3 ms·

Meh. Plutonium is safe below criticality.

scythe 4y ago
The 238Pu used in radioactive batteries is a lot more active than the more common 239Pu used in nuclear reactors/weapons.
- lazide 4y ago
  Nothing says fun times like hundred gram quantities of something with a half life of less than 100 years!
  - knorker 4y ago
    Good thing they won't find it in the next 100 years, then. It'll all be gone. Literally every single atom in about 7500 years.
GekkePrutser 4y ago
Safe? Almost all RTGs use Pu-238 which is an alpha emitter. It is so active it gets red hot from its own energy. The reason they use it is that alpha radiation consists of relatively large particles which are easy to capture and thus take advantage of their energy. Also, gamma radiation would probably interfere with instruments and it's super hard to block in a lightweight spacecraft. But it's not safe. Get a dust particle in your lungs where there is no protection from alpha particles (unlike the skin, which would at its worst develop easily-detectable skin cancer), and you'll die a slow and painful death. Not what I'd consider safe. Not instadeath either like I said, I know..
- knorker 4y ago
  Sure, but it sounded like you meant while not instadeath, it'll be eventua-death. I.e. the Simpsons view of plutonium, which is likely what's in most people's minds. Anyone encountering the probe will pretty much by definition be very advanced, to not only get to space but also intercept something going above their star's escape velocity. You'd expect them to wear gloves and stuff. Plutonium may not even be the most hazardous thing on there. They may be deadly allergic to gold. (though yes plutonium is the one thing on there we can pretty much guarantee is hazardous while existing in fairly large quantities) But who knows, maybe their equivalent of eyes get the equivalent of cancer from alpha radiation. Although by the time it reaches any aliens the plutonium is going to be all spent. Half life of 87.7 years. After only a thousand years all that's left is 0.037%. That's of course the thing about radioactivity: The more dangerous it is, the shorter a time it's dangerous. If Voyager were heading towards proxima centauri then it'd take 73 million years to get there. Lots of it is already gone: "As of June 17, 2022, Voyager 1 has 70.19% of the plutonium-238 that it had at launch. By 2050, it will have 56.5% left, far too little to keep it functional". After 73 million years it'll be 5.1e250573 times less. It was about 37.7kg at launch. If I calculate right then the last pu-238 atom decays after only about 7500 years or so. It's much less dangerous now than when it left earth, which is of course exactly why it's powering down. tl;dr: By the time they find it there may not even be a single plutonium atom left undecayed.

The 238Pu used in radioactive batteries is a lot more active than the more common 239Pu used in nuclear reactors/weapons.

lazide 4y ago
Nothing says fun times like hundred gram quantities of something with a half life of less than 100 years!
- knorker 4y ago
  Good thing they won't find it in the next 100 years, then. It'll all be gone. Literally every single atom in about 7500 years.

GekkePrutser 4y ago

Safe? Almost all RTGs use Pu-238 which is an alpha emitter. It is so active it gets red hot from its own energy. The reason they use it is that alpha radiation consists of relatively large particles which are easy to capture and thus take advantage of their energy. Also, gamma radiation would probably interfere with instruments and it's super hard to block in a lightweight spacecraft. But it's not safe. Get a dust particle in your lungs where there is no protection from alpha particles (unlike the skin, which would at its worst develop easily-detectable skin cancer), and you'll die a slow and painful death. Not what I'd consider safe. Not instadeath either like I said, I know..

knorker 4y ago
Sure, but it sounded like you meant while not instadeath, it'll be eventua-death. I.e. the Simpsons view of plutonium, which is likely what's in most people's minds. Anyone encountering the probe will pretty much by definition be very advanced, to not only get to space but also intercept something going above their star's escape velocity. You'd expect them to wear gloves and stuff. Plutonium may not even be the most hazardous thing on there. They may be deadly allergic to gold. (though yes plutonium is the one thing on there we can pretty much guarantee is hazardous while existing in fairly large quantities) But who knows, maybe their equivalent of eyes get the equivalent of cancer from alpha radiation. Although by the time it reaches any aliens the plutonium is going to be all spent. Half life of 87.7 years. After only a thousand years all that's left is 0.037%. That's of course the thing about radioactivity: The more dangerous it is, the shorter a time it's dangerous. If Voyager were heading towards proxima centauri then it'd take 73 million years to get there. Lots of it is already gone: "As of June 17, 2022, Voyager 1 has 70.19% of the plutonium-238 that it had at launch. By 2050, it will have 56.5% left, far too little to keep it functional". After 73 million years it'll be 5.1e250573 times less. It was about 37.7kg at launch. If I calculate right then the last pu-238 atom decays after only about 7500 years or so. It's much less dangerous now than when it left earth, which is of course exactly why it's powering down. tl;dr: By the time they find it there may not even be a single plutonium atom left undecayed.