Hydrogen bomb

  1. Could somebody explain exactly how a hydrogen bomb is supposed to work? I have a pretty basic idea, but I need more info.
    [?]
     
  2. jcsd
  3. LURCH

    LURCH 2,514
    Science Advisor

    The H-Bomb is a fusion device that fuses the nuclei of hydrogen isotopes, deuterium and tritium. The most basic bomb design includes a fission bomb which consists of several "lenses" of chemical explosive (lense-shaped to direct the blast) around a core of enriched uranium. The difference is that, at the center of the core of fissionable material, there is a ball (about the size of a grapefruit) of these fusable hydrogen isotopes. Or more accurately, the deuterium is present, mixed with lithium to form a stable metal (called lithium deuterate) that can be stored. Tritium has a very short half-life and is almost impossible to store, but we'll get to the solution for that problem in a moment.

    When the device is triggered, the fission bomb works in the normal way. The shaped charges deliver asymmetrical shock wave inward, compressing the fissionable material. At sufficiently high pressures and temperatures, the atoms of U-238 begin to split, releasing x-rays and neutrons. These neutrons collide with other atoms causing them to split, and a chain reaction is sustained.

    Now for the part that makes it and H-bomb and not just an A-bomb. The x-rays from the fission reaction heat the lithium deuterate to a high-energy state. Meanwhile, neutrons bombarding the lithium produce the hydrogen isotopes, tritium. When these two things have occurred, the result is deuterium and tritium contained in a small space, and very high temperature, and under extreme pressures. Under these conditions, deuterium fuses to tritium, and also to other deuterium.
     
  4. Now I get it.

    Thanks LURCH. Having a very limited knowledge and understanding of of how nuclear fusion works, it helped me quite a lot to have that more detailed explanation.
     
  5. pmb

    pmb 0

    Correct me if I'm wrong but there is also another design where two subcritical peices are fired together to produce a superctical mass. I.e. one piece is at the end of a tube. The other piece is at the other end. An explosive is detonated behing that pieve and rams it into the other.

    Pete
     
  6. LURCH

    LURCH 2,514
    Science Advisor

    Yes, I think it's usually reffered to as a "plutonium gun" design. But AFAIK, this design is only used for fission bombs, and not fusion. Although I can see where it might work for fusion, if one of the pieces has lithium deuterate in it. I've just never heard of it.
     
  7. russ_watters

    Staff: Mentor

    I believe that it was only used for ONE: one of the bombs we dropped on Japan. And I think it was a uranium bomb, not a plutonium one.
     
  8. Just to clarify a little for a child called Photon

    Hi photon and string,

    While I have no intention of raining on anyone's parade, I believe that my long time forums associate and friend, Lurch, will forgive my constructive (I hope)editing of his earlier post from a participant's viewpoint. Note: emboldenment below indicates "strekethroughs".

    The H-Bomb is a fusion device that fuses the nuclei of hydrogen isotopes, deuterium and tritium. The most basic bomb design includes a fission bomb, which consists of several "lenses" of chemical explosive (lens-shaped to direct the blast) around a core of enriched uranium (enriched U-235 was the primary fuel of the Hiroshima gun gadget and was wrapped around a reduced radius Pu-239 sphere - “composite core” in two U.S. models, VI and XIII). The difference is that, at the center of the core of fissionable material, (pure Pu-239 of radius 2.242 inches and of mass 13.8 kg = ~30 pounds, and having at its center an 11-mm diameter polonium-beryllium pellet neutron initiator). there is a ball (about the size of a grapefruit) of these (The) fusible hydrogen isotopes (were in a cigar-shaped Helium chilled dewar inclosing a tube of liquid deuterium – the axis of the cigar included the center of the Mark V fission device that was separated from the cigar end by perhaps ten inches and that included a U-238 blast protector.) Or more accurately, the deuterium is present, mixed with lithium to form a stable metal (called (as) lithium deuteride, a white powder,) that can be stored. Tritium has a very short half-life and is almost impossible to store, but we'll get to the solution for that problem in a moment.

