Geiger counter made easy. Homemade Geiger-Muller counter How to make a Geiger counter from a phone

The device invented by Hans Geiger, capable of detecting ionizing radiation, is a sealed cylinder with two electrodes into which a gas mixture consisting of neon and argon is pumped, which is ionized. A high voltage is applied to the electrodes, which in itself does not cause any discharge phenomena until the very moment when the ionization process begins in the gaseous environment of the device. The appearance of particles arriving from outside leads to the fact that primary electrons, accelerated in the corresponding field, begin to ionize other molecules of the gaseous medium. As a result, under the influence of an electric field, an avalanche-like creation of new electrons and ions occurs, which sharply increase the conductivity of the electron-ion cloud. A discharge occurs in the gas environment of the Geiger counter. The number of pulses occurring within a certain period of time is directly proportional to the number of detected particles.

It is capable of responding to ionizing radiation of the most various types. These are alpha, beta, gamma, as well as x-ray, neutron and ultraviolet radiation. Thus, the input window of a Geiger counter, capable of detecting alpha and soft beta radiation, is made of mica with a thickness of 3 to 10 microns. To detect X-ray radiation it is made of beryllium, and ultraviolet radiation is made of quartz. You can build your own simple Geiger counter, which uses a Geiger-Müller tube instead of an expensive and scarce one, using a photodiode as a radiation detector. It detects alpha and beta particles. Unfortunately, it will not be able to detect the gamma range of radiation, but this will be enough for a start. The circuit is soldered onto a small printed circuit board, and the whole thing is housed in an aluminum case. Copper tubes and a piece of aluminum foil are used to filter out radio frequency interference.

Photodiode Geiger counter circuit

List of parts needed for the radio circuit

• 1 BPW34 photodiode
• 1 LM358 op amp
• 1 transistor 2N3904
• 1 transistor 2N7000
• 2 capacitors 100 NF
• 1 capacitor 100 µF
• 1 capacitor 10 nF
• 1 capacitor 20 nF
• 1 10 MΩ resistor
• 2 1.5 Mohm resistor
• 1 56 kohm resistor
• 1 150 kohm resistor
• 2 1 kohm resistor
• 1 250 kohm potentiometer
• 1 Piezo speaker
• 1 Power switch

As you can see from the diagram, it is so simple that it can be assembled in a couple of hours. After assembly, make sure the polarity of the speaker and LED are correct.

Place copper tubes and electrical tape on the photodiode. It should fit snugly.

Drill a hole in the side wall aluminum body for the toggle switch, and on top for the photosensor, LED and sensitivity regulator. There should be no more holes in the case, since the circuit is very sensitive to electromagnetic interference.

Once all electrical components are connected, insert the batteries. We used three CR1620 batteries stacked together. Wrap electrical tape around the tubes to prevent them from moving. This will also help block light from reaching the photodiode. Now everything is ready to begin detecting radioactive particles.

You can check it in action on any test radiation source, which you can find in special laboratories or in school classrooms, after practical work on this topic.

Lefty 1995 No. 10

The device described above for measuring radiation levels is attractive primarily because of the simplicity of its manufacture. However, it also has its own small nuance: the most important part of the device, namely the radiation sensor, which, in fact, is the basis of the Geiger-Muller counter, is not accessible to everyone. And although the device of the counter is known from a physics textbook, it is almost impossible to make it at home - the device is quite complicated. However, don't despair! Instead of the device described in the previous article, you can make another one that is accessible to many. Instead of a counter, we will make a good substitute that will be quite capable of registering beta and gamma radiation.

Take a starter from a fluorescent pump and connect it to the network 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 meter works like this: after being connected to the network, a weak current begins to flow through the gas discharge gap in the starter between 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, bends slightly, touches column 2 and closes the circuit.

At this moment, incandescent lamp 3 lights up. After approximately 0.25 seconds, bimetallic plate 1 cools down, bends again, moves away from column 2, the current in the circuit weakens, and 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 repeats.

Theoretically, it should occur at some regular intervals, that is, incandescent lamp 3 should, for example, light up and go out every five seconds. This happens to some starters. However, starters for fluorescent lamps vary significantly in their parameters. Many enterprises often throw away metal fittings for fluorescent lamps during repairs, and if you select 15 - 20 220-volt starters at once, then among them there will certainly be one suitable one.

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 at all.

