[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-P03] Measurement of radon density in the atmosphere at Okayama, Kochi, Choshi and Kiyosumi, II

*Tohru Okabayashi¹, Kiyotaka Ninagawa², Isao Yamamoto³, Katsumi Hattori⁴, Chie Yoshino⁴, Haruna Kojima⁴, Nobuhiro Maeda (1.Department of Merical Risk and Crisis Management, Faculty of Risk and Crisis Management, Chiba Institute of Science, 2.Faculty of Science, Okayama University of Science, 3.Falcuty of Engineering, Okayama University of Science, 4.Graduate school of Science, Chiba University)

Keywords:radon, atmosphere, earthquake prediction

We report continuous measurement of radon density in atmosphere at Okayama for three years, Kochi, Choshi and Kiyosumi for two years. An increase of radon density in groundwater at Nishinomiya city [1] and in atmosphere [2] at the southern part of Hyogo Prefecture Earthquake in 1995 were reported, respectively. In the case of Tohoku Region Pacific Coast Earthquake, the data obtained the exhaust air monitor that peak duration was long and the peak decreased rapidly before earthquake has been reported at the radiation facility of Fukushima Medical College in Fukushima [3]. On the other hand, a PIN photodiode have been developed and used as a high sensitive alpha ray detector in Super Kamiokande [4]. Since 2016, we also made an experimental setup using PIN photodiode, and measured the radon density in atmosphere. Using a Si PIN photodiode (S3204-09, unsealed, Hamamatsu Photodiode K.K.) as an alpha ray detector, we constructed radon detection setup combined with aluminum pot as an air accumulator, H4083 (Hamamatsu) as a charge amplifier, C4900-01 (Hamamatsu) as a high voltage power supply module, a pulse shaped amplifier with time constant of 10 msec, a multi channel analyzer (MCA-LiteN), and a PC as a data analysis. Obtained alpha spectra of atmosphere showed 4 peaks originated from ²¹⁸Po, ²¹⁴Po and ²¹⁰Po of U series, and ²¹²Po of Th series. Since 2017, we newly started to measure at Kochi, Choshi and Kiyosumi using our apparatus. Details of observed data are discussed in addition the data at Okayama since 2016.
[1] Igarashi G., Saeki S., Takahata N., Sumikawa K., Tasaka S., Sasaki Y., Takahashi M. and Sano Y. : Ground-water radon anomaly before the Kobe earthquake in Japan, Science, 269, 60-61, 1995.
[2] Yasuoka, Y. and Shinogi, M.: Anomaly in atmospheric radon concentration: a possible precursor of the 1995 Kobe, Japan, earthquake. Health Physics, 72, 759-761, 1997.
[3] Nagahama H., Yasuoka Y., Suzuki T., and Homma Y.: Radon Variation in the Air Before the 2011 Tohoku Earthquake (Mw =9.0), Programme and Abstracts, A32-09, The Seismological Society of Japan. 2011, Fall Meeting.
[4] Nemoto, M., Tasaka S., Hori H., Okumura K., Kajita T., and Takeuchi Y. : Development of High Sensitive Radon Detector with Electrostatic Collection. Radioisotopes, 46, 710-719, 1997 (Japanese).