The source of energy in nuclear batteries is radiation from radioactive atoms. Several methods are used to convert nuclear energy into electrical energy in batteries.
Beta particles are electrons emitted from the nuclei of atoms. The emitter in a beta-emission battery is a source of pure beta particles, such as hydrogen 3, krypton 85, or strontium 90. As the electrons leave the emitter, they pass through a vacuum or a relatively unreactive material, such as plastic. Some of the electrons strike a collector made of carbon, and enter a circuit. Direct beta-emission batteries produce extremely high voltages (up to 500 volts or more) with extremely low current. They are used to charge capacitors.
use radioactivity to produce light, which in turn produces electric currents in photovoltaic cells. In one type, promethium 147, a radioactive byproduct of nuclear fission, is mixed with a phosphor and encased in transparent plastic. Electrons given off by the promethium cause the phosphor to glow, just as electrons in a television picture tube cause phosphors on the screen to glow. The light strikes a photovoltaic cell, which transforms the light into electrical current.