eli5 How come if highly radioactive radium was on watches that the wearers didn’t succumb to radiation poisoning at the wrist?

31 views
0

eli5 How come if highly radioactive radium was on watches that the wearers didn’t succumb to radiation poisoning at the wrist?

In: 186

Even a cheap wristwatch has the clock face encased in metal and glass, which would have provided at least some sheilding. Compare and contrast with the Radium Girls, who had a more direct, prolonged exposure to the radium paint.

It was usually a minuscule amount of radium-laced paint on the hands of the watch. The main reason why the watch factory workers (the “radium girls”) got radiation poisoning was because they worked with large quantities of radium paint on a daily basis. And since science was unaware of the radioactive effects at the time, they’d do stuff like lick the tips of their paintbrushes to taper the point, so they were actively ingesting it too.

Alpha radiation from radium consists of helium nuclei, which is a whole helium atom minus the electrons. These are (in relation to other forms of radiation) HUGE and easily stopped by almost anything, even a few centimeters of air are enough. You can shield yourself from alpha radiation literally by holding up a sheet of paper. So a watch or some thin glass cover would be sufficient.

I have a friend who has a uranium pellet encased in resin as a keychain, it was an official souvenir from visiting a nuclear power plant.

The entire radium decay chain* emits only alpha and beta particles (and no gamma radiators)

Alpha particles are blocked by a piece of paper, so these are mainly dangerous if you get the material inside your body (if you for example lick a brush with radium paint on it) and beta radiation is slightly better at penetrating materials but is generally stopped by a very thin sheet of metal (like the metal body of a watch).

There is also very little radium in a watch (very thin layer of paint that contains radium and a material that absorbs radiation and then emits that energy as a photon, ie visible light).

*Radium collapses into radon->Polonium 218->Lead 214->Bismuth 214 etc etc. Each time it emits either a helium-4 particle (alpha radiation) or an electron/positron (beta radiation).