No abstract

Continuous monitoring of radon concentrations can yield substantially more information than grab sampling in situations where concentrations vary significantly with time. Although several continuous monitors have been designed, calibration is usually difficult and not completely rigorous. In this work a simple and rigorous method is developed for the calibration and operation of all types of continuous flow-through instruments. Theoretical and experimental verification of the method is provided.

The collection efficiencies of parallel plate, inertial impactor and wire screen devices reported in the literature for measurement of the unattached fraction of radon (or thoron) daughters are calculated for collection of the attached fraction of the aerosol, using real uranium mine aerosol activity-size distributions. The attached activity collection efficiencies may be as much as 4.3%, which, given the typically low values of the unattached fraction (a few per cent), results in a very substantial error in the measurement of the latter. Published unattached fraction measurements in the environment may therefore be high and should be interpreted with care.

A 411 gas proportional counter is operated as an Instant Working Level Meter (IWLM) by making two a and one p-counts. In uranium mines, the p background caused by y-activity may result in an uncertainty of about 9% at 0.3 WL if the IWLM is operated without shielding. Design options are described to reduce the y background if desired. Proportional counters are inexpensive and rugged, and allow easy replacement of wires and/or broken windows and their counting efficiency may be increased simply by increasing the size of the window. Portable commercial proportional counters can be used as the basis for an IWLM using the principles developed in this work.

No abstract