The atomic battery, also known as a nuclear battery or radioisotope thermoelectric generator (RTG), is a power source that uses the energy released from the decay of a radioactive isotope to generate long-lasting electricity. Unlike chemical batteries, this technology harnesses nuclear energy without initiating a chain reaction. This allows atomic batteries to provide a continuous, reliable flow of power for decades without the need for recharging or maintenance. They are valued for their high energy density and longevity, making them suitable for specialized, long-term applications.
How the Atomic Battery Generates Electricity
The most common type of atomic battery, the Radioisotope Thermoelectric Generator (RTG), converts heat directly into electrical energy. This process begins with the radioactive decay of an isotope, such as Plutonium-238 or Strontium-90. The decay releases high-energy particles, which are absorbed by surrounding materials, generating heat.
This heat is converted into electricity using solid-state components called thermocouples. Thermocouples operate based on the Seebeck effect, where a voltage is produced across two different electrical conductors when there is a temperature difference between their junctions. In an RTG, the heat from the radioactive source creates a hot junction, while the exterior casing acts as the cold junction.
The temperature difference drives the flow of electrons, generating a steady electric current. Materials like silicon-germanium or lead telluride are used in the thermocouples because they are efficient at converting this thermal gradient into electricity. Although the conversion efficiency is relatively low, typically between 5% and 10%, the continuous nature of the heat source ensures decades of uninterrupted power.
The Conceptual Origin of Nuclear Power Sources
The theoretical foundation for harnessing radioactive decay to produce power dates back to the early 20th century. British physicist Henry Moseley first demonstrated this possibility in 1913, long before a practical device was developed. Moseley’s experiment involved a radium source that emitted charged particles, which he used to generate a measurable current.
His work showed that the kinetic energy of particles emitted during radioactive decay could be directly converted into electrical energy. This initial demonstration, a non-thermal conversion method, is sometimes referred to as the first atomic battery. This early experiment provided a proof of concept for nuclear power sources, but the idea remained a theoretical curiosity until advancements in material science and nuclear technology made practical devices possible.
The Scientists Who Built the First Working Devices
The transition from theory to a functioning prototype occurred in the mid-1950s.
Early Betavoltaic Systems
In 1954, Paul Rappaport and his team at RCA Laboratories developed a device that used beta particles from the radioactive isotope Strontium-90 to bombard a semiconductor p-n junction. This process, known as a betavoltaic system, was a non-thermal conversion method that released enough electrons to operate a transistor. RCA’s successful thimble-sized battery was projected to run for up to 20 years.
The SNAP Program and RTGs
The most widely adopted design, the RTG, was simultaneously developed by government programs. The US Atomic Energy Commission (AEC) spearheaded the System for Nuclear Auxiliary Power (SNAP) program, which began in 1955. The odd-numbered models within the SNAP series, starting with SNAP-3, were the first deployable RTGs. SNAP-3, unveiled in 1959, was a small, five-pound generator that used a capsule of Polonium-210 to heat twenty lead telluride thermocouples. This design, a collaboration between The Martin Company and the Minnesota Mining & Manufacturing Co., produced a few watts of power for months. This development established the RTG design that would become standard for space exploration.
Primary Uses in Space and Medicine
Atomic batteries are indispensable due to their high energy density and long operational lifespan. In space exploration, they are the primary power source for spacecraft venturing far from the sun, where solar panels are impractical.
Space missions relying on RTGs include:
- The Voyager probes, launched in 1977, which continue to operate and send data from interstellar space.
- The Curiosity and Perseverance Mars rovers, which use Multi-Mission Radioisotope Thermoelectric Generators (MMRTGs) to power instruments and survive frigid Martian nights.
The reliability of these generators is demonstrated by the fact that no RTG has failed in over two dozen space missions. Atomic batteries also found a niche in the medical field, particularly in early cardiac pacemakers during the 1970s. These devices used isotopes like Plutonium-238 or Promethium-147 to power the pacemaker for a patient’s lifetime, eliminating the need for repeated battery replacement surgeries. While eventually replaced by more advanced chemical batteries, their use proved the viability of radioisotope power for long-term, low-power applications.