This study explores the potential of Raman Lidar for measuring water vapor and water clusters generated by radiation ionization, addressing challenges in detecting radioactive isotopes in high radiation environments. The most common method for measuring alpha nuclide contaminants is to place a detector close to the contaminant and measure the alpha rays emitted. In this study, on the fundamental experiment, pure water particles were injected into a cubic glass chamber, and Raman signals for water (403.7 nm) and water vapor (407.8 nm) were detected for 355 nm incident light. A narrow bandpass filter (1.5 nm bandwidth) effectively distinguished between the Raman signals of water and water vapor. This led to the development of a three-channel Raman lidar capable of detecting nitrogen (387 nm), water (404 nm), and water vapor (408 nm). Measurements were conducted in a humidity-controlled environment using sealed Americium radiation sources at the Japan Atomic Energy Agency. Results showed that as radioactivity increased, water vapor signals decreased while water signals increased. It is expected that water values will rise at a rate of 7.5 times relative to the decrease in water vapor, with observed results indicating a change rate of approximately six times. Future work will focus on evaluating these change rates, improving measurement reproducibility, and estimating the diameter of water clusters.
Hydrogen explosion on Fukushima No.1 nuclear power plant caused huge damage in real life. Especially its radiation damage caused widespread. Field works on intermediate storages and reuses of decontaminated soils has been started in earnest under government promotion since 2017. This study put a compact polarization lidar at the intermediate storage site, where was only 3 kilometers away from Fukushima No.1 plant. There was a difficult-to-return zone. The lidar system was remotely controlled at Chiba univ. Its observation range was 300m. It covered almost the whole of working field. The lidar monitoring was conducted at one month during Nov. and Dec. in 2017. The lidar scanned horizontally by crossing the dropping port of the decontaminated soils and capturing the suspended dusts on the soil preparation. The lidar monitoring was synchronized with 3 dust-samplers, and we obtained spatial distributions of dust density and estimated the distribution of the radioactivity concentration. The lidar counting rate for dust and the radioactivity concentration was estimated 0.001 mg/m3 /count and 10-9 – 10-10 Bq/cm3 , respectively. This estimation was much lower than the working rule of safety assessment of 10-5 Bq/cm3 . The expressions of these distributions are helpful as communication tool to civilians’ safe and workers’ secure.
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