In this age of technological disasters, it is necessary to protect yourself from their consequences in the form of radioactive contamination. And for this, ionizing radiation must be detected. Therefore, in the absence of industrial devices, any amateur radio operator can try to make a Geiger counter with their own hands.
What is a geiger counter?
To measure the radioactive background, scientists and engineers have developed instruments - Geiger counters. As a sensor of alpha, beta and gamma radiation, a sealed gas discharge tube is used, filled with a mixture of inert gases, named after the inventors by the Geiger-Muller counter. But professional devices are not widely accessible to the modern layman and are quite expensive.
Several varieties of such designs have been developed. Do-it-yourself Geiger counter from a neon lamp can make even the most unprepared stalker for survival in the post-apocalyptic world.
Varieties of designs of homemade Geiger counters
The Geiger counter with own hands has been developed and manufactured by many amateur designers. There are many design options. The most common home-made designs are known:
- A radiometer using a starter from a fluorescent lamp or a neon lamp as a sensor for beta and gamma radiation.
- A simple home-made radiation indicator based on the STS-5 sensor.
- The simplest dosimeter with an SBM-20 sensor.
- Small-sized radiation indicator based on the SBT-9 sensor.
- An ionizing radiation indicator based on a sensor from a semiconductor device - a diode.
- The simplest indicator of radiation with a homemade spark gap made from a PET bottle and a can.
Advantages and disadvantages of designs
The designs of home-made dosimeters and radiation indicators using the SBM-20, STS-5, SBT-9 sensors are quite simple, have high sensitivity. But they have a very important drawback - these are industrial sensors of ionizing radiation, which are difficult to access and expensive to buy.
A radiation indicator with a sensor from a semiconductor device is cheap, but, due to the nonlinearity of the characteristics of semiconductors, it is difficult to configure, sensitive to temperature changes and voltage supply.
A device with a homemade sensor from a PET bottle is extremely simple, but requires a circuit with a field effect transistor, which is not always available for a homemade man. In addition, field effect transistors are prone to breakdown under conditions of strong radiation.
The most affordable are the designs with sensors based on the starter from faulty fluorescent or neon lamps. The disadvantages of the sensor from the starter, as well as the neon lamp, include sensitivity to changes in temperature and supply voltage, the need to shield the sensor from light and electromagnetic radiation. The advantages include the ease of manufacturing and setting up a do-it-yourself Geiger counter.
Diagram of a radiation indicator with a neon lamp as a sensor
Making a Geiger counter with your own hands should begin by studying the circuit diagram of the device. In this circuit, a neon bulb is used as a gamma and beta radiation sensor.
Consider a circuit diagram.
To rectify the alternating current, a diode D1 is applied. To ensure a constant voltage of 100 V, a stabilization circuit based on a Zener diode D2 was used. The parameters of the resistor R1 are dependent on the supply voltage Vac and are calculated by the formula
R1 = (Vac-100V) / (5 mA).
Variable resistance R2 sets the voltage on the neon bulb slightly below the ignition voltage. The neon lamp in standby mode should not be lit. When radioactive particles pass through a glass flask, inert gas ionizes and the lamp bursts.
At the time of the lamp flash, a voltage drop will occur on the resistance R3, and a voltage will appear on the neon lamp, less than the hold voltage. There will be no current passing through the lamp until it is ignited by an ionizing particle. When the current flows briefly through the lamp, a loud click will sound in the speaker. After assembling the Geiger counter with your own hands from a neon lamp, you can begin to configure it.
Geiger counter setup and calibration
The developed model of a post-apocalyptic Geiger counter is easy to configure with your own hands. With a variable resistance R2, the device is put into standby mode, on the verge of a sensor from a neon lamp. Further, for the experiment, a dusty cloth is approaching the radioactivity indicator and the sensitivity of the device is adjusted by the control resistor R2. Since the dust is full of radioactive isotopes, the neon bulb of the radioactivity indicator, if correctly configured, should flash periodically, the loudspeaker head should emit chirping sounds and clicks.
For a more accurate calibration of the instrument, an accessible radiation source must be used. It can be a toggle switch from military radio equipment with a luminous radioactive phosphor deposited on it. Calibration is carried out using an exemplary standard dosimeter. The response frequency of a homemade Geiger counter is adjusted to the frequency of counting the radiation level of an industrial dosimeter. For calibration, a standard radiation source can also be used, which, as a rule, is equipped with a military dosimeter.
Materials and tools for assembling a Geiger counter
When assembling a Geiger counter with your own hands, any materials available to a radio amateur can be used. The main thing is that the denominations of the radio components correspond to the given diagram. It is necessary to choose the right neon lamp as a sensor, so that the ignition voltage approximately corresponds to 100 V. In this case, the radio components can be both imported and domestic. The parameters of the parts must be selected using the reference literature.
It is important to note that in the given circuit diagram, AC voltage from the mains Vac = 220 V was used according to the transformerless circuit, and this is dangerous due to electric shock. To prevent electrical injury, make the case of the device of electrical insulating material. For this purpose, plexiglass, getinax, fiberglass, polystyrene, and other laminated plastics are suitable.
When assembling a Geiger counter with your own hands, the most diverse tool is used:
- A 60 W electric soldering iron is required for soldering radio components.
- A hacksaw for metal is widely used for sawing foil fiberglass in the manufacture of printed circuit boards. It is used for cutting and cutting plastic parts of the case.
- An electric drill is used to drill holes in a printed circuit board, to assemble the housing at the corners.
- Tweezers are essential for working with small parts when soldering and mounting an electrical circuit.
- Side cutters are recommended for trimming the protruding terminals of the radio components.
- For commissioning of the device, an elementary tester is absolutely necessary, with the help of which it will be necessary to conduct voltage measurements at test points, as well as other electrical parameters.
- For autonomous power supply of a truly post-apocalyptic Geiger counter, it is desirable to connect a rechargeable battery with a voltage of 4.5-9 V, for which use any simple circuit of a voltage converter up to 220 V AC.
When working with electricity and radioactive materials , the safety requirements must be followed.