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Is this dangerous? Genuine question, it sounds like I should also be appalled but I don't know anything about plutonium. Edit: Answered my own question: > kee

Is this dangerous? Genuine question, it sounds like I should also be appalled but I don't know anything about plutonium. Edit: Answered my own question: > keeping bits of plutonium far apart is one of the bedrock rules that those working on the nuclear arsenal are supposed to follow to prevent workplace accidents. It’s Physics 101 for nuclear scientists, but has sometimes been ignored at Los Alamos

dreamcompiler 9y ago
It's the most dangerous thing that can happen at a nuclear weapons facility. Too much plutonium in one place and it starts going critical. It doesn't explode, but lots of radiation comes out suddenly and people die of radiation poisoning. People have died from such incidents in the past.
- hunta2097 9y ago
  Indeed, check out the infamous Demon Core: https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core
  - maccard 9y ago
    Funny, that happened at los alamos again. That place really doesn't have a good record
    - tyingq 9y ago
      That was 2 separate "demon core" incidents, about a year apart...so they clearly didn't learn much from the first one.
      - duskwuff 9y ago
        And at the time, Los Alamos was essentially the only place in the country -- probably the world -- doing that kind of research. So it's not really surprising that both incidents occurred there.
- marcosscriven 9y ago
  I don’t know for sure, but I thought I read somewhere it was called “tickling the dragon’s tail”?
  - disconnected 9y ago
    https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core > On May 21, 1946, physicist Louis Slotin and seven other Los Alamos personnel were in a Los Alamos laboratory conducting another experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. > It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core via a thumb hole on the top. As the reflectors were manually moved closer and farther away from each other, scintillation counters measured the relative activity from the core. Allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion > Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard straight screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing it. Scientists referred to this flirting with the possibility of a nuclear chain reaction as "tickling the dragon's tail", based on a remark by physicist Richard Feynman, who compared the experiments to "tickling the tail of a sleeping dragon". An aside: It's this kind of shit that scares the crap out of me with regards to nuclear energy. Some - literal - cowboy completely disregards the rules, endangers him and his colleagues, and then someone gets injured or killed. All for the benefit of showing off. We should do better than this, but incidents like this give me little faith. Unsurprisingly, this experiment killed Slotin: > On the day of the accident, Slotin's screwdriver slipped outward a fraction of an inch while he was lowering the top reflector, allowing the reflector to fall into place around the core. > [Slotin] received a lethal dose of 1,000 rad (10 Gy) neutron and 114 rad (1.14 Gy) gamma radiation in under a second and died nine days later from acute radiation poisoning.
    - 9y ago
- AdrianoKF 9y ago
  "A Review of Criticality Accidents" (http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-13638 http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lare...) provides a history of such incidents - an interesting, albeit quite shocking read! Quite ironically, the report was published by LANL.
jabl 9y ago
By itself, per se, no. But I imagine when dealing with weapons grade plutonium you want belts and suspenders turned to eleven. So such breaches of protocols are indeed serious business.
amelius 9y ago
Can't you store it inside a thick layer of lead?
- cocoablazing 9y ago
  Lead is a high-Z material, which provides a lot of electrons to interact with photons (and charged particles). It’s not good for stopping the neutrons that pose the danger here, because of the disparity in mass between the shield nuclei and the neutrons. For storing fissile materials in proximity, the optimal material is something with a high absorption cross section, like boron. Water and plastic are good at removing energy from neutrons and preventing leakage in typical large shielding scenarios, but in this case they would increase the danger, because they thermalize neutrons efficiently (as does a workers body) and this increases fission interaction probabilities and reduces the margin to criticality. For spent nuclear fuel, something like a boron-carbide plate is used. LANL may use something similar.
  - dreamcompiler 9y ago
    Indeed. The 2011 event was made worse by a worker using their hand to separate plutonium rods, which effectively placed a water barrier between them, making the likelihood of criticality higher. The link below describes the incident and how absurdly counterintuitive criticality safety can be. http://www.sciencemag.org/news/2017/06/near-disaster-federal-nuclear-weapons-laboratory-takes-hidden-toll-america-s-arsenal http://www.sciencemag.org/news/2017/06/near-disaster-federal...
drostie 9y ago
Yep! The mathematics is pretty simple and recurs in a bunch of other places, from the theory of evolution by natural selection, to the question of why things go viral on the Internet. The basic idea is that these sorts of objects are routinely seeing spontaneous nuclear decays -- there might be billions per millisecond of these. What's important is that each nuclear decay is an explosion which releases debris that can cause other nearby nuclei to decay as a result. So it becomes important to know: what is the average number N of nuclei which fall apart as a direct result of getting hit by the shrapnel of one decaying nucleus? Since nothing is terribly exact in physics there are two regimes to consider, N < 1 and N > 1. In that first regime we can roughly calculate that we need to multiply this baseline billions-per-millisecond rate of spontaneous decays by the number 1 + N + N² + N³ + ... = 1/(1 - N) The virality analogy is "Given one person shares it, what is the average number N of their friends who share it?" As you can see as this gets closer to N=1 it goes towards infinity. For N > 1 the same multiplier holds but it cannot be summed infinitely: instead we realize that each term takes a slightly longer time period and thus the growth goes something like e^(k t) for some k, it's an exponential growth towards a majority of the sample reacting. For fissile materials like plutonium, an easy way to increase N is to just bring two plutonium rods closer together: free debris from explosions in the one now cause new explosions in the other. This is called forming a "critical mass" hence the language about "criticality". Another way is to bring in these "neutron reflectors" that reflect the debris back into the same sample, it's basically the same principle.
- madengr 9y ago
  If the critical mass of Pu-239 is 11 kg, can you go below that, say 5 kg, by reflecting the neutrons. I just wondering how much below that 11 kg you can go.
  - Abekkus 9y ago
    Is there a static substance that reflects loose neutrons? I thought that the choices for a substance were either to let the neutron pass through, or to absorb the neutron
    - 9y ago
deleted 9y ago
[deleted]

