Authors / CoAuthors
Minty, B. | Wilford, J.R.
Abstract
A significant problem for ground-based gamma-ray spectrometric surveys is the effect of emanation radon on estimated uranium concentration estimates. Radon gas (a daughter product in the U238 decay series) escapes from rocks and soils near the earth?s surface into the lower atmosphere. Under early morning, still-air conditions, radon concentrates as a thin layer near the earth?s surface. If ground radiometric surveying is undertaken before this radon layer is mixed into the lower atmosphere, large errors in U concentration estimates result. This paper shows the effect of early-morning radon accumulation on a quad-bike gamma-ray spectrometric survey near Boorowa, NSW. Paddocks surveyed early-morning show much higher apparent uranium concentrations than those surveyed later in the day. We demonstrate the radon diurnal effect by recording the apparent U concentration at a fixed site over several weeks. Typically, there is a build-up of radon near the earth?s surface overnight. Radon concentration reaches a maximum at about 7 am before slowly dispersing over a period of 2-3 hours. The diurnal data also show the effect of rainfall on apparent U concentrations. Rain precipitates radioactive daughter products of atmospheric radon onto the ground resulting in a significant increase in apparent U concentration. These short-lived daughter products decay to insignificant concentrations within about 3 hours. Ground surveys should not be conducted within 3 hours of rain, or under early-morning, still-air conditions.
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nonGeographicDataset
eCat Id
61118
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- External PublicationScientific Journal Paper
- ( Theme )
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- geophysics
- ( Theme )
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- mapping
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2004-03-17T00:00:00
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