John Iovine: Geiger Counter Sanity Check

John Iovine: Geiger Counter Sanity Check

Clip from Images SI website

Through his company Images Scientific Instruments, John Iovine has been designing, making, and selling Geiger counters for nearly 15 years. MAKE’s Paul Spinrad talked with him about the recent run on Geiger counters, how (in)accurate and misleadingly described many of them are, and two new counters he’s designing for MAKE Volume 29: a standalone data-logging model and a steampunk-style counter.

1. Your company sold out of Geiger counters soon after the earthquake, tsunami, and reactor shutdowns in Japan. What was the chain of events between your learning the news about this disaster and selling out?
(Laughs) To be honest, I pay little attention to the news, so I didn’t know about the disaster all weekend. But I came in on Monday and saw 20 or 30 orders for Geiger counters, and I was saying, geez, that’s quite unusual.  Sometimes someone like Texas A&M will buy like 24 counters for their labs, but these orders were all from individuals. So I knew something was up, but I didn’t know what.

Other people contacting me through the site ( said that there had been a big tsunami in Japan, and even then I’m not getting answers. What does a tsunami have to do with radiation? But then I read about it and a lot of people were calling me up and asking questions. The New York Times did a little thing on me, and then NBC, Fox News, and then AP called up, and so on.

2. What did they ask?

They were asking how fast we sold out, which was immediately. They asked why people were buying the Geiger counters, and I said that basically a lot of people didn’t trust the government. And naturally, they assumed I was talking about people in Japan, but at first, it was people in California and Washington State calling me up and saying “I don’t trust anything these guys are telling me. I want to check in myself.” But soon I also started getting people from Japan saying they don’t trust the official radiation level reports and want to check things out for themselves.

Previously we were selling Geiger counters to schools and hobbyists, but this event really woke people up. Now everyone is interested in checking their food, checking the air quality, checking soil samples.

3. Is the Geiger-Müller tube the most difficult part for you to source?
Well, the tube is the heart of a Geiger counter, but any part can become the critical part if you can’t get it or find a good substitute. The piece that’s limiting our production now is actually the cases—we can’t get them machined fast enough. We order them, but these guys have other orders, and they’re not pushing it ahead for us.

John Iovine

4. What’s the landscape of tube suppliers?
We have a couple of good tube suppliers, because we’ve been in the business for a while. One of them just said to me, “We’ve got shoe makers calling us up, yesterday they were making shoes, and today they want to start making Geiger counters.”

I know exactly what he was saying. And, really, anybody can make a working Geiger counter. You just put together a high voltage circuit and detect the pulses. But how accurate is it, and what’s its longevity? It took us years to perfect making a Geiger counter—a good Geiger counter. It’s still like a black art. As with a lot of things, you really have to be in it for a while, and see all the crazy things that can happen, and this enables you to can build some resiliency into the circuit so that it will keep functioning properly.

These people who are just looking to make a quick buck are saying, “I can build a Geiger counter.” Yeah, you can build a Geiger counter, and it will probably work on some level, but you won’t know how to calibrate the thing, or even know that it’s in the ballpark of being accurate.

U.S. Government-licensed NRC [Nuclear Regulatory Commission] labs certify Geiger counters for accuracy. If you look at Geiger counters at around our price level, or even with some of the more expensive digital ones, ours are the selected few that are capable of getting NRC certification. You can send a Geiger counter to an NRC lab for testing, and they will give you a percentage rating of how accurate the counter is. If a Geiger counter isn’t within ±20%, they won’t certify at all. This is a pretty big constraint, because the tubes themselves run ±20%. So you can have very little play in the electronic circuit because there’s so much play in the sensor.

I have a Geiger counter that’s just coming back from NRC testing, and it was within ±5%. That’s unreal. 95% accuracy from 0 to 100 millirads. So I’m real happy with that, and once I get that one back, I’m going to be playing with it in-house and using it to set the standard for  the new circuits that I’m working on.

I’m constantly trying to improve our Geiger counter circuit. I’m always looking for a better way to do things. We were actually in the middle of a big redesign on the Geiger counter when the tsunami hit. We had our new GCA-07 model that was USB, and we were fine-tuning the circuit to actually make it even more accurate than what it is. But then we got hammered with this, and we had to stop development and take care of all the orders that were coming in.

5. So, there are a lot of uncertified Geiger counters out there.
Yes, but they don’t tell you they’re uncertified. You have to be careful. It’s an education if you read some of these specifications. They’ll say, “This Geiger counter is calibrated with a certified NIST source…” But that’s bullcrap. They’re just referring to the source that they’re calibrating with, and it doesn’t mean the Geiger counter itself is certified. You really have to parse what they’re saying in order to see that they’re not really calibrated or certified. They’ll give you accuracies, but they’re just quoting the tube accuracy. I can quote you a specification of  ±20% for the tube, but that doesn’t necessarily carry over to the whole instrument.

