Distribution Characteristics of Rn-222 Concentrations on Misasa Spa District, Tottori Pref., JAPAN

We have carried out convenient and highly sensitive radon measurement using absorption to means of a detecting active charcoal and a liquid scintillation spectrometer, Packard Pico-rad System. The α and β radioactivities of its decay products originated from radon gas absorbed detector exposed to air were measured. Its detection limit is 1.7Bq/m in air with an accuracy of about 10% on 200 minites of counting time, and correction coefficient, the ratio of measured radon concentration to standard radon concentration (about 300Bq/m) is 0.75 on the standard radon gas chamber of Japan Nuclear Cycle Development Institute. Misasa district, Tottori pref. is famous for the radioactive spa in Japan. We have measured the Rn-222 concentrations in air with a set of indoor and outdoor. The distribution range of Rn-222 concentrations in air on Misasa spa district from 1995 to 1998 are 8〜194Bq/m indoors, 2〜150Bq/m outdoors, the former generally are higher than those outdoor and these ratios fluctuate on the range 1.1〜2.3. Rn-222 concentrations in air on Asahi, Takeda and Misasa districts geologically formed from granite strata were higher than those on Mitoku and Osika districts formed from volcanic rocks (Andesite and Basalt), and its ratio of indoor to outdoor were similar trend too. The strata is also a influence on Rn-222 concentration in air. The Rn-222 concentrations on Higashi-osaka as control area are 4.9〜17Bq/m indoors and 0.33〜10Bq/m outdoors.