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Internal Report 561
Bollhöfer A & Fawcett M
Supervising Scientist Division, 2009
Department of the Environment, Water, Heritage and the Arts
This report summarises the results of a gamma dose rate survey conducted at the historic Sleisbeck mine in the Gunlom Land Trust in July 2008, after rehabilitation of the site was completed. 360 dose rate reading were taken over an approximately 7.6 ha area. The median terrestrial gamma dose rate measured across the area surveyed is 0.13 µGy∙hr-1. The arithmetic average is 0.23 µGy∙hr-1. The geometric mean, or ‘typical value’, is 0.14 µGy∙hr-1, similar to environmental background gamma dose rates measured in the area.
The remediation works have reduced the average terrestrial gamma dose rates across the Sleisbeck area by about threefold compared to the average pre rehabilitation dose rates in the area. Ninety-nine percent of the area surveyed exhibit terrestrial gamma dose rates below 1.25 µGy∙hr-1. This has resulted in a reduction of the annual doses received by the public accessing the area. Assuming that the area was occupied for one month during the dry season, effective doses from exposure to terrestrial gamma radiation are well below the annual dose constraint for the public for existing exposure situations of 10 mSv and lower than the 0.3 mSv dose constraint recommended in current ICRP (2007) guidelines for prolonged exposure from planned exposure situations.