Baseline environmental radioactivity

The purpose of establishing the basehne environmental radioactivity is to allow comparison with future environmental radioactivity surveys at the site. The survey may be developed on the basis of air, water, soil and biological samples. 

The area to be surveyed can be the local facihty site for hazard category 3 and within a 20 km radius for hazard category 2. For hazard category 1, an area within a 50 km radius of the site is suggested unless highly populated areas are present near the facility. In this case, the survey can include the areas hkely to be affected by a release of radioactive material. 

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Most of the effluent and environmental radioactivity measurements are made using gamma-ray spectrometry. This is a far more cost effective approach than radiochemical analysis the Instrumental measurement can be readily automated, and detection decisions can be made more or less simultaneously for many radionuclides. The validity of those decisions, and of the corresponding detection limits, however, requires either that the peaks be Isolated and lie on a linear baseline, or that a detection limit model be employed which Is more complex than that used for "simple" counting. Baseline or interference model uncertainties should be Included, and an iterative solution is required to estimate the detection limit when spectrum deconvolution is involved. Details are beyond the scope of this chapter, but a relatively simple limiting estimate can be derived by treating the estimated standard error for a low level radionuclide peak of interest as though it were the null standard error, [12, p. 81]. 

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