Betavoltaic device

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This article is about devices that generate electricity directly from beta particles. For devices that use photocells, see optoelectric nuclear battery.

A betavoltaic device (betavoltaic cell or betavoltaic battery) is a type of nuclear battery which generates electric current from beta particles (electrons) emitted from a radioactive source, using semiconductor junctions. A common source used is the hydrogen isotope tritium. Unlike most nuclear power sources which use nuclear radiation to generate heat which then is used to generate electricity, betavoltaic devices use a non-thermal conversion process, converting the electron-hole pairs produced by the ionization trail of beta particles traversing a semiconductor.<ref name=tr20091109>Katherine Bourzac (2009-11-17). "A 25-Year Battery: Long-lived nuclear batteries powered by hydrogen isotopes are in testing for military applications". Technology Review. MIT. Archived from the original on 2012-01-19.</ref>

Betavoltaic power sources (and the related technology of alphavoltaic power sources<ref>NASA Glenn Research Center, Alpha- and Beta-voltaics Archived 2011-10-18 at the Wayback Machine (accessed October 4, 2011)</ref>) 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.<ref name="tr20091109" />

History

Betavoltaics were invented in the 1970s.<ref>"Review and Preview of Nuclear Battery Technology". large.stanford.edu. Retrieved 2018-09-30.</ref> Some pacemakers in the 1970s used betavoltaics based on promethium,<ref name=olsen1973>Olsen, L.C. (December 1973). "Betavoltaic energy conversion". Energy Conversion. Elsevier Ltd. 13 (4): 117–124, IN1, 125–127. doi:10.1016/0013-7480(73)90010-7.</ref> but were phased out as cheaper lithium batteries were developed.<ref name="tr20091109"/>

Early semiconducting materials weren't efficient at converting electrons from beta decay into usable current, so higher energy, more expensive—and potentially hazardous—isotopes were used. The more efficient semiconducting materials used as of 2019<ref>Maximenko, Sergey I.; Moore, Jim E.; Affouda, Chaffra A.; Jenkins, Phillip P. (December 2019). "Optimal Semiconductors for 3H and 63Ni Betavoltaics". Scientific Reports. 9 (1): 10892. Bibcode:2019NatSR...910892M. doi:10.1038/s41598-019-47371-6. ISSN 2045-2322. PMC 6659775. PMID 31350532.</ref> can be paired with relatively benign isotopes such as tritium, which produce less radiation.<ref name="tr20091109"/>

The Betacel was considered the first successfully commercialized betavoltaic battery.

Proposals

The primary use for betavoltaics is for remote and long-term use, such as spacecraft requiring electrical power for a decade or two. Recent progress has prompted some to suggest using betavoltaics to trickle-charge conventional batteries in consumer devices, such as cell phones and laptop computers.<ref>"betavoltaic.co.uk". Archived from the original on 31 December 2019. Retrieved 21 February 2016.</ref>[unreliable source?] As early as 1973, betavoltaics were suggested for use in long-term medical devices such as pacemakers.<ref name=olsen1973/>

In 2018 a Russian design based on 2-micron thick nickel-63 slabs sandwiched between 10 micron diamond layers was introduced. It produced a power output of about 1 μW at a power density of 10 μW/cm³. Its energy density was 3.3 kWh/kg. The half-life of nickel-63 is 100 years.<ref>Bormashov, V.S.; Troschiev, S.Yu.; Tarelkin, S.A.; Volkov, A.P.; Teteruk, D.V.; Golovanov, A.V.; Kuznetsov, M.S.; Kornilov, N.V.; Terentiev, S.A.; Blank, V.D. (April 2018). "High power density nuclear battery prototype based on diamond Schottky diodes". Diamond and Related Materials. 84: 41–47. Bibcode:2018DRM....84...41B. doi:10.1016/j.diamond.2018.03.006.</ref><ref>"Prototype nuclear battery packs 10 times more power". Moscow Institute of Physics and Technology. Archived from the original on 2020-10-27. Retrieved 2020-09-01.</ref><ref>Irving, Michael (June 3, 2018). "Russian scientists pack more power into nuclear battery prototype". newatlas.com. Retrieved 2018-06-14.</ref>

In 2019 a paper indicated the viability of betavoltaic devices in high-temperature environments in excess of 733 K (460 °C; 860 °F) like the surface of Venus.<ref name="oconnor2019">O'Connor, Andrew; Manuel, Michele V.; Shaw, Harry (November 2019). "An extended-temperature, volumetric source model for betavoltaic power generation". Transactions of the American Nuclear Society. 121: 542–545. doi:10.13182/T30591. PMC 8269951. PMID 34248155.</ref>

