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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 "nop

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.
  - littlestymaar 9y ago
    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.
- godelski 9y ago
  The threat of dirty bombs is pretty low, there's a reason they aren't used. They are extremely hard to obtain, and don't add a significant amount more deaths (if the blast didn't kill you, the radiation will probably not. Though definitely send you to the hospital). They work great as weapons of terror, and there is a lengthy cleanup process, but there's a reason that they aren't common. The people working on the device are also more likely to die, and more easily caught. The materials are difficult to obtain, but definitely not impossible. It just probably isn't worth the time and effort when you could more easily make and/or obtain more conventional explosives. This is all assuming the smaller type of explosives used in acts of terror.
trumpsamerica 9y ago
I don't think adding half lifes here has any point. Fission is (as you mentioned yourself correctly) initiated by an external agent and half life (to my knowledge) has no relationship with "fissility" (as it relates to chain reaction)
caf 9y ago
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.
- monochromatic 9y ago
  Pu 238 doesn’t undergo spontaneous fission. It’s an alpha emitter.
  - taneq 9y ago
    How do you emit alpha particles without a nuclear process?
    - monochromatic 9y ago
      It’s a nuclear reaction. It just isn’t fission.
      - acidburnNSA 9y ago
        Right. Pu238 alpha decay is aneutronic so it doesn't contribute to a chain reaction. However heating from too much Pu238 (or more importantly, Pu240) would be a heat removal/thermal challenge.
  - deleted 9y ago
    [deleted]
  - caf 9y ago
    Quite so, I was actually thinking of Pu-240. One heavier rather than one lighter! (like Pu-238, Pu-240 is an alpha emitter. But unlike Pu-238, Pu-240 also undergoes spontaneous fission).
yummybear 9y ago
Isn't a 14 year half life very little for a bomb that should continue to work for decades? Or isn't it actually used for it, but just CAN be used for it?
- acidburnNSA 9y ago
  Yeah 241 is not commonly or ever used for weapons, it just could be. it's always easier and more practical to use u235 or pu239. Other fissile nuclides no one makes bombs out of include Americium-242m and Curium-244. Technically, sophisticated weaponeers can work with non-fissile but still fissionable nuclides like Pu240 but it's harder. But that's why the IAEA defines significant quantities of plutonium without specifying the isotopics.

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.
- littlestymaar 9y ago
  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.
godelski 9y ago
The threat of dirty bombs is pretty low, there's a reason they aren't used. They are extremely hard to obtain, and don't add a significant amount more deaths (if the blast didn't kill you, the radiation will probably not. Though definitely send you to the hospital). They work great as weapons of terror, and there is a lengthy cleanup process, but there's a reason that they aren't common. The people working on the device are also more likely to die, and more easily caught. The materials are difficult to obtain, but definitely not impossible. It just probably isn't worth the time and effort when you could more easily make and/or obtain more conventional explosives. This is all assuming the smaller type of explosives used in acts of terror.

trumpsamerica 9y ago

I don't think adding half lifes here has any point. Fission is (as you mentioned yourself correctly) initiated by an external agent and half life (to my knowledge) has no relationship with "fissility" (as it relates to chain reaction)

caf 9y ago

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.

monochromatic 9y ago
Pu 238 doesn’t undergo spontaneous fission. It’s an alpha emitter.
- taneq 9y ago
  How do you emit alpha particles without a nuclear process?
  - monochromatic 9y ago
    It’s a nuclear reaction. It just isn’t fission.
    - acidburnNSA 9y ago
      Right. Pu238 alpha decay is aneutronic so it doesn't contribute to a chain reaction. However heating from too much Pu238 (or more importantly, Pu240) would be a heat removal/thermal challenge.
- deleted 9y ago
  [deleted]
- caf 9y ago
  Quite so, I was actually thinking of Pu-240. One heavier rather than one lighter! (like Pu-238, Pu-240 is an alpha emitter. But unlike Pu-238, Pu-240 also undergoes spontaneous fission).

yummybear 9y ago

Isn't a 14 year half life very little for a bomb that should continue to work for decades? Or isn't it actually used for it, but just CAN be used for it?

acidburnNSA 9y ago
Yeah 241 is not commonly or ever used for weapons, it just could be. it's always easier and more practical to use u235 or pu239. Other fissile nuclides no one makes bombs out of include Americium-242m and Curium-244. Technically, sophisticated weaponeers can work with non-fissile but still fissionable nuclides like Pu240 but it's harder. But that's why the IAEA defines significant quantities of plutonium without specifying the isotopics.