How to Build a Geiger Counter

Alpha and Beta radiations are surprisingly abundant in nature. The third variety of radiation, Gamma, is more commonly associated with artificially produced radioactivity. The one device suitable for detecting radiation, in all its forms, is the Geiger counter. Once an expensive instrument, a Geiger counter can actually be built by a dedicated hobbyist. Assembling your own Geiger counter can be a fascinating exercise in discovery. Everything from antique watches to bricks let off small amounts of radiation that can be detected with the fully-capable Geiger counter outlined below.

Things You'll Need

• Geiger-Muller Tube
• Fiberglass PC board
• Permanent marker
• Tub
• Hydrogen peroxide
• Hydrochloric acid
• Gloves
• Soldering iron
• Hex inverting buffer
• Step-up transformer
• Diodes (2)
• Capacitors (2)
• Zener diodes (3)
• Resistor
• NPN resistor clamp
• 555 timer
• LED
• 3 pin speaker
• 9-volt battery
• Plastic enclosure
• Glue
• Styrofoam cubes
• Power drill

Instructions

1. Purchase a Geiger-Muller tube. This is the Geiger counter's most important component and the only one that cannot be built from scratch. This sealed cylinder is filled with neon, argon and halogen. A mica window caps one end of the tube, allowing for the entrance of radioactive particles. Current is applied to the gas mixture. The electrical state of the gas mixture is subtly altered whenever outside particles excite the cloud of atoms inside the tube. The reactions are then recorded as electrical pulses. Geiger-Muller tubes are sold by a variety of scientific suppliers (see Resources section).

2. Etch the circuit board. Building your own custom Geiger counter requires a proprietary circuit that helps route the proper amount of power to the anode of the Geiger-Muller tube, so you need to follow a proper schematic to etch a circuit board (see Resources section). Begin by drawing your circuit onto the board using permanent marker. Then mix a 2 to 1 combination of hydrogen peroxide and hydrochloric acid in a shallow tub. While wearing gloves, place your board in the acid solution and let sit for 2 to 3 minutes. The solution should turn a cloudy green. Remove your circuit board and rinse under cold water. The copper should have dissolved away except along your marker lines. Wash off the permanent marker and you should see the copper forming the necessary schematic lines.

3. Install the hex inverting buffer and the step-up generator. Drill mounting holes wide enough to allow the wiring to be fed through the circuit board, then solder the components to the schematic's copper through-line. These first two components will absorb energy from the 9-volt battery, then release it in pulses to the remaining circuitry.

4. Assemble and install the voltage doubler. The next component to be installed will ramp up the voltage to provide the necessary energy to charge the gas cloud within the Geiger-Muller tube. A voltage doubler consists of two diodes and two capacitors that should be soldered on to the left-hand side of the circuit board, immediately down the line from your step-up generator.

5. Install a series of zener diodes in order to regulate the voltage. Without this, the pulses of energy sucked from the 9-volt battery would be erratic and unsuitable for accurately charging the sensitive Geiger-Muller tube. A series of three zener diodes, soldered onto the circuit board immediately above one another, would produce a consistent flow of 500 volts. The first two zener diodes should have a 200-volt capacity and the third a 100-volt capacity.

6. Feed a regulated 500-volt output to the anode of the Geiger-Muller tube through a 10 ohm resistor. The resistor should be soldered directly on to the anode of the Geiger-Muller tube, then attached to the circuit board, which now feeds an even 500 volts through the resistor and into the Geiger-Muller tube thanks to the regulating zener diodes.

7. Solder the output of your Geiger-Muller tube to the NPN transistor clamp. This transistor clamp will detect the subtle alterations in voltage produced by the presence of radioactive particles, then relay the difference further down the circuit board.

8. Plug in a 555 timer to the circuit board immediately on the other end of the NPN transistor clamp.The pulses received from radiation detection are relayed through the circuit board to the timer. Your circuit board likely looks pretty busy by this point, so be careful when drilling new mounting holes for components. Breaking the copper circuitry can destroy the entire circuit.

9. Install your output notifiers. Once the signal leaves the 555 timer, your only remaining necessity is the mechanism by which your device will inform you of radiation's presence. The simplest method would be to continue the circuit from the 555 timer to activate an LED or produce a clicking sound transmitted to a speaker installed on to the circuit board.

10. Attach the 9-volt battery. The installed circuitry will amplify, then regulate the output of the battery, ensuring an even flow of electricity into the Geiger-Muller tube. Ambient environmental radiation should be provide a few clicks per minute, regardless of your location.

11. Mount your circuit board inside a plastic case with pre-drilled holes. Drill holes for the speaker outlet, LED and power switch. Mounting the actual circuit board is as simple as gluing down the corners. However, you may want to install squares of Styrofoam or some other non-conductive insulation to protect your circuit board from damage. Finally, drill a hole at the Geiger counter's top to allow visual access to the front window of the Geiger-Muller tube.

Tips & Warnings

• The Geiger-Muller tube is likely to be the most expensive component in your Geiger counter.

• The circuit board has a high voltage output, so do not attach battery until all components are in place. Radiation, gamma in particular, should never be sought out, no matter how awesome your new Geiger counter may be. Etch your circuit board in a well-ventilated area and remember to wear both gloves and safety goggles.

Resources

• Read this Article in Spanish
• Circuit Board Schematic
• Alternate Schematic
• Purchase a Geiger-Muller Tube
• How to Etch a Circuit Board