eli5 How come if highly radioactive radium was on watches that the wearers didn’t succumb to radiation poisoning at the wrist?
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Answer: With the watch you get a tiny dose. When you paint the watch faces you get that…..a few hundred times a day. Plus they were breathing the dust in, putting the brushes in their mouths….and since the company didn’t tell them it was dangerous or anything, actually totally safe no prob, they were using it as a cosmetic too, painting their nails and adding to their cosmetic powders and such. The dust got in their clothes so they were exposed to it in massive, massive doses.
As others explained, women hired to paint the face of watches so they would glow in the dark. They were told it was harmless and to use their lips on the brush tips.
It is a reason why organized labour and enforced health and safety laws is important.
The danger of radiation scales down with distance *squared*. If you double the distance, then you get only 1/4 the dose. (The opposite is true: if you get twice as close to the source, you get 4x the dose of radiation.)
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The danger from radiation scales up with time. If you spend twice as long with the source, you get double the dose.
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Let’s make some very rough estimations to get a ball-park idea of how to compare these two exposures to radiation.:
If you were working in this factories, you were told to use your lips to put the paitnbrush to a point and help you get the finesse to paint the watch-hand without wasting materials. Just to make the calculation easy, let’s *assume* that the amount of radium ingested and later extreted through the body each day was maybe the same amount as on the average watch, and let’s assume it takes 24 hours for you to excrete it all.
If you wear a watch, you get get a small amount of radium maybe on average about 50cm (or nearly 2 feet) from your centre of mass, for half the day while you wear the watch.
If you ingest the radium, well, it probably absorbed into your body, but let’s only assume that it passes through your digestive system. Your digestive system is through a lot of your body, but let’s assume that on average it was like 10cm (~4 inches) away from your cnetre of mass on average as it travelled through your body.
Also, if you injest the radium, then you have it in your for 24 hours, not just half the day.
So, even assuming you simply urinate/poo-out the radium, and none of it gets absorbed into your body, we’ve approximated that you have 2x duration, and are 5x closer to the source. We square the closeness factor, so 25x there. Stack 2x with 25x to get 50x as much radiation.
So, as a *very* rough estimate, being a radium girl was probably as bad as wearing 50 radium watches.
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It gets worse, because you don’t simply poo out all the radium. A google search suggests maybe 20% of it gets absorbed into your bloodstream. Some of that will later pass through your urine, but some of it will stay in your bones, and directly radiate those bones. Let’s say that makes it twice as bad on average (I think this is underestimating it!)
Then it is 100x as bad as wearing a radium watch, and might get worse and worse the longer you work there.
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Now, this was **not** a valid calculation I’ve just done here. It was a very rough estimate, based on some flawed assumptions. (e.g. trying to estimate your ‘distance’ from atoms literally inside your bones is kind of strange.)
However, an accurate calcualtion would consider factors similar to what we considered here, and though they’d have more sophisticated methods, you can see how there are important factors that set the radium girls apart from the customers who bought their watches.
Radium is not that radioactive. There’s not that much radium in the paint, and the glass and metal of the watch is more than sufficient to contain the alpha particles emitted by the radium.
Radium is not much of a health risk unless you eat it or breathe it in.
Radium emits alpha particles. They have very little penetrating power. Your skin is actually a sufficient barrier to stop it.
Alpha radiation is basically only dangerous if you ingest it. At that point it starts irradiating your internal organs directly. You’ve probably heard of the “radium girls” who worked painting the watches by hand and all died horrible painful deaths. The most significant issue for them was the standard practice was to lick the brush to form a point. This resulted in ingesting a fairly high amount of radium. Besides ingesting any alpha emitter in general being bad in the case of radium specifically the human body can’t distinguish it from calcium. As a result it gets incorporated permanently into your skeleton. This results in long term irradiation as well as brittle bones because it can’t actually do the same job as calcium.
Frankly, the answer to this is that radiation is almost always way less dangerous than people imagine.
Sometimes radiation does crazy things. Inside a working reactor there’s some science-fiction-like bizarre stuff going on, it’s hard to exaggerate how wild those conditions are. Elements transmuted, sun-like temperatures, the toughest materials swollen and broken down. People can hear about that kind of thing and mistakenly think that how radiation works usually, instead of as an extreme example.
A blacksmith’s forge might be so hot that it’s dangerous to literally look at it (UV hazard). But that doesn’t mean the heat from a regular wrist watch is harmful at all. There’s very little of it and some shielding between its source and your body.
Radiation is often the same way. There’s always radiation around us, dose makes the poison and all that, and legal limits on radioactive dose/contamination are usually extremely low.
Radium is an alpha particle emitter. Alphas are big, slow moving particles which are easily stopped by the back of the watch case. The Radium dial painters licked the brushes they used to get a finer point. They had radium inside their bodies, where it could do damage.
A lot of radioactive material doesn’t penetrate very far through through even air let alone metal/glass.
The way you get issues is typically from ingesting/inhaling radioactive material, or worst case scenario the stuff you’re ingesting is not only radioactive but also bioaccumulates (your body mistakes it for something it needs and uses it, making it remain in your body to cause damage for a long period of time).
Because there are different kinds of ionizing radiation.
Gamma rays penetrate basically everything and do a ton of damage.
Alpha and Beta are much less penetrative. A sheet of paper or your outermost layer of skin will easily stop the radiation from Alpha-emitters, and Beta isn’t much worse. The radioactive substance mostly has to get directly on or inside you to do damage. Inside you, even alpha and beta rays can do damage and increase cancer risk.
Guess which kind Radium emits?
All of them.
But unless you’re close to a LOT of it, the gamma emissions from just a dab on a watch dial isn’t enough to worry about. The watch casing blocks the alpha and beta. “The dose makes the poison” in this case.
The Radium Girls had *occupational* exposure, though. They worked with Radium paint day in and day out, and ended up ingesting it when they would lick the brushes and similar. Radium ingested can get into your bones and teeth (can be mistaken for Calcium by the body). It’s downhill from there.
Read Radium Girls by Moore. An incredible account of the young women who were poisoned by radium on the job in the 1920s.
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