Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

How do plutonium-powered pacemakers work?

blog.plover.com

Post reply on HN
Print view View original

21–30 of 87 posts

Re: How do plutonium-powered pacemakers work?

#21

Post by QAPereo »

fratlas wrote: post #4

Dumb question, but would it be possible to have a nuclear-powered object in your body producing energy for your body to use?

I don’t think that’s dumb, and the answer is... sort of. The easiest way to make it work would be to have the device somehow help to heat and cool you internally, which would save you energy. You might be able to use the power to produce ATP or some other metabolic necessity, and deliver it where needed.

The problem is that you’d need a respectable amount of radioactive material in you, waaaaay more than you’d need for a pacemaker. It would probably make more sense just to keep some glucose syrup and a hand warmer around.

Re: How do plutonium-powered pacemakers work?

#22

Post by ComputerGuru »

acidburnNSA wrote: post #12
ComputerGuru wrote: post #9

Earlier quoted context omitted.

It wouldn’t really be feasible, the power requirements would require a large amount.

It probably wouldn't be feasible, mostly because if it got smashed by a car, a fairly potent alpha emitter would possibly be released, which is an ingestion and inhalation hazard. The radioisotope usually used (Pu238) is also not produced very much right now so it's in short supply. You make it in special Neptunium-237 targets inside nuclear reactors. In terms of power you can get well up into the hundreds of Watts f…

Definitely agree. I didn’t know about the supply/production issue, though. Thanks for that.

My answer was of course a pure hypothetical, focusing on the pragmatism in a world where the safety issues were non-existent, presuming demand would drive supply.

Re: How do plutonium-powered pacemakers work?

#23

Post by ComputerGuru »

Rjevski wrote: post #17
snarf21 wrote: post #13

Earlier quoted context omitted.

That's true but isn't 80% of our energy usage used to heat and regulate our body temp? I was wondering if we would then need less "food" for daily calories...

Isn't heat essentially a by-product of muscles "burning" the glucose? I'm not sure we actually need more heat besides what's already being generated as a by-product.

No, you can actually induce greater caloric expenditure by lowering the ambient temperature (within reason), if I’m not misremembering.

This is, after all, the distinguishing characteristic of mammals. Reptiles have no shortage of muscle mass (just look at aligators or crocs!) but still can’t raise their body temperature to compensate for cooler weather or environments.

Re: How do plutonium-powered pacemakers work?

#24

Post by gji »

shagie wrote: post #14
bruxis wrote: post #7

I did not know about these. They are so cool! I wonder how long a plutonium-powered cell phone could operate...

Not that long... or rather, it could work for a very long time but wouldn't be that useful because of the low power provided. From Wikipedia - https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge... Plutonium-238 has a half-life of 87.7 years, reasonable power density of 0.54 watts per gram - that's heat energy.And then there's math on that which has a rather low efficiency (somewhere around 23% for a stirlin…

Those numbers aren't that bad, actually. A cell phone's peak power draw isn't much more than 5W, so you'd need 10g / efficiency. At 10% efficiency, that's 100g, which is 5 cm^3 for plutonium. A cell phone battery is about 3 times that size, assuming 3000 mAh and an energy density of 600 Wh/L. Of course you'd have to build in a heat engine, but perhaps even a peltier would work given the generous efficiency allowance.

Re: How do plutonium-powered pacemakers work?

#25

Post by tim333 »

>Wikipedia says the technique was abandoned because of worries that the capsule wouldn't be absolutely certain to survive a cremation. (Cremation temperatures go up to around 1000°C; titanium melts at 1668°C.)

You'd think they could switch to tungsten if that was the issue?

Re: How do plutonium-powered pacemakers work?

#26

Post by whoisthisdude »

gji wrote: post #24
shagie wrote: post #14

Earlier quoted context omitted.

