ON CE, C-LAMBDA AND THE EFFECTIVE WALL MATERIAL OF A BALDWIN-FARMER CHAMBER

An expression relating the constant A to the characteristics of an ionisation chamber is developed. This constant, used to obtain the mass ionisation from the instrument reading, appears in expressions for CE and Clambda, and is a function of the chamber wall material. Measurements with a Baldwin-Farmer chamber are described, and indicate that the effective wall material is more nearly equivalent to Lucite than to air in 60Co gamma radiation. The resulting value of A is nearly 1.5% lower than the figure commonly used.