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 Good explanation of Gamma variations 
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Joined: Fri Jul 03, 2015 7:04 pm
Posts: 164
Location: Toronto Canada
This NRC report has a good description of daily Gamma variations as well as rain-related and soil drying contributions to explain much of the variations we see in the outdoor detectors. It is available on Google Books (link below, browser cookies required to view for free). Page A-10 to A-12 describe a typical 11 day graph. Here is an excerpt:
...Rather, the cyclic action occurred on a daily basis as a result of changes in the radon progeny levels in the air which, in turn, arose from changes in the stability of the atmosphere. Extremely stable conditions produce what is known as an inversion layer (that is, the air temperature is lower at ground level than above, which is opposite to the norm). In the early morning hours before sunrise, conditions are typically calm, and the radon (which seeps from the soil into the air) stays near ground level, thus causing the radiation level to rise. When the sun rises, the ground warms up and air near it rises, producing a mixing effect that sweeps away the radon and its progeny to higher levels in the atmosphere, thus lowering the radiation level. The process cycles like this from day to day.

"Generic EIS in Support of Rulemaking on Radiological Criteria for Decommissioning of NRC-licensed Nuclear Facilities, 1994"

_________________ Toronto, Ontario, Canada SBM-20 indoors

Tue Jul 05, 2016 9:01 pm
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