High sensitivity two filter radon/thoron detectors with a wire or nylon screen as a second filter.

Abstract

A study is made of the use of wire and nylon screens as a second filter in two radon or thoron detectors. It is shown that acceptable detection efficiency is obtained at flow rates comparable to those used in detectors in which other types of filter are used. The main advantage of the screens is their very low flow impedance. Several designs of detector which exploit this feature are discussed. Details are given of the performance of three prototypes: a 32 L radon detector with a limit of detection of 0.0027 Bq m-3 and power consumption of 25 watts; and a portable thoron emanometer capable of detecting fluxes as low as 1 m Bq m -2 s-1. The radon detectors are rugged and simple. They can operate with no routine maintenance and are suited to remote locations where only infrequent technical support is available.