Thread by @PhysicistLisa

This radioactive teapot tweet has gotten a lot of attention. I make it a policy to not 'splain to people unless they ask and writer of the tweet has not asked me to.
However a lot of people in the replies WERE interested so I'm gonna chat here about it :)

First let's discuss why this teapot is radioactive! As recently as 1973 ceramic manufacturers used uranium oxide/depleted uranium as a pigment to make a Very Popular glaze for dishware. Fiestaware was the big one, but other manufacturers have done it too!

So my best guess is that this teapot is from that era & this detector is detecting that. But you should always be wary of something that is going to relate cpm (or counts per minute) to your health.
There's a couple big reasons that this little chart is misleading!

Reason 1: Well frankly the values on it are pretty alarmist. 0.013 mSv/hr isn't nothing, but it's not an immediate danger to your life, health, or safety.

It's a little more than 1/5th of what would legally be termed a Radiation Area ( 0.05 mSv/hr). Now you certainly don't want untrained / uninformed personnel standing in Radiation Areas all the time! But you could spend a bit of time here before you'd even hit a public dose limit.

But this takes us to a much more important issue here, which is Reason 2:
CPM of what? The source of your radiation matters!

A Sievert (Sv) is a measurement of dose. Dose is a measurement of how much energy is deposited in you, you big ole sack of water, you. As radiation interacts with the molecules in your body, it deposits energy. That's overly simplified but good enough for here :)

A reading in CPM alone doesn't tell you anything about how energetic your source is, critical information needed to calculate a dose! Without knowing your source, you can't know how much energy is deposited or how likely one of these interactions is!

(if you're thinking "isn't the type of radiation important too?" you're not wrong. But in this case we have a GM counter, which should only be detecting gamma and energetic beta radiation so you can wave away this issue here, more or less)

Sometimes we know what an instrument is calibrated to and we can make rough dose estimates off counts. It's generally 5 counts per second per 1 uSv/hr Cs-137. This card doesn't line up with that fairly standard assumption, which makes it even more dubious, imo!

I'm committing a big health physics sin and using the word dose when I should be using the word exposure. Sv and R are a measure of exposure not dose... but for the purpose of external exposures of gamma radiation, they are equal! And I think dose is a more accessible word here.

Anyway back to reasons.
Reason 3: this measurement is a problem because the distance from the source matters! Radiation counts will decrease with a distance of 1/distance^2. So if you have 100 cpm a foot away from something, you'd have 25 cpm 2 feet away.

This means that a measurement right on the surface isn't going to tell you too much about how much radiation your whole body is going to get exposed to. A measurement taken with the detector somewhere near your stomach or chest is going to be a much better read.

Reason 4 I am dubious of this cpm to mSv/hr card here is that the efficiency of a detector is really important for translating to Sv, aka how much radiation this detector sees compared to how much radiation is actually there.

Most hand held detectors like this are not 100% efficient. That means that to get to Sv you need to know some factor to convert with. Without a detector that is regularly calibrated to know this efficiency, you really can't quantify radiation with it.

Un-Calibrated detectors give qualitative, relative assessments, but not quantitative info. This requires special sources & knowledge, and it is usually done at LEAST once a year to instruments used for quantitative measurements. It's unlikely an at-home detector has this rigor.

So to sum it all up: This isn't how you'd take a measurement for exposure to the human body, this instrument probably isn't capable of this accurate of an assessment, and that card is unlikely to be accurate for the source of radiation present here.

If you're interested in the actual doses from fiesta ware, the good folks at ORAU have some estimates published here for you:
orau.org/ptp/collection…

If you read this you'll see that the biggest pathway for dose isn't standing near these dishes at all, but rather from eating off them! Ingesting uranium is not a great idea.

Uranium is radioactive, but even more importantly, uranium is also a chemical toxin that impacts your kidneys. Uranium is a more potent chemical toxin than it is a radiological hazard. I, personally, wouldn't eat off uranium glaze dishware with any regularity.

This was a tiny overview of the issues with that weird little card... but I hope your takeaway message is this:

You can't just go directly from counts per minute to something related to your health without a lot more information. And don't eat uranium.