Homemade geiger sensor instead of sbm 20. Simple radiation indicator

In this article you will find a description of simple dosimeter circuits on the SBM-20 counter, which have sufficient sensitivity and record 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 by ZP1400, ZP1320 or ZP1310.

A simple scheme of the dosimeter on the SBM-20

The structure is connected to only one AA battery AA type. As you know, the operating voltage of the SBM-20 sensor is 400 volts, so it becomes necessary to use a voltage converter.

The boost converter is based on a simple blocking oscillator. High-voltage pulses from the secondary winding of the transformer are rectified by a high-frequency diode.

If the SBM-20 counter is located outside the radiation zone, both transistors VT2 and VT3 are closed. Sound and light alarms are not active. As soon as radioactive particles enter the counter, the gas inside the sensor is ionized, and a pulse appears at its output, which passes to transistor amplifier and a click is heard in the phone speaker and the LED lights up.

With a weak natural radiation intensity, LED flashes and clicks are repeated every 1 ... 2 seconds. This only speaks of normal background radiation. As the level of radioactivity increases, the clicks will become more frequent and, at critical values, merge into one continuous crackle, and the LED will be constantly on.

Since the amateur radio design has a microammeter, the tuning resistance is used to adjust the sensitivity of the readings.

The converter transformer is assembled using an armored core having a diameter of 25 mm. Windings 1-2 and 3-4 are made of copper wire with a diameter of 0.25 mm and contain 45 and 15 turns, respectively. The secondary winding is also made of copper wire, but with a diameter of 0.1 mm - 550 turns.

Simple design radioactivity counter on SBM-20 option 2

Main specifications dosimeter:

The dosimeter sensor is a Geiger counter SBM20. The blocking generator generates a high voltage at its anode - from the step-up winding of the transformer, the pulses follow through the diodes VD1, VD2 and charge the capacitance of the filter C1. The resistance R1 is the counter load.

The single vibrator is made on the elements DD1.1, DD1.2, SZ and R4, they convert the pulses coming from the Geiger counter and having a prolonged decline into rectangular ones. On the elements DD1.3, DD1.4, C4 and R5, a generator is made audio frequency. Threshold amplifier, assembled on a DD2 chip.

The voltage across capacitance C9 depends on the pulse repetition rate from the Geiger counter; when it reaches the opening level of the transistor included in DD2, the HL1 LED lights up, the blinking frequency of which will increase with the increase in radiation quanta falling on the sensor.

The T1 transformer is made by hand on a ring core M3000NM K16x10x4.5 mm. The primary winding contains 420 turns of PEV-2-0.07 wire. The secondary winding consists of 8 turns of wire with a diameter of 0.15 ... 0.2 mm; third winding 3 turns with the same wire.

Measurement of the level of radioactive background is carried out using a special device - a dosimeter. It can be purchased at a specialized store, but home craftsmen will be attracted by another option - to make a dosimeter with your own hands. A household modification can be assembled in several variations, for example, from improvised means or with the installation of an SBM-20 counter.

Naturally, it will be quite difficult to assemble a professional or multifunctional dosimeter. Household portable or individual devices register beta or gamma radiation. The radiometer is designed to study specific objects and read the level of radionuclides. In fact, a dosimeter and a radiometer are two different devices, but household versions often combine both the first and the second. Thin terminology plays a role only for specialists, therefore even combined models are called in general terms - a dosimeter.

By choosing one of the proposed schemes for assembly, the user will receive the simplest device with low sensitivity. There is still a benefit in such a device: it is able to register critical doses of radiation, this will indicate a real threat to human health. Although homemade device many times inferior to any household dosimeter from the store, to protect your own life it is quite usable.

Before choosing one of the assembly schemes for yourself, read general recommendations for the manufacture of the device.

1. For a device of their own assembly, choose 400 volt meters if the converter is designed for 500 volts, then you need to adjust the circuit setting feedback. It is permissible to choose a different configuration of zener diodes and neon lamps, depending on which dosimeter circuit is used in the manufacture.
2. The output voltage of the stabilizer is measured with a voltmeter with an input resistance of 10 MΩ. It is important to check that it is actually 400 volts, charged capacitors are potentially dangerous to humans, despite the low power.
3. Near the counter, several small holes are made in the case for the penetration of beta radiation. Access to circuits with high voltage must be excluded, this must be taken into account when installing the device in the housing.
4. The circuit of the measuring unit is selected based on the input voltage of the converter. The connection of the node is carried out strictly with the power off and the storage capacitor discharged.
5. At natural radiation background a homemade dosimeter will give out about 30 - 35 signals in 60 seconds. Exceeding the indicator indicates high ion radiation.

