Radon measurements—discussion of error estimates for selected methods
Introduction
Radon measurement is complicated process and the correct estimation of appropriate uncertainties is very important. The purposes of radon measurements can be different—from the measurement of current value of radon concentration at workplace to retrospective assessment of average radon concentration for the last 20–50 years during epidemiological studies. The problems of measurements precision and accuracy of measurement results interpretation arise. The sources of uncertainties for grab sampling, short-term measurements (charcoal canisters), long term measurements (track detectors) and retrospective measurements (surface traps) were analyzed using data of Radon Calibration Laboratory of Ural State Technical University and experimental data obtained in the Institute of Industrial Ecology UB RAS. In general the typical radon measuring devices used in Russian Federation were considered.
The sources of uncertainties for practically all instrumental radon measurements can be divided in two groups—calibration errors and measurement errors. The calibration errors include in the systematic bias of reference equipment, random Poisson errors due to count statistic, non-Poisson random errors and residual systematic bias of calibration. The main sources of measurement errors are calibration bias, random Poisson errors (under typical concentration of radon), random non-Poisson errors and residual systematic bias of the measurement. It should be noted that some uncertainties of instrumental radon measurement techniques are common both to grab sampling and to integrating techniques. The error assessment was conducted by the estimation of Poisson error from counting statistic and calculation of non-Poisson error on the base of total measured random error and estimated Poisson error.
The common source of calibration error for all instrumental measurements is a residual systematic bias of calibration standard. The guaranteed by the state center of standards residual systematic error for the secondary calibration reference device (AlphaGUARD PQ 2000) used in the regional Radon Calibration Laboratory is 10%. The calibration of reference radon monitor AlphaGUARD in our laboratory using the NIST emanating radon source and GENITRON Gmbh calibration chamber gives the real residual systematic error wising 8–9%. The other sources of residual systematic biases during the calibration (except of systematic bias of reference device) are individual and depend on the kind of instrumental measurement. Our experience shows that such kinds of biases rarely exceed 3%.
Section snippets
Grab sampling devices
The most typical equipment in Russian Federation for grab sampling radon concentration measurements are RRA01-01 and RRA01-03 devices developed on the base of electrostatic chamber. For the assessment of measurement uncertainties of these devices the data of Radon Calibration Laboratory of Ural State Technical University for period 1998–2007 were analyzed. For devices passed the calibration procedure the difference between the calibrated device and reference device readings is not symmetric
Conclusions
The presented data shows that for instrumental methods of radon concentration measurements the most important sources of biases are the random errors due to count statistic (Poisson errors) and non-Poisson random errors aroused during the measurements. The influence of calibration error is less significant. The understanding of the origin of non-Poisson error and its decreasing will allow considerable improving of the quality of radon measurements. For retrospective radon measurements the most
Acknowledgments
This work was supported by Russian Foundation for Basic Research (grant RFBR 06-08-00744a).
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