Not that long... or rather, it could work for a very long time but wouldn't be that useful because of the low power provided. From Wikipedia - https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge... Plutonium-238 has a half-life of 87.7 years, reasonable power density of 0.54 watts per gram - that's heat energy.And then there's math on that which has a rather low efficiency (somewhere around 23% for a stirlin…

Those numbers aren't that bad, actually. A cell phone's peak power draw isn't much more than 5W, so you'd need 10g / efficiency. At 10% efficiency, that's 100g, which is 5 cm^3 for plutonium. A cell phone battery is about 3 times that size, assuming 3000 mAh and an energy density of 600 Wh/L. Of course you'd have to build in a heat engine, but perhaps even a peltier would work given the generous efficiency allowance.

At 10% efficiency you'd still be dumping out around 45 watts of heat in your pocket. We'll just need some aluminum pants for the heatsink!

Re: How do plutonium-powered pacemakers work?

#27

Post by Laforet »

bunderbunder wrote: post #16
acidburnNSA wrote: post #8

FTA: > I wondered if there wasn't also worry about plutonium being recovered for weapons use, but the risk seems much smaller The answer here is a simple "nope." Plutonium in radioisotopic thermal generators is always Plutonium-238 with a 87.7 year half-life. You can't make bombs out of it. The fissile isotopes of Plutonium are 239 (24,000 year half-life) and 241 (14 year half-life, but a beta emitter instead of alph…

It sounds to me like it's only a simple "nope" if the only weapons you are worried about are nuclear weapons. Pu-238 could still be useful for radiological weapons such as dirty bombs. If you're worried about them then it becomes a (slightly) more nuanced, "How many morgues do I have to raid, and can I do it before the authorities catch on to the Crematorium Bandit?"

From what I could gather, pacemakers contain up to 4 curies of Pu-238 which is less than 300mg of pure metal. Enough to poison a few people but nowhere near enough to create WMD considering the effort. Industrial radiation sources, in contrast, typically contains tens and sometimes hundreds of curies of mostly undecayed cobalt or iridium isotopes, and is usually much less guarded.

Re: How do plutonium-powered pacemakers work?

#28

Post by sitharus »

ComputerGuru wrote: post #23
Rjevski wrote: post #17

Earlier quoted context omitted.

Isn't heat essentially a by-product of muscles "burning" the glucose? I'm not sure we actually need more heat besides what's already being generated as a by-product.

No, you can actually induce greater caloric expenditure by lowering the ambient temperature (within reason), if I’m not misremembering. This is, after all, the distinguishing characteristic of mammals. Reptiles have no shortage of muscle mass (just look at aligators or crocs!) but still can’t raise their body temperature to compensate for cooler weather or environments.

You're correct, mammals have systems to convert energy in to heat without movement and regulate this very effectively.

This isn't a distinguishing characteristic of mammals though - all birds and a few fish can regulate their body temperature. The distinguishing feature of mammals is the mammary gland - the production of milk for young.

Re: How do plutonium-powered pacemakers work?

#29

Post by monochromatic »

caf wrote: post #20
acidburnNSA wrote: post #8

FTA: > I wondered if there wasn't also worry about plutonium being recovered for weapons use, but the risk seems much smaller The answer here is a simple "nope." Plutonium in radioisotopic thermal generators is always Plutonium-238 with a 87.7 year half-life. You can't make bombs out of it. The fissile isotopes of Plutonium are 239 (24,000 year half-life) and 241 (14 year half-life, but a beta emitter instead of alph…

In fact to create weapons-grade Pu, you need to remove as much Pu-238 as you can, because if Pu-238 is contaminating your Pu, its high fission rate means the bomb explodes too early in the implosion process.

Pu 238 doesn’t undergo spontaneous fission. It’s an alpha emitter.

Re: How do plutonium-powered pacemakers work?

#30

Post by taneq »

monochromatic wrote: post #29
caf wrote: post #20

Earlier quoted context omitted.

In fact to create weapons-grade Pu, you need to remove as much Pu-238 as you can, because if Pu-238 is contaminating your Pu, its high fission rate means the bomb explodes too early in the implosion process.

Pu 238 doesn’t undergo spontaneous fission. It’s an alpha emitter.

How do you emit alpha particles without a nuclear process?
Post reply on HN