    [A thirteen-year half-life of tritium has not impeded the DOD from tolerating weapon storage for more than a decade, at which time it can be updated.]

    When the device is triggered, the fission bomb works in the normal way. The shaped charges deliver a symmetrical shock wave inward, compressing the fissionable material. At sufficiently high pressures and temperatures, the atoms of U-238 (PU-239) begin to split [from first neutron to bang is about 5 millionths of a second] releasing x-rays and neutrons. These neutrons collide with other atoms causing them to split, and a chain reaction is sustained.]

    Now for the part that makes it and H-bomb and not just an A-bomb. The x-rays* from the fission reaction heat the lithium deuterate to a high-energy state. Meanwhile, neutrons bombarding the lithium produce the hydrogen isotopes, tritium. When these two things have occurred, the result is deuterium and tritium contained in a small space, and very high temperature, and under extreme pressures. Under these conditions, deuterium fuses to tritium, and also to other deuterium.
    *In the Mike device, there was a channel between the thick U-238 jacket and the cigar dewar cylinder; there was also a tapered liner of the jacket made of polyethylene and lead that converted the radiant gamma wave to a cylindrical implosion that compressed the liquid deuterium – the “stick velocity” of the deuterium burn was perhaps 50+ km/sec compared with 7 or so km/sec for TNT.

    [There was no lithium in the Mike device of operation Ivy so I have no details concerning the previous paragraph. I do know that the probability (so-called “cross section”) (n, p) reactions being touted above are not even listed; for the usual Li-7 the c. s. for (n, gamma) is 0.035 barns and the c. s. for Li-6 (n, alpha) is 945 barns. It is notable that the outer U-238 ballistic jackets on earlier US “dry” bombs did result in a tertiary fissioning of those jackets - in the particular unit that resulted in the demise of Japanese fishermen, I recall that about half the 14 megaton yield was due to tertiary fission yield.]

    [Although the US “wet” design was conducted to prove the H-bomb efficiency, it was unique and the “dry” design of the USSR’s first H-Bomb became the deliverable weapon type model for both the US and the USSR.
    I tried to convince the hierarchy at Los Alamos that, because the inter-atomic spacing of hydrogen atoms in dodecaborane was 1.30 units compared with that in liquid hydrogen of 1.29, that boron hydride might be a better dry salt; my mission was thwarted completely when a grad student (it surely couldn’t have been a professor) at UNM somehow accidentally blew up a chem. lab with only a small amount of the stuff.]

    Thanks for your audience, cheers, Jim
     
    Last edited: Sep 21, 2003
  9. pmb

    pmb 0

    That was what I was refering to.

    Thanks

    Pete
     
  10. LURCH

    LURCH 2,514
    Science Advisor

    Oh yeah, that's right. "Fat Man" (Hiroshima) was a shaped-charge implosion device, but "Little Boy" (Nagasake) was a Uranium-gun design.

    NEO, wow, much better description. More accurate in the details. But, are you saying that the tritium is produced and then stored within the device? I thought the whole reason for mixing the deuterium with lithium was so that tritium would not need to be stored, because it would be produced during the fission stage.

    Photon, turns out there's a description at "How Stuff Works" that has an animation. Pretty cool.
     
  11. when you drop the bomb, it explodes and everyone dies
     
  12. More about Tritides

    Hi again Lurch,
    The so-called "Little Boy", as named by the media, was known inside as the "25 Gadget" {element #92 and isotopic mass of U-235; on the inside, "Fat Man" was called: "49 gadget". Because weapon-grade U-235 was slow coming (one per month)and over-fueled by a factor of three (in order to quarantee success without a pre-test),it was essentially on hand before the Nagasaki "Fat Man" design was being tested at Operation Trinity on 7/16/1945.

