Background radiation from terrestrial sources of uranium, thorium, and potassium complicate the counting of radiation from a weak source. Although radiation from a localized point source decreases as the inverse square of the distance from the source, moving a counter further from a concrete table or floor does not decrease the background. Measurements of the intensity of radiation versus height above a local surface were made and found not to vary with height. A simple model is proposed assuming a uniform volume distribution with self-absorption as a source. It is shown that most of the radiation comes from relatively close surroundings. (C) 2007 American Association of Physics Teachers.
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