An improved gas counting system for absolute activity measurement of radioactive gases

The calibration of gas monitoring instruments with beta emitting gases is an important procedure for increasing the reliability of the measurements for radiation protection. For example, gas standards of 3 H, 85 Kr and 133 Xe are frequently used for the calibration of gas effluent monitors of the nuclear power plants. The internal gas counting with proportional counters is the most frequently method for preparing gas standards. This method is based on a complex counting system composed of two length compensated proportional detectors, a gas handling system and two spectrometric counting channels. By virtue of their different lengths, the detectors permit compensation to be done for the end effect (non-uniform detection of ionizing events caused by beta particles which takes place near to the ends of the counters). To reduce the complexity and cost of the internal gas counting system, a proportional detector was manufactured with electric field corrections at the ends for canceling the end effect. As a result, a counting system was made using only one proportional detector and only one spectrometric counting channel . (authors)