6. You sell radioactive sample too, right?
Yes, the radioactive isotopes have also been selling like crazy, which is actually a problem. We drop ship our orders from our supplier in Tennessee who is licensed to ship radioactive isotopes, but some people who are ordering these radioactive isotopes are out of the country, and they don’t do all the paperwork they need to. So it gets stuck in their customs department, and we have to do all the paperwork for them. We don’t have that kind of customer service time built into our margins, so I get a little annoyed with that. It’s like, didn’t you realize that you might need to fill out some forms when you order radioactive materials from another country?

7. Do you need a radioactive sample like that to calibrate a counter? Or could you use a smoke detector or something else that’s more readily available?
What I would tell a novice who’s building their first Geiger counter is that, first of all, you’re not going to calibrate it. If you want to get into calibration and millirads and stuff like that, it’s time consuming. You start needing certified sources, and you’ll have to send your counter out to a NRC licensed lab and have them tell you how close the Geiger counter’s display radiation level is to reality. You can use this information to adjust your Geiger counter, but you may have to adjust it and then send it back for NRC testing two or more times to get it to read accurately. This can be both time consuming and expensive.

What you can do, however, is just sit back and count how many radioactive particles your circuit detects in the period of a minute. Do that for 10 to 20 minutes, write them all down, and take an average. That is going to establish your minimum, maximum, and average background radiation, and if the background deviates from that significantly, you know that something is happening.

Many people ask me how to check water and food for radiation. I always advise them to go to the U.S. government’s NRC and EPA websites for this information. I am not qualified to answer these questions, this is above my pay grade, but here’s what I have heard. Say you want to check some rainwater. Collect a barrel of rainwater, put your probe as close as you possibly can to that water, and start counting pulses per minute. If it’s above your established baseline background radiation, you have a situation which you’ll want to have checked further by experts.

I have heard that this procedure will work whether you’re checking water, soil, tuna fish, or whatever else.  The key is that  you usually need a large quantity of whatever you’re testing. People watch CSI on television and think that you can derive all this information from these microscopic pieces of material, but you shouldn’t be testing 10 cc’s of water to check it for radioactivity. You’ll need more like 10 or 20 gallons, all accumulated in one spot. You’re not gonna find higher radiation levels in 10 cc’s of water, or if you do see it, oh my god, you’ve got a major problem. And it’s the same thing with food.

Radiation Network Map
Radiation Network Map - USA

8. Since more people are uploading their Geiger counter data to platforms like Radiation Network and Pachube, I wonder how they deal with wide variations in device sensitivity and accuracy.
I was talking to Tim [Flanegin, who publishes and] about that just a few days ago. I said, you don’t know who’s using what out there, so it can’t be that accurate. He said yeah, I know—like, if somebody’s using a pancake probe, which has a larger surface area than a hotdog probe, they’re going to get a much higher background count than somebody with a hotdog probe. He said they were going to work on that, try to normalize the data from all the different sources, but they haven’t put that in that yet.

Incidentally, all of our Geiger counters and kits are compatible with the software and hardware. We will be putting this up on our website shortly,

John Iovine with dog Chancey

9. I’m excited that you’ll be writing an article about radiation detection and Geiger counters for MAKE magazine vol. 29, and I’d love to hear more about what you’ll be doing for that.
The article will include designs for two new Geiger counters, a steampunk one and one that logs data standalone, not connected to any computer, so you can put it somewhere and collect data over time. The data logging one will use an EL-USB-5 logger from DataQ and write its data onto an EEPROM chip as comma separated values, so you can graph it in Excel or whatever.

For the steampunk one, I’ve actually been wanting to make a steampunk Geiger counter for a couple of months now, and have acquired a couple of parts for it. What I’m planning is, it won’t use a modern electronic circuit with a 555 timer or a multivibrator or anything like that. It’s going to be steampunk inside and out. I’ll use a high voltage battery, or maybe seven or eight 9V batteries in series to bring me up to 60-70V. Then there will be a step-up transformer, a capacitor, and a pushbutton.

So to use it, you’ll push the button maybe 10 or so times, and each time it will send a pulse through the step-up transformer. That will charge a capacitor until it reaches 500 volts, which will activate the tube. Then you’ll be able to detect radioactivity for several minutes, until the charge depletes on the capacitor, at which point you can charge it up again by hitting the button a few more times. It’s going to be really Victorian, a real working circuit, but without any advanced electronics. So that’s the plan.

I’m a sci-fi nut, so I find that Steampunk, Jules Verne type of stuff attractive. I think it’s really cute. It’s taking Victorian science and taking it up to our level of technology.

10. That steampunk Geiger counter sounds great, I’m really looking forward to it.  It sounds like something you’d take into a cave or something!

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Paul Spinrad is a broad-spectrum enthusiast, writer, maker, and dad who lives in San Francisco. He hatches schemes at

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