Scheme No. 1 - elementary

To design a detector for registering beta and gamma radiation "quickly and simply", this option is the best fit. What you need before construction:

• a plastic bottle, or rather, a neck with a lid;
• tin can without lid with finished edges;
• ordinary tester;
• a piece of steel and copper wire;
• transistor kp302a or any kp303.

To assemble, you need to cut off the neck of the bottle so that it fits snugly into the tin can. A narrow, tall jar, like from condensed milk, is best suited. Two holes are made in the plastic cover, where you need to insert a steel wire. One of its edges is bent with a loop in the form of the letter “C” so that it holds securely on the lid, the second end of the steel bar should not touch the can. The lid is then screwed on.

KP302a shutter leg is screwed to the loop steel wire, and the terminals of the tester are connected to the drain and source. Around the jar you need to wrap the copper wire and fix it to the black terminal at one end. Capricious and short-lived field-effect transistor you can replace, for example, connect several others according to the Darlington circuit, the main thing is that the total gain should be equal to 9000.

A homemade dosimeter is ready, but you need it calibrate. To do this, use a laboratory source of radiation, as a rule, the unit of its ionic radiation is indicated on it.

Scheme No. 2 - installing a meter

In order to assemble a dosimeter with your own hands, an ordinary counter SBM-20- you will have to buy it in a specialized store for radio components. An anode, a thin wire, passes along the axis through a sealed cathode tube. The internal space at low pressure is filled with gas, which creates an optimal environment for electrical breakdown.

The voltage of the SBM-20 is about 300 - 500 V, it must be adjusted in such a way as to exclude arbitrary breakdown. When a radioactive particle hits, it ionizes the gas in the tube, creating a large number of ions and electrons between the cathode and anode. Similarly, the counter is triggered for each particle.

It is important to know! For a home-made device, any meter designed for 400 volts is suitable, but the SBM-20 is the most suitable, you can purchase the popular STS-5, but it is less durable.

Dosimeter scheme consists of two blocks: an indicator and a mains rectifier, which are assembled in plastic boxes and connected with a connector. The power supply is connected to the network for a short period of time. The capacitor is charged up to a voltage of 600 W and is the power source of the device.

The unit is disconnected from the network and from the indicator, and the connectors are connected to the contacts high impedance phones. Capacitor should be selected good quality, this will extend the operating time of the dosimeter. A homemade device can function for 20 minutes or more.

Technical features:

• the rectifier resistor is optimally selected with a dissipating power of up to 2 watts;
• capacitors can be ceramic or paper, with the appropriate voltage;
• you can choose any counter;
• eliminate the possibility of touching the resistor contacts with your hands

Natural background radiation will register as rare signals in phones, the absence of sounds means that there is no power.

Scheme No. 3 with a two-wire detector

You can design a home-made dosimeter with a two-wire detector, for this you need a plastic container, a pass capacitor, three resistors and a single-channel damper.

The damper itself reduces the oscillation amplitude and is installed behind the detector, directly next to the feed-through capacitor, which measures the dose. For this design, only resonant rectifiers, but the expanders are practically not used. The instrument will be more sensitive to radiation but will take longer to assemble.

There are other schemes on how to make a dosimeter yourself. Many variations have been developed and tested by radio amateurs, but most of them are based on the circuits described above.

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In connection with the environmental consequences of human activities related to nuclear energy, as well as industry (including the military), using radioactive substances as a component or basis of their products, studying the basics of radiation safety and radiation dosimetry is becoming enough today hot topic. In addition to natural sources of ionizing radiation, every year more and more places appear contaminated with radiation as a result of human activity. Thus, in order to preserve your health and the health of your loved ones, you need to know the degree of contamination of a particular area or objects and food. A dosimeter can help with this - a device for measuring the effective dose or power of ionizing radiation over a certain period of time.

Before you start making (or buying) this device it is necessary to have an idea about the nature of the measured parameter. Ionizing radiation (radiation) is a stream of photons, elementary particles or fission fragments of atoms, capable of ionizing a substance. It is divided into several types. alpha radiation is a stream of alpha particles - helium-4 nuclei, alpha particles born during radioactive decay can be easily stopped by a sheet of paper, so it poses a danger mainly when it enters the body. beta radiation- this is the flow of electrons that arise during beta decay, to protect against beta particles with energies up to 1 MeV, an aluminum plate a few millimeters thick is enough. Gamma radiation has a much greater penetrating power, since it consists of high-energy photons that do not have a charge; heavy elements (lead, etc.) with a layer of several centimeters are effective for protection. The penetrating power of all types of ionizing radiation depends on the energy.

