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The Use of Gamma Ray Data to Define the Natural Radiation Environment

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The Use of Gamma Ray Data to Define the Natural Radiation Environment IAEA-TECDOC-566 THE USE OF GAMMA RAY DATA TO DEFINE THE NATURAL RADIATION ENVIRONMENT A TECHNICAL DOCUMENT ISSUED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1990 The SAEA does not normally maintain stocks of reports in this series. However, microfiche copie f thesso e reportobtainee b n sca d from IN IS Clearinghouse Internationa! Atomic Energy Agency Wagramerstrasse5 0 10 x P.OBo . A-1400 Vienna, Austria Orders shoul accompaniee db prepaymeny db f Austriao t n Schillings 100, in the form of a cheque or in the form of IAEA microfiche service coupons which may be ordered separately from the INI S Clearinghouse. THE USE OF GAMMA RAY DATA TO DEFINE THE NATURAL RADIATION ENVIRONMENT IAEA, VIENNA, 1990 IAEA-TECDOC-566 ISSN 1011-4289 Printed by the IAEA in Austria September 1990 FOREWORD The accident at the nuclear reactor at Chernobyl in the USSR in April 1986, and the confusion in the public mind over the nature and extent of the resulting fallout pointed up the neemorr fo de widespread awarenes naturae th f so l radiation background in which people live. An examination of the possibilities for acquiring these data led to the recognition of the work of the uranium exploration community over the yearimportann a s sa t yetsourcs a ., unusedeof , natural radiation data. These data have been collecte purpose th r efo d of locating uranium deposits in many countries, frequently publif o througe cus funde hth developmenr so t funds mose .Th t extensive effor thas U.S.Ate wa t th carrien .i whert dou e eth whol countrf eo s flowywa n with airborne gammy ara spectrometer surveys durin Nationae gth l Uranium Resources Evaluation (NURE) project. These data have been compiled and issued as background radiation maps that have been of great value in locating areas of potential radon hazard, in addition to their use in geological mapping and mineral exploration for a numbe metalsf ro . They fundamentaf wilo e lb l importancn ei the International Geological Correlation Programme (IGCP)/UNESCO projec Internationan to l Geochemical Mapping ultimate producinwhicth f o s m hha eai g Geochemical Mapf so the World. The IAEA is playing a coordinating role in the production of the Radioelement Geochemical Maps. This manual is designed to encourage and assist in the use of preexisting gamm y survera a y dat produco t a enaturae mapth f so l radiation environment. The manual is the work of three consultants; Dr. J. S. Duval of the United States Geological Survey, Dr. Anders Linden of the Swedish Geological Company, and Dr. Milan Matolin of Charles University in Prague, Czechoslovakia. These three combine a great many years of experierce in natural radiation measuremen developmene th n i methode th d tan f t o o st their high leve sophisticationf lo Agence .Th y wishe thano st k most sincerely these thre contributinr efo g their timd ean expertise to the task. The Agency staff member responsible for the project was Arthur Y. Smith of the Division of Nuclear Fuel Cycle. EDITORIAL NOTE In preparing this material for the press, staff of the International Atomic Energy Agency have mounted and paginated the original manuscripts and given some attention to presentation. The views expressed necessarilynot do reflect those governments ofthe Member ofthe States organizationsor under whose auspices manuscriptsthe were produced. thisin The bookuse of particular designations of countries territoriesor does implynot any judgement publisher,the legalby the IAEA,to the status as of such countries territories,or of their authorities and institutions or of the delimitation of their boundaries. The mention of specific companies theirof or products brandor names does implynot any endorsement recommendationor IAEA. partthe the of on CONTENTS 1. INTRODUCTION ......................................................................................... 7 2. THE NATURAL RADIATION ENVIRONMENT ................................................. 8 2.1. Source f naturao s l radiation ......................................................................8 . 2.2. Radiation units and conversion factors .......................................................... 10 2.3. Occurrenc f potassiumeo , uranium, thoriu othed man r radiation sources environmene inth t .................................................................................1 1 . 2.3.1. K, U and Th in rock and soil ........................................................... 11 2.3.2. K, U and Th and their daughter products in the atmosphere, hydrospher biospherd an e e .............................................................4 1 . 2.3.3. Cosmic radiation ........................................................................... 