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22-2/F54-3/6-18 Contour interval = 0.5

22-2/F54-3/1-18 Contour interval = 0.5

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The individual surveys that comprise Australia's national airborne gamma-ray spectrometric radioelement database are not all registered to the same datum. Older survey results are presented in units of counts/sec, which depend on factors such as survey flying height and detector volume. Even recent surveys can have a significant mismatch along common borders due to limitations in spectrometer calibration and data processing procedures, as well as environmental effects that result in temporal changes in the gamma-radiation fluence rate at the earth's surface. These problems limit the usefulness of the national radioelement database for uranium exploration, and other applications, as it is difficult to compare radiometric signatures observed in different parts of the continent. Geoscience Australia has recently undertaken an Australia-Wide Airborne Geophysical Survey (AWAGS), funded under the Australian Government's Onshore Energy Security Program, to serve as a radioelement baseline for all current and future airborne gamma-ray spectrometric surveys in Australia. The survey data were acquired and processed according to international standards, and the final estimates of radioelement concentrations along the AWAGS lines are consistent with the International Atomic Energy Agency's (IAEA) radioelement datum. The AWAGS survey has been used to adjust the hundreds of surveys that comprise the national radioelement database to a common datum. This was achieved by estimating, for each survey in the national database, correction factors that, once applied, minimize both the differences in radioelement estimates between surveys (where these surveys overlap) and the differences between the surveys and the AWAGS traverses. This effectively levels the surveys to the IAEA datum to produce a consistent and coherent national gamma-ray spectrometric coverage of the continent. The levelled database has been used to produce the first "Radiometric Map of Australia" - levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100 m resolution. Interpreters can now reliably relate geochemical patterns observed in one area to similar patterns observed elsewhere, and better appreciate the significance of broad-scale variations in radioelement concentrations. There are several applications that will benefit from the updated database. These include uranium and thorium exploration through the ability to make quantitative comparisons between radiometric signatures in different survey areas, and the derivation of a radiation risk map of Australia for natural sources of radiation.

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No abstract available