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October 9th, 2009

World’s smallest nuclear battery

Published on October 9th, 2009 | By: pwray@ceramics.org

Via a press release from University of Missouri, we learn that researchers are developing a nuclear battery that is smaller, lighter and more efficient. It is the size and thickness of a penny.

Jae Kwon, assistant professor of electrical and computer engineering at MU, who has been working on building a small nuclear battery, admits that people get the wrong idea when they hear the term “nuclear battery” and think of something hazardous. Although nuclear batteries generate electricity from atomic energy like nuclear reactors, they don’t use a chain reaction, instead using the emissions from a radioactive isotope to generate electricity. So there’s no risk of the battery in a pacemaker suffering a meltdown.

The battery being developed by Kwon and his research team, based on betavoltaic conversion technologies, is currently the size and thickness of a penny, and is intended to power various micro- and nanoelectromechanical systems. The team’s innovation is not only in the battery’s size, but also in its semiconductor, which is liquid rather than solid.

Kwon has been collaborating with J. David Robertson, chemistry professor and associate director of the MU Research Reactor, and is working to build and test the battery at the facility. In the future, they hope to increase the battery’s power, shrink its size and try various other materials. Kwon said that the battery could be thinner than the thickness of human hair.

“The critical part of using a radioactive battery is that when you harvest the energy, part of the radiation energy can damage the lattice structure of the solid semiconductor,” Kwon said. “By using a liquid semiconductor, we believe we can minimize that problem.”

In a paper in the July issue of the Journal of Applied Physics Letters, some of the betavoltaic liquid-semiconductor technology is explained:

The semiconductor property of selenium was utilized along with a 166 MBq radioactive source of 35S as elemental sulfur. Using a liquid semiconductor-based Schottky diode, electrical power was distinctively generated from the radioactive source. Energetic beta radiations in the liquid semiconductor can produce numerous electron hole pairs and create a potential drop. The measured power from the microbattery is 16.2 nW with an open-circuit voltage of 899 mV and a short-circuit of 107.4 nA.

In another paper to be published in the Journal of Radioanalytical and Nuclear Chemistry, Kwon and others describe even more of the details:

The specific energy density from radioactive decay is five orders of magnitude greater than the specific energy density in conventional chemical battery and fuel cell technologies. As a result, radioisotope micro‐power sources hold great promise for the development of small power sources with dimensions consistent with the miniaturization advances being made in microelectromechanical systems. While a number of conversion schemes can be employed in RIMS, betavoltaic conversion technologies are compatible with the semiconductor manufacturing processes used in MEMS. We are currently investigating the use of liquid semiconductors based betavoltaics as a way to avoid the radiation damage that occurs in solid state semiconductor devices due to non‐ionizing energy loss. Sulfur‐35 was selected as the isotope for the liquid semiconductor tests because it can be produced in high specific activity and because it is chemically compatible with liquid semiconductor media. Sulfur‐35 is a pure beta emitter with an average beta energy of 49 keV and a half‐life of 87.2 days. It was produced at the University of Missouri Research reactor via the 35Cl(n,p)35S reaction by irradiating potassium chloride discs in a thermal neutron flux of approximately 8×1013/cm2• second. A 150-hour irradiation produced on average 200 mCi per gram of KCl. The 35S was separated from the irradiated target and converted into elemental sulfur. The 35S was then mixed with selenium and incorporated into a liquid semiconductor device fabricated here at the University of Missouri.

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5 Responses to World’s smallest nuclear battery

  1. Robert says:

    I am very curious with regards to the expected product life path from cradle to grave. By that I mean how would you expect to design, produce, store, distribute, use, and dispose of the residual waste if any? I am sure that if you can accomplish what you have so far, I am very impressed and thanks for doing so, that you have considered all aspects of the products life. Thanks. Great work.

  2. John Kelly says:

    Brian, other stories put the shelf life (also the service is life) at decades, maybe centuries. Looks to me like the sulfur-35’s energy output drops about like a conventional carbon-zinc battery’s; if they pack in some extra when they build the battery and then regulate its final output, it could put out a consistent current for a very long time.

  3. Casey says:

    My thought’s exactly as to scaling up especially for electric cars, or even solar or wind on down times. But I realize that this is a fledgling technology and demand will drive it ASAP if it is really this efficient.

  4. brian says:

    Would someone please comment on what the half life of 87 days will do to the shelf life of the battery? If you were to use that battery in a pacemaker, would it provide power for very long? or did they use the Sulfur Isotope because it was compatible with their system?

  5. Derek says:

    Instead of scaling the technology down this far, why not come up with a reasonable size that can run an electric vehicle or, at least, recharge the vehicle’s main battery while parked?

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