Ever more attention has been focused on naturally occurring radiation, thanks to the shift of public concern and scientific interest from high to low-level radiation in recent years. There are many places in the world that are known to have high levels of terrestrial background gamma radiation as well as highly concentrated radon and their decay products in the air, soil and drinking water. Various scientific investigations have been conducted in those areas to collect information on radiation doses and their health effects, contributing greatly to advancing our knowledge. In recent years, technologically enhanced naturally occurring radioactive material (TENORM) has also attracted attention. The 6th International Conference on High Levels of Natural Radiation and Radon Areas was held in Osaka, Japan from September 6-10, 2004, for the purpose of exchanging information and experience regarding investigations in this field. These proceedings contain more than 100 papers presented at the meeting, which aimed to discuss the following major topics: 1) risk assessment, radiation protection, environmental transfer pathways and ecological impacts related to natural radiation and TENORM, 2) dosimetry of natural-radiation, including radon, thoron, and cosmic rays, and its technological aspects, e.g., individual dosimetry and retrospective measurements, and 3) in vitro and in vivo biological studies of low-level radiation, including molecular mechanisms.Preface. Conference Officers and Committees. Acknowledgements. Invited papers. What did we learn from radiobiological and genetic studies in HBRAs? Chromosome study in high background radiation area in Southern China (C. Wang et al.). Investigations on the health effects of human population residing in the high-level natural radiation areas in Kerala in the southwest coast of India (M.V. Thampi et al.). New findings in the very high natural radiation area of Ramsar, Iran (M. Ghiassi-Nejad et al.). Factors for the induction of DNA rearrangements leading to malignant disease. Chromosomal mutations by low dose radiation vs. those by other mutagenic factors (I. Hayata). Extranuclear target and low dose radiation risk assessment (T.K. Hei, H. Zhou, M. Suzuki). Molecular dissection of in vivo DNA rearrangements induced by radiation and chemical mutagens (T. Nohmi, K.-i. Masumura). Other topics on cytogenetics and biology. Chromosome aberrations in peripheral lymphocytes of individuals living in dwellings with an increased level of indoor radon concentrations (G. Stephan, U. Oestreicher, R. Lehmann). Cytogenetic studies of populations exposed to Chernobyl fallout (D.C. Lloyd). Can we estimate individual radiation doses of HBRA residents? Results of Yangjiang study in China and an experience of Ramsar survey in Iran (N. Fujinami et al.). Individual dose estimation - our experience with the Karunagappally study in Kerala, India (K. Raghu Ram Nair et al.). Indoor radon, thoron, and thoron daughter concentrations in Korea (Y.J. Kim et al.). The Spanish experience on HBRA (L.S. Quindos et al.). Radon exposure and its potential risk. Lung cancer risk due to radon in dwellings - evaluation of the epidemiological knowledge (H.E. Wichmann et al.). Thoron in the living environments of Japan (H. Yonehara et al.). Occupational exposure to radon-experience and approach to regulatory control (E. Ettenhuber). Radon retrospective measurements (C. Samuelsson). Significance of radon and thoron measurements on dose estimation. Thoron versus radon: measurement and dosimetry (N.H. Harley et al.). Rn-Tn discriminative measurements and their dose estimates in Chinese loess plateau (Y. Yamada et al.). Radon dosimetry and its implication for risk (A. Birchall, J.W. Marsh). Reference fields and calibration techniques for Rn-220 measuring instruments (E. Gargioni, D. Arnold). Other topics on dosimetry. Dosimetric considerations for environmental radiation and NORM (S.L. Simon). Measurements to determine the radiological impact of uranium and thorium in soils in the