Charcoal measurements

The major drawback to using the Florida study to support the correlation between indoor and soil measurements was that the indoor measurements were obtained from 3-day closed-house charcoal measurements, and soil radon was obtained from 1-month alpha track measurements buried 1 ft beneath the soil surface. Comparisons of charcoal and alpha track data are generally not recommended since they are quite different measurement techniques, and represent radon levels over different time periods. However, the study was subjected to numerous quality control checks including deployment of alpha track detectors in 10% of the houses to obtain a check on indoor air measurements made by charcoal canisters. In spite of the measurement drawbacks, the study indicates that soil radon measurements taken alone are not a dependable predictor of potential indoor radon concentration. 

The heat of combustion of charcoal measured by DSC amounts to much lower values depending on the air pressure in the DSC cell (tests in air, flow rate 5 cmVmin )3= 10 K/ min) ... 

Ma.nufa.cture. The preparation of sulfuryl chloride is carried out by feeding dry sulfur dioxide and chlorine into a water-cooled glass-lined steel vessel containing a catalyst, eg, activated charcoal. Alternatively, chlorine is passed into Hquefted sulfur dioxide at ca 0°C in the presence of a dissolved catalyst, eg, camphor, a terpene hydrocarbon, an ether, or an ester. The sulfuryl chloride is purified by distillation the commercial product is typically 99 wt % pure, as measured by ASTM distillation method D850. 

The conclusion is that for chemisorption measurements in a CSTR, the matter in the empty space must be minimized, which calls for low (atmospheric) pressure, and low concentration of the chemical, in a low flow of carrier gas. Even at low pressure it will work only for very large surface area materials, like molecular sieves or active charcoals. 

It was observed by de Saussure in 1814 that heat is evolved during the adsorption of gases on charcoal, and quantitative measurements were made by Favre (24) (1874), Chappuis (1888), and Dewar (25) (1904). 

Catalysts such as charcoal can be used to maintain the equilibrium ratio of ortho-hydrogen to para-hydrogen with decreasing temperature.1 When this happens, heat capacity measurements give the equilibrium value for the entropy of hydrogen. 

This document provides procedures for measuring radon concentrations with continuous radon monitors, charcoal canisters, alpha-track detectors, and grab radon techniques. 

The method of measurements is based on a combination of activated charcoal and TLD, and the integration time used is 5-7 days. Details on the principle of the dosimeter and its calibration have been published elsewhere. (Stranden et al, 1983.)... 

The method for the exhalation rate measurements is based on the same activated charcoal/TLD combinations as the dosimeter for measurements of indoor Rn-222. Details on the method is published elsewhere. (Stranden et al, 1985.)... 

The instruments include an ionization chamber, the charcoal-trap technique, a flow-type ionization chamber (pulse-counting technique), a two-filter method, an electrostatic collection method and a passive integrating radon monitor. All instruments except for the passive radon monitor have been calibrated independently. Measurements were performed... 

Charcoal-Trap Method (ACC). The Charcoal-Trap Method has been used for sampling radon gas in the atmospheric air and for measuring radon emanation rate from the soil surface by some researchers (e. g. 

Shimo, M., Y. Ikebe, J. Maeda, R. Kamimura, K. Hayashi, and A. Ishiguro, Experimental Study of Charcoal Adsorptive Technique for Measurement of Radon in Air, J. Atomic Energy of Japan, 25 562-570... 

The accuracy of the measurement of radon concentrations with bare track detectors was found to be unsatisfactory due mainly to the changes of the deposition rate of radon progeny onto the detector as a result of air turbulence. In this work, therefore, a method was developed which can correct the contributions of the deposition to the track densities by classifying the etched tracks according to their appearance, i.e. round or wedge shaped. Using this method, about 30% improvement in the error of measurements was achieved. The calibration coefficient ob tained by experiment was 0.00424 tracks/cm /h/(Bq/m ), which agreed well with the calculated value. Comparison was also made of the present method with other passive methods, charcoal and Terradex, as to their performance under the same atmosphere. 

In order to assess the accuracy of the present method, we compared it with two other methods. One was the Track Etch detector manufactured by the Terradex Corp. (type SF). Simultaneous measurements with our detectors and the Terradex detectors in 207 locations were made over 10 months. The correlation coefficient between radon concentrations derived from these methods was 0.875, but the mean value by the Terradex method was about twice that by our detectors. The other method used was the passive integrated detector using activated charcoal which is in a canister (Iwata, 1986). After 24 hour exposure, the amount of radon absorbed in the charcoal was measured with Nal (Tl) scintillation counter. The method was calibrated with the grab sampling method using activated charcoal in the coolant and cross-calibrated with other methods. Measurements for comparison with the bare track detector were made in 57 indoor locations. The correlation coefficient between the results by the two methods was 0.323. In the case of comparisons in five locations where frequent measurements with the charcoal method were made or where the radon concentration was approximately constant, the correlation coefficient was 0.996 and mean value by the charcoal method was higher by only 12% than that by the present method. 

Cohen, B.L., A Diffusion Barrier Charcoal Adsorption Collector for Measuring Rn Concentrations in Indoor Air, Health Phys. 50 457 (1986). 

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