The operating mode of the counter is based on the phenomenon that a weak discharge cannot heat the plate, but at the moment the particle passes, the current intensifies, the plate heats up and momentarily touches the column. This is where the incandescent lamp flashes. The starter then goes into standby mode again. The irregularity of the outbreaks just indicates that we are in working mode. The interval between flashes can vary from 0.1 to 3-5 s with, we repeat, a complete lack of regularity.

The physics textbook says that a standard factory Geiger counter does not register particles at the moment of the spark (click or trigger of the indicator). With our counter this moment is significantly greater. 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 passage of particles, the results of the counter are satisfactory. There should be approximately 12 to 25 flashes per minute.

For factory meters, there is a dependence of the number of operations N on the voltage U (Fig. 2). If the battery produces low voltage, then not all particles are detected. When the calculated voltage for a given counter is applied, a Geiger plateau appears on the graph, that is, all particles are registered. With a further increase in voltage, the number of false alarms 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 is lying on the table, the counter fires less often, and if you bring a dusty rag to the starter, the number of flashes per minute increases - after all, dust always contains radioactive isotopes.

Fluctuations in the current strength in the circuit should also be taken into account, but for 20-30 minutes it is usually constant. It is also preferable to take measurements in the late evening. If you have a tuning transformer-stabilizer with a built-in voltmeter from an old TV, that’s absolutely great. The main thing is that our counter allows you to carry out relative measurements - to determine the degree of radioactivity of, say, vegetables or items of interest to you. Finally, you can calibrate the meter according to the standard factory calibration, borrowing it for a short time from one of your friends or acquaintances.

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Below is a diagram of a Geiger counter on PIC microcontroller 16F84, printed circuit board in PCAD and microcontroller firmware.

Device characteristics:
Power: 9V
Current consumption without LCD backlight: 7 mA
with LCD backlight: 11 mA (depending on brightness)
Measuring range: 0 µR - 144 mR (limit of the SBM-20 counter)

I had to order the LCD because... There weren't any stores that were the right size. An 8-character, 2-line LCD based on the HD44780 controller is optimally suited for these purposes.
In principle, any 2-line LCD based on the HD44780 controller should be suitable

The step-up transformer is wound on a ferrite ring 16x10x4.5

Winding I - 420 turns of wire PEV 0.1
Winding II - 8 turns of wire PEV 0.15 - 0.25
Winding III - 3 turns of wire PEV 0.15 - 0.25

The housing is a digital multimeter DT-830. It turned out to be cheaper to buy a multimeter for its housing than to buy the housing separately :)

Minor revision

We take out the giblets, remove the sticker, and use a utility knife and file to bring it to perfection.
We also drill the necessary holes:

When designing, I did not take into account one thing - finding a small-sized button and switch to mount on the case turned out to be difficult.
Therefore, I had to make an additional small seal to mount the switch from the faulty multimeter, and secure the button with a clamp on the inside of the front panel.

Checking the device:

First, we check the correct installation, connection of the transformer and LCD, as well as the polarity of the connection of the SBM-20 meter.
We serve food.
ATTENTION! There is high voltage in the circuit!
There should be a voltage of at least 200 volts across capacitor C1 (when measured with a digital multimeter, since its internal resistance is not high enough, a voltage drop occurs; in fact, there should be about 350 volts across capacitor C1!).

The text appears on the LCD:

After initialization, the display shows the equivalent radiation dose readings. On average, about 14-22 microR, but it can be more.
In the future, the readings are updated every second, specifying the average equivalent radiation dose per unit of time.

Next, you need to check that the counter really works and can show something more than the natural background radiation.
To do this, you can buy “potassium nitrate” (KNO3) at the fertilizer store. KNO3 contains its radioactive isotope, to which the device must react.

The container with KNO3 must be placed as close as possible to the sensitive side of the device (where the SBM-20 meter is located).

Again, the result may vary, but the reading should be significantly higher than the natural background.

A Geiger-Muller radiation counter is a relatively simple instrument for measuring ionizing radiation. In the simplest case, it is done with one sensor. To increase sensitivity, the design presented here contains 3 Soviet STS-5 detector lamps. This is important for measuring natural sources with low radiation levels, such as soil, rocks, and water.

The operating principle of a gas-discharge Geiger-Müller counter is that when high voltage (typically 400 V) is applied to the sensor, the tube does not normally conduct electricity, but does for a short period when particle emission occurs. These pulses arrive at the detector. The level of ionizing radiation is proportional to the number of pulses detected in a constant time interval.

The radiation counter consists of two electrodes, the ionizing particle creates a spark gap between them, in order to reduce the amount of current that occurs in this situation, a resistor is placed in series with the tube. Marked in the diagram as R5. Eat different ways receiving a signal from the tube, in the case presented here, a resistor is connected in series between the tube and ground, the change in voltage across the resistor is measured using a detector. This resistor is designated R6.