dreamcompiler 9y ago

It's the most dangerous thing that can happen at a nuclear weapons facility. Too much plutonium in one place and it starts going critical. It doesn't explode, but lots of radiation comes out suddenly and people die of radiation poisoning. People have died from such incidents in the past.

hunta2097 9y ago
Indeed, check out the infamous Demon Core: https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core
- maccard 9y ago
  Funny, that happened at los alamos again. That place really doesn't have a good record
  - tyingq 9y ago
    That was 2 separate "demon core" incidents, about a year apart...so they clearly didn't learn much from the first one.
    - duskwuff 9y ago
      And at the time, Los Alamos was essentially the only place in the country -- probably the world -- doing that kind of research. So it's not really surprising that both incidents occurred there.
marcosscriven 9y ago
I don’t know for sure, but I thought I read somewhere it was called “tickling the dragon’s tail”?
- disconnected 9y ago
  https://en.wikipedia.org/wiki/Demon_core https://en.wikipedia.org/wiki/Demon_core > On May 21, 1946, physicist Louis Slotin and seven other Los Alamos personnel were in a Los Alamos laboratory conducting another experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. > It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core via a thumb hole on the top. As the reflectors were manually moved closer and farther away from each other, scintillation counters measured the relative activity from the core. Allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion > Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard straight screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing it. Scientists referred to this flirting with the possibility of a nuclear chain reaction as "tickling the dragon's tail", based on a remark by physicist Richard Feynman, who compared the experiments to "tickling the tail of a sleeping dragon". An aside: It's this kind of shit that scares the crap out of me with regards to nuclear energy. Some - literal - cowboy completely disregards the rules, endangers him and his colleagues, and then someone gets injured or killed. All for the benefit of showing off. We should do better than this, but incidents like this give me little faith. Unsurprisingly, this experiment killed Slotin: > On the day of the accident, Slotin's screwdriver slipped outward a fraction of an inch while he was lowering the top reflector, allowing the reflector to fall into place around the core. > [Slotin] received a lethal dose of 1,000 rad (10 Gy) neutron and 114 rad (1.14 Gy) gamma radiation in under a second and died nine days later from acute radiation poisoning.
  - 9y ago
AdrianoKF 9y ago
"A Review of Criticality Accidents" (http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-13638 http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lare...) provides a history of such incidents - an interesting, albeit quite shocking read! Quite ironically, the report was published by LANL.

