Energy diagram of photoexcitation and thermalization processes. Photoexcitation and thermalization processes initiated by gamma-ray and beta particles from radioactive materials increase the conduction band population, creating a large thermionic current. The thermal energy generated by radioactive coupling and decaying processes is converted by the TE device. (Image: NASA)

Innovators at the NASA Langley Research Center have developed the Multi-Layer Nuclear Thermionic Avalanche Cell (NTAC), a novel electrical generator, which transforms nuclear gamma-ray photon energy directly to electric power by liberating intra-band atomic inner shell electrons.

The invention consists of several NTAC layers arranged in a radially concentric series separated by a vacuum gap space. It is comprised of a gamma-ray source and various layers of emitters, collectors, and insulators. Ideal emitter materials include elements with high atomic numbers, while ideal collector and insulator materials include elements with low atomic numbers.

A high-energy gamma-ray (tens of keV to MeV) is used to liberate a large number of intra-band, inner-shell electrons from atoms within the emitter material for power generation through the primary interactions of photoelectric, Compton scattering, photonuclear, and electron/positron pair production processes. Secondary and tertiary electrons are liberated in the avalanche process as well.

If a power conversion process effectively utilizes all liberated electrons in an avalanche mode through a power conversion circuit, the power output is drastically increased. Because power conversion is determined by the absorption rate of high energy photons, increasing power output requires either thicker collector material or a sufficient number of layer structures to capture the high energy photons, leaving no liberated electrons escaping (i.e., minimizing the leak of radioactive rays).

The selection of materials, the thicknesses of the emitter, collector, and insulator, as well as the number of NTAC layers required are all determined by the energy of photon source. The thermal energy from radioactive decay can also be converted to electricity using a thermoelectric device to further increase power output.

The Multi-Layer NTAC technology can be manufactured using existing semiconductor fabrication technology and can be tailored for small-to-large scale power needs, including kilowatt and megawatt applications.

The device provides a compact, reliable, and continuous electrical source with high power density capable of long-life operation without refueling. The Multi-Layer NTAC is based on previous work at NASA in which a single emitter device captured high energy photons; use of a multi-layer structure greatly improves the performance of the electrical generator.

Applications include power for systems on small satellites, drones, commercial airliners, spacecraft, electric vehicles, long-lived nuclear batteries, and others.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .