Science Applications International Corporation

John M Wettroth

Kenneth H Valentine

A radiation measurement apparatus and method extends the measurement range of a single Geiger Mueller tube (GMT). The apparatus may operate in a either a conventional mode, used to measure low radiation levels, e.g. background radiation, or an extended range geiger (ERG) mode, used to measure high radiation levels. Both modes utilize the same GMT and basic operating circuitry, including a power supply for generating a GMT anode voltage, a GMT anode voltage control circuit, a GMT trigger circuit, a clock circuit, and a GMT pulse counter circuit. In the conventional mode, the radiation rate is determined as a function of the number of GMT pulses counted over a prescribed time period. In the ERG mode, an additional counter is employed to count trial intervals of a prescribed duration. The radiation rate is determined in the ERG mode statistically as a function of the ratio of the GMT pulse count and the trial interval count, with a prescribed number of trial interval counts being rejected after each GMT pulse in order to assure known initial conditions.

Extended range geiger counting apparatus and method utilizing a single

Small, light-weight portable radiation measurement apparatus provides accurate quantitative measurment of radiation dosage and dosage rates. Such apparatus, referred to as a dosimeter, is housed in a ruggedized housing that is only about 1/2 the volume of a package of cigarettes, may easily be clipped to clothing or carried in a shirt pocket, and is powered by a conventional alkaline AA-sized battery. Included in the housing are a geiger tube for detecting radiation, a high voltage power supply for providing power to the geiger tube, a counting circuit for counting geiger pulses generated by the geiger tube, a microprocessor circuit for processing the geiger pulses in accordance with a prescribed program to determine the does or dosage rate to which the geiger tube has been exposed, and a digital display that displays the dosage rates thus determined. The microprocessor program is stored in memory circuits, included as part of the microprocessor circuit. An audible alarm is generated whenever the dose or dosage rate exceeds a programmable threshold. The circuitry and display allow a wide range of radiation levels to be detected and displayed. All the circuits are designed for low power consumption, allowing 500-600 hours of continuous use before having to replace the battery. A dielectrically coupled communications port allows necessary data, e.g., calibration coefficients or dosage data, to be transferred to and from the dosimeter circuitry without direct physical contact.

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San Diego, CA, United States of America

John M Wettroth