Polonium were marketed by Firestone from 1940 to 1953. While the amount of radiation from the plugs was minuscule and not a threat to the consumer, the benefits of such plugs quickly diminished after approximately a month because of polonium's short half-life and because buildup on the conductors would block the radiation that improved engine performance. (The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the motor to fire more quickly and efficiently.) Polonium is
Discover Card card was used. A 1989 study found that Discover had strong consumer adoption in the U.S.; the number of households with Discover cards increased by 2.1 million, or 14 percent, in 1989. Discover was also noteworthy for being the only credit card accepted by the U.S. Customs Service to pay customs duty, effective Feb. 19, 1987. Since it did not charge a percentage fee to retailers, unlike Visa, MasterCard, and American Express, Discover was also the only credit card accepted at Sam's Club; the retailer has since started to accept MasterCard and American Express (see below). The plan to create