Nonlinear Amplifier for Use in Mixed Radiation Rem Responding Radiation Meters

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Abstract
The objective of this work is the development of a survey instrument suitable for measurements in mixed radiation fields around nuclear reactors and accelerators. A 4-in. diameter Rossi-type "tissue-equivalent" spher ical proportional counter is used as the radiation detector. Pulses from the counter are amplified by a special operational amplifier which serves to convert the detector output into a pulse spectrum which is weighted for quality factor and thus represents dose equivalent. In the preliminary laboratory studies an analog-to-digital converter is employed to transform the operational amplifier output pulses to pulse trains which can be counted or passed through a count -rate-meter. The required gain characteristics of the nonlinear operational amplifier were determined by considering theoretical pulse height spectra expected from the detector when exposed to fields of radiation containing particles of both single and mixed LET [ linear energy transfer]. Design principles of a circuit which has approximately the required gain are discussed along with preliminary laboratory tests of the overall system response to pure and mixed radiation fields. The amplifier has a wide dynamic range, making it possible to measure dose from particles having LET from 0.2 keV/[mu] of tissue to about 200 keV/[mu] of tissue.