Radioisotope Power SourcesGrant MeadowsNovember 2015Modern Physics Fall 2015

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Outline• Describe the fundamentals of nuclear energy sources,

including the radioisotope power source (RPS)• Review radioactivity, the fundamental phenomena of

radioisotope power sources• Explain interactions of radiation with matter• Finally, conclude with the energy transfer mechanisms of

RPS’s

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Fundamentals of Nuclear Energy Sources• RPS uses heat from decay of radioactive elements to

generate electricity• Difference between nuclear fusion, nuclear fission, and

RPS’s:• Nuclear fusion uses the energy released from fusing (combining)

light elements, like hydrogen, into heavier elements, like helium• Although the sun is powered by nuclear fusion, no device on earth

has ever released more energy than consumed. Hence, they cannot be used to generate electricity yet

• Nuclear fission uses energy released by fissioning (breaking apart) uranium or plutonium to create heat for generating electricity• All commercial nuclear reactors use fission• Fission reactors produce radioactive elements, but only part of their

reaction process

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Nuclear Fusion, Fission

Fig 1: Nuclear fusion reactor. The Tokamak Reactor. Digital image. CEA Cadarache, n.d. Web. 22 Nov. 2015.

Fig 2: Nuclear fission reactor. Reactor Pulseat Texas A&M Nuclear Science Center. Digital image. Texas A&M University Nuclear Science Center, 03 Dec. 2013. Web. 22 Nov. 2015.

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Characteristics of RPS• The radioisotope power source is practical, unlike fusion,

yet cannot be turned on and off, unlike fission• Great application as a long-lasting, dependable, high

energy density supply of electricity• Can work in extreme environments and isolated locations

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Historical Use• Characteristics have historically created appeal for pacemakers and

NASA space missions• Examples of NASA space missions include all Apollo missions,

Viking 1 and 2, Voyager 1 and 2, Mars pathfinder, and New Horizons

Fig 3: Nuclear-Powered Cardiac Pacemaker. Digital image. The Off-Site Source Recovery Project. Los Alamos National Laboratory, n.d. Web. 22 Nov. 2015.

Fig 4: New Horizons Spacecraft RPS. PHOTO NO: KSC-05PD-2411. Digital image. John F. Kennedy Space Center.NASA, 04 Nov. 2005. Web. 22 Nov. 2015.

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What is Radioactivity?• Stable and radioactive elements throughout periodic table• Two charts are useful to understand radioactivity: Chart of

Stability, and Binding Energy Curve

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Chart of Stability and Binding Energy Curve

Fig 6: Binding Energy Curve. Digital image. Scienceblogs.com. Pearson Prentice Hall and University of Wisconsin Stevens Point, 2005. Web. 22 Nov. 2015.

Fig 5: Chart of StabilityBazin, Daniel. Nuclear Landscape. Digital image. Nature.com.Nature Publishing Group, 20 June 2012. Web. 22 Nov. 2015.

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Interactions of Radiation With Matter

• Alpha Particles- ionized Helium-4 particles interact through Coulomb Scattering• Coulomb Scattering involves transferring kinetic energy of He-

4 particles to electrons, which gradually slows them down• Beta Particles- positrons or electrons interact through

Coulomb Scattering with other electrons• Also interact through bremsstrahlung radiation, which are x-

rays emitted because of electrons decelerating

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Interactions of Radiation With Matter

• Gamma Rays- Interact through:• Photoelectric Absorption

• Photon is absorbed by atom, releases electron • Compton Scattering

• Photon scatters free electron, losing kinetic energy to it• Pair Production

• Photon disintegrates into an electron-positron pair, which annihilates soon after creation, leaving as two equal energy photons Gran

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Fuel Source Considerations• Lifetime of sources is proportional to half-life• For shielding purposes, gamma rays are difficult to shield, so

beta and alpha emitting isotopes are primarily used• Popular fuel sources:• Plutonium 238• Strontium 90

Fig 7: Plutonium 238Plutonium Pellet. Digital image.Department of Energy, 1997. Web. 22 Nov. 2015.

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Types of Radioisotope Power Sources• Radioisotope Thermoelectric Generator:

• Uses Seebeck Effect to generate current from hot and cold ends of two different elements. Heat comes from decay of particles

Fig 8: Seebeck Effect.Thermoelectrics. Digital image. Department of Physics. University of Oslo, 28 Nov. 2012. Web. 23 Nov. 2015.

Fig 9: Multi-Mission Radioisotope Thermoelectric Generator. Digital image. NASA, n.d.

Web. 23 Nov. 2015.

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Types of Radioisotope Power Sources• Stirling Cycle Radioisotope Generator:• Uses heat output to drive a mechanical device under the

Stirling Cycle, which moves a magnet to generate electricity

Fig 10: Stirling Radioisotope Generator.ASRG Labeled Cutaway. Digital image. Wikipedia. Wikimedia Commons, 26 Feb. 2012. Web. 23 Nov. 2015.

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Conclusion• Radioisotope power sources are different from nuclear fusion

and nuclear fission• RPS’s use the laws of radioactivity to generate electricity

through creative ways of harnessing heat production• Are great for long-lasting, high energy density, steady-power

applications

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Sources• Anderson, David, Wayne Wong, and Karen Tuttle. "An Overview and Status of NASA's

Radioisotope Power Conversion Technology NRA." 3rd International Energy Conversion Engineering Conference (2005): n. pag. Web.

• "Radioisotope Power Systems." NASA and Department of Energy, n.d. Web. 23 Nov. 2015.• Schmidt, George R., Robert L. Wiley, Rebecca L. Richardson, and Richard R. Furlong. "NASA's

Program for Radioisotope Power System Research and Development." AIP Conference Proceedings (2005): n. pag. Scitation.aip.org. Web. 23 Nov. 2015.

• Anderson, David J. "An Overview and Status of NASA's Radioisotope Power Conversion Technology NRA." Space Technology and Applications International Forum (2005): n. pag. Stanford University. NASA Glenn Research Center, Nov. 2005. Web. 23 Nov. 2015.

• Krane, Kenneth S., and David Halliday. Introductory Nuclear Physics. New York: Wiley, 1988. Print.

• "Nuclear-Powered Cardiac Pacemakers." Facts about Pacemakers. Los Alamos National Laboratory, n.d. Web. 23 Nov. 2015.

• United Nations. International Atomic Energy Agency. Vienna, Austria. Industrial Uses of Large Radiation Sources. Vol. II. Salzburg: Conference Proceedings, 1963. International Atomic Energy Agency. Web. 23 Nov. 2015.

• "Thermoelectrics." Department of Physics. University of Oslo, 28 Nov. 2012. Web. 23 Nov. 2015.• Lange, Robert G., and Wade P. Carroll. "Review of Recent Advances of Radioisotope Power

Systems." Energy Conversion and Management 49.3 (2008): 393-401. Web.

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