PEP-4B.
On Uncertainty in Surface Activity Concentration Measurements DO Stuenkel*, U.S. Environmental Protection Agency
Abstract: Many environmental measurements involve the measurement of surface activity concentrations. These include walls, floors, or ceilings in buildings, or the top layer of soil outdoors. For measurements of surfaces in buildings, ISO 7503-1:2016, “Measurement of radioactivity — Measurement and evaluation of surface contamination — Part 1: General principles” provides guidance for measurements of surface activity concentrations of radionuclides that emit alpha, beta, and/or photon radiation. In addition to estimating the surface activity concentration, it is also important to estimate the uncertainty in the measurement. Guidance for determining the uncertainty for any measurement is provided by “Joint Committee for Guides in Metrology, Evaluation of measurement data – Guide to the expression of uncertainty in measurement” (JCGM 100:2008). This PEP presents the eight-step method outlined in the “Guide to the expression of uncertainty in measurement”, along with the use of different probability distributions, such the uniform, triangular, normal, and Poisson to represent various input quantities. Applications of the GUM method to surface activity concentration measurements, including stationary (i.e., static) measurements, averages of multiple static measurements, and quantitative scanning surveys are developed and presented. Finally, this PEP provides a brief overview of Monte Carlo methods for estimating quantities their uncertainties, along with a demonstration of software tools, such as the NIST Uncertainty Machine and Keith McCroan’s GumCalc. Participants are encouraged but not required to bring a laptop or tablet.
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