Hey Dr. Zoomie – what’s with this C-14 powered battery I just read about? Is this for real? Won’t that be sort of dangerous for the folks using them? I know “atomic batteries to power” was part of the startup procedure for the Batmobile – but that was just a comic book/TV show.
Well…one way to use radioactive material to produce energy is to harvest the heat generated by radioactive decay in a radio-isotopic thermal generator (RTG) usually sent into the outer Solar System on space probes. But those use plutonium, not carbon-14 – not what you read about. So for starters I did a search and found a few promising-looking articles online:
- https://ccfe.ukaea.uk/diamonds-are-forever-worlds-first-carbon-14-diamond-battery-produced/
- https://interestingengineering.com/energy/worlds-first-carbon-14-diamond-battery
- https://www.newsweek.com/diamond-battery-carbon-14-radioactive-decay-first-1996250
- https://www.popularmechanics.com/science/green-tech/a63108297/diamond-battery/
These give enough information to answer part of your question, although it’s not completely clear tome how the battery generates electricity – I’ll get to that in a few minutes, but let’s start with the easy part – the radiation safety bit.
Carbon-14 emits relatively low-energy beta radiation. The low energy part means that the beta particles can’t penetrate through much material and it doesn’t pack much of a punch. So with a battery of any size, most of the beta radiation will be absorbed by the materials making up the battery itself, and the betas that escape from the battery won’t have enough energy to penetrate beyond the outermost layers of skin. Although, having said that, even those could be shielded completely simply by encasing the battery in a thin plastic case. And since the C-14 atoms are part of the diamond (pure diamond is 100% carbon), there’s no need to worry about contamination. So these batteries don’t seem to create a big radiation safety problem. Oh – and the C-14 comes from radioactive waste, so this is also a great way to get some use out of what would otherwise cost a lot of money for disposal. So there’s that! Having said that, any source with more than 100 microCuries of C-14 requires a radioactive materials license unless the source is exempt from regulation (under 10 CFR30.71) – so there’s that.
The battery itself doesn’t produce much energy – not enough (for example) to run a watch, let alone a car or a home. But it does produce enough energy to run small-scale electronics and, since C-14 has a half-life of over 5700 years, it will run them for millennia without needing recharging.
All that being said – let’s talk a little about how the batteries work!
In the aughts (around 2005 or so) I was involved in a project to develop “alpha-voltaic” power cells to generate energy for deep-space missions. What these did was to interleave an alpha-emitting radionuclide (e.g. Am-241) with a scintillator – zinc sulfide for alpha emitters. So the Am-241 would give off an alpha particle that would interact with the zinc sulfide, emitting light (photons) when it did so. Those photons were then absorbed by a photocell, producing electrical current. Beta-voltaics work the same way, except that they interact with a plastic material such as anthracene that produces light (photons) when beta radiation strikes it. Those photons are absorbed by the photocells where they produce electricity, the same as with a rooftop solar energy setup.
While I haven’t played with beta scintillators, I have had a chance to play with alpha scintillators – they give off a pretty purplish glow when alpha particles are striking them. And I’ve seen the bluish-purple bremsstrahlung from spent reactor fuel. I’m imagining that the photons given off from beta and gamma radiation are the same – or at least close enough.
But they might not work that way…. The Popular Mechanics article says that the diamond batteries “capture fast-moving electrons from radioactive decay,” which suggests a different mechanism – that makes it sound as though the beta particles themselves (beta radiation consists of high-energy electrons emitted from the nucleus of unstable atoms) might be harnessed to create a small electrical current. Or maybe that they harness the electrons knocked off of atoms by the ionization process. For these to make sense we need to remember that electrical current is measured in terms of electrical charges flowing through a circuit and wattage (or, in this case, micro-wattage) is a measure of the energy of those electrons. And it doesn’t matter where those electrons come from – from ionization or from beta decay or from the chemical reactions that power most batteries – what matters is how many electrons are moving through the battery and how much energy they can produce.
No matter the exact mechanism, I feel comfortable with making a few general comments about these batteries:
- They can only produce low levels of energy but, because of the long half-life of C-14, they can produce these low levels for millennia without much loss of output
- The radioactivity that powers them does not pose a substantial health risk to those who use them
- And, unless regulations change, these batteries would likely require having a radioactive materials license.