Absolute measurement of the activity of 222Rn using a proportional counter

A measuring set-up comprising a proportional counter of calculable 222Rn efficiency and quantifiable active volume (δV<0.1%) is described. On account of the special design of the end caps, the counter is suitable for absolute activity measurements on gaseous radiation sources. The 222Rn efficiency is determined by computer simulation of the measured α-spectra. The procedures necessary for absolute measurements by means of the counter are described, and the suitability of the counter for absolute measurements of the 222Rn activity is proved by experiments. Thus, a new method for the realization of the unit of activity of 222Rn is obtained, which is independent of the unit of activity of 226Ra.