Use of a radioactive check device for redundancy check of ionization chambers

The use of a radioactive check device containing Strontium 90 was investigated to carry out the redundancy checks of Farmer-type ionization chambers. It was not possible to meet the recommended tolerance limits of the redundancy checks without taking into account the angular response of the ionization chambers. The ionization chambers exhibited a maximum variation of 1% in the angular response in this check device. After accounting for the angular response the maximum variation of the short-term repeatability was 0.14% with a standard deviation of +/-0.05%. The long-term constancy checked over a period of nine months was less than +/-0.6% for measurements, taking into account the angular response of the ionization chambers. No significant effect of the background radiation levels was observed on the measurements.