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I recently started rock tumbling with my preschool-age kids and bought a cheap geiger counter to check out rocks we find (more from curiosity than concern). Specifically it's a GQ GMC-500Plus model with two tubes that should be able to detect beta, gamma, and x-ray.

We've watched it click for background radiation (~0.12 μSv/h) but I'd like to show the kids how it behaves in the presence of a discrete source. So far none of our rocks are radioactive. I could buy samples of uranium ore or specific isotopes for calibration, but I'm more interested in things that might already exist in my house or neighborhood.

Here's a partial list:

  • Smoke detectors - Americium - Primarily alpha particles, probably not detectable by my counter.
  • Bananas - Potassium 40 - Probably not strong enough to detect.
  • Pre-1970s Fiestaware and other red/orange ceramics
  • Vaseline glass
  • Granite countertops

(I don't have any Fiestaware, Vaseline glass, or granite counters.)

What are some other likely household radiation sources that might be detectable with a cheap geiger counter?

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    $\begingroup$ Coleman lamp mantles used to be impregnated with thorium dioxide. Supposedly, illegal to manufacture in or, import into the U.S.A. since the early 1990s, but whatever the non-thorium substitute is, it doesn't shine as brightly, and I've heard rumors that the thorium-impregnated version still is manufactured in countries where electricity is a luxury, and health and safety regulations are sparse. $\endgroup$
    – Solomon Slow
    Commented May 17, 2022 at 21:51
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    $\begingroup$ @SolomonSlow All my camping/emergency lamps are LED, but that's a good one to be aware of. $\endgroup$
    – Robert
    Commented May 17, 2022 at 22:07
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    $\begingroup$ The old thorium dioxide-containing Coleman lamp mantles are still available, as old stock, on ebay, if the posts are to be believed. $\endgroup$
    – Ed V
    Commented May 17, 2022 at 23:01
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    $\begingroup$ If you live near a beach with black sand, it may contain thorium, and possibly uranium. $\endgroup$
    – PM 2Ring
    Commented May 18, 2022 at 8:48
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    $\begingroup$ Possibly, the glowing numbers or dots on older watches $\endgroup$
    – Toffomat
    Commented May 18, 2022 at 8:54

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Frankly (and luckily...) I doubt that something useful will be suggested beyond what you already list. But depending on where you live, you could try to measure a difference in the radioactivity in your basement versus outside. If not vented properly, and somewhat deep, and in the right surrounding rock, basements can have 100s of Becquerel of activity per cubic meter of air from the radon decay chain. That gives plenty of gamma activity too. Not trivial to measure that though, you will need to average the count rate over significant time.

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    $\begingroup$ Fortunately the digital geiger counter I bought has excellent facilities for collecting and graphing activity over time! But unfortunately I don't have a basement. I suspect you're correct that there's nothing much else out there, but I'll leave the question open for a couple of days just in case. $\endgroup$
    – Robert
    Commented May 17, 2022 at 22:06
  • $\begingroup$ Radon-222 itself is primarily an alpha emitter, but several of the isotopes it its decay chain are beta emitters. en.wikipedia.org/wiki/Uranium_series $\endgroup$
    – PM 2Ring
    Commented May 18, 2022 at 8:55
  • $\begingroup$ indeed, the radon decay chain has it all, alpha, beta, gamma, even some neutrons come out $\endgroup$
    – rfl
    Commented May 18, 2022 at 8:59
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You can get thoriated tungsten electrodes from welding supply shops.

Rock samples differ considerably in their radioactivity, so try different rocks. Here in northeast Massachusetts there's quite a bit of thorium in the glacial gravel.

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A banana doesn't contain as much potassium as most people think. An average banana has a mass of about 120 g and contains about 400 mg of potassium (about 1/12 of the USDA recommended daily intake).

By comparison, a 89 g shaker of potassium chloride*, often used as a salt substitute, contains about 43 g of potassium. So you are much more likely to detect emissions from a salt substitute (ideally pure KCl) than a banana.

* I do not endorse this product

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Potassium carbonate or Potash works reasonably well if you measure for some minutes. In Germany it is commonly used as baking agent, maybe you can also get it in normal stores. enter image description here

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ALL OF THEM. ALL EM frequency devices emit radiation...radio, microwave, infrared, visible light, ultraviolet, x-ray, and gamma rays, upper tiers not essentially...... but the low frequency waves by virtually all devices

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    $\begingroup$ OP said, "...radiation detectable with a Geiger counter." Radio, microwave, infrared, visible, and ultraviolet aren't going to make the counter click. $\endgroup$
    – Solomon Slow
    Commented May 18, 2022 at 16:51

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