To register ionizing radiation, Geiger-Muller counters are mainly used. This simple and effective device is usually a metal or glass cylinder metallized from the inside and a thin metal thread stretched along the axis of this cylinder, the cylinder itself is filled with rarefied gas. The principle of operation is based on impact ionization. When ionizing radiation hits the walls of the counter, electrons are knocked out of it, electrons, moving in gas and colliding with gas atoms, knock electrons out of atoms and create positive ions and free electrons. The electric field between the cathode and the anode accelerates the electrons to energies at which impact ionization begins. An avalanche of ions arises, leading to the multiplication of primary carriers. At a sufficiently high field strength, the energy of these ions becomes sufficient to generate secondary avalanches capable of maintaining an independent discharge, as a result of which the current through the counter increases sharply.

Not all Geiger counters can register all types of ionizing radiation. Basically, they are sensitive to one radiation - alpha, beta or gamma radiation, but often they can also detect other radiation to some extent. So, for example, the SI-8B Geiger counter is designed to detect soft beta radiation (yes, depending on the energy of the particles, the radiation can be divided into soft and hard), but this sensor is also somewhat sensitive to alpha radiation and gamma radiation. radiation.

However, approaching nevertheless the design of the article, our task is to make the most simple, naturally portable, Geiger counter, or rather a dosimeter. For the manufacture of this device, I managed to get only SBM-20. This Geiger counter is designed to register hard beta and gamma radiation. Like most other meters, SBM-20 operates at a voltage of 400 volts.

The main characteristics of the Geiger-Muller counter SBM-20 (table from the reference book):

This counter has a relatively low accuracy of measuring ionizing radiation, but sufficient to determine the excess of the permissible dose of radiation for humans. SBM-20 is currently used in many household dosimeters. To improve performance, several tubes are often used at once. And to increase the accuracy of measuring gamma radiation, dosimeters are equipped with beta radiation filters; in this case, the dosimeter registers only gamma radiation, but rather accurately.

When measuring radiation dose, there are several factors to consider that may be important. Even in the complete absence of sources of ionizing radiation, the Geiger counter will give a certain number of pulses. This is the so-called custom counter background. This also includes several factors: radioactive contamination of the materials of the counter itself, spontaneous emission of electrons from the cathode of the counter, and cosmic radiation. All this gives a certain amount of "extra" pulses per unit time.

So, the scheme of a simple dosimeter based on the Geiger counter SBM-20:

I assemble the circuit on a breadboard:

The circuit does not contain scarce parts (except, of course, the meter itself) and does not contain programmable elements (microcontrollers), which will allow you to assemble the circuit in a short time without much difficulty. However, such a dosimeter does not contain a scale, and it is necessary to determine the radiation dose by ear by the number of clicks. This is the classic version. The circuit consists of a voltage converter 9 volts - 400 volts.

A multivibrator is made on the NE555 chip, the frequency of which is approximately 14 kHz. To increase the frequency of operation, you can reduce the value of the resistor R1 to about 2.7 kOhm. This will be useful if the choke you have chosen (or maybe made) will make a squeak - with an increase in the frequency of operation, the squeak will disappear. Inductor L1 is required with a rating of 1000 - 4000 μH. The fastest way to find a suitable choke is in a burned-out energy-saving light bulb. Such a choke is used in the circuit, in the photo above it is wound on a core, which is usually used to make pulse transformers. Transistor T1 can use any other field n-channel with a drain-source voltage of at least 400 volts, and preferably more. Such a converter will give only a few milliamps of current at a voltage of 400 volts, but this is enough for a Geiger counter to work several times. After turning off the power from the circuit on the charged capacitor C3, the circuit will work for about another 20-30 seconds, given its small capacitance. The suppressor VD2 limits the voltage at 400 volts. Capacitor C3 must be used for a voltage of at least 400 - 450 volts.

Any piezo speaker or speaker can be used as Ls1. In the absence of ionizing radiation, no current flows through resistors R2 - R4 (there are five resistors in the photo on the breadboard, but their total resistance corresponds to the circuit). As soon as the corresponding particle enters the Geiger counter, the gas ionization occurs inside the sensor and its resistance decreases sharply, as a result of which a current pulse occurs. Capacitor C4 cuts off the constant part and passes only a current pulse to the speaker. We hear a click.

