Homemade Geiger counter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Homemade Geiger counter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Dosimeters

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Take a starter from a fluorescent pump and plug it into the mains in series with a 15 watt incandescent lamp (see Figure 1). So we got the simplest Geiger counter. Now the main thing is to get into working mode. Our counter works like this: after being connected to the network, a weak current begins to flow through the gas discharge gap in the starter between the bimetallic plate 1 and column 2; its strength is not enough to burn lamp 3. Some time later, the curved bimetallic plate 1 heats up, unbends a little, touches column 2 and closes the circuit.

At this moment, the incandescent lamp 3 lights up. After about 0,25 seconds, the bimetallic plate 1 cools down, bends again, moves away from the column 2, the current in the circuit weakens, and the incandescent lamp 3 goes out. A glow discharge occurs again between bimetallic plate 1 and column 2, the plate heats up again, and the process is repeated.

Theoretically, it should go on with some regular frequency, that is, the incandescent lamp 3 should, for example, light up and go out every five seconds. V some starters and it happens. However, starters for fluorescent lamps vary considerably in their parameters. During repairs, many enterprises often throw away metal fittings for fluorescent lamps, and if you pick up 15-20 220-volt starters at once, then there will surely be one suitable among them.

For some starters, the glow discharge in the discharge gap is not sufficient to heat the plate and close the circuit, and incandescent lamp 3 does not light up at all.

Homemade geiger counter

The operating mode of the counter is based on the phenomenon that a weak discharge cannot heat the plate, but at the moment of passage of the particle, the current increases, the plate heats up and touches the column for a moment. This is where the incandescent lamp comes on. The starter then goes back into standby mode. The irregularity of outbreaks just indicates that we are in the operating mode. The interval between flashes can vary from 0,1 to 3-5 s with, we repeat, the complete absence of regularity.

The physics textbook says that a standard factory Geiger counter does not register particles at the moment of a spark (click or indicator). In our counter, this moment is much larger. The plate needs to heat up, and the incandescent lamp needs to flash and go out. But since the natural background of radioactivity is low, and the response time is 20 - 30 times less than the period of flight of particles, the results of the counter operation are satisfactory. There should be about 12 to 25 flashes per minute.

Factory meters have a dependence of the number of operations N on the voltage U (Fig. 2). If the battery gives a low voltage, then not all particles are registered. When the voltage calculated for this meter is applied, the Geiger plateau appears on the graph, that is, all particles are recorded. With a further increase in voltage, the number of false positives increases, and then a continuous breakdown occurs - the curve on the graph goes up.

All this is true for our counter. Thus, the particle registration mode is relative. If the starter lies on the table, the counter works less often, and if you bring a dusty rag to the starter, then the number of flashes per minute increases - because dust always contains radioactive isotopes.

Current fluctuations in the circuit should also be taken into account, but within 20-30 minutes it is usually constant. It is also preferable to take measurements in the late evening. If you have a trimmer stabilizer with a built-in voltmeter from an old TV, it's great. Most importantly, our counter allows you to carry out relative measurements - to determine the degree of radioactivity, say, vegetables or items of interest to you. You can finally calibrate the counter according to the standard factory one, taking it for a while from one of your friends or acquaintances.

See other articles Section Dosimeters.

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