UC professor uses radioactive decay to power cellphones

Earlier this year, my friend Will and I were driving from Las Vegas to his apartment in Los Angeles when both of our phones died. It wasn’t a big deal – we both knew where we were going – but it did cause some panic since we had detoured through Death Valley. Will had the A/C on full blast, and as we headed west, the California sun disappeared behind the folds of the Sierra Nevada Mountains.

Taking the road out of Death Valley with the sun long gone is an eerie experience. There are no street lights, no buildings or homes, no road signs to reassure you, no signs of life at all – just an endless expanse of desert, lit poorly by the illumination of distant stars.

It’s even more eerie without a cellphone.

As we climbed one of the many hills that make Death Valley a valley, Will’s 2002 Honda Civic started shaking. The orange engine light flashed, and the car felt like it was coughing up something nasty. A million things flashed through my mind, none worse than the thought of being lost in the middle of the desert without a working cellphone.

We slowed to a roll, as if we were giving the car a moment to catch its breath. Eventually the engine light stopped blinking, and the car regained its strength. We cautiously got back up to speed. At the first gas station we saw, some sixty miles down the road, I bought a portable phone charger. 

We rely on our cellphones to text friends, navigate cities, Google questions and check Twitter. And occasionally, we rely on them to save us when we get stranded in the middle of the desert. So nothing’s more frustrating – or scary – than when these phones die.

Without plugging them into a charger every night, phone batteries hardly last the entire day. But what if these batteries for phones, computers and tablets could last forever, without ever needing a charge?

University of Cincinnati professor of nuclear and radiological engineering Henry Spitz, PhD, is exploring ways to create batteries for electronics that never die. The key, he says, is radioactive decay. 

But isn’t there a problem with having radioactive material around? When we think of radiation, we think of radioactive waste, nuclear bombs or mushroom clouds emerging from test sites in the middle of Nevada (perhaps not too far from my Death Valley misadventure). In other words, we think of things we don’t want anywhere near our back yards, let alone our back pockets.

But radiation, says Spitz, is actually in every home in the country. Halfway through our interview, perhaps sensing my confusion on how radiation could be applied safely to cellphones, Spitz leaves the office and returns with a smoke detector.

“So long as you have a smoke detector in your house,” he says, putting the plastic device between us, “you have radiation.”

It turns out that smoke detectors contain a small source of radioactivity called americium-241. Spitz opens the smoke detector, revealing a small silver disc the size of a collared-shirt button underneath its cover. “This is what we’re talking about,” says Spitz, pointing to the disc. “It’s not nuclear waste. It’s what’s in your smoke detector.” 

Smoke that enters the detector absorbs some of the radiation from the source, reducing the current generated in the detector sensor and sounding the alarm.

Smoke detectors are effective partially because of the long-lasting nature of isotopes. Americium-241 has a half-life of more than 400 years, meaning it won’t stop working any time soon. Just as important for Spitz’s case, people are comfortable with this isotope in their homes. 

The negative public perception about radiation is greatly exaggerated, says Spitz. Spitz describes how early heart pacemakers made in the 1970s contained small sources of plutonium to generate electricity. Many those old plutonium pacemakers are still in use, nearly 50 years after they were installed. Because of the negative associations with plutonium, however, pacemakers eventually had to be designed without plutonium.  Traditional batteries used in new pacemakers have to be replaced every few years.

“It’s hard to change the public perception about radioactivity,” says Spitz. “But we have smoke detectors everywhere, and they’re saving lives.”

That’s why a familiar isotope like americium-241, one everyone has in their house, could actually have commercial success, he said.

Spitz and his colleagues are using americium-241 and a silicon-type detector to generate charge for their battery prototypes. They have already achieved a simple prototype design and are scaling it up and trying to make it more efficient with more activity from the isotope.

Just like a smoke detector, the team’s device will have its own type of detector. Spitz compares this detector to the same silicon chips you’d find in a cellphone or computer. There are even several apps that let you to use your smartphone as a radiation detector. 

Featured image at top: University of Cincinnati professor Henry Spitz talks about his research into battery technology. Photo/Corrie Stookey/CEAS Marketing