Here the MC34063 chip is a converter direct current, since high voltage is required for normal operation. Its advantage over the simple NE555 or similar generators is that it can control the output voltage and adjust the parameters to make it stable (elements R3, R4, C3).

The op-amp chip IC1A is used as a comparator to filter noise and generate a binary signal (low - no pulse on this moment, maximum - the impulse has passed). The supply voltage of the circuit is 5 V, the current consumption is 30 mA.

Startup and troubleshooting

The voltage at C4 must be within acceptable limits for the Geiger-Muller counter used. It is usually around 400V - be careful when taking measurements! If the voltage is outside the range, then using C1 (frequency DC/DC converter), C3, R3, R4 (feedback voltage DC/DC converter) can be adjusted.

The next important point is the presence or absence of pulses on R6. If there are no pulses, you need to check whether the detector tube is connected according to the polarity. Similar to a diode, a Geiger counter has its own polarity and will not work correctly if connected in the opposite direction.

If the pulses on R6 are visible, but the output state of IC1A does not change, then R7, R8 must be changed, they set the threshold value of the signal. As can be seen in the photograph, a 32F429I digital frequency counter was used to count pulses and visualize the results. The circuit presented in this project can be adjusted to work with any other Geiger radiation sensors - they differ in the required voltage.

You can't see or feel radiation, but you can recognize its presence different ways by exposure of photographic film, by light flashes on the display, but most practically - using a particle counter that creates an electrical impulse when a particle hits it. Basically, all Geiger-Muller counters consist of a sealed tube, which is the cathode and a wire stretched through it along the axis - the anode. The space inside is filled with gas at low pressure to create optimal conditions for electrical breakdown. The voltage on the meter is about 300 - 500 V and is adjusted so that an independent breakdown does not occur and current does not flow through the meter. But when a radioactive particle hits, it ionizes the gas in the tube, and a whole avalanche of electrons and ions appears between the cathode and anode - a current begins to flow. But after a fraction of a millisecond, the counter returns to its original state and waits for the next particle to pass.

The photo shows the most common meter SBM-20. It is sensitive to beta and gamma radiation (X-rays). The number of pulses recorded by it in 40 seconds is equal to the radiation intensity in microroentgens per hour (µR/h). The normal level is usually 12 - 16 microR/h. But in the mountains it can be several times higher.

The homemade dosimeter circuit consists of two blocks assembled in small plastic boxes: a network rectifier and an indicator.

The blocks are connected to each other by connector X1. When power is applied, capacitor C3 begins to charge to a voltage of 600 V and then serves as the power source for the meter. Having disconnected the power from the outlet and turned off the indicator, we begin to listen to clicks in high-impedance phones.

As you may have guessed, a click on the phone means that a radioactive particle has entered the counter. The operating time of the indicator after one charge depends on the leakage current of the capacitor, so it must be good quality. As a rule, the device can work for ten or forty minutes without recharging, depending on the intensity of radioactive radiation.

The end of the capacitor charge can be judged by the cessation of clicks in high-impedance phones. Part ratings are not critical. Resistor R1 should be powerful 1-2 W. Counter B1 can be anything you can find.

A generator designed for a frequency of 1000 Hz is assembled using elements DD1.1 and DD1.2 K176LA7. Rectangular pulses through a differentiating chain C2R3 open the VT1 KT315 transistor operating in key mode. Pulses from its collector junction, passing through the primary winding of the transformer, induce a high pulse voltage with a potential of about 100 V in its secondary winding. The VD1 diode is designed to protect the transistor collector from overvoltage that may occur on an inductive load - the transformer.

The sixfold multiplying rectifier produces a constant 400 V voltage, which is supplied to the meter cathode through current limiting resistor R4. Negative pulses from the anode of the counter, caused by the passage of radioactive particles, switch element DD1.3 and, extending in duration to fractions of a second, fall on DD1.4, since rectangular pulses of a frequency of 1 kHz are received at its other input. The output of the element produces tonal audio signals, and the HL1 LED also lights up at the same time.

With a natural background of radiation, “squeaking” sounds are rare once every few seconds; when the radiation level increases, the tone sounds more often, and at dangerous values sound signal sounds continuously and the LED is constantly on. The circuit uses a SI13G counter, but similar ones can also be used. It is produced in a glass flask and has smaller dimensions than the SBM-20 counter, but also lower sensitivity.