darling scarp (L.F. Toussaint). What did we learn from epidemiological studies in HBRAs? Cancer and non-cancer epidemiological study in the high background radiation area of Yangjiang, China (J. Zou et al.). What did we learn from epidemiological studies in high background radiation area in India (P. Jayalekshmi et al.). Mortality and morbidity from cancer in the population exposed to high level of natural radiation area in Ramsar, Iran (A. Mosavi-Jarrahi et al.). Pattern of cancer mortality in some Brazilian HBRAs (L.H.S. Veiga, S. Koifman). WHO network and international collaborative project on residential radon risk (Z. Carr, M. Repacholi). Commentary on information that can be drawn from studies of areas with high levels of natural radiation (C. Elisabeth). Cosmic rays. High-level doses brought by cosmic rays (K. Fujitaka). Factors affecting cosmic ray exposures in civil aviation (G.M. Kendall). Depleted uranium. Properties, use and health effects of depleted uranium (W. Burkart, P.R. Danesi, J.H. Hendry). Public health and environmental aspects of DU (J.P. McLaughlin). A comparison of human exposure to natural radiation and DU in parts of the Balkan region (Z.S. Zunic, K. Fujimoto, I.V. Yarmoshenko). Summary. Summary of HBRA epidemiological studies (Q. Sun, Z. Carr). Summary of dosimetry (radon and thoron) studies (S. Tokonami). Summary of biological studies (S. Kodama). Overall summary and comments (M. Kai). Contribution of HBRA studies to health risk assessments and regulatory control. Contribution of high natural background radiation area studies to an evolved system of radiological protection (M. Kaneko). Problems with HBRA studies in health risk assessment (G.M. Kendall). New public dose assessment from internal and external exposures in low- and elevated-level natural radiation areas of Ramsar, Iran (M. Sohrabi, M. Babapouran). Oral presentations. Cytogenetics and biology. Changes of chromosome aberration rate and micronucleus frequency along with accumulated doses in continuously irradiated mice with a low dose rate of &ggr,-rays (K. Tanaka et al.). Dose and dose rate effects of low dose ionizing radiation on activation of p53 in immortalized murine cells (T. Sugihara et al.). Histologic assessment of regenerating rat liver under low-dose rate radiation exposure (D.V. Guryev). Increased radiosensitivity of splenic T lymphocytes in pregnant mice (Y. Igari et al.). Effects of low dose-rate irradiation on the glucose metabolism in type II diabetes model mice (T. Nomura, K. Sakai). Adaptive response, split dose and survival of mice (A. Bhan Tiku, R.K. Kale). Heavy ion induced transformation of telomerase immortalized human small airway epithelial cells (C.Q. Piao et al.). Mechanisms of liver carcinogenesis by chronic exposure to alpha-particles form internally deposited Thorotrast (L. Wang et al.). Mangiferin, a glucosylxanthone, protects against the radiation-induced micronuclei formation in the cultured human peripheral blood lymphocytes (G.C. Jagetia, V.A. Venkatesha). Association of glutathion S-transferase and chromosomal aberrations as a means to determine occupational exposure (A. Movafagh et al.). Hormone levels associated with immune responses among inhabitants in HLNRAs of Ramsar-Iran (F. Zakeri, A. Kariminia). Radioadaptive responses induced in lymphocytes of the inhabitants in Ramsar, Iran (S.M.J. Mortazavi et al.). Dosimetry. Elevated radon concentrations in a Pleistocenic cave operating as a show cave (C. Papastefanou et al.). Radon in groundwater: analysis of causes using GIS and multivariate statistics: A case study in the Stockholm county (K. Skeppström, B. Olofsson). Current studies on radon gas in Thailand (P. Wanabongse, S. Tokonami, S. Bovornkitti). Natural radioactivity in the high background radiation area at Erasama beach placer deposit of Orissa, India (D. Sengupta et al.). High radon areas in Norway (T. Strand et al.). Levels of indoor radon, thoron, and their progeny in Himalaya (R.C. Ramola). Long-term measurements of radon progeny concentrations with LR 115 SSNTDs (K.N. Yu et al.). Convenient methods for evaluation of indoor thoron progeny concentrations (W. Zhuo, S. Tokonami). Radon exhalation from a ground surface during a cold snow season (H. Yamazawa et al.). The migration of U-238 in the system 'soil-plant' and its effect on plant growth (A.A. Kasianenko et al.). 