2014 Volume 77 Issue 4 Pages 324-332
Objectives: Radon (222Rn) is a noble gas and a component of water in many hot spring spas. The Hot Springs Law and the Guideline of Analytical Methods of Mineral Springs (revised edition) of Japan classify springs containing 74 Bq/kg or more of radon as “hot springs” and those with radon levels exceeding 111 Bq/kg as “medical springs”, also called “radioactive springs”. Komono Town, one of the foremost spa and health resort destinations in Mie Prefecture, is the site of many radioactive springs. For the purpose of regional vitalization of this area through radioactive springs, it is necessary to confirm the safety and effectiveness of their use. To evaluate the exposure dose due to radioactive spring usage, it is important to measure radon concentration in air, especially in high-humidity air such as in bathing rooms.
Methods: The concentration of radon in air was analyzed using an activated charcoal detector (PICO-RAD; AccuStar Labs) with a desiccant (Drierite; 8-mesh anhydrous calcium sulfate; W.A. Hammond Drierite Company, Ltd.) and a liquid scintillation counter (LSC LB-5; Hitachi Aloka Medical, Ltd.). A DPO (2,5-diphenyloxazole) + POPOP (1,4-bis- (5-phenyl-2-oxazolyl)-benzene) toluene solution (Wako Pure Chemical Industries, Ltd.) was used as a liquid scintillator. Activated charcoal detectors were set up in and around the radioactive spring facilities.
Results and Discussion: In a radioactive spring facility, radon concentration in air in the bathing room and changing room were relatively high at about 50 Bq/m3. In the corridor on all floors and at the entrance, these values were approximately 10-30 Bq/m3, indicating that radon in hot spring water diffuses into the air and spreads within the facility. Outdoors, radon concentration was 12.5 Bq/m3 at a campsite near the discharge point of the radioactive spring.
Exposure dose is calculated under the assumption of a two-day stay, during which the visitor will use the bath for several hours. The results obtained show that the exposure dose at the hot spring facility is lower than the exposure dose from daily environmental radiation or medical devices. These conclusions are considered sufficient to confirm the safety of the hot spring facility.
