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

Abstract

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 /spl plusmn/3/spl middot/10/sup -16/ A over the environmental range of temperature (-40 to +40/spl deg/C). Using a single 10/sup -11//spl Omega/ feed-back resistor, the electrometer accurately measures currents over a range from 3/spl middot/10/sup -15/ A to 3/spl middot/10/sup -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 /spl mu/R h/sup -1/), the new system measures radiation levels up to the point where the collection efficiency of the ion chamber begins to drop off, typically /spl sim/27 pA at 1 mRh/sup -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. >