Development of a high-range gamma ion chamber for space critical applications

The development of a gamma ionisation chamber as an alternative to Geiger Mueller (GM) counters for space critical applications has been described. The chamber has an overall diameter and length of 27 and 53 mm, respectively. It has a gamma sensitivity of 10 pA/R/h and its response is linear within 1% from 80 to 9600 R/h as compared to the GM counters, which have a non-linear response (the percentage loss of counts is 70% at 1000 R/h) at high gamma fields. The chamber has a uniform energy response from 660 keV to 1.25 MeV. The special technique of nickel-plating used to convert one of the surfaces of an alumina insulator into an electrode has resulted in the indigenous development of a compact and mechanically robust ionisation chamber.