A second-generation ionization current comparator

A solid state ionization current comparator is described in detail and the design parameters are discussed. The circuit operation of this instrument depends on direct amplification of the ionization chamber current and on instantaneous electronic computation of the quotient of the measuring chamber current and reference chamber current. Three forms of output may be produced: numerical, analogue and binary coded decimal. The comparator is intended for application in photon and electron dosimetry in both twin- and single-chamber modes as well as for dosimetry requiring high detection sensitivity. The instrument is particularly well suited for measuring beam data in a form needed by computer treatment planning systems, or for drawing isodoses using the decrement lines principle.