210Po and 210Pb content in environmental and human body samples in the Ramsar area, Iran (H. Samavat et al.). High resolution analyses of temporal variations of airborne radionuclides (K. Komura et al.). Naturally accumulated radiation doses and dating of archaeologically burnt materials using luminescence from white minerals (T. Hashimoto, Y. Nakata, T. Yawata). Epidemiology and radiation protection. Case-control study of residential radon and childhood leukemia in Japan: results from preliminary analyses (S. Yoshinaga et al.). The risk of lung cancer in HBR area in India - a case control study (V.S. Binu et al.). Improvement of the radon situation at former uranium mining and milling sites in East Germany (P. Schmidt, J. Regner). Investigation and reduction of personnel exposure levels in Bavarian water supply facilities (S. Körner, M. Trautmannsheimer, K. Hübel). The ENVIRAD project: a way to control and to teach how to protect from high indoor radon level (A.M. Esposito et al.). Radiation hazard and protection for the nuclear weapon terrorism (J. Takada). Posters. Cytogenetics and biology. Effects of radon and thermal therapy on osteoarthritis (K. Yamaoka et al.). Induction of micronuclei in rat tracheal epithelial cells following radon exposure at air-liquid interface culture (K. Fukutsu et al.). Simplification of analysis for comparison of radioactive characteristics and its application to some minerals for radon therapy (K. Hanamoto, K. Yamaoka). Bystander cellular effects in normal human fibroblasts irradiated with low-density carbon ions (M. Suzuki et al.). Effects of low dose-rate long-term gamma-ray irradiation on DNA damage in mouse spleen (K. Otsuka, K. Sakai). Detection of radiation-induced mutations in the liver after partial hepatectomy using HITEC transgenic mice (A. Ootsuyama, F. Kato, T. Norimura). Role of p53 gene in genetic instability induced by ionizing radiation (K. Igari et al.). Adaptive response of bone marrow stem cells induced by low-dose rate irradiation in C57BL/6 mice (K. Shiraishi et al.). The life saving role of radioadaptive responses in long-term interplanetary space journeys (S.M.J. Mortazavi, J.R. Cameron, A. Niroomand-Rad). Biosorption of chromium(III) by new bacterial strain (NRC-BT-2) (M. Rabbani et al.). Uptake and removal of nickel by new bacterial strain (NRC-BT-1) (H. Ghafourian et al.). Biosorption of Cs+ by new bacterial strain (NRC-BT-2) (Y. Nazeri et al.). The effect of low dose-rate &ggr,-radiation on the chemiluminescence of blood serum at chronic inflammation in rats (N. Klimenko et al.). Measurements. An intercomparison exercise for thoron gas measurement (T. Ishikawa, A. Cavallo, S. Tokonami). Particle size measurement of radon decay products using MOUDI and GSA (S. Tokonami et al.). Practicality of the thoron calibration chamber system at NIRS, Japan (Y. Kobayashi et al.). Measurements of radon, thoron and their progeny in a dwelling in Gifu prefecture, Japan (C. Németh et al.). Soil radon flux and outdoor radon concentrations in East Asia (W. Zhuo et al.). Estimation of radon-222 exhalation rate and control of radon-222 concentration in ventilated underground space (J. Moriizumi et al.). Measurements of concentrations and its ratio of radon decay products in rainwater by gamma-ray spectrometry with a low background germanium detector (M. Takeyasu et al.). Radon exhalation rate monitoring in/around the closed uranium mine sites in Japan (Y. Ishimori, Y. Maruo). Radon-222 concentrations and the environmental radiation dose rates at Misasa spa districts, Japan (M. Inagaki et al.). Distribution characteristics of natural radionuclides at some spa districts in Japan (T. Koga et