Gamma ray driven photovoltaic cells: an interface between nuclear and semiconductor physics

We explore the possibility of utilizing low energy gamma-photon radiation from single or multiple radioactive sources, for the production of electron-hole pairs in the semiconductors of photovoltaic cells. Our aim is to produce and store electric energy using this mechanism. The radioactive sources in the GRPVC (gamma ray photovoltaic cell) can be either naturally occurring or manufactured nuclear isomers. The gamma-photon intensity can be controlled, hence the output and efficiency can also be controlled. A spherical GRPVC of 40 cm diameter, with the nuclear isomer Th*-229 (E-gamma = 3.5 eV, T-1/2 = 45 h) can produce a maximum open circuit voltage V-ocmax = 2.626 V, at maximum efficiency eta(max) = 52.2% initially, which occurs when the semiconductor energy gap, E-g, equals the gamma-photon energy, E-gamma. This reduces to the lower value V-oc = 0.5 V at eta = 12% after 188 days. The ultimate efficiency for the GRPVC studied here is about 70%, which occurs for E-g = E-gamma similar to 10 eV, and is above 40% for E-g = E-gamma (with E-gamma >= 3 eV). It is also shown that nuclear isomers with long half-life can keep the GRPVC operating at high Voc and high efficiency levels for many decades, and even for centuries.