Two weeks ago I wrote a post about the wide variety of radioactive artifacts found in museums, such as uranium glassware, radioactive minerals, Pierre and Marie Curie lab memorabilia and Manhattan project relics.
I decided to give radium-containing artifacts their own post, in part because the radium isotope Ra-226 appears in such a curious variety of items from 1898 through to the 1960s. Pretty much anything that needed to glow in the dark got coated with radium paint during that era.
For example, a National Parks Service bulletin warns museum curators to keep an eye out for radium-containing chamber pot lids, light-switches, doorknobs and religious statues. (I searched long and hard, and sadly in vain, for an image of a radium glow-in-the-dark Virgin Mary or Shiva or Jesus.)
Of course glow-in-the dark-radium paint is best known for making watch and compass faces as well as cockpit gauges visible at night.
(A moment of silence, please, for the 4000 female workers in factories that produced these products in the 1910s and 20s. Repeated licking of the paintbrushes used to apply the radium–in order to keep said brushes pointy–took a serious toll: Many workers suffered serious illnesses ranging from bone disease to cancer.)
The radium-226 found in glow-in-the-dark watches and other artifacts has a half-life of 1600 years, decaying by means of an alpha particle. Radium-226 also eventually turns in to radon-222—not precisely the world’s most loved gas.
Given the prevalence of glow-in-the-dark radium-226-containing dials and gauges in aircraft (and spacecraft), I called up Lisa Young, a conservator at the Smithsonian’s National Air and Space Museum (NASM) to find out how she deals with radioactive objects in their collection.
Young explained that the government sets limits for the amount of radiation that can emerge from a museum display: 2 milli Roentgen (mR) per hour. “But we aim for under 1 mR/hr at the NASM to err on the safe side,” she added.
I needed some context for what 2 mR/hour dose means so I did a back-of-the-envelope calculation:
According to the Health Physics Society, people who work with radiation in the US can only be exposed to 5000 mR in a year. This means you’d have to stand in front of a radioactive museum display for at least four months, 24-hours a day to get the same amount of radiation permissible to an X-ray technician at work in a year. Since most people don’t spend more than an hour or two in a museum, this 2 mR/hour dose limit makes for a pretty low risk experience.
Of course, museum staff has to monitor radioactive objects in their collection to make sure emissions are within the legal limit. Young told me that last year she and some colleagues did an extensive survey of NASM artifacts to ensure just that.
After the survey, the team only decided to make a few minor changes to displays, Young said, such as closing cockpit doors to add an extra barrier between radioactive dials and the public, or moving radioactive artifacts in display cases to the very back, so as to increase distance between viewer and object.
As for that vintage radium-painted watch heirloom hanging around your house: I’d get a scintillator and measure how much radioactivity you’re being exposed to. In addition to ensuring your exposure is not too high, you may also be subject to a new federal register for radium-containing objects enacted by the National Regulatory Commission in 2007.
A quick peek on eBay reveals there’s a reasonably robust trade for radium-watches online, although some folks donate such items to museums for safekeeping.
“People are always bringing me in watches with radium dials,” said Karen Green, a curator the National Atomic Testing Museum near Las Vegas. “I say “thank you” and then they go in to a lead-lined bag. We try to keep exposure at a minimum.”