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A bomb anatomy and fusion construction

  1. Mar 22, 2003 #1
    There is the hydrogen bomb and there is the nuclear weapon that uses plutonium. As far as I know the atomic structure of hydrogen versus plutonium are at the opposite ends of the chemical chart spectrum. Hydrogen having the least atomic weight of all elements and plutonium having a very high number of orbiting electrons. Can someone please help me to understand what it is that these two elements have in common that allow for nuclear fission to take place?

    Does anyone know what 'heavy water' is and how it is involved in the nuclear chain reaction creation?

    In the opposite energy producing activity of fusion, what is the cause of power generation? Is it always two hydrogen particles coming together to form helium? How does such action generate energy?
     
  2. jcsd
  3. Mar 22, 2003 #2

    drag

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    Greetings !
    Welcome to PF Selnex !

    In the order of your questions :
    1. These elements have nothing in common (except
    being elements...:wink:).
    Nuclear Fusion is when two atomic nuclei join
    together (like hydrogen into helium).
    Nuclear Fission is when an atomic nuclei falls
    appart into "lighter" atomic nuclei.
    Fusion releases energy (and possibly other things
    like neutrons) until the 54th element - iron (as far
    as I remember).
    Fission releases energy above that element.
    The reason is some effect of nuclear forces binding
    the atomic nuclei together.
    Fusion (of hydrogen in bombs) releases greater energy.

    2. "Heavy Water" are water molecules containing
    an isotope of hydrogen - Deuterium.
    It has one neutron (and one proton of course).
    Fusion reactions using deuterium and tritium (another
    type of hydrogen isotope with 2 neutrons) require
    lesser energy to enitiate.
    There is about one "heavy water" molecule in 10,000
    in sea-water.

    3. "Heavy" atomic nuclei fall apart into smaller ones
    (and other particles) - releasing energy.

    4. No, all atomic nuclei can be fused given sufficient
    energy.

    5. Like I said, "lighter" elements fusing together
    release energy (in the form of EM waves and other
    particles "flying away") due to the nuclear energy
    differences per neutron/proton in the nuclei.
    Two protons fusing into a helium isotope are
    in a "lower" nuclear energy state.

    More questions ?

    Live long and prosper.
     
  4. Mar 22, 2003 #3
    Thank you Drag for your welcoming into the PF and thank you for your detailed answers. I am curious to know where you have obtained all of your in depth answers and what your background is. I am curious because as you asked, I do have many more questions and depending on your background I could tailor my questions suitably.

    But for now let me simply continue the discussion on the explosive power of fusion and fission. Perhaps you will be able to answer more of the quesitons on the subject. During explosions, energy is released? What is your working definition for energy?
     
  5. Mar 22, 2003 #4

    Janus

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    First of all, Hydorgen undergoes fusion and Plutonium under goes fission. These are two separate processes.

    Fission involves a large nucleus "breaking apart" into smaller pieces (lighter elements.) This results in a large release of energy.

    Fusion involves taking two lighter nuclei and forcing them to together (fusing them) into one heavier nucleus. This alos results in a release of energy.

    As you go up the the Periodic table, you get less and less energy out of fusion, and when you reach Iron, it actually takes more energy to cause fusion tthen you get out.

    From the other end, as you go down the table, you get less and less energy out of fission, until , once again at Iron it begins to take more energy to cause the fission then you get out.

    Heavy water is water that is formed from deutrium rather than regular hydrogen. The deutrium nucleus consists of a proton and a neutron (rather than the more common hydrogen which only has a proton) It is chemically the same as hydrogen, just more massive (thus heavy Water.

    Heavy water is used in nuclear reactors as a moderator.

    Fission is initiated by a nucleus absorbing a neutron. (And in the process more neutrons are released which go on to cause fission in other atoms)

    The chances of a neutron causing fission goes up when it is moving more slowly. The neutrons given off by fission move fast. The moderator(heavy water) helps to absorb some of the energy of the neutrons and increases the chance that they will initiate fission and keep the reaction going.
     
