As you may recall, a couple of weeks ago I penned a blog titled Is that a Geiger counter in your pocket (or are you just happy to see me)? As part of this I mentioned that I would like to own a Geiger counter…
Well, my chum Brian pointed me at the Kits USA website, where they have all sorts of educational do-it-yourself kits, including a bunch of Geiger Counters.
I was immediately attracted to the C-6979 Sensitive Geiger Counter Kit (on the basis that this was the cheapest [grin]). According to the website, this uses a Russian Geiger-Mueller tube and is sensitive to Beta and Gamma rays. As the folks at Kits USA cheerfully say:
Want to know if that orange colored plate that was all the rage in the 60's is radioactive, how about your dad's radium dial watch, or the mantles on your camping lantern – this will tell you! This kit produces the familiar audio clicks and lights up a blue/green LED in response to radioactive sources. Random clicks are even heard from your kit as cosmic rays strike the tube!
Uses a Russian GM tube that was made during the cold war (we test every one for proper operation), various resistors, capacitors, and a special miniature speaker. Operates from one 9V battery (not included). Comes with all parts, PC board, GM Tube and instructions (no case available). Size of PC board 4-5/16" x 1-1/2". Skill Level 2. Requires soldering.
“Ah Ha!” I thought, “I know which end of the soldering iron is the hot one” (it took a while, but I learned over time), so I immediately placed an order. (Actually, on the off-chance you are tempted to purchase one of these kits yourself, I should give you a “heads up” that the folks at Kits USA charge an “arm and a leg” for shipping and handling – seriously, I just checked the invoice and they charged me $26.85, which I think is a bit “naughty” of them.)
I was jolly excited when my kit arrived
Now I have to say that – generally speaking – the instructions that came with the kit are first rate. Even a complete ding-bat like myself should have no trouble assembling one of these. Thus it was that I shortly had the assembled kit sitting on my desk. So with great excitement I connected the battery, turned the power switch to its ON position, the LED lit up, the speaker clicked once, and … nothing else happened.
I thought to myself. The thing was that I didn’t have a radiation source to hand. I remember the good old days when wristwatches had glow-in-the-dark numbers based on the use of highly radioactive radium … until the powers-that-be realized that this was not a good idea. But my current wristwatch does not boast this feature [actually it can’t even boast that it keeps accurate time (it gains about 5 minutes a day, so I have to reset it every morning), but it looks good, and I always say that you can’t put a price on “cool” (grin)].
So I went for a wander around the building in which my office is located to see if anyone had a glow-in-the-dark watch. Perhaps not surprisingly, the first person I asked responded by saying “Why do you want one?”
When I explained, he told me that a few minutes before he had seen Bruce (the guy who owns the company that owns the building) wandering around carrying a puck of radioactive material (see the photo below).
My assembled kit and the puck of radioactive material
Yes, I know, I know... before you leap into action and post a clever comment, I am fully aware that there is no battery connected in this photo (you see how well I know you [grin]).
So I hunted Bruce down, and sure enough he had a puck of radioactive cesium that emits beta and gamma radiation in his pocket. Why? I didn’t ask. As the years have gone by I’ve found it makes my life a lot simpler if I don’t inquire too deeply about this sort of thing. So I borrowed Bruce’s puck and held it next to my Geiger counter… still nothing…
When I reported back to Bruce, he did point out that his puck was only mildly radioactive at 5 micro-Sieverts, which really isn’t much in the scheme of things (see the Radiation Chart
on the XKCD website). So is this enough to trigger my counter? Who knows?
Now, the instructions that came with the kit do include some trouble-shooting instructions. They start with “Check that you’ve connected the battery,”
type directions, but build up to more useful things like “Use a wire to briefly connect the two sides of the GM tube and you should hear a click.”
When I do this I do indeed hear a click (hurray) and the LED dims a little, so I think this sort of indicates that things are generally working…
Now it may be that I have a duff GM tube. On the other hand, the creators of the kit do say that they’ve checked all of the tubes. One thing that puzzled me is that the LED is always on. I guess that I would have thought it would be better to have the LED usually off and for it to flash when a radiation event was detected. On the other hand, maybe the kit’s creators thought it would be better to have the LED on so (a) you know that at least something is working and (b) you know when the board is powered up.
But the instructions don’t say whether or not the LED should be on by default, and I’ve not had the time to work it out from the schematic (see below).
I tried calling the makers of the kit – Chaney Electronics
– but they didn’t want to talk to me because I hadn’t purchased the kit directly from them. So then I tried calling the folks at Kits USA
, but they said that they were selling so many of these kits that they hadn’t actually had a chance to play with them themselves. They did say that they would ask the kit manufacturer for me, but I’ve not heard anything back at the time of this writing.
