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"Nuclear lightbulb" creates electricity.

University of Missouri-Columbia nuclear engineers successfully have used diamond film to craft an electrical cell that directly converts nuclear energy to electricity and allows the development of portable nuclear power sources. The cell is the key to a process known as the nuclear lightbulb, which would produce electricity at least twice more efficiently than now possible. The process is being worked on by a research team led by Mark Prelas, professor of nuclear engineering, who first proposed the project in 1981. It will bypass the intermediate steps in the current power generation process whereby nuclear radiation first is converted to heat, which generates steam to turn a turbine that then drives a generator.

"Although there has been some research in high-bandgap semi-conductors, [the University of Missouri] is the only research center in the world developing high-bandgap photovoltaic cells for nuclear energy conversion," Prelas points out. "The technology could be used to power spacecraft or lasers, to run remote railroad crossings, or to provide a portable source of power. It could even be used to create useful chemicals such as hydrogen, which has been suggested as a possible alternative fuel for automobiles."

To conduct electricity, a material's electrons must be energized, or heated, in orderto reach the level of the material's "conduction band" from a "valence" band of lower energy levels that are filled with electrons. "Bandgap" refers to the difference between the valence and conduction bands. With the nuclear lightbulb, charged particles from the nuclear reaction excite a gas such as argon or xenon, both of which emit light in the ultraviolet range. Sodium, potassium, or mercury, which emit light in the blue to green range, also can be used. The ultraviolet or bluegreen radiation then activates the photovoltaic cell to produce energy.

If the bandgap is low, meaning the valence and conduction bands are close together, less energy is required for the material to conduct electricity. For instance, copper's bandgap is near zero because the conduction and valence bands touch each other. No extra heat is necessary for copper to conduct electricity. However, silicon's bandgap is in a middle range. It is called a "semi-conductor" because it conducts at high, but not at low, temperatures.

If the bandgap is high, such as in a diamond, much more energy is needed to conduct electricity. Because high-bandgap materials need high energy, they work well with the high-energy light emitted by the nuclear lightbulb, and much less of the energy produced by the nuclear lightbulb is wasted than when heating a lower-bandgap material.

The portable power source technology could employ either fissile or fusion fuels or radioisotopes from spent nuclear fuel. Specifically, the latter possibility would utilize gaseous isotopes that would be safe for human use because their radiation disperses quickly and, because they are inert, are not ingestible by the human body.

In addition, within 20 years, similar high-bandgap technology could form the basis for a new type of solid-state electronics. Research that focuses on semi-conductors made of diamonds and other high-bandgap materials is being done by other countries and by the military.
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Publication:USA Today (Magazine)
Date:Jun 1, 1993
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