University of Missouri researchers are developing a nuclear energy source that is smaller, lighter and more efficient. Jae Kwon, assistant professor of electrical and computer engineering at MU. “The radioisotope battery can provide power density that is six orders of magnitude higher than chemical batteries.” The nuclear batteries are providing power for a decade or more. There are various radiation sources for energy levels of watts to kilowatts. Higher power levels would tend to need radiation shielding. The smaller devices would provide a fraction of a watt, but again last for a decade.
The Navy thinks it is feasible to scale liquid nuclear batteries to the 100 kw to 1 MW levels. For that kind of application, you could have the radiation shielding.
Kwon and his research team have been working on building a small nuclear battery, currently the size and thickness of a penny, intended to power various micro/nanoelectromechanical systems (M/NEMS). Although nuclear batteries can pose concerns, Kwon said they are safe.
“People hear the word ‘nuclear’ and think of something very dangerous,” he said. “However, nuclear power sources have already been safely powering a variety of devices, such as pace-makers, space satellites and underwater systems.”
His innovation is not only in the battery’s size, but also in its semiconductor. Kwon’s battery uses a liquid semiconductor rather than a solid semiconductor.
“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.”
Jae Kwon's recent paper submitted to the 15th International Conference on Solid-State Sensors, Actuators and Microsystems was awarded the honor of being selected as "outstanding paper"
"The hard part of using radioactive decay is that when you harvest the energy, part of that energy goes towards creating defects that damage a solid-state semiconductor," Robertson, associate director of the research reactor, said. "Our hypothesis is that with a liquid-state semiconductor, the same damage won't happen. So we created a battery without that part degrading over time."
A long-lived power source not much larger than a MEMS device could be a hot property in the MEMS manufacturing industry. But Kwon says that there is "a long way to go" before his battery is ready for commercial marketing.
"Not necessarily in terms of a long time, but we have a lot of work before it is ready for industry. At this moment, we're still at the fundamental research level," he said.
Kwon, Robertson and their team are currently focused on increasing the power output and shrinking the size of the battery even further - among other things, they are exploring using other materials besides the sulfur-35 isotope they are currently using. They've also filed for a provisional patent.
"In the future, the battery can be thinner than the thickness of a human hair," Kwon said.
The research papers of the MEMS group at the University of Missouri
D. Meier, A. Garnov, J.D. Robertson, T. Wacharasindhu and J.W. Kwon, "Production of 35S for a Liquid Semiconductor Betavoltaic," Journal of Radioanalytical and Nuclear Chemistry, in-print.
PRODUCTION OF 35S FOR A LIQUID SEMICONDUCTOR BETAVOLTAIC.
Meier, D.(1,2), Garnov, A.(2), Robertson, J.D.(1,2) Wacharasindhu, T.(3) Kwon,
J.W.(3) 1. Department of Chemistry 2. Research Reactor 3. Department of Electrical
Engineering University of Missouri‐Columbia.
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 (RIMS) hold great promise for the development of small power sources with dimensions consistent with the miniaturization advances being made in microelectromechanical (MEMS) 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 (NIEL). 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 8x10^13 s‐1·cm‐2. 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. Results of the separation chemistry and device testing will be presented.
R. Almeida and J.W. Kwon, "Evaporation Controlled Ejeection with Thin Liquid-Film-Based Micorofluidic Valve," International Conference on Miniaturized Systems for Chemistry and Life Sciences, (South Korea), Nov. 1-5, 2009, Accepted.
C. Kirkendall and J.W. Kwon, "Liquid Damping Isolation on Quartz Crystal Microbalance for Effective Preservation of High Q and Sensitivity in Liquid," IEEE Conference on Sensors, (New Zealand), Oct. 25-28, 2009, Accepted.
T. Wacharasindhu, J.W. Kwon,D. Meier, and J.D. Robertson, "Radioisotope Microbattery Based on Liquid Semiconductor," Journal of Applied Physics Letters, 95, 014103, 2009.
A liquid semiconductor-based radioisotope micropower source has been pioneerly developed. 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.
T. Wacharasindhu, J.W. Kwon, D.E. Meier, and J.D. Robertson, "Liquid-Semiconductor-Based Micro Power Source Using Radioisotope Energy Conversion," IEEE International Conference on Solid-State Sensors, Actuators and Microsystems, (Denver, CO), June 21-25, 2009, pp656-659.
D.E. Meier, Alex Garnov, J.D. Robertson, T. Wacharasindhu and J.W. Kwon, "Production of 35S for A Liquid Semiconductor Betavoltaic," International Conference on Methods and Applications of Radioanalytical Chemistry (Kailua-kona, HI), April 5-10, 2009.
T. Wacharasindhu and J.W. Kwon, "Liquid Semiconductor Diode as a Thermal Harvester for High Temperature Applications," PowerMEMS"08, (Sendai, Japan), Nov9-12, 2008, pp. 53-56
Jae Kwon faculty page at University of Missouri
Introduction to Nuclear Batteries-Betavoltaics
A collection of links on betavoltaics.