A Feed-back Amplifier for Ionization Currents

Abstract

A direct reading X-ray intensity meter comprising a small thimble chamber on the end of a flexible cable, and measuring dose rates of 1 to 50 r per min. with a rapid response, is described. A large degree of negative feed-back is used to stabilise against changes in valves and supply voltages, and gives a precision measuring device with a linear response to radiation intensity. Circuit details are given, and it is explained how, by simple switching, the instrument may be used to measure also small doses of X rays, such as occur in diagnostic work. The cost is not great, and the general design appears to lend itself to other problems where it is necessary to measure small voltages either of a constant or slowly varying character.