Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources;
11. Baeza, A., del Ri$\acute{o}$, M., Miro, C., and Paniagua, J.M., 1992, Natural radioactivity in soils of the province of C$\acute{a}$ceres (Spain), Radiat. Prot. Dosim., 45(1/4), 261-263
12. Jacobi, W., 1988, Lung cancer risk from environmental exposure to radon daughters. ICRP publication 50, Radiat. Prot. Dosim., 24(1-4), 19-23
13. Megumi, K., Oka, T., Yaskawa, K., and Sakanoue, M., 1982, Contents of natural radioactive nuclides in soil in relation to their surface area, J Geophys. Res., 87, 10857-10860
14. Myrick, T.E., Berven, B.A., and Haywood,.F.F., 1983, Determination of concentrations of selected radionuclides in surface soil in the U.S., Health Phys., 45(3), 631-642.
15. Porstend$\ddot{o}$rfer, J. and Reineking, A., 1992, Indoor behaviour and characteristics of radon progeny, Radiat. Prot. Dosim., 45(1/4), 303-311
16. UNSCEAR, 1993, Ionizing Radiation: Sources and Biological Effects, 1993 report, pp. 33-90, United Nations, New York