15 2.3.4. Natural nuclei concentrate . ...............................r relocate do n ma y db 5 1 . 2.3.5. Artificial nuclei in nature ................................................................ 15 2.4. Measurin naturae gth l radiation environment .................................................6 1 . 2.5. Equivalent dose to man from natural radiation ................................................ 17 3. GAMMA RAY SURVEYS .............................................................................. 18 3.1. Instrumentation .....................................................................................8 1 . 3.2. Calibration and reporting units ................................................................... 19 3.3. Geological gamm surveyy ra a s ..................................................................0 2 . 3.4. Suitable data .........................................................................................0 2 . 4 STANDARDIZATION TECHNIQUES ..............................................................2 2 . 4.1. General concep f standardizatioo t n .............................................................2 2 . 4.1.1. General considerations .................................................................... 22 4.1.2. Conversion of radioélément concentrations to air dose rate ............. ........ 23 4.2. Levellin f datgo a withi nsurvea y area .........................................................4 2 . 4.2.1. Factors causing level differences ......................................................4 2 . 4.2.2. A mathematical approach to levelling ................................................. 26 4.2.3. Levelling of data using image techniques ............................................ 28 4.3. Levellin f datgo a between survey areas ........................................................2 3 . 4.4. Procedure for standardization of spectrometer surveys ...................................... 32 4.4.1. Gamma ray spectrometer surveys with calibrated equipment ..................... 32 4.4.2. Gamma ray spectrometer surveys with uncalibrated equipment .................. 32 4.5. Procedures for standardizing total count surveys ............................................. 34 4.5.1. General problem f totao e l scounus relatee th t o surveydt s ......................4 3 . 4.5.2. Total count surveys with calibrated equipment .....................................7 3 . 4.5.3. Total count surveys with uncalibrated equipment ..................................8 3 . 5. DATA PRESENTATION ................................................................................ 38 5.1. Graphical form ....................................................................................... 38 compilatiop 5.2Ma . n ....................................................................................9 3 . 5.2.1. Manual compilation ....................................................................... 39 5.2.2. Digital compilation ........................................................................ 41 6. INTERPRETATION AND USE OF THE MAPS .................................................. 42 REFERENCES ................................................................................................... 45 l. INTRODUCTION The natural radiation environment is the major source of radiation exposure to man and consists of both internal and external sources mose Th t. significant internal sourcee sar radioactive th e element 222d Ran n K whics 40 takee har n inte oth body. The external sources are cosmic rays and naturally occurring radioactive isotope 40e K,th 238 232f d sUo T, an h decay series, some or all of which can be found in the ground, in construction materials, and in the air. Both internal and external radiation levels functioa var geologicae s ya th f no l materials, type of dwelling, and elevation above sea level. This report has been prepared to provide a guide for the use of existing gamm survey ara y dat defino at naturae eth l radiation environment wilt ,bu l onl concernee yb d wite hth gamma ray exposure resulting from radiation originating in geological materials. Chapte below, r2 , discusse naturae sth l radiation environment in greater detail. Because natural radiation levels represent the minimum exposure attainable, the usee comparisor yar fo d n when judging the significance of exposure from man-made sources such as medical x-rays, nuclear weapons fall-out, and nuclear power plants entire Th . e issu man-madf eo e radioactivity becomes more importan numbee th nucleaf s tro a r power plants, research reactors, medical and industrial isotope sources, etc. increases. The study of the natural radiation environment has been actively carried out since the discovery of radioactivity. In recent year sseriea symposif so a [1], [2], [3], [4], dedicate subjece th o dt
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