In my case, two batteries from old phones are used as a power source (two, since necessary nutrition must be more than 5.5 volts to start the circuit due to the applied element base).

So, the circuit works, occasionally clicks. Now how to use it. The simplest option - it clicks a little - everything is fine, clicks often or even continuously - bad. Another option is to roughly count the number of pulses per minute and convert the number of clicks to microR / h. To do this, you need to take the sensitivity value of the Geiger counter from the reference book. However, different sources always have slightly different numbers. Ideally, laboratory measurements should be made for the selected Geiger counter with reference radiation sources. So for SBM-20, the sensitivity value varies from 60 to 78 pulses / μR according to various sources and reference books. So, we calculated the number of impulses in one minute, then we multiply this number by 60 to approximate the number of impulses in one hour and divide all this by the sensitivity of the sensor, that is, by 60 or 78 or whatever you get closer to reality and as a result we get the value in µR/h. For a more reliable value, it is necessary to take several measurements and calculate the arithmetic mean between them. The upper limit of the safe level of radiation is approximately 20 - 25 microR/h. The permissible level is up to about 50 μR / h. IN different countries figures may vary.

P.S. I was prompted to consider this topic by an article on the concentration of radon gas penetrating into rooms, water, etc. in various regions of the country and its sources.

List of radio elements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
IC1	Programmable timer and oscillator	NE555	1			To notepad
T1	MOSFET transistor	IRF710	1			To notepad
VD1	rectifier diode	1N4007	1			To notepad
VD2	Protective diode	1V5KE400CA	1			To notepad
C1, C2	Capacitor	10 nF	2			To notepad
C3	electrolytic capacitor	2.7uF	1			To notepad
C4	Capacitor	100 nF	1	400V

IN this review a description is given of a simple and sufficiently sensitive dosimeter that detects even insignificant beta and gamma radiation. The domestic type SBM-20 acts as a radiation sensor.

Outwardly, it looks like a metal cylinder with a diameter of 12 mm and a length of about 113 mm. Its operating voltage is 400 volts. The foreign sensor ZP1400, ZP1320 or ZP1310 can serve as an analogue to it.

Description of the operation of the dosimeter on the Geiger counter SBM-20

The dosimeter circuit is powered by just one 1.5 volt battery, since the current consumption does not exceed 10 mA. But since the operating voltage of the SBM-20 radiation sensor is 400 volts, a voltage converter is used in the circuit to increase the voltage from 1.5 volts to 400 volts. In this regard, extreme care should be taken when setting up and using the dosimeter!

The dosimeter boost converter is nothing more than a simple blocking generator. Appearing high voltage pulses on the secondary winding (terminals 5 - 6) of the transformer Tr1 are rectified by the diode VD2. This diode must be high-frequency, since the pulses are quite short and have a high repetition rate.

If the Geiger counter SBM-20 is outside the zone of radiation, there is no sound and light indication, since both transistors VT2 and VT3 are locked.

When beta or gamma particles hit the SBM-20 sensor, the gas inside the sensor is ionized, as a result of which a pulse is generated at the output, which goes to the transistor amplifier and a click is heard in the BF1 telephone capsule and the HL1 LED flashes.

Outside the zone of intense radiation, LED flashes and clicks from the telephone capsule follow every 1 ... 2 seconds. This indicates a normal, natural radiation background.

When the dosimeter approaches any object that has strong radiation (the scale of an aircraft instrument from the time of the war or to the luminous dial of an old clock), the clicks will become more frequent and may even merge into one continuous crackle, the HL1 LED will be constantly on.

The dosimeter is also equipped with a pointer indicator - a microammeter. A tuning resistor is used to adjust the sensitivity of the reading.

Dosimeter details

The converter transformer Tr1 is made on an armored core having a diameter of approximately 25 mm. Windings 1-2 and 3-4 are wound with copper enameled wire with a diameter of 0.25 mm and contain 45 and 15 turns, respectively. The secondary winding 5-6 is wound with copper wire with a diameter of 0.1 mm, contains 550 turns.

It is possible to put the LED AL341, AL307. In the role of VD2, it is possible to use two KD104A diodes by connecting them in series. Diode KD226 can be changed to KD105V. Transistor VT1 can be changed to KT630 ​​with any letter, to KT342A. A telephone capsule must be selected with an acoustic coil resistance of more than 50 ohms. Microammeter with total deflection current 50 μA.