    Tritium is created by cosmic ray type spallation reactions or by impinging fast neutrons on nitrogen N^14(n,T)C^12. DT reactions are the copious source of fusion created 14.5 MeV neutron in a vacuum tube type gadget in which a hot positively charged T-salted "cathode" boils off a beam of tritons that are accelerated at 180 kilovolts into a negatively charged Deuteron salted "plate". Also, not unlike white powder Li-tritide other tritium salting such as Hafnium-DT/DD, Uranium-DT/DD used the fusion aspect to replace the neutron source of stockpiled fission weapons. The little pellet that earlier,pre-1951, was filled with Polonium/Beryllium, was replaced with DD and/or DT salts that were squeezed at pressures in excess of 6 megabars. The upshot of the change was: with the Po-Be iniator, only 6 neutrons were typically avaiable in the 5 microsecond reflected decompression wave window after which criticallity dropped below "one"; the new pellet produced up to 10^10 neutrons during the same window. Thanks for your audience. Cheers, Jim

    Photon, turns out there's a description at "How Stuff Works" that has an animation. Pretty cool. [/B][/QUOTE]
     
    Last edited: Sep 24, 2003
  13. Uhmm, Lurch, you've got that, the names and the targets, backwards......Referance
     
  14. LURCH

    LURCH 2,514
    Science Advisor

    Yeah, I noticed that the next day, but was just too darned lazy to go fix it!
     
  15. That H bomb design is the Russian one. Not that it makes much difference, but I think the American design had a single chem lens.
     
  16. Not so, VBP

    Hi VB,
    Earlier in this string, I mentioned that a complete 32 Lens Mark V plutonium-239 fueled fission bomb was the source of the radiant gamma wave pressure that was used to compress the cigar shaped liquid deuterium filled "dewar" cylinder in the original American H-Bomb. The Mark V explosive layer, including lenses had an outer diameter of 39 inches (another trial of this model that was abandoned had a diameter of 45 inches) and the Aluminum "pusher" and depleted uranium-238 "tamper" had been thinned out and the standard Trinity Pu core had been levitated on a thin-walled U-238 conic structure. Cheers, Jim
     
  17. This explanation of the way a hydrogen bomb works by LURCH, is it the most current, I mean, do they use any other substances or isotopes for the fusion bomb?
     
  18. if you want a related site, this one had been posted somewheres, but I couldn't find that link, but I found the site again, so's.....

    "How to make an H Bomb"

    But be forewarned of these issues cited from that site, herein,
    Followed by this 'lovely' (Sarcasm) piece of advice...
    It should be clearly noted (by anyone with a brain) that the manner of getting U235 to generate 'neutron expulsions' is by COMPRESSION!

    Hammering a metal is a form of "attempted compression", hence you could easliy arrive at the idea that pounding away at your malleable u235 is likely to generate "neutronal emissions", the radioactivity, (hence DOSE) that that is.

    Please DON'T try this at home, or anywheres else for that matter!
     
    Last edited: Nov 25, 2003
  19. The gun design only works for uranium, not plutonium. This is why it's so "easy" to make a nuclear bomb with U235. Uranium (gun) bombs are less efficient in their fission process than the focused implosion bombs which use plutonium. The latter tends to give higher blast yields.

    As mentioned, the "Little boy" bomb dropped on HIroshima was a gun trigger at about 12-15 kt. Nagasaki was a plutonium device, estimated to be in the 20-22 kt range.
     
  20. So far (i think) that no one has mentioned the use of Beryllium in nuclear device. It is placed between the nuclear material and the explosives to increase the efficeincy of the explosion by reflecting neutrons back into the active area. With this, instead of 11Kg Pu only 4Kg would be needed (with an explosion equivalent o Nagasaki). The most crazy thing of this is that 4Kg of Pu is about the size of an orange and can destry so much.
     
  21. Uhmm sure 'bout that?? Beryllium is used (AFAIK) because it is a hard/strong enough metal to be able to withstand the explosion that propels the "soon to be fissioned" material together, nothing to do with that actual explosion from fission or fusion.

    That is the reason why it is on a list of "Internationally restricted trade" items......

    But you are right, takes very little to disrupt alot, just like in class, in school, one person can ruin the entire classes experiences...
     
    Last edited: Dec 21, 2003
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