Airborne gamma survey of the upper South Alligator River valley: Third Report


Internal Report 383
Pfitzner K, Ryan B, Bollhöfer A & Martin P
Supervising Scientist Division
Department of the Environment, Water, Heritage and the Arts

About the report

A number of small uranium mining and milling operations took place in the 1950s and 1960s in the upper South Alligator Valley. The sites were abandoned in 1964, with no effort to rehabilitate any effects that mining and milling may have resulted in. A hazard reduction program has since been undertaken. Staff from oss regularly monitor the abandoned mine sites for erosion and revegetation, which is supplemented with periodic radiological inspections. In October 2000, an airborne gamma survey was flown over the upper South Alligator River area in order to gain an overview of the location of any radiological issues within the area. This type of survey is done from an aeroplane with an instrument onboard called a "gamma ray spectrometer". The particular gamma ray spectrometer used measures the emissions from the decay of three radioactive elements in surface material like soils and rocks. The signals originate from the decays of potassium (K), thorium (Th), and uranium (U). These signals give measures of the abundance of the elements in the ground over which the aeroplane flies. From this survey, eriss is preparing images of the radioactivity levels around the valley area. eriss have also carried out other field-based measurements in the area. This is being done to help Parks Australia North (PAN) prepare a management plan for old uranium mine and mill sites in the area.