One such place is the monitoring of military equipment. “Everything the Department of Defense puts out has to have antitamper protection so that if someone gets their hands on the seeker head of a missile, or an entire aircraft, it would be very difficult to reverse-engineer it,” says Christian Adams, a chemist at Lockheed Martin Missiles and Fire Control. The memory chips that control such antitamper systems, says Adams, require very low continuous power over a long time. Military specifications also require that these devices withstand extreme conditions that normal batteries can’t tolerate: they must operate in temperatures from -65 to 150 ˚C and withstand high-frequency vibrations, high humidity, and blasts of salt. “If the battery freezes out or dies out, the memory circuit loses its configuration,” and the device fails, says Adams.
“Widetronix is the first out of the gate with something that can be tested to military specifications,” says Adams. Lockheed received the company’s prototypes last week. If the betavoltaics pass the test, Lockheed will probably have them in antitamper products in about a year’s time, he says. Lockheed is also working with the company to develop higher-power betavoltaics for remote monitoring of missiles. Sending out a radio signal to say “I’m healthy” requires microwatts of power, says Adams. Widetronix is also testing its batteries with medical-device company Welch Allyn. It expects to sell the batteries for $500.
City Lab’s Cabauy says that though the prospect of nuclear batteries, especially for medical implants, may raise eyebrows, tritium is safe. Besides the beta particle, other products of tritium’s decay are an antineutrino and an isotope of helium that is not radioactive. “A piece of paper can stop the radiation from tritium,” says Cabauy.
The future promise of betavoltaics might be in very cheap sensors embedded in buildings and bridges where “you don’t ever want to change the battery,” says Amit Lal, professor of electrical and computer engineering at Cornell University. However, this would require companies such as Widetronix to move to longer half-life materials, such as nickel isotopes that last 100 years. While tritium has a half-life of only 12.3 years, one of its chief advantages, besides safety, is that it can be secured cheaply from Canadian nuclear reactors that produce heavy water as a by-product. Longer half-life isotopes such as nickel-63 must be purchased abroad at high prices. “Since the end of the Cold War, there is no government support for radioisotope infrastructure in the United States,” says Lal. “Making batteries that last forever is probably good reason to build that infrastructure.”