What would happen if one were to take a pure plutonium sphere the size of a basketball, and throw it into an active volcano?
I think that a sphere of plutonium that size would have already exceeded critical mass.
In other words, as you start to walk to the volcano, it would explode.
but why does simply meeting or exceeding the critical mass cause an explosion? is it that the spontaneous fission of some of the plutonium atoms (and therefore the release of some free neutrons) is enough to start the fission chain reaction on its own?You would score the winning point and then die a few hours later if by some miracle the thing didn't already explode. All it takes is a ball about the size of your two fists to reach critical mass.
particles decay all the time, in the case of plutonium and uranium it's enough to begin the chain reaction.but why does simply meeting or exceeding the critical mass cause an explosion? is it that the spontaneous fission of some of the plutonium atoms (and therefore the release of some free neutrons) is enough to start the fission chain reaction on its own?
but why does simply meeting or exceeding the critical mass cause an explosion? is it that the spontaneous fission of some of the plutonium atoms (and therefore the release of some free neutrons) is enough to start the fission chain reaction on its own?
I think that a sphere of plutonium that size would have already exceeded critical mass.
In other words, as you start to walk to the volcano, it would explode.
I remember reading a Hardy boys book (it was one of the later series of books... hardy boys casefiles) about this. AFAIK it was a story that took place over three novels and had the evil guy planning on putting a nuke into a volcano in the south pacific. Blowing the nuke up on a plate boundary would cause half of California to fall into the ocean and cause earthquakes and volcanos to go nutso all around the pacific rim. Or so the story went anyways.
but why does simply meeting or exceeding the critical mass cause an explosion? is it that the spontaneous fission of some of the plutonium atoms (and therefore the release of some free neutrons) is enough to start the fission chain reaction on its own?
In the case of plutonium, Pu-240 has a high spont. fission rate, and Pu-238 exceedingly high spontaneous fission rate. These contaminants introduce huge numbers of neutrons into a plutonium fissile core. The core assembly technique above won't work for Pu, as the chain reaction will begin well before the cores are fully assembled, giving a weak explosion - estimated at about 1 kiloton. Therefore a much faster method is required - hence plutonium cores are imploded from a low-density form into a high-density form using a series of shaped high-explosive charges.
this answers my question. thanks Mark. i'm actually more familiar with detonation methods than i am with why the nuclear reaction begins. but you've since cleared that up. i also found a diagram depicting the two methods of detonation of a fission bomb which, as you mention, depends on the type of core used (courtesy of Wiki):Because the chain reaction depends on something starting the chain, there is potentially a brief delay before an uncontrolled reaction begins, once a supra-critical core is assembled. The amount of delay depends on how many background neutrons are present in, or around, the core. Neutrons are available from spontaneous fission of the fissile material, or from a variety of radioactive interactions (e.g. interactions between atoms and alpha particles, or gamma rays. A beryllium atom hit by an alpha particle will emit a neutron, or a deuterium atom hit by a high-energy gamma ray will emit a neutron...
...In the case of plutonium, Pu-240 has a high spont. fission rate, and Pu-238 exceedingly high spontaneous fission rate. These contaminants introduce huge numbers of neutrons into a plutonium fissile core. The core assembly technique above won't work for Pu, as the chain reaction will begin well before the cores are fully assembled, giving a weak explosion - estimated at about 1 kiloton. Therefore a much faster method is required - hence plutonium cores are imploded from a low-density form into a high-density form using a series of shaped high-explosive charges.
What would happen if one were to take a pure plutonium sphere the size of a basketball, and throw it into an active volcano?
nvrmdbut why does simply meeting or exceeding the critical mass cause an explosion?
but why does simply meeting or exceeding the critical mass cause an explosion? is it that the spontaneous fission of some of the plutonium atoms (and therefore the release of some free neutrons) is enough to start the fission chain reaction on its own?
Runaway fission reaction is why. Take your sub-critical, golf ball sized lump of fissile material however, and dump that in a Volcano and you've basically just got a dirty bomb. (Then your hands and other valuable appendages will rot off, not unlike a particularly nasty case of syphillis).
I do rather enjoy these thought experiments
I'm sure that in 1985 plutonium is available in every corner drug store, but in 1955 it's a little hard to come by.
You would die a quick death in the next few days. As said above, that much plutonium would be above critical mass. Would probably explode violently, but not kiloton style mushroom cloud effect. If it didn't explode, you would receive a lethal dose of radiation poisoning: http://en.wikipedia.org/wiki/Demon_core
That core was much smaller than a basketball, and emitted enough radiation in a half second of criticality that the guy died in 9 days.
Interesting article about the scientist who died : Louis Alexander Slotin.
About the radiation accident : What i do not understand is why they did not make a simple apparatus to lower the half hemisphere from a save shielded distance. I mean they used scintillation counters to monitor the radiation. It makes no sense to be that stupid, they knew how dangerous it was.
The principles of 'safe working practices' weren't well developed at that time. There was still a lot of belief that even dangerous things 'were safe if you were careful'. As long as you took care not to make a mistake things would be fine.
This is how early skyscrapers were built - there was no scaffolding, no safety nets or supports. Men just walked along the girders, carrying bricks and tools. Occasionally, some fell off or got blown off by wind.
The realisation now is that you can't rely on humans to get it right all the time, and that you have to have a contingency plan. This is taught at all levels, and is second nature to most people now. It wasn't then.
It had been ominously augured by a very similar tragedy six months earlier. Harry Daghlian, Slotin's friend and laboratory assistant, had fallen victim to "the invisible killer". Deeply saddened by the mishap, Slotin spent many hours at his assistant's bedside during the month it took Daghlian to die. Thomas Brock quotes from a June 1946 letter from Emily Morrison, Philip Morrison's wife, to a friend. It reveals the "series of strange coincidences" involved in both mishaps: "Both Louis' and Harry Daghlian's accidents occurred on Tuesday the 21st; both used the same piece of material; and both died in the same room in the hospital." After the 24-year-old Daghlian's death, Nobel Laureate Enrico Fermi warned Slotin that he wouldn't last a year - "if you keep doing that experiment." Following the Daghlian accident two tiny spacers were developed to prevent the beryllium spheres from closing completely together. It was hoped that this would prevent similar incidents. But Slotin preferred a hands-on approach to experimentation. Raemer E. Schreiber, a Slotin colleague who still lives in Los Alamos, stated in a 1993 letter to the author: "I'm quite sure that several of us knew that he was using the Pu [plutonium) hemispheres for demonstrations of simple critical assemblies, but were not aware of his unsafe method until it was too late. After all, he was the expert in this work. But he should have never made the assembly by lowering the upper section down onto the lower one so a slip would close the gap and make the system supercritical. He should have fixed the upper assembly in position and raised the lower section gradually to increase the reactivity. Then if anything slipped, the assembly would open harmlessly. Louis knew this, of course, but apparently thought he could get by with the simpler assembly."
Slotin's death ended all hands-on critical assembly work at Los Alamos. We immediately started work on a remote control system with the critical assembly equipment and the operating crew separated by roughly a quarter mile. We had no more criticality deaths or injuries. Tributes, of all sorts, came in following Slotin's death. On 14 June 1946 the Los Alamos Times published "Slotin - A Tribute", a poem by associate editor Thomas P. Ashlock.