al.). Optimization of measuring methods on size distribution of naturally occurring radioactive aerosols (K. Yamasaki et al.). Measurement of radon concentration in water using direct dpm method of liquid scintillation counter (Y. Yasuoka et al.). Airborne and waterborne radon concentrations in houses with the use of groundwater (T. Ishikawa, S. Yoshinaga, S. Tokonami). Emanating power of 220Rn from a powdery radiation source (T. Iimoto et al.). The environment dose measurement using the OSL dosimeter (I. Kobayashi et al.). Eolian dust may be an effective expander of HBRA: a case of China-Ryukyu connection (M. Furukawa et al.). Radon and thoron in Yongding Hakka Earth Building in Fujian Province of China (M. Wei et al.). Natural radiation levels in Fu'an city in Fujian Province of China (Y. Luo et al.). A pilot survey on indoor radon and thoron progeny in Yangjiang, China (G. Qiuju, C. Bo, S. Quanfu). High background radiation valley formed by Peitou Hot Spring (C.-J. Chen, P.-H. Lin, C.-C. Huang). Natural radionuclide distribution in soil samples around Kudankulam Nuclear Power Plant Site (Radhapuram taluk of Tirunelveli district, India) (G.M. Brahmanandhan et al.). Measurement of activity concentrations of 40K, 238U and 232Th in soil samples of Agastheeswaram taluk, Kanyakumari district, India (D. Khanna et al.). Study of primordial radionuclide distribution in sand samples of Agastheeswaram taluk of Kanyakumari district, India (J. Malathi et al.). Primordial radionuclides concentrations in the beach sands of East Coast region of Tamilnadu, India (K.S. Lakshmi et al.). Measurement of primordial radionuclide distribution in the soil samples along the East coast of Tamilnadu, India (V. Meenakshisundaram et al.). Indoor gamma dose measurement along the East coast of Tamilnadu, India using TLD (S. Selvasekarapandian et al.). Study of background radiation from soil samples of Udumalpet Taluk of Coimbatore district, India (R. Sarida et al.). Study of background radiation from soil samples of Pollachi taluk, Tamilnadu, India (R. Amutha et al.). Enrichment of natural radionuclides in monazite areas of coastal Kerala (Y. Narayana, P.K. Shetty, K. Siddappa). Thoron (220Rn) levels in dwellings around normal and high background areas in India (T.V. Ramachandran et al.). Background radiation exposure levels: Indian scenario (T.V. Ramachandran, K.P. Eappen, Y.S. Mayya). Radiological impact of utilization of phosphogypsum and fly ash in building construction in India (V.K. Shukla et al.). Indoor and outdoor radon levels and their diurnal variations in the environs of southwest coast of India (N. Karunakara et al.). Study of indoor gamma radiation in Coimbatore City, Tamilnadu, India (J. Malathi et al.). Natural radioactivity in South West Coast of India (N. Karunakara, H.M. Somashekarappa, K. Siddappa). Transportation of radionuclides from Western Ghats to Arabian sea through some major rivers of South India (K.M. Rajashekara et al.). Application of well-type NaI(Tl) detector for indoor radon measurements (D. Al-Azmi). Assessment of exposure to the population of Russia from radon (A.M. Marenny et al.). Altai Region of Russia - a high radon potential area (V.P. Borisov, I.P. Saldan, A.P. Strokov). Assessment of exposure to the population of Moscow from natural sources of radiation (A.M. Marenny et al.). Comparison of contemporary and retrospective radon concentration measurement in dwellings in Poland (J. Jankowski et al.). Radon on underground tourist routes in Poland (J. Olszewski, W. Chru&sacute,cielewski, J. Jankowski). Radioactivity in vine cellars in Hungary and Slovenia (P. Szerbin et al.). Tenorm's around coal fired power plant tailings ponds in Hungary (P. Szerbin et al.). Evaluation of the technologically enhanced naturally occurring radioactive material in Hungary (L. Juhász, P. Szerbin, I. Czoch). Inaccuracies in assessing doses from radon in workplaces (C. Németh et al.). Naturally occurring alpha emitting radionuclides in drinking water (Hungary) (T. Kovács et al.). Public