41–50 of 87 posts
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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.
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.
(like Pu-238, Pu-240 is an alpha emitter. But unlike Pu-238, Pu-240 also undergoes spontaneous fission).
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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.
I went to a lecture recently by a researcher who is investigating the mechanisms of photosynthesis. The chlorophyll uses the energy from the photon to pump an electron, which (after a long and poorly-understood chain of reactions, which is what he was studying) creates an energy gradient which powers ATP synthase to produce ATP. Presumably if we understood and could recreate this reaction, we could create the electro…
How long to these pacemakers last? Have people had to get the plutonium "batteries" replaced?
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 a…
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?
How long to these pacemakers last? Have people had to get the plutonium "batteries" replaced?
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 a…
> Easier to replace the whole pacemaker than the battery
unfortunately, this statement:
> 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.
only partially applies in this case. That pacemaker has a lot of work to do (stimulate every single heart beat), and depending on the quality of the electrodes on the heart, and the cables that lead to them, some needed to be replaced after two or three years. If one lasts 7 years, that is a very welcome respite, but quite the exception.
That said, pacemakers have come a long way. The first on that this person had implanted had a fixed beat. The current generation has sensors for oxygen saturation and movement, and be configured and maintained through a wireless interface, they log unusual events etc.
Earlier quoted context omitted.
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 a…
> 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 outpu…
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.
How long to these pacemakers last? Have people had to get the plutonium "batteries" replaced?
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 [2] https://en.wikipedia.org/wiki/Voyager_1
I highly recommend this podcast episode with one of the Voyager project managers: 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).
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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!
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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.
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.
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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.
https://www.newscientist.com/article/mg21228411-700-killer-f...