Betavoltaics are generators of electrical current, in effect a form of battery, which use energy from a radioactive source emitting beta particles (electrons). A common source used is the hydrogen isotope, tritium. Unlike most nuclear power sources, which use nuclear radiation to generate heat, which then generates electricity (thermoelectric and thermionic sources), betavoltaics use a non-thermal conversion process.
Betavoltaics are particularly well-suited to low-power electrical applications where long life of the energy source is needed, such as implantable medical devices or military and space applications.[1]
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History
Betavoltaics were invented over 50 years ago. "The first pacemakers used betavoltaics based on the radioactive element promethium, but these betavoltaics were phased out when cheaper lithium-ion batteries were developed."[1]
"Early semiconducting materials weren't efficient enough at converting electrons from beta decay into a usable current, so they had to use higher energy, more expensive--and potentially hazardous--isotopes. More efficient semiconducting materials can be paired with relatively benign isotopes such as tritium, which produce weak radiation."[1]
Applications
The primary use for betavoltaics is for remote and long-term use, such as spacecraft requiring electrical power for a decade or two. The recent progress in technology has prompted some to suggest using betavoltaics to trickle-charge conventional batteries in consumer devices, such as cell phones and laptop computers. As early as 1973, betavoltaics were suggested for use in long-term medical devices such as pacemakers.
Although betavoltaics use a radioactive material as a power source, the beta particles used are low energy and easily stopped by shielding, as compared to the gamma rays generated by more dangerous radioactive materials. With proper device construction (i.e.: shielding), a betavoltaic device would not emit any dangerous radiation. Leakage of the enclosed material would of course engender health risks, just as leakage of the materials in other types of batteries leads to significant health and environmental concerns.
Drawbacks
Betavoltaic devices suffer internal damage to their components as a result of the energetic electrons.[citation needed] Additionally, as the radioactive material emits, it slowly decreases in activity (refer to half-life). Thus, over time a betavoltaic device will provide less and less power. For practical devices, this decrease occurs over a period of many years. For tritium devices, the half-life is 12.32 years. In device design, one must account for what battery characteristics are required at end-of-life, and ensure that the beginning-of-life properties take into account the desired usable lifetime.
Liability connected with environmental laws and human exposure to tritium and its beta decay must also be taken into consideration during risk assessment and product development. Naturally, this increases both time-to-market and the already high cost associated with tritium. A 2007 report by the UK government's Health Protection Agency Advisory Group on Ionizing Radiation declared the health risks of tritium exposure to be double those previously set by Sweden's International Commission on Radiological Protection.[2]
See also
- Atomic battery
- Optoelectric nuclear battery
- Radioisotope thermoelectric generator
- Radioisotope piezoelectric generator
References
- ^ a b c A 25-Year Battery: Long-lived nuclear batteries powered by hydrogen isotopes are in testing for military applications, Katherine Bourzac, Technology Review, MIT, 17 Nov 2009.
- ^ Olsen, L.C. (December 1973). "Betavoltaic energy conversion". Energy Conversion (Elsevier Ltd.) 13 (4): 117–124, IN1, 125-127. doi: .