Direct irradiation

Background

Airborne radiometric survey rehabilitated Nabarlek mine site

Map of the uranium distribution across the former Nabarlek Minesite, using data from the airborne radiometric survey

Uranium-bearing soils and rock emit three types of radiation, called alpha, beta and gamma radiation. Of these, gamma radiation is the most penetrating, so that a dose can be received even when a person is standing several metres away from the source. By contrast, alpha and beta radiation are usually only of significance if the radioactive material has been ingested or inhaled. Protection from gamma radiation usually involves maintaining a suitable distance from the source material and/or the use of shielding.

For members of the public, direct irradiation is unlikely to be a major source of radiological dose during mining operations, as public access to the site will be restricted. However, it may become important post-rehabilitation once access is not restricted. It is important to determine whole-of-site gamma radiation doses for rehabilitated or abandoned mine sites to determine radiological risk from accessing the sites. In addition, as radiological guidelines for closure will be based on the extent to which the site compares with the pre-mining background radiation dose, it is essential that robust estimates of the pre-mining conditions are obtained. To obtain such information eriss conducts research into developing robust methods for ground-truthing of airborne gamma data, both recent and historic, so that estimates of doses to members of the public can be made.

Current research projects

Airborne radiometric surveys of the old South Alligator River Valley mine and mill sites

The South Alligator River valley (SARV) is part of Kakadu National park and is well known not only as a popular tourist destination but also for its uranium deposits. At the legacy sites in the SARV various types of mining were employed during the 1950s and 60s, including open cut, cut and fill, and shaft mining. The mines were very small, and a lack of environmental awareness and legal requirements meant that they were simply abandoned when mining ceased. Most of the mined ore was milled at the South Alligator mill, near the Rockhole mine and Rockhole Mine Creek. Two airborne gamma surveys (AGS) were commissioned in 2000 and 2002, respectively, to characterise the extent and intensity of the radiological contamination in the SARV. This project aims to use ground-based gamma dose and gamma spectrometric measurements to test the usefulness of such airborne surveys for reliable surveying of environmental impacts.

Project leader: Dr Andreas Bollhöfer.

Pre-mining radiological conditions at Ranger mine

AGS coupled with ground truthing surveys have been efficiently used for area wide assessments of radiological conditions at rehabilitated and historic mine sites such as Nabarlek and the South Alligator River valley. The aim of this project is to ground truth historical AGS data at an undisturbed radiologically anomalous site in order to extrapolate to pre-mining radiological conditions at Ranger. This work is required because there is no detailed pre-mining gamma radiation ground survey data for the Ranger mine area.

An AGS of the Alligator Rivers Region was flown in 1976, and analysis of the data has shown that the natural Anomaly 2, to the south of the Ranger lease, is a potential candidate for a pre-mining analogue. An extensive groundtruthing program was conducted in 2007-2008. Data analysis is currently underway.

Project leader: Andrew Esparon

Some relevant publications

Bollhöfer A, Pfitzner K., Ryan B., Martin P., Fawcett M. and Jones D.R. (2008) Airborne gamma survey of the historic Sleisbeck mine area in the Northern Territory, Australia, and its use for site rehabilitation planning. Journal of Environmental Radioactivity 99, 1770-1774.

Martin P, Tims S, McGill A, Ryan B & Pfitzner K 2006. Use of airborne g-ray spectrometry for environmental assessment of the rehabilitated Nabarlek uranium mine, northern Australia. Environmental Monitoring and Assessment 115, 531-553.

Pfitzner K 2005. Mining and exploration: Radiation assessment, Position June/July 2005, 54-47.

Pfitzner K, Ryan B & Martin P 2003. Airborne gamma survey of the Sleisbeck mine area. Internal Report 400, January, Supervising Scientist, Darwin. Unpublished paper.

Bollhöfer A, Ryan B, Pfitzner K, Martin P & Iles M 2002. A radiation dose estimate for visitors of the South Alligator River valley, Australia, from remnants of uranium mining and milling activities. In Uranium Mining and Hydrogeology III, eds BJ Merkel, B Planer-Friedrich & C Wolkersdorfer. Technical University, Bergakademie Freiberg. 931-940.

Pfitzner K, Ryan B, Bollhöfer & Martin P 2001. Airborne gamma survey of the upper South Alligator River valley: Third Report. Internal Report 383, Supervising Scientist, Darwin. Unpublished paper.

Pfitzner K, Martin P & Ryan B 2001. Airborne gamma survey of the upper South Alligator River valley: Second Report. Internal Report 377, Supervising Scientist, Darwin. Unpublished paper.