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Authors: 1. Rio Furukawa (NMIJ, Japan), 2. Miroslaw Janik (NIRS, Japan), 3. Satoshi Kodaira (NIRS, Japan), 4. Seiya Manabe (NMIJ, Japan), 5. Tetsuro Matsumoto (NMIJ, Japan), 6. Chihiro Shimodan (NMIJ, Japan), 7. Yasushi Sato (NMIJ, Japan), 8. Hideki Harano (NMIJ, Japan).
Radon (Rn-222) and its progeny is regarded as the largest contributor to an effective dose for the public globally. A variety of radon monitoring devices has been developed worldwide. The exact calibration of these devices is required. In Japan, a primary radon standard had not been developed. The National Metrology Institute of Japan (NMIJ) has been developing radon standard using the multi-electrode proportional counter (MEPC). The MEPC is a cylinder type detector and its length is 30 cm and its radius is 3.5 cm. The anode wire is arranged in the center of the cylinder and consists of tungsten with a thickness is 50 µm. P-10 gas (nominally argon 90% and methane 10%) is used as the counting gas. Six ring electrodes have been concentrically embedded in the inner sides of the flanges at a distance of 0.5 cm from each other. Electric voltages are applied to these rings to compensate for the field distortions normally occurring at the counter ends. The voltages are calculated by the finite element method. The alpha spectrometry of radon and its short half-life progenies (Po-218 and Po-214) by the MEPC was carried out at the QST NIRS radon facility. And the energy resolution was enough for separating 3 peaks. The applied anode voltage was 1100 V which was in the plateau region. Radon is a gas and fills the MEPC uniformly. However, its short half-life progenies are metal ions and are presumed to be attached to inside walls. With the geometrical condition, the counting efficiency η for radon and its short half-life progenies is approximated as 0.5. The counting efficiency η was calculated by the Monte Carlo particle transport simulation codes Particle and Heavy Ion Transport code System (Sato et al., 2018). η was smaller than the prior research (Busch, 2002). It seems to be reasonable because MEPC manufactured in this study is bigger than the prior research. In this study, the uncertainty will be evaluated.
<References>
Sato, T. Iwamoto, Y. Hashimoto, S. Ogawa, T. Furuta, T. Abe, S. Kai, T. Tsai, P.-E. Matsuda, N. Iwase, H. Shigyo, N. Sihver, L. Niita, K, J. Nucl. Sci. Technol. 55 (2018) 684.
Busch, H. Greupner, U. Keyser, Nucl. Instr. and Meth. A 481 (2002) 330.
