8 ms·

How do plutonium-powered pacemakers work?

172 points by luu 9y ago

saagarjha 9y ago
How long to these pacemakers last? Have people had to get the plutonium "batteries" replaced?
- QAPereo 9y ago
  http://www.prutchi.com/pdf/implantable/nuclear_pacemakers.pdf http://www.prutchi.com/pdf/implantable/nuclear_pacemakers.pd... Last paragraph on page 2... quite a long damned time; by 35 years it was still going strong.
- acidburnNSA 9y ago
  The half-life of Pu-238 (the isotope used in these) is 87.7 years [1]. So they pretty much last a lifetime. For the same reason, Voyager 1 is still kicking even though it's out of the solar system [2]. [1] https://en.wikipedia.org/wiki/Plutonium-238 https://en.wikipedia.org/wiki/Plutonium-238 [2] https://en.wikipedia.org/wiki/Voyager_1 https://en.wikipedia.org/wiki/Voyager_1
  - deleted 9y ago
    [deleted]
  - perlgeek 9y ago
    Still, Voyager 1 is slowly shutting down its scientific instruments due to decreased power supply. I highly recommend this podcast episode with one of the Voyager project managers: https://www.listentospacepod.com/episodes/2016/8/5/episode-57-voyaging-to-the-edge-of-the-solar-system-with-suzy-dodd https://www.listentospacepod.com/episodes/2016/8/5/episode-5... (about 20 minutes long, iirc) (In fact, I'd highly recommend the whole podcast, not just this episode, but this one actually talks about power consumption and battery life of Voyager).
    - effie 9y ago
      The project manager Suzy Dodd talks a lot about shutting down instruments in order to save the power. But the power output of radioisotope thermoelectric generator does not depend on how much power is drawn. Is there a conventional electric battery on the Voyagers that the instruments draw their power from instead?
      - c3833174 9y ago
        By saving power she means leaving enough margin to keep the supply voltage stable, running the machine near the limit could cause voltage sag when another device like the tape drive is turned on. Just like apple limits power draw of it's devices to avoid possible reboots when too much current is demanded from an old battery.
        effie 9y ago
        That makes sense. I still wonder if there is battery that would be recharged by the RTG. Seem like it could save some useful energy for the future time when it is needed.
        perlgeek 9y ago
        I don't know, but it wouldn't surprise me if no such battery was on the spacecraft. You have to remember that Voyager is way past its originally planned mission life span, and that the nuclear battery was more than fine for the planned life span. Batteries tend to be heavy, not operate well at very low temperatures, and wear down quicker than the 40+ years since construction of the space craft. From the perspective of the original mission design, even with incredible foresight, it seems to be not worth the trade-offs.
- Kelbit 9y ago
  Easier to replace the whole pacemaker than the battery, for a couple of reasons: * Pacemakers are hermetically sealed, usually laser-welded in a titanium case. Adding a replaceable battery with seals would complicate this arrangement. * By the time the battery winds down, there may be a newer, better pacemaker on the market that fits the patient's needs. * Since a battery replacement necessitates surgery, you might as well replace the whole unit and get all new parts rather than put an old one back in that may be reaching MTTF. As for how long the cells last, modern Lithium Thionyl Chloride cells last 5-10 years depending on the pacemaker. They probably actually last longer, manufacturers are pretty conservative with lifetime estimates. As for plutonium supplies like those in the article, they don't really die since they're thermoelectric. The amount of current you can draw will be proportional to the amount of heat generated by the isotope and the temperature gradient. Since the heat is related to the amount of isotope remaining, the power available will follow an exponential decay. The half-life of Pu-238 is about 88 years, so the battery will last a very long time. The exact lifetime depends on how much current the pacemaker takes to operate. Most people had these devices replaced with more modern versions, but there are still a few people who have the old plutonium devices which were implanted decades ago.
  - bigiain 9y ago
    > The exact lifetime depends on how much current the pacemaker takes to operate. Not so sure. I don't think the plutonium decay is affected by the current drawn via the thermocouple - it'll just keep putting out the same power (well, the same decaying power curve anyway) no matter how much current you try and draw. I suspect the thermocouple's voltage will just sag so the maximum drawn power will be the thermal output less the efficiency of the conversion (which, I guess, might be non-linear with current?). But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right?
    - perlgeek 9y ago
