Build a Pocket Ionizing Radiation Detector (PIRD)




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Here is a video testing it using a small amount of radioactive Americium found in a smoke detector:

Step 1: How It Works

This geiger counter works on similar principles that any other ordinary geiger counter works on. Essentially there is a small gap between two wires - a high dc voltage is applied to both wires, and when an ionizing particle moves between the wires, an ion channel is created and electrons arc across the wires, creating an audible "click" on a radio. Normally, the gap is inside of what is called a "geiger muller tube," where gases ideal for ionization are held for increased sensitivity. With this geiger counter, the absence of gases ideal to ionization is made up for by placing the wires in closer proximity to one another (so close that to the human eye they appear to be touching). The process of slowly moving the wires closer to one another is called "spark gap quenching".

Step 2: Finding a Radio

Any radio will do, just as long as when you create a "spark" (touching a wire to a battery) you hear a "click" on the radio. I tested my radio on the oscilloscope in this video: 
As you can see, there are little valleys when I create sparks. This means that the radio is detecting the disturbances properly. The radios I used were a $1 mini radio and a larger more sensitive radio I salvaged from my grandfather.

Step 3: Making a High Voltage DC Power Supply

A high voltage DC power supply can be created from a disposable camera. First, take out the big black capacitor. Take out the smaller capacitor near it and place it where the bigger capacitor used to be. This will be used as a "filter capacitor." Take off all the unnecessary odds and ends (the xenon flash tube, the battery contacts, etc.) refer to the before and after photographs. I added a potentiometer to adjust the output voltage, but this is not necessary (that's the blue thing, don't worry about it). Make sure that if your camera had a "charge" button, solder the two contacts for the button together so that the unit is always in "charge" mode.

Be careful! The output from this unit will be around 400-600v! Test it out by touching two AA batteries to the + and - spots that were taken out, and the red LED should be on (or whatever other light is there).

Step 4: Spark Gap Quenching

This part is a bit tricky. You now need to put the hv output wires from the camera unit so that they are almost touching, but not arcing continuously. This may take a while to do.

Once you do this correctly, there should be arcs every so often, but not continuously (maybe once every couple of minutes). This means that the unit is detecting ionizing radiation! To hear the "clicks," turn on the radio. 

I have attached a picture in which I have produced a spark gap between an alligator clip and a screwdriver, but any type of gap would work (between a wire and a plate, between two plates, between two wires, etc.). 

Here are some videos of proper operation (notice and listen carefully for the audible "clicks"):

Step 5: Boxing It Up

Now, all that needs to be done is to box it up and make it all look pretty. With a bit of patience and lots of tape, spark gap quenching is possible in the little box too!

I added a switch and added an LED popping out from the box to replace the LED in the camera HV DC board. After gutting the mini radio, everything fits in a little altoids tin (perfect for pocketing).

The wires may need to periodically be re-calibrated, and the unit needs to be held still for it to work (vibration can cause an arc). Don't blow on the spark gap!

I hope you enjoyed this instructable! Rate, comment, and vote!

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    55 Discussions


    3 months ago

    Hmm, If you need a Radioactive source or Sources that Civilians can get try E-bay for Thorium welding rods 2-4 percent, Uranium Ore (Sort of Recommended!!), Uranium glass beads, etc. Maybe you could attach a Portable Oscilloscope to the output carefully to make a visual display. eBay sells 200 kHz ones for 30 dollars and 2 MHZ for 60 dollars from China. Try calibrating the Oscilloscope for good results!


    7 years ago on Introduction

    Hi, I like your project. However I am not convinced you're detecting gamma radiation. If you like to verify the function of your detector, it's a pretty straight forward test. Bring a radioactive source close to your detector. If it is detecting radioactivity you ought to see and hear an uptick in the number of radioactive particles detected when the source is close by.

    9 replies

    I don't have any radioactive samples, I'll try to get my hands on some Americium. But judging by the fact that I only hear the clicks once or twice every couple on minutes, it's a safe bet. Also, a similar idea was published on the CERN website as an educational experiment for use in detecting gamma radiation


    Reply 1 year ago

    I have used a simple Coleman Gas Lamp Mantle in the past. It is easily detected with a real detector. Cheap. Give it a try b4 spending $ on sources.


    Reply 2 years ago

    Get yourself a chunk of granite, it is mildly radioactive and shows a noticeable increase on a Geiger counter compared to background radiation. I'm a school science technician and this is what I issue for students to handle, as the sealed radioactive sources can only be used for teacher demonstrations.

    Unfortunately I'm about 4 years late with this comment... but felt the need to add this for reference!!


    Reply 3 years ago

    You can buy uranium on Amazon.


    Reply 4 years ago on Introduction

    My friends in the medical business tell me that nobody is allowed near rad sources, except the patient and the technician. It's a security issue. And rooms where those treatments occur will not be "leaking" outside the clearly marked areas. It would be a bad thing to detect radiation outside those limits.

    But, if you do know how to get some low-risk samples to test this I would really like to hear about it. :) Good luck!


    Spark detectors can detect alpha particles but not beta, gamma or x-rays. If you look at this youtube video you can see a video of a alpha particle spark detector I built a while ago.


    1 year ago

    I find this quite cool. However If you want to play with radation please get a good beta, alpha and gamma meter like this. They allow accurate detection of Counts Per Minute and uS an Hr.


    6 years ago on Step 3

    How should a potentiometer be soldered into the circuit in order to adjust the voltage output? With one AA battery, I'm getting 360V, and with two AA batteries, I'm getting 650V. I'd like to be right around 400.

    1 reply

    Reply 5 years ago on Introduction

    Add in a variable resistor in the positive side of the output circuit, and then connect a GM tube to the rest of the output circuit and adjust the resistor.