exposure to radon and thoron progeny in Romania (O. Iacob, C. Grecea). Radon exposure in Slovenian kindergartens and schools (J. Vaupotic, I. Kobal). Blower door method and measurement technology in radon diagnosis (A. Fronka, L. Moucka). Radon programme in the Czech Republic-experience and further research (A. Fronka, J. H&uring,lka, J. Thomas). Effective dose calculation using radon daughters and aerosol particles measurement in Bozkov Dolomite Cave (L. Thinova et al.). Measurement of radon daughters in water and in air using the detection unit \'YAPMARE\' with a YAP:Ce scintillation detector (L. Thinova et al.). A radon survey in some regions of Turkey (Y. Yarar, T. Günaydi, E. Kam). Environmental radioactivity concentrations of Tekirdag (Y. Yarar, E. Kam). Radiological impact in an area of elevated natural radioactivity background: the case of the island of Ikaria-Aegean Sea, Greece (T. Georgia, F. Heleny). Beyond track etch monitoring-the gap between passive and active devices has been bridged! (T. Streil, S. Feige, V. Oeser). MyRIAM: an active electronic online personal inhalation dose meter for detection of &agr,- and &bgr,-radiation on aerosols (T. Streil, V. Oeser). Estimation of the radon dose in buildings by measuring the exhalation rate from building materials (V. Steiner et al.). Retrospective radon assessments in a high radon dwelling in Ireland (J.P. McLaughlin et al.). Radiation exposure from high-level radiation area and related mining and processing activities of Jos Plateau, central Nigeria (I.I. Funtua, S.B. Elegba). Radon concentrations in caves of Parque Estadual do Alto Ribeira (PETAR), SP, Brazil: preliminary results (S. Albergi, B.R.S. Pecequilo, M.P. Campos). Distribution pattern of natural radionuclides in Lake Nasser bottom sediments (A.E. Khater, Y.Y. Ebaid, S.A. El-Mongy). Natural radioactivity contents in tobacco (N. Abd El-Aziz, A.E.M. Khater, H.A. Al-Sewaidan). 235U-&ggr, emission contribution to the 186 keV energy transition of 226Ra in environmental samples activity calculations (Y.Y. Ebaid, S.A. El-Mongy, K.A. Allam). Determination of radium isotopes in mineral water12 samples by &agr,-spectrometry (G. Jia et al.). Variation of terrestrial gamma radiation in Toki, Japan - comparison between gamma-ray spectrometry using Ge semiconductor and ICP-MS measurement (Y. Fujikawa et al.). Spectrometry characteristics of photon fields and atmospheric radionuclide deposits monitoring in one part of Southern Bohemia (J. Kluson et al.). GPS-based handheld device for measuring environmental gamma radiation and mapping contaminated areas (J. Paridaens). Development of a remote radiation monitoring system using unmanned helicopter (S. Okuyama et al.). Thermoluminescence mechanism on SiO2 phosphor (M. Takami, M. Ohta, H. Yasuda). Radon anomaly related to the 1995 Kobe earthquake in Japan (Y. Yasuoka et al.). Generation of runaway electrons induced by radon progeny products in thunderstorm electric fields and the initiation of lightning discharges (T. Torii et al.). Epidemiology and radiation protection. Residential radon and childhood leukemia: a metaanalysis of published studies (S. Yoshinaga, S. Tokonami, S. Akiba). New approach to dose optimization for members of the public (T. Hattori, K. Sakai). A study on the necessity of boarding control for international flights (H. Yasuda, K. Fujitaka). Cancer risk due to exposure to high levels of natural radon in the inhabitants of Ramsar, Iran (S.M.J. Mortazavi, M. Ghiassi-Nejad, M. Rezaiean). Living in high natural background radiation areas in Ramsar, Iran. Is it dangerous for health? (A.S. Monfared et al.). The need for considering social, economic, and psychological factors in warning the general public from the possible risks due to residing in HLNRAs (S.M.J. Mortazavi et al.). Lung cancer risk due to radon exposure for 10 or 20 years (J. Chen). Radiation doses to cardiovascular system due to absorbed radon (J. Chen, R.B. Richardson). Award of honor. Concluding remarks. Author index. Keyword index.