Method for Analyzing Statistical Information Obtained in Dosimetric Measurements

Abstract

The dose rate of ionizing radiation is measured using dosimetric devices which are based on counting the number of pulses of a radiation detector followed by statistical analysis of the counts obtained over the measurement time. When dosimeters are powered with drycell batteries, it is difficult to operate the devices for a long time without replacing the batteries frequently. The large amounts of energy consumed by such dosimeters make it impossible to produce small devices which can operate for a long period of time. The detectors used in such devices require a stable high-voltage power supply. The scheme for stabilizing the voltage for powering the detector requires a comparatively large amount of electricity. To produce miniature dosimeters, it is important to conserve electricity, even for measurements performed at the natural background level. It is especially important to conserve electricity with a high radiation level, when the number of counts can be many times higher. In this case, the operating time of the dosimeter in an autonomous mode will be substantially shorter, and it will become impossible to produce operable devices. The proposed method for analyzing the statistical information from the detector in a dosimeter makes it possible to decrease substantially the effect of this drawback on the working capacity of the dosimeter, to decrease by a factor of 5‐10 the energy consumption of devices of this type, to increase the service life of the detectors, to increase the measurement range for ionizing radiation, and to expand the frequency characteristics of the devices. A simplified view of the scheme implementing the method for processing statistical information from the detector in a dosimeter is displayed in Fig. 1. It preserves the general principles for obtaining the supply voltage for a detector and ext racting the working pulse of a detector, but the time interval chosen for measurement is divided into shorter, equal intervals during which only one pulse is recorded and all other pulses during this interval are cut off by locking the operation of the powe r supply. This makes it possible to reduce electricity consumption by a factor of 5 as a result of a decrease in the number of th e electric discharges through the detector and a decrease in the time required to maintain a stable supply voltage. The generator producing the time-interval pulses (it can also be a component of an electronic clock circuit) with variable frequency generate s pulses from a quartz generator, whose duration and amplitude must be sufficient for the scheme to work. The dosimeter operates as follows. As is well known, for random events, such as radioactive decays, when a single pulse of a detector is recorded with a prescribed statistical reliability of measurements at a level of, for example, 0.997, the average number of pulses over the measurement time must exceed 5. If the detector has recorded one pulse during the prescribed interval, the other pulses are not required for detection and they can be passed. This makes it possible to conserve, on the average, the electricity required to record four pulses and for period of time during which the device for stabilizing the supply voltage is off, which on the average equals 4/5 the interval duration. The random processes governing radioactive decay follow the Poisson law. The probability of no pulses from a detector in time t is P 0 = exp(‐n t ),