over a wide area of Fukushima Prefecture by the clockwise movement of the plume from south to northwest on 15 March. In contrast, radioactive cesium released after midnight on 16 March contained no CsMPs and instead existed mainly in water-soluble forms. The study also demonstrated that the deposition of CsMPs onto soil strongly depended on rainfall patterns and the number of airborne particles.

“These findings provide important insights into how radioactive microparticles released during nuclear accidents disperse in the environment and are expected to contribute to future environmental risk assessments for nuclear disasters. Furthermore, the knowledge and research approach established in this study represent an important step toward the creation of a new research field, Advanced Radioactive Particle Science,” says Prof. Satoshi Utsunomiya.

Figure caption

(Left) The size of each circle represents the number of CsMPs contained in 1 g of surface soil. The color within each circle indicates the fraction of total radioactive cesium attributable to CsMP-derived radioactivity.

(Right) Distribution of the number of CsMPs per 1 m³ of radioactive plume air. The size of the red circles represents the number of CsMPs and is overlaid on a representative plume distribution map for 15 March 2011.

It has been featured in the following articles and news releases.

Physics.org: https://phys.org/news/2026-05-radioactive-cloud-fukushima-particle-contamination.html

Eurekalert: https://www.eurekalert.org/news-releases/1127804

Asia Research News: https://www.asiaresearchnews.com/content/unveiling-widespread-dispersion-highly-radioactive-cesium-rich-microparticles-released

自由時報:　https://news.ltn.com.tw/news/life/breakingnews/5454594?utm_medium=R&utm_campaign=SHARE&utm_source=LINE

中文版

釐清福島第一核電廠事故中含高放射性銫微粒（CsMPs）之擴散機制 ——2011年3月15日的污染大氣擴散與沉降決定了CsMP的分布——

2026年5月8日

由國立臺灣大學、九州大學、日本原子力研究開發機構、國立極地研究所、綜合研究大學院大學、筑波大學、南特大學、赫爾辛基大學以及史丹佛大學組成的國際聯合研究團隊，已定量釐清2011年福島第一核電廠事故中所釋放之「含高放射性銫微粒（CsMP）」的釋放時期、擴散量與沉降量。本研究成果已發表於國際知名學術期刊《Journal of Hazardous Materials》（危險材料學報）。

論文資訊

·       論文標題： Uncovering Hidden Dispersion Patterns of Radioactive Cesium-Rich Microparticles from Fukushima Daiichi

·       發表期刊： Journal of Hazardous Materials (Available online 21 April 2026, 142180)

·       DOI： https://doi.org/10.1016/j.jhazmat.2026.142180

·       免費公開存取連結（至6月20日止）： https://authors.elsevier.com/a/1n14W15DSld5sz

CsMP是在爐心熔毀（Meltdown）時於反應爐內形成，其粒徑約數微米，放射性強度約1貝克（Bq）左右，屬於不溶於水的玻璃質微粒。雖然單一微粒的放射性強度並不算高，但因其內部含有高達數個百分比的高濃度放射性銫，因此吸入體內後對健康的影響以及在周邊環境中的分布情況，一直備受各界關注。

本研究針對2011年7月前於福島縣內100個地點採集的土壤樣本（圖左），應用於2018年所開發的CsMP定量法（QCP法）。QCP法是一項由Ikehara等於2018年發表於在《Environ. Sci. Technol.》，其利用定量放射自顯影術（Quantitative Autoradiography）量測單一放射性微粒的放射性強度後，再根據粒徑上限與CsMP的放射性強度下限來計算CsMP的數量。

根據QCP法的分析結果，土壤中CsMP的豐度介於0至52.3個微粒/克之間，其放射性貢獻率（CsMP釋出的放射性強度／土壤整體的放射性強度）最高達61.9%。此外，雖然在西北和東南方向的微粒數量較多，但東南方向的放射性貢獻率較高，西北方向則較低。

圖右則進一步將本研究獲得的CsMP定量分布圖，與世界通用之緊急時環境線量情報預測系統（WSPEEDI）的大氣擴散模擬結果相結合，以詳細解析其釋放時期與擴散過程。結果顯示，CsMP的釋放始於2011年3月15日凌晨2點至3點左右，並持續釋放至當天深夜。在此期間釋放的放射性煙羽（包含大量放射性核種的大氣氣流）僅經歷一次由南向西南再轉向西北方向的迴旋移動，將CsMP輸運至福島縣內，造成福島縣全境主要的銫微粒污染。此外，研究結果亦顯示3月16日0時以後釋放的物質中並不包含CsMP，其成分全數為水溶性銫。

研究顯示，CsMP的分布與沈降的總銫量分布並不一致，其分布受降雨量以及煙羽中CsMP數量顯著影響。尤其伴隨降水而產生的沉降，更促進了CsMP在地表的累積。根據煙羽的放射性強度、沉降銫中CsMP的放射性貢獻率，以及單一微粒的平均放射性強度，估算核電廠附近煙羽中的CsMP數量最高可達約4,700個微粒/立方公尺，西南方向則約為2,070個微粒/立方公尺。這些結果揭示了與傳統放射性銫擴散及沉降截然不同的「CsMP污染」之實際樣貌。

本研究不僅針對福島第一核電廠，對於評估未來各種核能災害所引起的放射性微粒環境風險，亦提供了具備指導方針意義的重要成果。