      > But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right? True. The power requirements can still vary between patients (due to varying quality of the electrical contacts, which tends to deteriorate over time), so there is an individual component, it's just not based on the power drawn from the battery.
- nukeop 9y ago
  I'm sure that in 1985, plutonium is available in every corner drugstore, but in 1955, it's a little hard to come by.
fratlas 9y ago
Dumb question, but would it be possible to have a nuclear-powered object in your body producing energy for your body to use?
- johnhenry 9y ago
  The ability to metabolize radiation does exist (https://en.wikipedia.org/wiki/Radiotrophic_fungus https://en.wikipedia.org/wiki/Radiotrophic_fungus) so we might be able to modify our genes such that our bodies can use this energy directly.
- Rjevski 9y ago
  Keeping nuclear material (safely) in your body is the easy part, the hard part is converting that energy into something your body can use. The issue is, our (badly designed) meat-hardware runs on glucose instead of heat or electricity, and there's no easy (or any way that I know of really, but then I'm not a scientist) to convert heat/electricity into glucose.
  - snarf21 9y ago
    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...
    - Rjevski 9y ago
      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.
      - ComputerGuru 9y ago
        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.
bruxis 9y ago
I did not know about these. They are so cool! I wonder how long a plutonium-powered cell phone could operate...
- ComputerGuru 9y ago
  It wouldn’t really be feasible, the power requirements would require a large amount.
  - acidburnNSA 9y ago
    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 fairly easily but it can get big. Here's the one used in Mars Curiosity rover [1]. [1] https://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_Thermoelectric_Generator https://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_The... People talk about using isotopes from nuclear waste for this kind of thing a lot but they're usually considered too expensive.
    - ComputerGuru 9y ago
      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.
    - sargun 9y ago
      I wish it was easier to get your hands on refined isotopes. I believe it'd spawn quite a bit of interesting industrial research that's being held back right now. A lot of this waste is a nuisance, but I believe if it was easier to get access to it, we'd see someone start to solve the waste problem.
- 9y ago
acidburnNSA 9y ago
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 alpha). The fission cross section (probability) of Pu-238 is >100 less than Pu-239 for a "normal-speed" neutron and also a lot less at fission-spectrum energies.
- bunderbunder 9y ago
  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?"
  - Laforet 9y ago
    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.
    - lostlogin 9y ago
      Covered in the article, though the author suggests even less Pu. A supplier could have a few few devices in a warehouse, but nowhere near the numbers described. > a pacemaker has only around 135 mg, if I did the conversion from curies correctly. Even so, if I were in charge of keeping plutonium out of the wrong hands, I would still worry about this. It does not seem totally out of the realm of possibility that someone could collect 25,000 pacemakers. Opening 25,000 titanium capsules does sound rather tedious.
    - 9y ago
blibble 9y ago
author seemed a bit concerned about Pu-238 being used for weapons, but I think that's the wrong isotope (238 being not fissile, as well as physically hot)
tim333 9y ago
>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?
- taneq 9y ago
  Titanium is nicely biocompatible. Tungsten can be poisonous. https://patient.info/doctor/tungsten-poisoning https://patient.info/doctor/tungsten-poisoning
  - josu 9y ago
    Could you have an inner layer of tungsten to seal the plutonium, and an outer layer of titanium to avoid poisoning the host?
    - taneq 9y ago
      I guess that'd work - the patient is going to stop worrying about biocompatibility long before the titanium gets near its melting point!
elnurmen 9y ago
I got curious when i misread pacemaker as pEacemaker
- vectorEQ 9y ago
  rofl, sounds like they need some peace over there EVERY THING EVAPORATING
jlebrech 9y ago
I can see unscrupulous sports people having a plutonium powered lactic acid scrubbing device, or an extra lung.
nukeop 9y ago
Uh, does it run, like, on regular unleaded gasoline? Unfortunately, no. It requires something with a little more kick. Plutonium.
dfox 9y ago
I'm under the impression that most nuclear powered pacemakers were not based on RTGs which is what the article describes but on betavoltaics (which does not use heat of decay as energy source, but converts beta radiation directly to electricity).

