Ionization chamber

The wall of an ionization chamber containing a filling of air is formed of an alloy of Be with at least one of the elements Al, Mg and Si, the proportion of Be being such that the co-efficient of response of the wall to b radiation and to g and X-ray photons is substantially identical with the co-efficient of response of air, the co-efficient of response of a material being defined as the ratio of energy absorbed in the material to energy absorbed in human body tissues. Suitable alloy compositions are by weight:- (1) Be 81-89%, preferably 85 \sB 0.5% A1 remainder (2) Be 77-85%, preferably 81 \sB 0.5% Mg remainder (3) Be 84-92%, preferably 88 \sB 0.5% Si remainder (4) Be 85.35% A1 13.25% Si 1.4%