Radon levels and dose assessment at the basement workplaces of hospitals in different regions of Taiwan

The basements of large hospitals in Taiwan are usually working areas for image radiometry, radiation therapy, and nuclear medicine, where the radon concentration can be accumulated. This study investigated radon concentrations in the basement working environments of 30 hospitals in different regions with various geology of Taiwan, aiming to explore the relationship between geological conditions and radon concentrations and estimate the radiation dose received by the working staff. Portable MR107+ semiconductor radon detectors calibrated with a radon chamber were used for radon measurement at the hospital basement working areas according to the protocol of MAH-2019 instrument placement recommendations from the US EPA. The excess lung cancer risk (ELCR) as well as the lung cancer cases per million persons (LCC) were further derived from the radiation dose. The basement working areas investigated are located on the first to sixth underground floors of hospitals in Taiwan mainland and islands, Penghu and Kinmen. The 222 Rn concentration higher than 100 Bq/m 3 was observed at CH-1 (122.1 Bq/m 3 ) in Changhua City and CY-1 (114.7 Bq/m 3 ) in Chiayi City. This is attributed to that the central air conditioning systems of these hospitals were turned off during off-duty hours. The radon concentrations of all hospitals were lower than the action level, 150 Bq/m 3, regulated by the US EPA. No significant relationship was found between radon concentration and the geological characteristics of the measured sites. That is, the ventilation of the basement working areas in hospitals is more important than local geological characteristics on indoor radon concentration, and therefore proper ventilation is crucial for reducing radon gas concentration in the hospital basements. Estimated annual effective dose from 222 Rn for the hospital staff was higher than 1 mSv/y at YL (1.24 mSv/y), CH-1 (1.64 mSv/y), CY-1 (1.54 mSv/y), CY-2 (1.34 mSv/y), and PH-2 (1.14 mSv/y), and that for the rest sites was <1 mSv/y. The maximum mean ELCR was found to be 0.63% at CH-1, and the related LCC was estimated to be 29.5 per million persons.