A Low-Level Radon Counting System

Abstract

A stable, convenient system for low‐level counting of radon is described. The system permits a precision of ±1 percent with an efficiency of about 80 percent. The lower limit of measurement is the amount of radon in equilibrium with about 10⁻¹⁴ gram of radium. A vibrating reed electrometer is used to amplify slow pulses obtained from an ionization chamber operated at 300 volts. The cumulative pulse count is recorded by a mechanical register following amplification of the output of the electrometer. Special care in construction and selection of the ion chamber materials permits an alpha background as low as 15 cph for a 4‐liter volume. Chemical pretreatment of the gases is unnecessary for most samples.