[H-CG21] Monitoring the Comprehensive Nuclear-Test-Ban Treaty: Status, operations, and scientific application

[HCG21-P03] Source term estimation of Xe-135 observed in the noble gas measurement network in Japan

*Akiko FURUNO¹, Hisanori Tateoka², Yoichi Yamamoto¹, Kurihara Toshiyuki¹, Yutaka Tomita¹ (1.Japan Atomic Energy Agency, 2.East Japan Institute of Technology Co. Ltd.)

Keywords:CTBT, Noble gas joint measurement project, Atmospheric dispersion, Source term estimation

Our team operates and manages the Takasaki Radionuclide Monitoring Station of the CTBT International Monitoring System, as well as the monitoring stations of the Noble gas joint measurement project with CTBT. Radioactive xenon is observed irregularly and frequently at these stations, and it is very important to identify the source of the emissions in order to ensure detection of nuclear tests. CTBT officially monitors the following four noble-gas nuclides; Xe-133, Xe-131m, Xe-133m, and Xe-135. Xe-133 is the most frequently detected of the four nuclides. However, it is difficult to identify the release source of Xe-133 because it has a half-life of 5.2 days and may affected by Xe-133 from distant facilities (e.g., Europe or Russia) due to meteorological conditions and release amounts. Xe-135, on the other hand, is detected less frequently, but its short half-life of 9.1 hours limits possible sources to a relatively narrow range. We estimated the source of Xe-135 for two examples observed in 2021 at the past conference. In this presentation, we focus on the Xe-135 detection events to date and discuss possible release sources that could affect the background of radioactive noble gases in Japan.