
How do plutonium-powered pacemakers work? - luu
https://blog.plover.com/tech/seebeck-effect.html
======
acidburnNSA
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
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
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.

~~~
littlestymaar
I wouldn't be enough to kill many people, but if a certain amount (even non-
dangerous, like 1µS/h) of radiations were detected in all Manhattan, the panic
would cause lasting damages.

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

~~~
Rjevski
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.

~~~
wolfgang42
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 electrochemical gradient directly,
and then use it to power the ATP synthase and subsequent glucose-production
mechanisms.

~~~
WalterBright
Biochemists at Caltech were studying photosynthesis back in the 70s, with an
eye towards artificially replicating the process.

I see not much progress has been made.

~~~
c12
This is a paper from two years ago but it shows that progress is still being
made in this field.
[http://science.sciencemag.org/content/352/6290/1210](http://science.sciencemag.org/content/352/6290/1210)

------
dfox
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).

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

~~~
Kelbit
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.

~~~
rplnt
Wouldn't wireless charging pad work well for this? Or is it unnecessary
complicated considering how long batteries last?

~~~
ctdonath
The issue being rather close to my heart, I'd rather have a single-use 7-year
battery + full modern replacement of unit, than have to fiddle with periodic
recharging just to prolong use of aging technology. Nobody much wants their
life relying on >10 year old computers. (Remember: it's already "old
technology" when you first get it implanted.)

~~~
Kelbit
Rumor is Medtronic pacemakers still use 6502 processors (albeit on modernized
custom silicon) with code written in the 80s. Big medical OEMs are loathe to
change.

~~~
toomuchtodo
You don’t fix what isn’t broken when it’s a life critical system.

------
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?

~~~
taneq
Titanium is nicely biocompatible. Tungsten can be poisonous.
[https://patient.info/doctor/tungsten-
poisoning](https://patient.info/doctor/tungsten-poisoning)

~~~
josu
Could you have an inner layer of tungsten to seal the plutonium, and an outer
layer of titanium to avoid poisoning the host?

~~~
taneq
I guess that'd work - the patient is going to stop worrying about
biocompatibility long before the titanium gets near its melting point!

------
bruxis
I did not know about these. They are so cool!

I wonder how long a plutonium-powered cell phone could operate...

~~~
shagie
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...](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

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 stirling engine approach).
And well... its hot. And how old is your phone? I don't think my 20 year old
phone would still work... why charge power it with something that would last
30 years when the technology that drive it is gone in half a decade.

~~~
gji
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.

~~~
whoisthisdude
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!

~~~
baybal2
Saying along those lines used to be a popular joke among Soviet nuclear
scientists.

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

------
nukeop
Uh, does it run, like, on regular unleaded gasoline?

Unfortunately, no. It requires something with a little more kick. Plutonium.

------
blibble
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)

------
elnurmen
I got curious when i misread pacemaker as pEacemaker

~~~
vectorEQ
rofl, sounds like they need some peace over there _EVERY THING EVAPORATING_

