A resistance-coupled amplifier for measuring ionization currents

Abstract

A description is given of a simple two-stage resistance-coupled vacuum-tube amplifier for use in measuring ionization currents down to the order of 10~ 13 ampere. Commercial dry-cell vacuum tubes are used. It can be calibrated and will retain its calibration over considerable periods within 1 percent. Where comparative measurements are required—for example, standardizing radium preparations—it is capable of a much higher accuracy. Readings are made on a pointer-type microammeter. The stability of the circuit indicates that a more sensitive instrument could be used if more feeble currents are to be measured. A description of interchangeable ionization chambers, suitable for use with such an amplifier, is given.