Gamma-ray spectrometric data-processing techniques
gamma-ray spectrometric data-processing techniques
BMB PTOUCATK) COS5PACTUS
B.R.S. Minty
Bureau of Mineral Resources, Geology and Geophysics
DEPARTMENT OF PRIMARY INDUSTRIES & ENERGY BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS
A REVIEW OP AIRBORNE GAMMA-RAY SPECTROMETRIC DATA PROCESSING TECHNIQUES by B.R.S. Minty (Division of Geophysics)
AUSTRALIAN GOVERNMENT PUBLISHING SERVICE CANBERRA, 1988
DEPARTMENT OF PRIMARY INDUSTRIES & ENERGY Minister for Resources : Senator The Hon. Peter Cook Secretary : G.C.Evans
BUREAU OF MINERAL RESOURCES, GEOLOGY & GEOPHYSICS Director: R.W.R. Rutland AO
Published for the Bureau of Mineral Resources, Geology & Geophysics by the Australian Government Publishing Service
?Commonwealth of Australia 1988 This work is copyright. Apart from any fair dealing for the purpose of study, research, criticism, or review, as permitted under the Copyright Act, no part may be reproduced by any process without written permission. Copyright is the responsibility of the Director, Publishing & Marketing, AGPS. Inquiries should be directed to the Manager, AGPS Press, Australian Government Publishing Service, GPO Box 84, Canberra, ACT 2601.
ISSN 0084-7100
ISBN 0 6 4 4 0 8 1 4 9
Edited by A.G.L. Paine. Line drawings by N. Kozin. Word-processing by P. Burrell
P r i n t e d i n A u s t r a l i a by Graphic S e r v i c e s P t y . L t d .
CONTENTS
Page
ABSTRACT
V
INTRODUCTION
1
BASIC PRINCIPLES
Gamma spectrometry
2
Disequilibrium.
4
Background radiation.
.
5
Properties of airborne gamma-ray spectra...........
8
PROCESSING
Drift correction (or 'energy calibration1)
15
Dead-time correction
16
Background corrections
17
Terrain-clearance correction
19
Reduction to elemental countrates
2 0
Conversion of countrates to elemental abundances... 21
Filtering of statistical noise
22
DISCUSSION AND CONCLUSIONS
Automatic estimation of attenuating cover
2 3
Minimising errors: optimising the processing options 2 3
Background estimation
2 5
Coincident detection technique
28
RECOMMENDATIONS
2 9
ACKNOWLEDGMENTS
3 0
REFERENCES
3 0
APPENDICES
1. Background estimation using an upward-looking
detector
3 5
2. Temperature and pressure corrections
3 8
3. Reduction to elemental countrates
39
4. Inversion of airborne gamma-ray spectrometer data
42
iii
FIGURES
Page
1. Interaction of gamma rays with matter.
3
2. The radon daughter gamma energy spectrum.
6
3. The cosmic gamma energy spectrum.
7
4. The aircraft gamma energy spectrum.
8
5. The uranium line spectrum.
9
6. The thorium line spectrum.
9
7. The potassium gamma energy spectrum.
10
8. The uranium gamma energy spectrum.
11
9. The thorium gamma energy spectrum.
11
10. Pulse height vs energy response of an Nal detector. 13
11. Spectra from U ore covered by various depths of water. 14
12. Relative sensitivity of the 'up1 detectors to the
'down' detectors for terrestrial radiation.
2 6
13. Relative sensitivity of the 'up' detectors to the
'down' detectors for airborne radon.
27
14. Use of a coincident detection technique to allow
directional detection of radiation.
28
TABLES
2 38
1.
U decay series.
44
235
2.
U decay series.
45
232
3.
Th decay series.
46
4. Mass attenuation coefficients and half-thicknesses
for various gamma-ray energies in air, water, and
concrete.
47
5. Convential window settings for three channel
spectrometers.
4 8
iv
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