Of course, one of the things that sparked all of this off in the first place is that I live only about 15 miles from the Browns Ferry Nuclear Plant
, which is run by the Tennessee Valley Authority (TVA)
. So I sent an email to the TVA pointing out that we were actually a match made in heaven – here I am with a Geiger counter but with no radioactive source with which to test and calibrate it – and there they are with a great big nuclear power plant with nothing better to do than generate a lot of electricity. I also mentioned that I would be more than happy to drive over there so that we could use my Geiger counter to make sure that everything was as it should be at their end. Sad to relate, I haven’t heard back from them thus far, but I live in hopes…
In the meantime, I sent an email to my friend Arthur in England. Arthur is one of the world’s foremost experts in Cosmic Rays, but he decided that it would be more fun to run a small farm with his dad, so most of the messages I see from him these days focus on things like bee hives and strange problems with cows. Anyway, Arthur responded as follows:
Hi Max, you should get some clicks from natural back ground radiation, not very many, but say every few minutes. The tube you have looks to be gamma and beta sensitive, but probably not sensitive to muons, which arrive at earth at around 0.1/cm**2/s. The case is also too thick to allow alpha particles into it.
The source you have is likely 5 micro-Sieverts and should be 'see-able' with your tube. But I have a friend in Oxford who built a Maplin kit and we couldn't get any response out of it, either with an x-ray source or in front of a CRT tube, source of x-rays, in a big TV.
The tubes contain gas which can leak out so that might be a problem as by shorting out the tube you are verifying that the click circuit is working and likely the HV too. I have known them fail due to HV leaking from the tube across the PCB. The board has to be very clean, free of any flux etc. Often commercial ones are attached with Teflon spacers to minimize charge leakage.
Does the supplier give any info on what the back ground rate is with the device? Something else might come to mind but for the moment I can't think of any other suggestions. Regards – Arthur
I’ve also received a few suggestions via email as follows:
Don writes: Hi Max, I enjoy your musings in your articles. Try an ionizing smoke detector. It should contain a small amount of Americium (element 95 in atomic table). The exact value should be called out inside the cover of the detector. Or you could check someone’s basement for radon gas!
Edith says: Hi Clive, a classic radiation source is a lamp mantle. They are little nets that are hung in a camp lantern over a kerosene flame to help create more light. If they still make them, they should be in a good hunting type outdoor equipment store. Or an old glowy watch face, or a classic red piece of Fiestaware pottery (the uranium in the glaze was a bonus). Otherwise you could just hold it against your thyroid and see if the static sounds louder…
Rolf commented: Hi Max, you could try to find an old watch or clock at an antique shop that has a radium dial.
James said: Hey Max,your comment about DIY Geiger counters reminded me of a demonstration that I saw as a high school student... Back in the early '90s, Atomic Energy Canada hired a spokesman that looked and talked like the old scientist from the 'Back to the Future' movies. His job was to spread the love of all things nuclear. As part of his seminar he showed us that radiation is all around us. The one source that was the most surprising was a wick from a Coleman lantern. As purchased off the shelf from the local hardware store, these little items (aka scamps) made the Geiger counter sing loudly. High school was a long time ago so I don't know if Coleman still uses nuclear powered wicks, but it was unexpected and impressive.
And Rob noted: Hi Max, there are several sources you can use. My counter (old Civil Defense version) from the 60s had a sample on the side. But I found some others.
- Standard smoke detector which has Americium (a soft radioactive silvery-white metal) which emits alpha particles which smoke will block hence setting off the alarm (very short version).
- Coleman mantels for gas camping lanterns. Treated with Thorium will set off you detector. Some off brands don’t seem to be treated.
- Old analog wrist watches have Radium painted on the hands (and dots).
- You can also go to the doctor and have them do a stress test on you and when they shoot you up with Barium you can play with yourself for several days (…never mind) as it has a half-life of (I was told so don’t quote me) about 36 hours. Of course your body passes it in about 2-3 days.
- And one I have yet to find but I am told that some are quite hot, granite counter tops. I have been meaning to take my detector to Home Depot but have not had a chance yet.
All good suggestions – not the least that the Home Depot stocks a lot of these items like granite and smoke detectors (maybe even Coleman mantels). On the other hand, I’m not sure what they would think of my skulking up and down the aisles with my home-made Geiger counter in my hands – especially if it started clicking furiously (I dream of the day, so long as I'm the instigator of its leaping into action).
This evening I will take my Geiger counter home and hold it near to the smoke detector in my house … but even if it still doesn’t work, that may not mean there’s anything wrong with it – it may just mean that my smoke detector doesn’t use a radioactive source to detect smoke.
If all else fails, I might do it to go down to an old antique (junk) shop to see if I can find an old clock with glow-in-the-dark numbers on it…