The transformer is homemade, wound on a miniature W-shaped ferrite core Ш4×8, the primary winding of which contains 100 turns of PEL 0.1 wire, the secondary winding contains 1200 turns of PEL 0.06 wire. Winding must be done in bulk; 1 - 2 layers of insulation are laid between the windings.

In this article you will find a description simple circuits dosimeter on the SBM-20 counter, which have sufficient sensitivity and register the smallest values ​​of beta and gamma radioactive particles. The dosimeter circuit is based on a domestic radiation sensor of the SBM-20 type. It looks like a metal cylinder with a diameter of 12 mm and a length of about 113 mm. If necessary, it can be replaced with ZP1400, ZP1320 or ZP1310.

The device is based on a Geiger-Muller counter of the SBM-20 type. This is a metal cylinder with two electrodes at the ends. Gas inside. These electrodes are supplied with a constant voltage of about 400V. When an ionizing particle passes through the counter, an electrical breakdown occurs and the resistance of the device sharply decreases from infinite to very noticeable. Thus, with each ionizing particle passing through the counter, it creates a short pulse.

This household dosimeter using a microcontroller is capable of recording excess radiation levels in the range from 0 mR to 144 mR. The design consists of a step-up voltage converter and a microcontroller that counts the generated pulses and transmits information to a digital indicator.

After the disaster in Japan, the demand for individual means of monitoring radioactivity increased sharply, and not only ready-made devices, but also domestic Geiger-Muller counters became in short supply. Therefore, we had to pay attention to “foreign experience”, or rather, to the foreign element base. Here is a product from the well-known company Philips - the ZP1300 counter. Unlike domestic analogues, it requires a supply voltage of 700V. Otherwise everything is the same. The figure shows a diagram of a sound radioactivity indicator based on the ZP1300 counter.

Each time an ionizing particle passes through the counter, the device emits a short tone. The higher the radiation, the more often it sounds. The 700V voltage generator circuit is made on the basis of a miniature power transformer type HRE3005000 with two windings - a secondary winding at 6V and a mains winding at 230V. The transformer is very small in size and has a power of less than 1W. This transformer here is used to obtain high voltage. It is turned on in reverse, that is, in this circuit the low-voltage winding acts as the primary. It is included in the collector circuit of the transistor VT1, the base of which receives pulses from the generator on the A1 chip, an integrated timer of type 555. To obtain the necessary 700V turns of the secondary winding of the transformer are not enough, so there is also an additional voltage multiplier on diodes VD2-VD6.

To ensure stabilization of the output voltage, the circuit has feedback, which is carried out through resistors R3 and R4. Through them, voltage is supplied to pin 2 of A1, the value of which is proportional to the value of the output voltage. Accordingly, the duty cycle of the pulses generated by microcircuit A1 changes and the voltage at the output of the multiplier changes. Thus, the voltage at the output of the multiplier is maintained stably and depends little on the supply voltage. Set the output voltage by adjusting resistor R1. It should be noted that a conventional multimeter is not suitable for accurately measuring the output voltage due to its low input resistance. You need to use a high-resistance voltmeter or measure with a multimeter through a voltage divider, for example, made up of resistors with a resistance of 10 megaohms and 100 kiloohms.

In this case, the multimeter reading will need to be multiplied by 100 (that is, “7V” = 700V). Diode VD1 protects transistor VT1 from emissions of self-induction of the transformer winding. A voltage of 700V from the output of the multiplier through resistor R9 is supplied to the Geiger-Muller counter F1. The load of the counter is resistor R7, on which a very short pulse appears when an ionizing particle passes. This pulse is sent to the waiting multivibrator on chip A2. Diode VD7 protects the input of the microcircuit from high voltage, limiting the amplitude of the pulse to the value of the circuit supply voltage.

When a pulse arrives at pin 2 of A2, the waiting multivibrator starts and produces a train of pulses that goes to speaker B1. A short high-pitched sound is heard. This circuit can also be used as part of a digital dosimeter. Pulses to its counter will need to be supplied from pin 3 of A2. Details. The main part - the Geiger-Muller counter - can be replaced with another one, for example, a domestic one. But this will require a corresponding change in the supply voltage of the meter (usually 400V for ours). That is, it will be necessary to reduce the number of voltage multiplier stages. Transformer T1 can be replaced with almost any low-power power transformer with secondary winding 6V. Or wind it yourself. Speaker B1 is a capsule from small-sized headphones. Its resistance should be in the range of 16-50 Ogl. The adjustment consists only of setting the high voltage by adjusting the tuning resistor R1.