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.
REFERENCES
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D.
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Amptek, www.amptek.com/, offers a highly portable PMCA with 76 by at exceptional resolution. It is unique in that the high voltage is generated in the low mass tube base powered by two AA batteries. These batteries are placed far from the detector in the PMCA unit, which houses the multi-channel analyzer. All controls are from an external laptop that may be removed during measurements to further reduce the influence of the mass of the detection system on the surroundings being measured. The package is an outgrowth of space instrumentation projects such as ROVER, with a minimal mass and probably the lowest portable power consumption available.
14.
Nicholas
Tsoulfanidis
, Measurement and Detection of Radiation
, 2nd ed. (Taylor and Francis
, Washington, DC, 1995), pp. 267
–288
. Reference 9, pp. 312–342, also has a good discussion on response functions.© 2007 American Association of Physics Teachers.
2007
American Association of Physics Teachers
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