jabl 9y ago

By itself, per se, no. But I imagine when dealing with weapons grade plutonium you want belts and suspenders turned to eleven. So such breaches of protocols are indeed serious business.

amelius 9y ago

Can't you store it inside a thick layer of lead?

cocoablazing 9y ago
Lead is a high-Z material, which provides a lot of electrons to interact with photons (and charged particles). It’s not good for stopping the neutrons that pose the danger here, because of the disparity in mass between the shield nuclei and the neutrons. For storing fissile materials in proximity, the optimal material is something with a high absorption cross section, like boron. Water and plastic are good at removing energy from neutrons and preventing leakage in typical large shielding scenarios, but in this case they would increase the danger, because they thermalize neutrons efficiently (as does a workers body) and this increases fission interaction probabilities and reduces the margin to criticality. For spent nuclear fuel, something like a boron-carbide plate is used. LANL may use something similar.
- dreamcompiler 9y ago
  Indeed. The 2011 event was made worse by a worker using their hand to separate plutonium rods, which effectively placed a water barrier between them, making the likelihood of criticality higher. The link below describes the incident and how absurdly counterintuitive criticality safety can be. http://www.sciencemag.org/news/2017/06/near-disaster-federal-nuclear-weapons-laboratory-takes-hidden-toll-america-s-arsenal http://www.sciencemag.org/news/2017/06/near-disaster-federal...

drostie 9y ago

Yep! The mathematics is pretty simple and recurs in a bunch of other places, from the theory of evolution by natural selection, to the question of why things go viral on the Internet. The basic idea is that these sorts of objects are routinely seeing spontaneous nuclear decays -- there might be billions per millisecond of these. What's important is that each nuclear decay is an explosion which releases debris that can cause other nearby nuclei to decay as a result. So it becomes important to know: what is the average number N of nuclei which fall apart as a direct result of getting hit by the shrapnel of one decaying nucleus? Since nothing is terribly exact in physics there are two regimes to consider, N < 1 and N > 1. In that first regime we can roughly calculate that we need to multiply this baseline billions-per-millisecond rate of spontaneous decays by the number 1 + N + N² + N³ + ... = 1/(1 - N) The virality analogy is "Given one person shares it, what is the average number N of their friends who share it?" As you can see as this gets closer to N=1 it goes towards infinity. For N > 1 the same multiplier holds but it cannot be summed infinitely: instead we realize that each term takes a slightly longer time period and thus the growth goes something like e^(k t) for some k, it's an exponential growth towards a majority of the sample reacting. For fissile materials like plutonium, an easy way to increase N is to just bring two plutonium rods closer together: free debris from explosions in the one now cause new explosions in the other. This is called forming a "critical mass" hence the language about "criticality". Another way is to bring in these "neutron reflectors" that reflect the debris back into the same sample, it's basically the same principle.

madengr 9y ago
If the critical mass of Pu-239 is 11 kg, can you go below that, say 5 kg, by reflecting the neutrons. I just wondering how much below that 11 kg you can go.
- Abekkus 9y ago
  Is there a static substance that reflects loose neutrons? I thought that the choices for a substance were either to let the neutron pass through, or to absorb the neutron
  - 9y ago

deleted 9y ago

[deleted]