IAEA-TECDOC-1363 Guidelines for radioelement mapping using gamma ray spectrometry data July 2003 The originating Section of this publication in the IAEA was: Nuclear Fuel Cycle and Materials Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria GUIDELINES FOR RADIOELEMENT MAPPING USING GAMMA RAY SPECTROMETRY DATA IAEA, VIENNA, 2003 IAEA-TECDOC-1363 ISBN 92–0–108303–3 ISSN 1011–4289 © IAEA, 2003 Printed by the IAEA in Austria July 2003 CONTENTS 1. INTRODUCTION ............................................................................................................ 1 1.1. Purpose of the report........................................................................................... 1 1.2. Historical review................................................................................................. 1 1.3. Gamma ray methods........................................................................................... 2 1.4. Scope of the report.............................................................................................. 2 2. PRINCIPLES OF RADIOACTIVITY ............................................................................. 4 2.1. Basic radioactivity .............................................................................................. 4 2.2. Types of radioactive decay................................................................................. 4 2.3. Statistical nature of radioactive decay................................................................ 5 2.4. Natural sources of radiation................................................................................ 6 2.5. Disequilibrium.................................................................................................... 7 2.6. Interaction of gamma rays with matter............................................................... 7 2.7. Detectors and instruments................................................................................ 12 2.8. Quantities and units .......................................................................................... 14 2.8.1. SI derived quantities and units and non-SI units accepted for use with SI................................................................................................... 15 2.8.2. Ground radioelement concentration units and conversion constants................................................................................................ 16 2.8.3. Conventional ground reporting units .................................................... 17 2.9. Natural and man-made absorbed doses ............................................................ 18 3. FUNDAMENTALS OF GAMMA RAY SPECTROMETRY....................................... 20 3.1. Sources of gamma radiation ............................................................................. 20 3.2. Properties of gamma ray spectra ...................................................................... 20 3.2.1. The detector response ........................................................................... 21 3.2.2. Source-detector geometry..................................................................... 21 3.3. Measurement of gamma radiation .................................................................... 25 3.4. Physical models................................................................................................ 25 3.5. Environmental effects....................................................................................... 29 4. GROUND RADIOMETRIC METHODS ...................................................................... 31 4.1. Portable gamma ray spectrometry .................................................................... 31 4.1.1. Instrumentation ..................................................................................... 31 4.1.2. Field measurement................................................................................ 31 4.1.3. Instrument calibration........................................................................... 34 4.1.4. Data processing procedure.................................................................... 38 4.1.5. Errors .................................................................................................... 39 4.2. Car-borne gamma ray spectrometry ................................................................. 40 4.2.1. Instrumentation ..................................................................................... 40 4.2.2. Field measurement................................................................................ 40 4.2.3. Instrument calibration........................................................................... 41 4.2.4. Data processing procedure.................................................................... 41 4.3. Borehole gamma ray spectrometry................................................................... 42 4.3.1. Instrumentation ..................................................................................... 42 4.3.2. Field measurement................................................................................ 43 4.3.3. Instrument calibration........................................................................... 43 4.3.4. Data processing procedure.................................................................... 43 4.4. Laboratory gamma ray spectrometry................................................................ 45 4.4.1. Rock samples and laboratory equipment .............................................. 45 4.4.2. Laboratory determination of natural radionuclides .............................. 46 4.4.3. Instrument calibration........................................................................... 48 4.4.4. Data processing procedure.................................................................... 48 4.4.5. Laboratory determination of gamma ray sources ................................. 49 4.5. Marine gamma ray spectrometry...................................................................... 50 4.5.1. Instrumentation ..................................................................................... 50 4.5.2. Field measurement................................................................................ 50 4.5.3. Instrument calibration........................................................................... 51 4.5.4. Data processing procedure.................................................................... 51 5. AIRBORNE GAMMA RAY SPECTROMETRY FOR NATURAL RADIOELEMENT MAPPING ...................................................................................... 52 5.1. Instrumentation................................................................................................. 52 5.2. Survey methodology......................................................................................... 52 5.3. Calibration data requirements........................................................................... 54 5.3.1. High-altitude aircraft/cosmic background flights ................................. 54 5.3.2. Ground calibration using radioactive pads ........................................... 54 5.3.3. Calibration range flights ....................................................................... 55 5.3.4. Radon background calibration flights................................................... 55 5.3.5. Calibration frequency ........................................................................... 55 5.4. Survey monitoring procedures.......................................................................... 55 5.4.1. Calibration integrity test ....................................................................... 56 5.4.2. Daily thorium source tests .................................................................... 56 5.4.3. Daily system resolution test.................................................................. 56 5.4.4. Monitoring spectral stability................................................................. 56 5.4.5. Survey test line...................................................................................... 57 5.5. Data processing and calibration procedures ..................................................... 57 5.5.1. Pre-processing....................................................................................... 57 5.5.2. Spectral smoothing techniques ............................................................. 58 5.5.3. Live time (or dead time) correction ...................................................... 59 5.5.4. Energy calibration................................................................................. 60 5.5.5. Aircraft and cosmic background corrections ........................................ 60 5.5.6. Radon background correction............................................................... 62 5.5.7. Stripping corrections............................................................................. 65 5.5.8. Height correction .................................................................................. 67 5.5.9. Reduction to elemental concentrations ................................................. 68 5.5.10. Levelling the data.................................................................................. 69 5.6. Sources of noise and error propagation ............................................................ 69 6. DATA STANDARDIZATION AND SURVEY BACK-CALIBRATION ................... 72 6.1. Motivation .......................................................................................................