172 points by luu 9y ago

saagarjha 9y ago

How long to these pacemakers last? Have people had to get the plutonium "batteries" replaced?

QAPereo 9y ago
http://www.prutchi.com/pdf/implantable/nuclear_pacemakers.pdf http://www.prutchi.com/pdf/implantable/nuclear_pacemakers.pd... Last paragraph on page 2... quite a long damned time; by 35 years it was still going strong.
acidburnNSA 9y ago
The half-life of Pu-238 (the isotope used in these) is 87.7 years [1]. So they pretty much last a lifetime. For the same reason, Voyager 1 is still kicking even though it's out of the solar system [2]. [1] https://en.wikipedia.org/wiki/Plutonium-238 https://en.wikipedia.org/wiki/Plutonium-238 [2] https://en.wikipedia.org/wiki/Voyager_1 https://en.wikipedia.org/wiki/Voyager_1
- deleted 9y ago
  [deleted]
- perlgeek 9y ago
  Still, Voyager 1 is slowly shutting down its scientific instruments due to decreased power supply. I highly recommend this podcast episode with one of the Voyager project managers: https://www.listentospacepod.com/episodes/2016/8/5/episode-57-voyaging-to-the-edge-of-the-solar-system-with-suzy-dodd https://www.listentospacepod.com/episodes/2016/8/5/episode-5... (about 20 minutes long, iirc) (In fact, I'd highly recommend the whole podcast, not just this episode, but this one actually talks about power consumption and battery life of Voyager).
  - effie 9y ago
    The project manager Suzy Dodd talks a lot about shutting down instruments in order to save the power. But the power output of radioisotope thermoelectric generator does not depend on how much power is drawn. Is there a conventional electric battery on the Voyagers that the instruments draw their power from instead?
    - c3833174 9y ago
      By saving power she means leaving enough margin to keep the supply voltage stable, running the machine near the limit could cause voltage sag when another device like the tape drive is turned on. Just like apple limits power draw of it's devices to avoid possible reboots when too much current is demanded from an old battery.
      - effie 9y ago
        That makes sense. I still wonder if there is battery that would be recharged by the RTG. Seem like it could save some useful energy for the future time when it is needed.
        perlgeek 9y ago
        I don't know, but it wouldn't surprise me if no such battery was on the spacecraft. You have to remember that Voyager is way past its originally planned mission life span, and that the nuclear battery was more than fine for the planned life span. Batteries tend to be heavy, not operate well at very low temperatures, and wear down quicker than the 40+ years since construction of the space craft. From the perspective of the original mission design, even with incredible foresight, it seems to be not worth the trade-offs.
Kelbit 9y ago
Easier to replace the whole pacemaker than the battery, for a couple of reasons: * Pacemakers are hermetically sealed, usually laser-welded in a titanium case. Adding a replaceable battery with seals would complicate this arrangement. * By the time the battery winds down, there may be a newer, better pacemaker on the market that fits the patient's needs. * Since a battery replacement necessitates surgery, you might as well replace the whole unit and get all new parts rather than put an old one back in that may be reaching MTTF. As for how long the cells last, modern Lithium Thionyl Chloride cells last 5-10 years depending on the pacemaker. They probably actually last longer, manufacturers are pretty conservative with lifetime estimates. As for plutonium supplies like those in the article, they don't really die since they're thermoelectric. The amount of current you can draw will be proportional to the amount of heat generated by the isotope and the temperature gradient. Since the heat is related to the amount of isotope remaining, the power available will follow an exponential decay. The half-life of Pu-238 is about 88 years, so the battery will last a very long time. The exact lifetime depends on how much current the pacemaker takes to operate. Most people had these devices replaced with more modern versions, but there are still a few people who have the old plutonium devices which were implanted decades ago.
- bigiain 9y ago
  > The exact lifetime depends on how much current the pacemaker takes to operate. Not so sure. I don't think the plutonium decay is affected by the current drawn via the thermocouple - it'll just keep putting out the same power (well, the same decaying power curve anyway) no matter how much current you try and draw. I suspect the thermocouple's voltage will just sag so the maximum drawn power will be the thermal output less the efficiency of the conversion (which, I guess, might be non-linear with current?). But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right?
  - perlgeek 9y ago
    > But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right? True. The power requirements can still vary between patients (due to varying quality of the electrical contacts, which tends to deteriorate over time), so there is an individual component, it's just not based on the power drawn from the battery.
nukeop 9y ago
I'm sure that in 1985, plutonium is available in every corner drugstore, but in 1955, it's a little hard to come by.

