INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND.

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0 mSv, respectively, and as 5.9-9.0 mSv in total.

Identifying indoor radon sources in Pa Miang, Chiang Mai, Thailand.

Radon is the leading source of lung cancer mortality after smoking in Chiang Mai, Thailand. Finding a source of carcinogens is one of the important measures for preventing the cancer risk for this region. Specific sites at Pa Miang, Doi Saket have the highest incidences of lung cancer and have a combination of factors that influence indoor radon concentration. Our study identified the sources of indoor radon within several houses. The results indicate that geological and topographic characteristics, including active faults and mountain terraces, are the main sources of indoor radon, especially for wooden houses. Besides building materials, the design of the houses, ventilation conditions, and lifestyle choices are all factors influencing indoor radon concentrations and its associated risk. Although radon levels (29-101 Bq m-3) and total indoor annual effective doses (0.9-3.8 mSv year-1) received from all sources at these sites have shown no significant health risk due to radon exposure , this investigation will be useful as a starting point to guide strategies to respond and prevent the risk of lung cancer, especially in Chiang Mai.

CAR-BORNE SURVEY OF NATURAL BACKGROUND GAMMA RADIATION IN WESTERN, EASTERN AND SOUTHERN THAILAND.

Natural background gamma radiation was measured along the main roads in the eastern, western and southern regions of Thailand using a car-borne survey system with a 3-in × 3-in NaI (Tl) scintillation spectrometer. The system was able to quickly survey a large area and obtain outdoor absorbed dose rate in air from a gamma ray pulse height distribution. A total of 19 219 data of the outdoor absorbed dose rate in air were collected. The average outdoor absorbed dose rate in air in the eastern, western and southern regions were found to be 8-127, 16-119 and 16-141 nGy h -1 , respectively. The highest outdoor absorbed dose rate in air was detected in the southern region of Thailand. The corresponding average outdoor annual effective dose to the public ranged from 11.7 to 80.8 µSv.

Mitigation of the effective dose of radon decay products through the use of an air cleaner in a dwelling in Okinawa, Japan.

Field measurements were conducted to assess the effects of an air cleaner on radon mitigation in a dwelling with a high radon concentration in Okinawa, Japan. The measurements included indoor radon concentration, individual radon progeny concentration, equilibrium equivalent concentration of radon (EECRn), unattached fraction, and size distribution of aerosol-attached radon progeny. These measurements were conducted in a 74 m(3) room with/without the use of an air cleaner. The results showed that the mean radon concentration during the measurement was quite high (301 Bq m(-3)). The operation of air cleaner decreased the radon progeny activity concentration, EECRn and equilibrium factor by 33%, 57% and 71%, respectively, whereas the unattached fraction increased by 174%. In addition, the activity concentration of attached radon progeny in the accumulation mode (50-2000 nm) was obviously deceased by 42%, when the air cleaner was operated. According to dosimetric calculations, the operation of air cleaner reduced the effective dose due to radon progeny by about 50%.