"Exact" and approximate methods for analysis of total error in radiation measurements

Radiation measurement results are typically stated as an estimated activity concentration with an associated 95% error bound. Very frequently, however, the error bound cited at the "95% confidence level" is nothing more than counting error and, especially at higher levels of activity, counting error may constitute a gross understatement of the total error that should reasonably be attributed to the measurement. This paper compares the measurement confidence limits obtained using a typical approximate error propagation procedure with the "exact" confidence limits. A Monte Carlo error propagation method is also considered. The results of the three methods are compared using 222Rn measurement procedures for illustrative purposes.