A pressurized ion chamber monitoring system for environmental radiation measurements utilizing a wide-range temperature-compensated electrometer

The performance of a complete pressurized ion chamber (PIC) radiation monitoring system is described. The design incorporates an improved temperature-compensated electrometer which is stable to ±3·10^-16 A over the environmental range of temperature (-40 to +40°C). Using a single 10^-11Ω feed-back resistor, the electrometer accurately measures currents over a range from 3·10^-15 A to 3·10^-11 A. While retaining the sensitivity of the original PIC system (the instrument responds readily to small background fluctuations on the order of 0.1 μR h^-1), the new system measures radiation levels up to the point where the collection efficiency of the ion chamber begins to drop off, typically ~27 pA at 1 mRh^-1. A data recorder and system controller was designed using the Tattletale Model 4A computer. Digital data is stored on removable solid-state, credit-card style memory cards