*Article* **Passive-Type Radon Monitor Constructed Using a Small Container for Personal Dosimetry**

**Yuki Tamakuma 1,2, Chutima Kranrod 1, Takahito Suzuki 2,**†**, Yuki Watanabe 3,**‡**, Thamaborn Ploykrathok 1,§, Ryoju Negami 2, Eka Djatnika Nugraha 2, Kazuki Iwaoka 4, Mirosław Janik 4, Masahiro Hosoda 1,2 and Shinji Tokonami 1,\***


Received: 14 July 2020; Accepted: 2 August 2020; Published: 5 August 2020

**Abstract:** The International Commission on Radiological Protection (ICRP) recently recommended a new dose conversion factor for radon based on the latest epidemiological studies and dosimetric model. It is important to evaluate an inhalation dose from radon and its progeny. In the present study, a passive radon personal monitor was designed using a small container for storing contact lenses and its performance was evaluated. The conversion factor for radon (222Rn), the effect of thoron ( 220Rn) concentration and the air exchange rate were evaluated using the calibration chamber at Hirosaki University. The minimum and maximum detectable radon concentrations were calculated. The conversion factor was evaluated as 2.0 <sup>±</sup> 0.3 tracks cm−<sup>2</sup> per kBq h m−3; statistical analyses of results showed no significant effect from thoron concentration. The minimum and maximum detectable radon concentrations were 92 Bq m−<sup>3</sup> and 231 kBq m−<sup>3</sup> for a measurement period of three months, respectively. The air exchange rate was estimated to be 0.26 <sup>±</sup> 0.16 h<sup>−</sup>1, whose effect on the measured time-integrated radon concentration was small. These results indicate that the monitor could be used as a wearable monitor for radon measurements, especially in places where radon concentrations may be relatively high, such as mines and caves.

**Keywords:** passive radon monitor; development; sensitivity; detection limit; air-exchange rate
