Gamma radiation indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Gamma radiation indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Dosimeters

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The device in question is designed to detect gamma radiation at home, in the country, on a hike. Gamma particles are registered by a Geiger-Muller counter. The indicator is the dynamic head of the loudspeaker. When a certain number of particles pass through the counter, a click is heard. The number of clicks per unit of time is directly proportional to the intensity of gamma radiation.

The figure shows the diagram of the indicator. In order to increase the input resistance, the first stage of the pulse amplifier of the BD1 counter is assembled according to a circuit with a common collector on the transistor VT1. Pulses of positive polarity from the VGO output through the germanium diode VD1 start a single vibrator on transistors VT2 and VT3. The output stage on a composite transistor VT4, VT5 is loaded with a dynamic head BA1 with a rated power of 0,1 W.

(click to enlarge)

A voltage converter is assembled on the transistor VT6 to power the counter BD1. The high voltage rectifier consists of diodes VD2, VD3 connected in series and a smoothing capacitor C6. The latter must be selected from those with low leakage and for an operating voltage of at least 500 V (for example, K78-2 or KSO).

The magnetic circuit of the transformer T1 is a ferrite plate from a set of parts for assembling the Yunost radio receiver, intended for the manufacture of a magnetic antenna. The surface of the magnetic circuit is covered with two layers of thin capacitor paper or adhesive tape. Then the secondary winding is wound in one layer turn to turn - 700 turns of PEV 0,1 wire. Next, two layers of paper or adhesive tape are applied and the primary winding is wound from 14 turns of PEV 0,6 wire with a tap from the middle. The turns of the primary winding are laid in increments, evenly distributing them along the entire length of the magnetic circuit. The finished transformer is insulated with another layer of paper or tape. The winding leads are made of MGTF wire - a thin stranded wire in fluoroplastic insulation.

The BD1 counter is fixed with two spirals of uninsulated copper wire with a diameter of 0,8 ... 1 mm, wound directly on the cylindrical terminals of the counter. The ends of the spirals are fixed in the mounting holes of the device board.

The collected indicator does not require any adjustment. If the installation is completed without errors, and all parts are in good order, it starts functioning immediately after being connected to a power source - the Krona battery and consumes a current of approximately 5 mA from it. The performance of the voltage converter can be assessed "by ear" - the transformer T1 makes a barely audible sound during operation.

If the SI1G gas-discharge counter is installed as BD37, each click of the BA1 dynamic head, recorded for a minute, corresponds to 5 μR / h. Therefore, if three clicks were heard in a minute (time is measured by the second hand of the clock), the radiation intensity is 5 μR / h x 3 \u15d 1 μR / h. This is a normal natural background. If it is necessary to estimate the radiation level with increased accuracy, perform several measurement sessions lasting XNUMX min each and take the arithmetic mean of their results.

Author: R. Tigranyan, Moscow

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