Use of nitrogen-filled ion chamber for wide-range gamma monitoring

A gamma-sensitive ion chamber has been developed for area gamma monitoring. It has 800 cc sensitive volume filled with nitrogen at 120 psig pressure. With a current sensitivity of 0.6 nA/R/h the chamber needs 250 V for 90% saturation at 10 R/h. However, the use of the tanh formula proposed by Fallone and Podgorsak has enabled the authors to develop an instrument to derive exposure rates as high as 80,000 R/h with the help of a single current reading at an applied voltage of 300 V. The instrument can be used to measure unknown exposure rate with accuracy within ± 3.5%. (author)