Scientists have made what they say is the first ground level map of natural gamma radiation across part of Sydney.
They used handheld detectors and soil tests to show where background radiation is a little higher or lower across the city.
The work looked at a 10 by 10 kilometre area. It combined in person measurements with lab gamma spectroscopy of soil samples.
The testing measured naturally occurring radionuclides including uranium 238, thorium 232 and potassium 40.
The researchers reported an average annual terrestrial gamma dose of about 0.24 millisieverts per year. They also reported a separate cosmic component of about 0.173 millisieverts per year.
They said both figures are within global background levels. They said this means the differences across the map reflect normal changes in geology and soil, not an unusual hazard.
The study found the broad radiation pattern closely matched local geology. It also found small pockets where readings were higher than nearby areas.
The team said these differences were mostly explained by the rock types underneath and the amount of radionuclides in the soils. They said their statistical method explained most of the variation in the data.
The authors said the map fills a data gap for Sydney. They said it could help set a baseline for future environmental monitoring, planning work and public understanding of background radiation.
They also said using relatively low cost portable devices could make wider mapping possible including citizen science style surveys in other Australian cities.
