Multi-Layer Nuclear Thermionic Avalanche Cell

The Multi-Layer NTAC 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. Innovators at the NASA Langley Research Center (LaRC) 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. A large number of electrons liberated within the emitter material are emitted from the surface, which has a tightly spaced array of nanometer-scale emitter points. Liberated electrons go across the vacuum gap and arrive at the collector to efficiently convert energy derived from radioactive materials into usable electricity. 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 LaRC in which a single emitter device captured high energy photons; use of a multilayer structure greatly improves the performance of the electrical generator.