The nuclear energy source that powers the Perseverance rover on Mars is a radioisotope thermoelectric generator, or RTG. This uses 5kg (11lbs) of plutonium dioxide to generate electricity by a process known as the ‘Seebeck effect’.
The RTG on board Perseverance originally produced about 110W of electricity, declining by a few per cent each year, as the plutonium gradually decays.
RTGs are a great way to power distant space probes, but plutonium-238 is highly toxic and definitely not something that you would want in domestic gadgets.
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Luckily, the batteries recently developed by Chinese manufacturer Betavolt use a completely different process. Some radioactive isotopes decay by beta-emission, which means that they give off electrons.
If you sandwich thin layers of such an isotope between layers of semiconductor, you can catch the electrons and turn them into useful electricity.
Betavoltaic batteries based on the rare element promethium were used in some early heart pacemakers in the 1970s, but were phased out in favour of cheaper lithium batteries.
The newer Betavolt batteries use the isotope nickel-63 between layers of diamond semiconductor.
The power output is quite small – just 100 micro watts compared to around 2.4W for an ordinary AA battery. But the AA battery will be flat after an hour of this output, whereas a Betavolt battery is claimed to be able to deliver a useful voltage for 50 years.
That’s because nickel-63 decays quite slowly with a half-life of 101 years.
Betavoltaic batteries are pretty safe because electron emission is less damaging to living tissue than alpha particles or gamma rays, and the electrons are easily blocked by the metal of the battery case or even clothes.
You would need to break the battery open and swallow it to cause any harm. The radioactive nickel eventually decays to non-radioactive copper.
This article is an answer to the question (asked by Will Steadman, Chester) 'What is a nuclear battery and how does it work?'
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