fratlas 9y ago

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

johnhenry 9y ago
The ability to metabolize radiation does exist (https://en.wikipedia.org/wiki/Radiotrophic_fungus https://en.wikipedia.org/wiki/Radiotrophic_fungus) so we might be able to modify our genes such that our bodies can use this energy directly.
Rjevski 9y ago
Keeping nuclear material (safely) in your body is the easy part, the hard part is converting that energy into something your body can use. The issue is, our (badly designed) meat-hardware runs on glucose instead of heat or electricity, and there's no easy (or any way that I know of really, but then I'm not a scientist) to convert heat/electricity into glucose.
- snarf21 9y ago
  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...
  - Rjevski 9y ago
    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.
    - ComputerGuru 9y ago
      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.

bruxis 9y ago

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

ComputerGuru 9y ago
It wouldn’t really be feasible, the power requirements would require a large amount.
- acidburnNSA 9y ago
  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 fairly easily but it can get big. Here's the one used in Mars Curiosity rover [1]. [1] https://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_Thermoelectric_Generator https://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_The... People talk about using isotopes from nuclear waste for this kind of thing a lot but they're usually considered too expensive.
  - ComputerGuru 9y ago
    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.
  - sargun 9y ago
    I wish it was easier to get your hands on refined isotopes. I believe it'd spawn quite a bit of interesting industrial research that's being held back right now. A lot of this waste is a nuisance, but I believe if it was easier to get access to it, we'd see someone start to solve the waste problem.
9y ago

acidburnNSA 9y ago

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 alpha). The fission cross section (probability) of Pu-238 is >100 less than Pu-239 for a "normal-speed" neutron and also a lot less at fission-spectrum energies.

bunderbunder 9y ago
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?"
- Laforet 9y ago
  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.
  - lostlogin 9y ago
    Covered in the article, though the author suggests even less Pu. A supplier could have a few few devices in a warehouse, but nowhere near the numbers described. > a pacemaker has only around 135 mg, if I did the conversion from curies correctly. Even so, if I were in charge of keeping plutonium out of the wrong hands, I would still worry about this. It does not seem totally out of the realm of possibility that someone could collect 25,000 pacemakers. Opening 25,000 titanium capsules does sound rather tedious.
  - 9y ago

blibble 9y ago

author seemed a bit concerned about Pu-238 being used for weapons, but I think that's the wrong isotope (238 being not fissile, as well as physically hot)

tim333 9y ago

>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?

taneq 9y ago
Titanium is nicely biocompatible. Tungsten can be poisonous. https://patient.info/doctor/tungsten-poisoning https://patient.info/doctor/tungsten-poisoning
- josu 9y ago
  Could you have an inner layer of tungsten to seal the plutonium, and an outer layer of titanium to avoid poisoning the host?
  - taneq 9y ago
    I guess that'd work - the patient is going to stop worrying about biocompatibility long before the titanium gets near its melting point!

elnurmen 9y ago

I got curious when i misread pacemaker as pEacemaker

vectorEQ 9y ago
rofl, sounds like they need some peace over there EVERY THING EVAPORATING

jlebrech 9y ago

I can see unscrupulous sports people having a plutonium powered lactic acid scrubbing device, or an extra lung.

nukeop 9y ago

Uh, does it run, like, on regular unleaded gasoline? Unfortunately, no. It requires something with a little more kick. Plutonium.

dfox 9y ago

I'm under the impression that most nuclear powered pacemakers were not based on RTGs which is what the article describes but on betavoltaics (which does not use heat of decay as energy source, but converts beta radiation directly to electricity).