The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose.
This radiometric thorium grid has a cell size of 0.004 degrees (approximately 410m) and shows thorium element concentration of the Newcastle, Singleton NSWGS, NSW, 1984 survey. The data used to produce this grid was acquired in 1984 by the NSW Government, and consisted of 20500 line-kilometres of data at 1500m line spacing and 150m terrain clearance.