- Here's a story that's doing the rounds on the blogs -
Scientists Invent 30 Year Continuous Power Laptop Battery.
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- The story is written in peculiarly convoluted prose,
but appears to be saying that a breakthrough in nuclear energy technology
means that we'll all be running around with magic batteries in mobile and
laptop, in "two to three years". They'll be perfectly safe, will
save the world, and will probably last longer than you will.
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- Sadly, no. As with the best techno-rubbish, there is
a story in there, but you'll be pootling around the skies in jetpacks before
you're powering your Dell from neutron decay.
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- That story is betavoltaics. This is a way of generating
electricity much as solar cells generate power from photons, only by using
high energy electrons generated from the beta decay of certain radio-isotopes.
If you pick your isotope well -- the examples given use tritium, a radioactive
form of hydrogen - the other decay products are inert, and in theory you
can generate useful amounts of power for a reasonable length of time. As
with every radioactive system, it has a half-life depending on the isotope;
tritium's half-life is around twelve years, so every decade or so your
battery will halve in power - but that won't change, no matter how little
or much power you take out in the duration.
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- Beats Duracell, right?
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- Again, sadly, no. There are a few small problems.
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- One is that the sort of atomic structures that generate
power when bombarded with high energy electrons are the sort that tend
to fall apart when bombarded with high energy electrons. While solar cells
have the same problem, it's to a much lesser extent. There's a lot of research
into making materials that don't suffer so much, but it remains a serious
issue.
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- Secondly, while it's true that a tritium-powered battery
will eventually turn into an inert, safe lump of nothing much, and while
it's also true that a modest amount of shielding will keep the radioactivity
within the battery the while, there's the small problem that if you break
the battery during its life the nasties come out.
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- Thirdly, they don't have a great conversion efficiency.
Around 25 percent is the best you can get - which is pretty good, but leaves
75 percent sloshing around as heat. That means a 25 watt battery will get
plenty warm.
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- Lastly, they're not very good batteries. Even the latest
devices, which are very clever in the way they saturate a porous structure
with the gas and thus usefully capture quite a large number of the energetic
electrons, have an energy density of the order of twenty five watts per
kilo. Lithium ion batteries, the sort you have in your laptop, manage 1.8
kilowatts per kilo. That's 72 times more bang per gram. Do you fancy carrying
a battery 72 times heavier than the one you have at the moment, especially
if it's hotter than a sixty watt light bulb?
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- Which is not to say that betavoltaics aren't useful.
There are some interesting ideas for using small betavoltaic cells to constantly
trickle charge more conventional batteries, which helps circumvent some
of the capacity issues.
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- And there are plenty of places where it's difficult or
dangerous to have to change or recharge the power source, and many of those
only need small amounts of juice.
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- Those places do not currently include your lap. You may
possibly be relieved to hear this.
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