A prototype betavoltaic battery announced in early 2024 by the Betavolt company of China contains a thin wafer providing a source of beta particle electrons (either Carbon-14 or nickel-63) sandwiched between two thin crystallographic diamond semiconductor layers.<ref name=NA>"Betavolt says its diamond nuclear battery can power devices for 50 years". David Szondy for New Atlas, 16 January 2024. Accessed 17 January 2024.</ref><ref>"贝塔伏特公司成功研制民用原子能电池" ('Betavolt successfully develops atomic energy battery for civilian use'), on Betavolt website (in Chinese). Accessed 17 January 2024.</ref> The Chinese startup claims to have the miniature device in the pilot testing stage.<ref name=AC>Anthony Cuthbertson (12 January 2024). "Nuclear battery produces power for 50 years without needing to charge". The Independent. Retrieved 14 January 2024.</ref> Unveiled in January 2024, it is allegedly generating 100 microwatts of power and a voltage of 3V and has a lifetime of 50 years without any need for charging or maintenance.<ref name=AC/> Betavolt claims it to be the first such miniaturised device ever developed.<ref name=AC/> It gains its energy from a sheet of nickel-63 located in a module the size of a very small coin.<ref name=NA/><ref name=AC/> Once the decay period has passed, the isotopes turn into stable, non-radioactive isotopes of copper, which pose no environmental threat.<ref name=AC/>

Drawbacks

As radioactive material emits radiation, it slowly decreases in activity (refer to half-life). Thus, over time a betavoltaic device will provide 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 in 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 the International Commission on Radiological Protection located in Sweden.<ref>Edwards, Rob (29 November 2007). "Tritium hazard rating 'should be doubled'". NewScientist.</ref>

As radioactive decay cannot be stopped, sped up or slowed down easily, there is no way to "switch off" the battery or regulate its power output. For some applications this is irrelevant, but others will need a backup chemical battery to store energy when it isn't needed for when it is. This reduces the advantage of high power density.

Availability

Betavoltaic nuclear batteries can be purchased commercially. Devices available as per 2012 included a 100 μW tritium-powered device weighing 20 grams<ref>"Commercially-available NanoTritium battery can power microelectronics for 20+ years". New Atlas. 2012-08-16. Retrieved 2020-09-01.</ref>

Safety

Although betavoltaics use a radioactive material as a power source, the beta particles are low energy and easily stopped by a few millimetres of shielding. With proper device construction (that is, proper shielding and containment), a betavoltaic device would not emit dangerous radiation. Leakage of the enclosed material would engender health risks, just as leakage of the materials in other types of batteries (such as lithium, cadmium and lead) leads to significant health and environmental concerns.<ref>Maher, George (October 1991). "Battery Basics". County Commissions, North Dakota State University and U.S. Department of Agriculture. North Dakota State University. Retrieved August 29, 2011.</ref> Safety can be further increased by transforming the radioisotope used into a chemically inert and mechanically stable form, which reduces the risk of dispersal or bioaccumulation in case of leakage.

Efficiency

Due to the high power density of radioisotopes and the need for reliability above all else in many applications of betavoltaics, comparatively low efficiencies are acceptable. Current technology allows for single digit percentages of energy conversion efficiency from beta particle input to electricity output, but research into higher efficiency is ongoing.<ref>"Betavoltaic Devices".</ref><ref>Sachenko, A. V.; Shkrebtii, A. I.; Korkishko, R. M.; Kostylyov, V. P.; Kulish, M. R.; Sokolovskyi, I. O. (1 September 2015). "Efficiency analysis of betavoltaic elements". Solid-State Electronics. 111: 147–152. arXiv:1412.7826. Bibcode:2015SSEle.111..147S. doi:10.1016/j.sse.2015.05.042. S2CID 94359293.</ref> By comparison thermal efficiency in the range of 30% is considered relatively low for new large scale thermal power plants and advanced combined cycle power plants achieve 60% and more efficiency if measured by electricity output per heat input.<ref>"The Most Efficient Thermal Power Generation Plants in America".</ref> If the betavoltaic device doubles as a radioisotope heater unit it is in effect a cogeneration plant and achieves much higher total efficiencies as much of the waste heat is useful. Similar to photovoltaics, the Shockley–Queisser limit also imposes an absolute limit for a single bandgap betavoltaic device.<ref>Maximenko, Sergey I.; Moore, Jim E.; Affouda, Chaffra A.; Jenkins, Phillip P. (26 July 2019). "Optimal Semiconductors for 3H and 63Ni Betavoltaics". Scientific Reports. 9 (1): 10892. Bibcode:2019NatSR...910892M. doi:10.1038/s41598-019-47371-6. PMC 6659775. PMID 31350532.</ref>

Ultimate efficiency

Since the highest energy that can possibly be extracted from a single EHP is the bandgap energy, the ultimate efficiency of a beta-battery can be estimated as:

<math>\eta_{max}={E_g \over E_{EHP}}</math>

where <math display="inline">E_g</math> and <math display="inline">E_{EHP}</math> are semiconductor band gap and electron-hole pair creation eneregy respectively. The energy to generate a single EHP by a beta-particle is known to scale linearly with the bandgap as <math display="inline">E_{EHP}=AE_g+B</math> with A and B depending on the semiconductor characteristics.<ref>Evstigneev, Mykhaylo; Afkani, Mohammad; Sokolovskyi, Igor (November 2023). "Limit Efficiency of a Silicon Betavoltaic Battery with Tritium Source". Micromachines. 14 (11): 2015. doi:10.3390/mi14112015. ISSN 2072-666X. PMC 10673167. PMID 38004872.</ref>

See also

References

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External links

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Betavoltaic device
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