A Technique for Measuring Extremely Low Ionization Chamber Currents Using MOS FET Circuitpry

A circuit has been developed for an Isotope Calibrator which will accurately measure ionization chamber currents in the order of 10-14 to 10-7amps. The circuit incorporates a self-zeroing feedback network which virtually eliminates drift, as well as high impedance MOS FET switches and a MOS insulated gate FET source follower in the input circuit to minimize errors due to leakage currents.