Vintage Firestone polonium M-40 spark plug in original box

Description

This vintage Firestone spark plug is in the original box. It still has the oil paper wrapping and cardboard covering. The plug has a bit of surface rust in the threads but is in great condition overall. It is an M-40 plug containing polonium. Firestone made spark plugs with polonium in the electrode during the 1940's and early 50's.
The theory behind these plugs was that the radioactive alpha particles emitted by the decay of the polonium would ionize the gas creating a stronger spark and boosting performance. The idea of using radioactivity to boost a spark plugs performance was first patented in 1929 by Alfred Hubbard but it was not used till later.
In reality the polonium did not make a lot of difference, in part because of the deposits that build up on the surface of a spark plug's electrode. The usefulness of these radioactive plugs was further demenished by the short (138 day) half life of the polonium 210 which was used in them. This abbreviated half life combined with the small amount of polonium used meant that within a few months the plug would no longer emit an appreciable amount of radiation. They would be no different from any other spark plug.
Because these spark plugs emitted alpha particle radiation they could be used safely when they were new. This is do to the fact that alpha particles can not penitrate skin. The plugs are 100% safe to have now as the polonium in them is so far past its half life that it is no longer radioactive. This collectible Firestone 'radioactive' polonium spark plug is an interesting piece of automotive history.