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Harnessing the inherent energy found in the process of radioactive decay is how many spacecraft keep the lights on so far from home.
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Now, scientists have greatly improved the efficiency of these batteries on the micro scale by harnessing energy from alpha particles produced by the decay of americium—the most common isotope in nuclear waste.
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While this kind of technology won’t power, say, a car-sized Mars rover any time soon, it could be the perfect solution for remote sensors, or even pacemakers.
If you need to send something far from a recharge outlet, then you’re going need a nuclear battery. These long-running power sources come in all shapes and sizes, and have many different methods for drawing energy from the decay of a radioactive isotope.
The Curiosity Rover—the first Martian rover to not rely on solar panels (a good idea, considering how dusty Mars can be)—uses the natural decay of plutonium-238 to generate heat, which is then converted to 110 watts of steady electricity thanks to onboard thermoelectric devices. After seeing its impressive performance, NASA went ahead with the development of an upgraded version known as the Multi-Mission Radioisotope Thermoelectric Generator.
These batteries cost many millions of dollars, and power spacecraft that weigh as much of a compact car. But scientists are also interested in exploring ways to develop micronuclear batteries, capable of producing energy in the nanowatt or microwatt range for potentially thousands of years. Now, a team of scientists from Soochow University in China have improved such a battery by a factor of 8,000 by using the element americium, which most consider to be nuclear waste. The results of the study were published earlier this month in the journal Nature.
“Contrary to chemical batteries,” the authors wrote in the study, “the longevity of a micronuclear battery is tied to the half-life of the used radioisotope, enabling operational lifetimes that can span several decades. Furthermore, the radioactive decay remains unaffected by environmental factors such as temperature, pressure and magnetic fields, making the micronuclear battery an enduring and reliable power source in scenarios in which conventional batteries prove impractical or challenging to replace.”
Unlike the heat used by the Mars rovers to create electricity, this new device instead relies on radiated light.
Americium radiates energy in the form of alpha particles, and glows a borderline-cliche radioactive green. Those alpha particles usually lose their energy very quickly, but scientists figured out a way to access that energy anyway—embed this element into a polymer crystal and pair it with a photovoltaic cell that effectively converts the light into electricity. Amazingly, this tiny nuclear battery can be safely encased in a quartz cell no bigger than a millimeter.
Shuou Wang, senior author of the study, told New Scientist that after 200 hours of testing, the battery delivered a stable supply of energy with incredible efficiency—roughly 8,000 times more efficient than previous devices. Americium has a half-life of 7,380 years, but because the other components of the device are continually subject to radiation, the battery sadly can’t last that long. However, the authors estimate the devices could pump out power for several decades.
It’s worth remembering that these are micronuclear batteries, meaning that they are very, very small—so small, according to New Scientist, that it’d take 40 billion of them (yes, with a “b”) to power a 60-watt light bulb.
However, not all electronic applications need that much power. One Chinese startup called Betavolt has developed similar, pint-sized nuclear batteries as possible power sources for wearables or even pacemakers. But because the materials at the heart of these batteries are not naturally occurring, they’re too expensive to build for large-scale operations like, say, a Mars rover. So, it’s likely that these micronuclear batteries will remain a possible power revolution on the smaller end of the energy scale.
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