DOSES TO THE NORWEGIAN POPULATION FROM NATURALLY OCCURRING RADIATION AND FROM THE CHERNOBYL FALLOUT TERJE STRAND ISBN-B2-90187-4 I - 6 DOSES TO THE NORWEGIAN POPULATION FROM NATURALLY OCCURRING RADIATION AND FROH THE CHERNOBYL FALLOUT DOCTORAL DISSERTATION by TERJE STRAND NATIONAL INSTITUTE OF RADIATION HYGIENE P.O.Box. 55 N-1315 Østerås NORWAY INSTITUTE OF PHYSICS UNIVERSITY OF OSLO NORWAY Printed by support from The Norwegian Cancer Society LANDSFORENTNGEN I Hunfmnp «tOBIOlU IMooOMOMIS PREFACE This thesis work consists of eight papers presented in section II, preceded by a literature review in section I, with some general comments and conlusions. This work was carried out in the period 1985 - 1987 while I was a research fellow of the Norwegian Cancer Society attached to the National Institute of Radiation Hygiene. At the beginning of this work in 1985, the main purpose was to study the doses and possible carcinogenic consequences in the Norwegian population from natural external radiation. An extensive survey of natural external radiation levels in Nowegian dwellings were planned. These data were further to be used in a correlation study with cancer incidence data from the Norwegian Cancer Registry. However, due to the Chernobyl accident it was impossible to go further in the original project, and it was therefore necessary to change the study somewhat. In this thesis, the doses to the Norwegian population from naturally occuring radiation are extensively reviewed. Five papers (I - V) are connected to this discussion. In addition, the doses to the Norwegian population from the Chernobyl fallout are briefly discussed. Three papers (VI - VIII) are connected to this discussion. I am very grateful to all of those who helped me in the work. Special thanks are expressed to Or.philos. Erling Stranden at the National Institute of Radiation Hygiene and Dr.philos. Anders Storruste at the University of Oslo. Without their contribution, encouragement and inspiration it would have been impossible for me to reach this goal. It is further a pleasure for me to thank: Director Dr.philos. Johan Baarli and his staff at the National Institute of Radiation Hygiene for all their support and help through the work. Dr.philos. Knut Magnus (The Norwegian Cancer Registry), Or. Jon B. Reitan (National Institute of Radiation Hygiene) and Prof.Dr.philos. Per Oftedal (University of Oslo) for their friendly advice and support. Prof. John S. McKinley-McKee (University of Oslo) for his comments on the language. The Norwegian Cancer Society for their financial support and for giving me the oportunity to work with so many interesting problems during three years as a research fellow. SECTION I 1. INTRODUCTION 1 2. DOSES FROM NATURALLY OCCURRING RADIATION TO THE NORWEGIAN POPULATION t 2.1. NATURALLY OCCURRING RAOIATION - SOURCES 4 2.1.1. COSMIC RADIATION SOURCES 4 2.1.2. COSMOGENIC RADIONUCLIDES 6 2 1.3. PRIMORDIAL RADIONUCLIDES B 2.2. DOSES FROM COSMIC RADIATION 15 2.3. DOSES FROM EXTERNAL GAMMA RADIATION 20 2 .1 . 1 . OUTDOOR EXPOSURE 20 2.3.2. INOOOR EXPOSURE 30 2 3.3. ORGAN DOSES AND EFFECTIVE OOSE EQUIVALENT FROM EXTERNAL GAHMA RADIATION ... «1 2.;. DOSES FROM INTERNALLY 0EPOSITE0 RADIONUCLIDES «6 2.5. DOSES FROM INHALED RADIONUCLIDES 58 2.5 1. SOURCES OF INDOOR RADON AND THORON 61 2.5.1.1. BUILDING HATERIALS AND GROUND E3 2.5.1.2. HOUSEHOLD WATER AND NATURAL GAS ... 75 2.5.2. CHARACTERISTICS OF INDOOR ATHOSPHERES 77 2.5.3. OCCURRFNCE OF RAOON ANF THORON IN NORWAY ... 86 ?.5.*. OCCUPATIONAL EXPOSURE TO RADON AND fHORON DAUGHTERS 9t 2.5.5. DOSIMETRY 96 2.5 6. DOSES TO THE NORWEGIAN POPULATION FROM INHALATION 109 2 6 TOTA1 OOSES FROM NATURALLY OCCURRING RADIATION Ill 3. DOSES FROM THE CHERNOBYL FALLOUT TO THE NORWEGIAN POPULATION 113 3.1. THE FALLOUT 113 3.2. DOSES FROM EXTERNAL RADIATION 117 3.3. DOSES FROM INHALED RADIONUCLIDES 119 3.5. OOSES FROM INGESTED RAO [ONUCL tOES 12V 3.6. TOTAL OOSES FROM THE FALIOUT 1?6 APPENDIX I: NATURAL EXTERNAL GAMMA RAOIATION DATA 128 REFERENCES 130 SECTION II PAPER I : T. Strand and E. Stranden, "A method utilizing CaF :Dy without energy compensation for large scale surveys of naturally occurring gamma radiation in houses". Radiation Protection Dosimetry Vol.12 No.3 pp.261-267 (19651. PAPER II : T. Strand, K. Magnus and E. Stranden, "Sampling strategy for a large scale indoor radiation survey - A pilot prosject", Radiation Protection Dosimetry Vol.14 No.3 pp.251-255 (1986). PAPER III: E. Stranden and T. Strand, "Natural gamma radiation in a Norwegian area rich in thorium" Radiation Protection Dosimetry Vol.16 No.4 pp.325-328 (1987). PAPER IV : E. Stranden and T.Strand, "Radon levels in an alumshale rich Norwegian area", paper to be presented at The Fouth International Symposium on The Natural Radiation Environment, Lisboa, Postugal, December 7-11 1987. PAPER V : E. Stranden and T. Strand, "A dosimetric discussion based on measurements of radon daughter equilibrium and unattaced fraction in different atmospheres". Radiation Protection Dosimetry Vol.16 No.