AESC2006, Melbourne, Australia. 1Towards an Australian radioelement baseline database Brian Minty Geoscience Australia GPO Box 378Canberra, ACT, 2601 [email protected]INTRODUCTION Global prosperity depends almost entirely on the Earth’s natural resources. Mineral and hydrocarbon resources, building materials, and soil and waterunderpin our standard of living. The sustainable management of these natural resources is thus essential. Airborne geophysics is one of the most cost-effective tools that provide information for the mapping and management of the earth’s resources. Radioeleme nt mapping by airborne gamma-ray spectrometry, in particular, has been extensively used in the earth and environmental sciences. These data are widely used in geological mapping, mineral exploration, environmental studies, and land management – particularly in areas where public health is an issue. In Australia, radioelement data are also increasingly being used forsoil mapping, and as an essential ingredient in land degradation and salinity studies. Government agencies in Australia have funded the systematic mapping of the continent by airborne geophysical methods over the past 50 years. Approximately 75% of the continent is now covered by airborne gamma-ray spectrometric surveys (Figure 1). These data are publicly available, and comprise a valuable national resource. The quality of t he data from recent surveys is far better than that of older surveys. Data acquisition systems, as well as calibration and data processing procedures, have i mproved with time. Early surveys measured total count (TC) only. These give a measure of tota l radio activity. Later surveys used differential and multichannel spectrometers, and give estimates of the gamma radiation due to each ofpotassium (K), uranium (U) and thorium (Th). Current survey data conform to International Atomic Energy Agency (IAEA) standards, and are reported in absolute concentration units for K, U and Th, and in air-absorbed dose rate for total count. However, up unti l the early 1990’s, survey data were still reported in units of counts per second. The older survey data values thus depend on the instrumentation and survey parameters, and the data values on adjacent surveys are not necessarily comparable. These problems limit the usefulness of t he national gamma-ray spectrometric database. The main advantage of having all surveys registered to the same datum is that they are easily merged into largerregional compi lations. These facilit ate the recognition and interpretation of broad-scale regional features in the data. Lessons learnt in one area are more easi ly applied to other areas. Calibrated radioelement data are al so more easily interpreted in terms of public health issues – specifically radiation risk. Geoscience Australia and State Geological Surveys are working towards establishing a national baseline database of Australian gamma-ray spectrometric data that is consistent with the global radioelement baseline. If new survey data are acquired and processed according to IAEA standards, then they will be registered to the global radioelement baseline, and SUMMARY Approximately 75% of Australia is covered by public- domain, airborne gamma-ray spectrometric surveys. However, all the older surveys are in units of c/s and their data values depend on the survey instrumentation and acquisition parame ters. Also, many of the newersurveys were inadequately calibrated with the result that data values on adjacent surveys are not necessarily comparable. This limits the usefulness of these data. Geoscience Australia and State Geological Surveys are working towards establishing a national baseline database of Australian gamma-ray spectrometric data that is consistent with the global radioelement baseline established by the International Atomic Energy Agency. This will be achieved by: (a) ensuring consistency in the calibration and processing of new gamma-ray spectrometric data through the use of standard processing procedures and calibration facilities that are tied to the global datum, and; (b) adjusting older surveys to the global datum through back-calibration and automatic grid merging. Surveys that are registered to the same datum are easily merged into regional compilations which facilitate the recognition and interpretation of broad-scale regional features, and allow lessons learnt in one area to be more easily applied to other areas. Key words: gamma-ray spectrometery, airborne gamma- ray spectrometry, back-calibration, grid merging, radioelement baseline.
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