Investigation of parameters affecting the concentration of radon and its daughters in indoor atmospheres

Accumulation of the radioactive gas, radon (Rn-222), and its daughters in inhabited areas could significantly influence population exposure to natural radiations. Exposures to high concentrations of airborne radon daughters have been associated with the induction of lung cancer among uranium miners. This research is directed toward studying the parameters which affect the concentration of radon and its daughters inside a building contaminated with radium-226 deposits. Measurements were conducted in a building of an industrial park in southwestern Pennsylvania.

Ventilation rates inside the building were measured using carbon dioxide (as a tracer gas) which was detected by an infrared spectrometer. Ventilation rates were found to vary depending on the outdoor wind conditions. The technique of using carbon dioxide as a tracer gas coupled with infrared spectrometry proved to be an excellent and reliable technique.

Concentrations of radon gas inside the building at different locations were measured continuously using modified computer-based versions of the well-known Wrenn chambers. Measurements indicated that indoor radon concentrations vary according to the activities performed in the building as well as on the ventilation conditions. A pronounced increase in radon concentration was observed whenever airexchange rate was reduced.

Radon flux measurements were performed in order to quantify the individual indoor radon sources which contributed to the observed overall concentration. Radon flux emanating from the concrete floor

vi slabs, cracks, and floor drains was found to be the principal source of radon in the building. Radon flux measurements were accomplished by utilizing activated charcoal canisters as accumulators. Field measurements of this kind usually require a large number of canisters in order to obtain reliable results. The preparation and handling of large quantities of canisters became a time-consuming process. For this purpose, a crack monitor was designed and calibrated. This crack monitor is based on the idea of circulating the radon gas emanating from a certain crack length (one meter) and collected in a metal housing through an accumulator (charcoal canister). The accumulator thus collects the integral radon flux over the entire length of the crack monitor. Results showed that for a flow rate of 8 liters/minute the crack monitor records 70 percent of the actual radon flux. Radon flux emanating from drains in that building was measured also. A new method was developed for measuring radon flux emanating from drains without blocking natural convective flow into and from the drain. The method is referred to as the open-end, double-detector method, in which two canisters are connected back to back by a short brass pipe. The canister facing the drain will collect the integral flux emanating from the drain over the collection period, while the upper canister will collect the reverse flow if it may occur.

Radon daughter concentrations were measured using the technique devised (and later refined) by Kerr in which particulate radon daughters in building air are collected on a filter and then counted using a surface barrier alpha spectrometer. . Measured radon daughter concentrations vary considerably and are controlled to some extent by the concentration of radon gas as well as by ventilation conditions. No general correlation between radon concentrations and daughter concentrations was obtained in this particular situation.

An analytical model based on conservation laws was developed which incorporates the effect of parameters such as wall/floor material, airexchange rates, variations in atmospheric pressure, and outdoor radon concentration. Indoor radon gas was assumed to be removed by airexchange process, radioactive decay and interaction with walls. A linear model was introduced in order to evaluate the effect of variations in atmospheric pressure on the exhalation rate of radon from surfaces (wall/floor). A good agreement between experimentally measured radon concentrations and those calculated using this model for the west room of the building was obtained. Also measured and calculated working levels for the same room agreed very well.