* pp.313-318 (1967) PAPER VI : T. Strand and E. Stranden, 'Indoor gamma radiation in Norwegian dwellings during the first three months after the Chernobyl accident*. Radiation Protection Dosimetry Vol.18 No.1 pp.13 17 11487). PAPER VII: T. Strand, E. Stranden and A.L. Rudjord "External radiation doset to the Norwegian population from the Chernobyl fallout". Radiation Protection Dosimetry li, press). PAPER vl 11: T. Strand. P. Strand and J.Baarli "Doses to the Norwegian population from foodstuffs after the Chernobyl fallout*. Radiation Protection Dosimetry (in prest). - 1 - 1. INTRODUCTION Radiation in the environment from natural sources is the major source of radiation exposure to man. The natural radiation environment is quite complicated due to the many different possible source terms (rocks, soil, building materials, water, air, etc.,) available. For the general public, the most important sources are connected to exposure in dwellings from natural radioactivity in building materials and radon entry from the ground. In recent years, there has also been an increasing concern on fallout radiation from nuclear accidents (accidents in nuclear energy production, detonation of nuclear weapons etc.). On April 26, 1986, a severe reactor accident occurred in the nuclear power plant Chernobyl in the Sovjet Union. In this accident rather large quantities of radioactive material were released into the atmosphere, and due to the meteorological conditions, dispersed to rather distant areas from the power plant. This accident showed that radiation accidents may have consequences even in regions quite far from the accident point. In Chapter 2. the sources and doses of naturally occuring radiation are discussed. The doses from cosmic radiation, external t radiation, internally deposited radionuclides and inhaled radionuclides are discussed separately. It is apparent from this discussion that the doses from inhaled radionuclides dominate the picture. In Caoter 3. the doses to the Norwegian population from the Chernobyl fallout are discussed. In the same manner as in the discussion of doses from naturally occunng radiation, the doses from external radiation, ingestion and inhalation are discussed separately. Ihe papers >r» presented in section II: In paper I. a measurement method for large scale surveys of natural indoor i radiation is presented. This method is based on utilising thermoluminescent CaF.iOy (Hirshaw TlO-200) without energy compensation. Calibration is performed directly against a natural txectt m representing an average for Norwegian dwellings. - 2 - ln justifying the method, experiments and calculations were performed showing that the ratio between the low energy (<. 200 keV I and the high energy (> 200 keV) component to the total response function was found to be almost constant. This implies that the over-response from the low energy component due to the higher effective atomic number of CaF :Dy (15.21 compared to tissue, for natural indoor -y radiation spectrums, is almost constant. In paper H. optimisation of a stratified random sampling strategy for a large scale epidemiological survey is discussed. This sampling procedure were developed based on the results of -• small scale pilot project where variances in dose rates within different categories of houses were assessed. In oaner III. the results of indoor and outdoor gamma radiation measurements in a thorium-rich Norwegian area are reported, together with activity concentration measurements on rock samples from the ar»i. It is assumed that this area represent a maximum according to the level of external radiation from naturally occuring radionuclides in Norway. In paper IV. measurements of activity concentration; of soil and shale, radon exhalation from the ground and from geological samples. are reported together with measurement» of indoor radon levels in about 200 houses in the Hedemarken area of Norway. Oue to the high geological occurence of alum shale, this area has been the subject of an extensive study on indoor radon. It ii assumed that this area represent a maximum according to indoor radon levels in Norway. In paper v. a dosimetric discussion based on measurements of radon daughter equilibrium and the unattached fraction in different atmospheres Idwellingi, mines, hydro-electric power stations) is presented. Factors converting from radon exposure to effective dose equivalunt for the different atmospheres were assessed. In o».i»r vl and VII. calculations oi external radiation doses to the Norwegian populatior from the Chernobyl fallout are presented. These calculations are based on indoor HO measurements performed in about 100 randomly selected houses in the south eastern part of Norway m - 3 - the first and the sixth month after the accident, and on surface activity data based on measurements on soil samples from each municipality of the country. In paper VIII. the doses to the Norwegian population from foodstuffs after the fallout from the Chernobyl accident are discussed.