Abstract
The International Commission on Radiological Protection (ICRP) issued its Publication 137, Occupational Intakes of Radionuclides: Part 3 in which the radon equilibrium factor is fixed as 0.4 for tourist caves; however, several studies have reported a different value for the factor and its seasonal variation has also been observed. In this study, the radon concentration, equilibrium equivalent radon concentration and meteorological data were measured, and the equilibrium factor was evaluated in a tourist cave, Gyokusen-do Cave located in the southern part of Okinawa Island in southwestern Japan. Radon concentrations were measured with an AlphaGUARD and their corresponding meteorological data were measured with integrated sensors. Equilibrium equivalent radon concentration was measured with a continuous air monitor. The measured radon concentrations tended to be low in winter and high in summer, which is similar to previously obtained results. By contrast, the equilibrium factor tended to be high in winter (0.55 ± 0.09) and low in summer (0.24 ± 0.15), with a particularly large fluctuation in summer. It was concluded that measurements in different seasons are necessary for proper evaluation of radon equilibrium factor.
Highlights
Radon (222Rn) is the second leading cause of lung cancer after tobacco smoking [1]
This article described the results of measurements of radon concentration and the equilibrium equivalent radon concentration (EERC), and the evaluation results of equilibrium factor, Feq, in a tourist cave, the Gyokusen-do Cave located in the southern part of Okinawa Island, Japan
The evaluated equilibrium factor was different from the International Commission on Radiological Protection (ICRP) recommendation for it in caves, the same is true for many studies in caves around the world
Summary
Radon (222Rn) is the second leading cause of lung cancer after tobacco smoking [1]. The decay of 226Ra in soil and rocks generates radon gas and in a closed space such as a cave, it can be presumed that high radon concentrations will be observed due to the stagnant air. Commission on Radiological Protection (ICRP) issued Publication 137, Occupational Intakes of Radionuclides: Part 3 in which the commission recommends a dose conversion factor for radon progeny of 6 mSv per mJ h m−3 for indoor workplace workers who are engaged in substantial physical activities, and for workers in tourist caves [9,10]. This value is equivalent to 34 nSv per Bq h m−3, which is approximately four times the dose conversion factor of 9 nSv per Bq h m−3 recommended in the United Nations Scientific. It is important to evaluate the effective dose for workers in tourist caves from radon
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