Radiation indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Dosimeters
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It is possible to measure the level of radiation radiation not only with an expensive factory-made device. The simplest device (see diagram) can be done with your own hands if you have a counter (radiation sensor) of the SBM-20 type. It is powered by a 220 V network. On the diodes VD1, VD2 and capacitors C1, C2, a half-wave rectifier is made, assembled according to the voltage doubling circuit. Since capacitors C1 and C2 generate a constant voltage of approximately 310 V each, the total rectifier voltage is approximately 620 V.
However, not all 620 V are actually used. The fact is that resistors R5 and R3 form a voltage divider formed on capacitor C1, and resistors R6 and R4 - on capacitor C2. That is why a voltage of 3 V is created on resistors R4 and R200. Thus, the Geiger-Muller counter BD1 (radiation sensor) is powered by 400 V, while the neon lamp HL1 (radiation indicator) is only 200 V. The latter lights up only when open transistor VT1, and it opens when radiation ionizes the gas inside the sensor BD1. Resistor R1 contributes to the reliable closing of the transistor VT1 in the absence of radiation, and resistor R2 limits the base current of this transistor in the presence of radiation.
When there is no radiation source nearby, the natural radiation background causes 20...30 electrical impulses in the Geiger-Muller counter within one minute. Consequently, the transistor VT1 must open for a short time - the indicator lamp HL1 flashes after 2 ... 3 seconds, however, without strict periodicity. As the radiation level increases, the flashes of the HL1 lamp become more frequent. This can be checked by bringing an ordinary Christmas tree toy coated with phosphorus to the counter. When the level of radiation is very high, the lamp HL1 burns continuously.
In order not only to see the readings, but also to hear, an electromagnetic capsule (telephone) is switched on in series with the HL1 light bulb. Its volume is quite satisfactory if the winding resistance exceeds 1 kOhm.
Instead of a counter of the SBM-20 type, others are also acceptable, for example, SBM-11, SBM-21, STS-20, STS-5. The high-voltage transistor KT618A is interchangeable with KT605B, KT605BM, KT604B or KT940A, and the KD105B diodes are interchangeable with KD105V, KD105G, KD209A, KD209B, KD209V. As a neon lamp, instead of TN-0,2, you can use, say, TN-0,3, IN-1, MN-5, or even a starter lamp from a fluorescent lamp. All resistors here are of the MLT-0,5 or OMLT-0,5 type. Capacitors must have a rated voltage of at least 400 V. The radiation sensor - a Geiger-Muller counter - should be covered only with a thin plastic plate or plastic film.
Author: V.Bannikov
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