Indicator of beta and gamma radiation. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Indicator of beta and gamma radiation. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Dosimeters

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The figure shows a diagram of a simple indicator that detects even weak beta and gamma radiation. The sensor (VL1) is a domestically produced Geiger-Muller counter of the CTC-5 type, which has been produced for more than thirty years. It has the form of a metal cylinder about 113 mm long and 12 mm in diameter. Its operating voltage is 400 V. From foreign sensors, you can use the ZP1400, ZP1310 or ZP1320 from Philips.

(click to enlarge)

The device is powered by one galvanic cell with a voltage of 1,5 V and consumes a current of not more than 10 mA. The -12V voltage for powering the amplifier and the high voltage for powering the sensor are obtained from the converter on the transistor VT1. The converter transformer T1 is wound on an armored magnetic core with a diameter of about 25 mm. Winding 1-2 has 45 turns of wire with a diameter of 0,25 mm, 3-4 - 15 turns of the same wire, and 5-6 - 550 turns of wire with a diameter of 0,1 mm. The beginning of the windings in the diagram are marked with dots. The converter is a blocking generator. The high voltage pulses arising on the winding 5-6 of the transformer T1 are rectified by the high-frequency diode VD2.

Conventional rectifier diodes are unsuitable here, since the pulses are too short and their repetition rate is too high. While there is no radiation, there is no voltage at the input of the amplifier, made on transistors VT2 and VT3, and the transistors are locked. When beta or gamma particles hit the sensor, the gas with which it is filled is ionized and a pulse is formed at the output, which excites the amplifier, and a click is heard from the loudspeaker (telephone capsule) BF1, while the HL1 LED flashes. Outside the irradiation zone, clicks and flashes of the LED are repeated after 1-2 s. This is the reaction of the sensor to cosmic radiation and the natural background. If you bring the sensor closer to a radiating object (an old watch with a luminous dial or a wartime aircraft instrument scale), the clicks will become more frequent and finally merge into a continuous crackle, and the LED will glow continuously. Thus, it is possible to judge the frequency of particles hitting the sensor, and, consequently, the radiation intensity.

The device also has a pointer indicator. The alternating voltage taken from the telephone capsule is fed through the capacitor C5 to a full-wave rectifier on germanium diodes VD3, VD4 (they can be of any type).

The rectified voltage, after smoothing by capacitor C6, is fed through a variable resistor R5 to a microammeter (RA1). the resistance of the resistor is set so that with strong radiation the needle of the microammeter does not go off scale, and with weak radiation it noticeably deviates. If necessary, the device can be calibrated by comparing its readings with an industrial radiation meter. The device is assembled on a printed circuit board placed in a box measuring 150x90x40 mm. The sensor is located in a separate housing and is connected to the device by a cable with a connector. Transistor VT1 can be replaced with KT630 with any letter index, KT315B - with KT342A. The LED can be AL307, AL341. As VD2, you can use two KD104A diodes by connecting them in series. Diode KD226 can be replaced by KD105V. A telephone capsule should be selected with a voice coil impedance of at least 50 ohms. The pointer measuring head can be selected in any type with a total deflection current of 50 μA.

Publication: N. Bolshakov, rf.atnn.ru

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