An Air-Equivalent Ionization Chamber

The characteristics of an air-equivalent ionization chamber used for routine exposure measurements were investigated. The air-equivalent material used was a mixture of 91% polycarbonate [(C 16 H 14 O 3 ) n ] and 9% E-glass (54% SiO 2 ; 1% Fe 2 O 3 ; 1% Na 2 O 2 + K 2 O 2 ; 1% TiO 2 ; 15% CaO; 8% B 2 O 3 ). This is equivalent to a mixture of commercial thermoplastics consisting of 55% Makrolon-3100 natural and 45% Makrolon-8020 natural (Bayer). The parts of this chamber have been injection moulded and the chamber had volume of 1l and wall thickness of 2 mm. The inner surfaces of the chamber were coated with a conductive air-equivalent layer. The response of the chamber was slightly gamma-energy dependent in the 0.04 MeV to 1.25 MeV energy range.