A
beta emitter such as
technetium-99 or
strontium-90 is suspended in a
gas or
liquid containing
luminescent gas molecules of the
excimer type, constituting a "dust plasma". This permits a nearly lossless emission of beta
electrons from the emitting dust particles. The electrons then
excite the gases whose excimer line is selected for the conversion of the
radioactivity into a surrounding
photovoltaic layer such that a theoretical lightweight, low-pressure, high-efficiency
battery can be realized. (In practice, existing designs are heavy and involve high pressure.) These
nuclides are relatively low-cost
radioactive waste from
nuclear power reactors. The diameter of the dust particles is so small (a few micrometers) that the electrons from the
beta decay leave the dust particles nearly without loss. The surrounding weakly
ionized plasma consists of gases or gas mixtures (such as
krypton,
argon, and
xenon) with excimer lines such that a considerable amount of the energy of the beta electrons is converted into this light. The surrounding walls contain photovoltaic layers with wide
forbidden zones, such as
diamond, which convert the optical energy generated from the radiation into electrical energy. A German patent provides a description of an optoelectric nuclear battery, which would consist of an excimer of argon, xenon, or krypton (or a mixture of two or three of them) in a pressure vessel with an internal mirrored surface, finely-ground
radioisotope, and an intermittent
ultrasonic stirrer, illuminating a photocell with a
bandgap tuned for the
excimer. When the beta-emitting nuclides (e.g.,
krypton-85 or
argon-39) emit beta particles, they excite their own electrons in the narrow excimer band at a minimum of
thermal losses, so that this radiation is converted in a high-bandgap photovoltaic layer (e.g., in p-n diamond) very efficiently into electricity. The
electric power per weight, compared with existing radionuclide batteries, can then be increased by a factor 10 to 50 or more. If the pressure vessel is made from
carbon fiber/
epoxy, the
power-to-weight ratio is said to be comparable to an air-breathing engine with fuel tanks. The advantage of this design is that precision electrode assemblies are not needed, and most beta particles escape the finely-divided bulk material to contribute to the battery's net power.
Disadvantages • High price of the radionuclides. • High-pressure (up to 10 MPa or 100 bar) heavy containment vessel. • A failure of containment would release high-pressure jets of finely-divided radioisotopes, forming an effective
dirty bomb. The inherent risk of failure is likely to limit this device to space-based applications, where the finely-divided radioisotope source is only removed from a safe transport medium and placed in the high-pressure gas after the device has left Earth orbit. == As a DIY project ==