Intercomparison of the Sensitivity and Accuracy of Radon Measuring Instruments and Methods

Radon testing in the US has reached a plateau with about two dozen different types of instruments and methods being used to make about one million measurements per year. Knowledge of the sensitivity and accuracy of radon testing instruments can make it easier for testing firms and home inspectors to select the most appropriate device for their radon testing program. This paper compares the sensitivity and as a consequence the accuracy of every type of device that information was given by the manufacturer or cited from published literature. Some instrument manufacturers, did not make this information available. The sensitivity expressed in counts/minute per 4 pCi/L, was selected because most of the measurements for radon in the US are <4 pCi/L. The instruments listed in this paper represent passive and continuous radon monitors such as scintillation cell, pulse and current ionization chamber, solid-state alpha monitors and several diffusion barrier charcoal integrating collectors. For comparison, the sensitivity of one open face charcoal canister is also included. The sensitivity of alpha track detectors and electret ion chambers are also included in terms of number of tracks/cm 2 /4 pCi/L -1 D -1 and Volts/4 pCi/L -1 D -1 The sensitivities of continuous radon monitors ranges from 0.17 to 24 cpm/4 pCi L -1 ranging from 0.17 5.7 cpm/4 pCi/L, in the instruments most frequently used. By comparison the sensitivities of diffusion barrier charcoal vials or canisters range from 48-145 cpm/4pCi L -1 At radon levels of <4 pCi/L, most of the continuous radon monitors will provide poor results if counts are acquired at minute intervals. For this reason, EPA, requires continuous radon instruments to accumulate hourly counts to improve accuracy.