Radioactive elements in your local Super Wal-Mart or camping store! It sounds like a bad five o'clock news headline, but gas lamps containing the radioactive element Thorium are extremely common, with millions sold annually.
Why would a companies intentionally use a radioactive element in a consumer product? Let's find out.
Why use Thorium in lanterns?
Incandescent gas mantle lanterns work by using kerosene as a fuel to light a mantle, a bag of cloth covered in metallic salts. These salts are oxidized in the presence of a flame, yielding a bright, long lasting light. Chemist Carl Auer von Welsbach is the father of modern gas mantles, experimenting with several mixtures of rare earth metals before settling on a mantle mixture containing 99% Thorium dioxide. This mixture creates a bright white flame, but with one problem – the element Thorium is named after Thor (wait... that's not a problem) and is naturally radioactive.
The Coleman Company, one of the world's largest makers of camping supplies, continued to use Thorium to make their mantles until the mid-1990s when they changed to yttrium, a non-radioactive compound that does not burn as bright, but burns longer. Many mantles in retail lanterns still contain Thorium, with 50 million mantles sold in 2000 containing the radioactive element.
A reasonably safe radioactive element
For a radioactive element, Thorium is rather safe. One cannot power an explosive nuclear fission device with Thorium, as the element itself itself is not fissile. However, an atom of Thorium will absorb neutrons over time and then beta decay into Uranium-233, which can sustain a chain reaction of nuclear fission.
Thorium is an alpha particle emitter. Alpha particles are only effective for a few inches and can be blocked by a sheet of paper – they cannot penetrate human skin. Under the right conditions, the use of Thorium in gas lamps is not a bad idea – it is reasonably safe when contained under glass and the mantles provide for a great source of light. Problems with radioactivity arise in the long-term handling of the Thorium mantles, particularly in the manufacturing process, or when a lantern breaks and those gathered around the campfire earn a new scary story to tell about the time they inhaled radioactive dust.
Cases of extreme exposure
The danger from using these mantles around a campfire one or twice a year is not substantial, with exposure of roughly 0.005 millirems coming through a couple of nights spent by Thorium gas lantern light. Under extreme exposure conditions — 4800 hours during a year from simultaneous use of four different Thorium mantle lanterns — an individual is exposed to roughly 200 millirems. This is not a large amount, as 200 millirems is roughly the same amount exposure you would get from receiving a CT scan of your head.
Major issues develop via inhalation of Thorium by those working in the manufacturing process. When inhaled, Thorium bypasses the protection of the skin and can build up in the lungs. Decades of mishandling Thorium salts in processing at sites in Camden, New Jersey during the early 1900s led to contaminated soil, increasing the cancer risk of workers and citizens in the area. A 1981 survey of the area showed background radiation in commercial and residential areas to be much higher than acceptable values, leading to allocation of money into a New Jersey Superfund to provide cleanup and measures to block the radiation.
The next time you are looking for a camping lantern, grab a Geiger counter and head out to a flea market, big box store, or log on to eBay. The YouTube video above gives an idea of the Geiger-riffic fun in store if you are successful in tracking down a Thorium lantern. Most manufacturers are moving away from using Thorium, but you might be able to find it in a couple of older models.
Images courtesy of The Coleman Company and DC Comics. Sources linked within the article.