Evaluation of Three Passive-Integrating Charcoal Detectors for Measuring Radon Concentrations.

摘要

Three types of passive-integrating detectors that determine Radon-222 (Radon) concentrations in air samples were studied. Each detector type examined uses activated charcoal to adsorb radon from air samples that enter through a diffusion barrier. This results in a time-integrated sample. The three detector types analyzed were liquid-scintillation vials and canisters with and without moisture-absorbing desiccant. The LS vials contain a mixture of charcoal and desiccant. All three types of detectors were calibrated in a chamber of known radon concentration. Since the LS vials had not previously been studied at AFIT, the optimum procedure for exposing, processing, and counting the vials was established. An automated liquid-scintillation counter (LSC) was used for determining the radon levels of the LS vials. The variability in the radon concentrations computed by the LSC for repeated counting of a single vial was examined and was found to be between 1 and 4%. Reproducibility of radon adsorption by a group of vials exposed simultaneously was examined. Reproducibility values for a group of ten vials counted for 4 cycles had a standard error of 1.4%. A blind test was performed where the detectors were exposed to a known concentration, prepared, counted, and then the concentrations measured were compared to actual values. The measured values were within 0.2% to about 8% of the actual concentrations. Exposure times of 24 to 48 hours were recommended for the vials and 3 to 7 days for the canisters. Gas detectors; Radiation measuring instruments; Rare gases; Radon; Radium radioactivity; Natural radiation; Ionizing radiation; Alpha particles. Theses.