I want to test a Geiger Counter - can you help?

Does anyone have (or can recommend) a low level radiation source I can use in preparation for a Geiger Counter experiment? I’ll need it this week.

My Plan

My cat is going to have an Iodine-131 treatment next week (Hyperthyroid issues). I thought it would be interesting to get a cheap beta/gamma Geiger Counter to track his declining radioactivity once he returns home.

Iodine-131 has a half-life of about 8 days (decays through beta emissions) and is also excreted in urine, sweat, and saliva. He’ll be in quarantine at the vet for several days and then will be in solitary confinement for two more weeks once home.

The $40 Geiger Counter I ordered:

should arrive tomorrow.

I was wondering if someone had a low level radiation source (e.g. an old clock with radium-painted hands, some only-slightly-radioactive uranium ore, or similar) I could use so I could test whether the device works.

My Geekier Plan

If possible, I’d also like borrow the source for a few days for debugging as I throw together an Arduino Sketch to report the readings.

I was thinking of coupling it to an esp8266 and ping a web page to log the readings captured by placing the sensor next to his food bowl (or perhaps the litter box).

re: Radium

Radium decays by alpha emissions (which are blocked by glass and can’t be detected by this device), but other decay products in the decay chain emit beta and gamma emissions. I’m hoping something would make the detector “detect” (other than background radiation) so I can confirm it’s not just random noise in the circuit.

Other Sources

Bananas have Potassium-40 in them (which has a very long half-life). Eating one is supposed to be the equivalent radiation exposure as 1/10th the exposure of an arm radiograph.

Exposure is not ingestion, though: does anyone know if they emit enough beta emissions to be discernible in a reasonable amount of time simply by placing a Geiger Counter near a bunch of them?

Suggestions and critiques solicited and appreciated.

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There are some slightly radioactive materials in Science, I took a clas on them once last year. I had asked they be moved closer to the spiders :slight_smile: But seriously they should still be there.


Maybe an Americium smoke detector?

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I believe we have some low level radiation sources that were part of a class. I could check when I am up there on Saturday.

I don’t think the makerspace policy allows for things to be borrowed and taken home, unless I am misremembering. But you are free to work with the material in the science area.

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We tried this with a quite sensitive photomultiplier tube in school and weren’t very successful. I believe Geiger counters are on order of magnitude or more less sensitive.

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I know I can’t take DMS property offsite - I was hoping a member had a suitable source. If the device arrives in time, I’ll bring it to DMS tomorrow (Thursday) night and check it out in the science lab. Hopefully someone there will be able to locate the samples.

These primarily emit alpha particles, and only outside the device if you intentionally damage the radiation source - something I am unwilling to do. Alpha particles are blocked by almost anything (glass, skin, et al.) The detector I bought only detects beta and gamma emissions.

I suspected as much - thanks for the confirmation. I may try it with some bananas I already have at home anyway, just for the fun of it.

The samples are on the left hand side as you enter science. Most of them are in a locked steel box with a combination lock. @FairieCyanide if you need this code let me know.

Having donated a lot of those samples, here is what at least was included in my collection:

Caesium-138 (i uCi, sealed plastic disk source)
Uranium-238 (pure metal, inside glass vial. Do not open the vial for dust considerations)
Uraninite Ore (in a plastic container. Again dust considerations, but if appropriately handled this one can be removed)
Autunite Ore
One larger chunk of ore (it’s separate in a lead lined film bag), but I can’t remember what geological specimen it was off the top of my head.
Some Trinitite ( would recommend not opening the vial except with extreme care. It’s pretty low level, but you can’t take the stuff off the test site anymore so it’s getting harder to obtain legit samples like that)
some miscellaneous novelties to show applications of radioactive isotopes: like Uranium glass marbles (IIRC 0.5% Uranium Dioxide by weight in the ones I provided), a Tritium archery sight, etc

You should be able to test with the Uranium in the glass vial. Whilst it blocks most of its own radiation (70% denser than lead after all), it has a fairly diverse decay chain which means you get a little bit of everything out of it. If handling the Ore outside of the containers, ensure you have gloves, ideally a respirator (the common n95 type should be fine for this), and use the decontamination spray when complete as a scrub both for your hands/forearms as well as the table surface.
The biggest hazard is dust ingestion. These isotopes will typically pass through, however when ingested Alpha radiation is pretty bad. Unless you break apart a sample the actual dust kicked up is pretty minimal; just don’t rough handle them, but IMHO you should be able to keep them in the bags for what you need.



Thanks Jim. I’m mostly interested in checking whether the Geiger counter is operational, so I’m hoping I won’t have to open ANY container other than the steel box they are in. I might even be able to detect the emissions without needing to open the box at all. The tritium archery site or the uranium marbles will likely serve my needs.

These are actually not your best bet, as these really need high sensitivity detecters. Go for the glass uranium vial, the Caesium disk, or the ore samples in the plastic containers.


Fingers crossed for your kitty’s successful procedure!

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In Science, on the metal shelves, there is a Civil Defense Geiger Counter. It has a “Zero” position you use to zero the needle. Then you can set it to X100 and actually read Background Radiation. The detector tube is on the bottom front of the box, the closer you get it to the source, the better reading you will get. You can use this to check the accuracy of the detector you are building.

Do you plan to quarantine the Cat in a Box?

Please advise…

No Schroedinger experiments will be performed on this cat. He will have to spend several days in solitary at the Vet first, then two weeks in semi-solitary once back home. This includes:

  • 20 min people exposure/day
  • gloves while handling waste (I-131 is excreted in urine, sweat, and saliva)
  • no laps (this will be especially hard for him)
  • etc.
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Thoriated Tungsten electrodes, used for TIG, are slightly radioactive, as are gas lantern mantels.


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