  6. Mar 22, 2003 #5
    Devices like those used at Hiroshima (Gun-type Uranium device) and Nagasaki (Implosion-type Plutonium device) are based on chain reactions in fissionable material. Fission chain reactions take place when a fissionable material of a certain size goes critical. An atom of U238, when decaying produces, 2 smaller, atoms (that vary), energy and 3 free neutrons than go on to split other U238 or U235 atoms. Get enough material together and it's a runaway process....ie. explosion.

    Thermonuclear (Fusion) devices use fission devices to trigger fusion processes in Deuterium, Tritium or Lithium fuel by pressurising and heating it to intense temperatures, effectively burning the nuclear fuel. Fusion produces a great deal more energy than fission and produce megatonne+ yields.
     
  7. Mar 23, 2003 #6
    To what degree has fusion been able to be generated by scientists?
     
  8. Mar 23, 2003 #7
    Only in thermonuclear devices.....realising fusion reactors has remained elusive. What's the saying "Fusion power is 5 years away, and it will always be so"
     
  9. Mar 23, 2003 #8

    LURCH

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    Just a minor detail, this statement only refers to sustained fusion. Models of "pinched plasma" reactors have generated fusion, but could not sustain it. This is due to the fact that getting hydrogen isotopes to fuse together requires very high energy (which is why a fission bomb is used as a detonator in a fusion device). Pinched plasma fusion achieves these temperatures by heating up the hydrogen isotopes deuterium and tritium to a plasma state. This plasma is then heated further by various means. Then, magnetic fields are used to squeeze the plasma stream to a very small diameter. As you probably know, the same amount of heat restricted to a smaller area means higher temperature.

    By this method, engineers have achieved fusion. However, as soon as the isotopes begin to fuse tremendous amounts of energy are released. It is precisely a miniature of the explosion caused by an H-bomb. And, just like that explosion, it expands rapidly. This expansion causes the temperature to drop, and fusion ceases.
     
  10. Mar 23, 2003 #9
    ^^^ Just to elaborate a little, there are a number of working test fusion reactors, some which can impressive amounts of power. But they aren't efficient enough to maintain the necessary temperature for long, like Lurch said, and so are now run in short pulses.

    There are two big avenues being pursued for fusion: magnetically confined plasma reactors, often called tokamaks, are the most promising; Princeton is the leader here and in charge of ITER, the next-generation fusion plant under development. See http://www.pppl.gov/ and http://www.iter.org/ . The other is inertial confinement fusion, which uses lasers to generate a burst of fusion in fuel pellets; UW-Madison and others are working on this.
     
  11. Mar 23, 2003 #10
    Hi drag and Selnex,

    You kids are trying to put a full year of understanding in a few paragraphs and several folks are trying to help you and I would guess that most of them are leaning over backward in order not to give you a M.E.G.O experience. ( That means "My Eyes Glaze over" and I too am reluctant to give you a case of mental indigestion.
    The first day after I arrived at Los Alamos on March 24, 1944, my new civilian boss was dictating a list of tasks that I was expected to achieve and most I knew - geiger counter, scaler, vacuum system, coincidence counter, radium source and pig, a fishing chamber NO NO Jeem, phishon! and finally "fission" and more. The boss didn't explain the meaning of that word. That evening I asked another military Special Engineer in my barrack what the heck a fission was. He said, those scientists aren't gonna tell you any more that you need to know but I'll tell you - we're really working on a super-bomb called "Alarm Clock" that will explode a cubic meter of liquid Deuterium. Then he said The Germans are already way ahead on the fusion bomb but the British mission scientists claim that it can't be squeezed hard enough to detonate unless we first make an atom bomb. I learned all about everthing in one day - NOT!

    Concentrating on the fusion end of energy production I will copy the lead paragraph of an essay that I prepared to explain why a kitchen table fusion experiment I was preparing for peer review of a Phys Revs Letter had to be abandoned because of faults in the original modeling. the purpose of the following paragraph is to show why a fusion reaction could not be sustained because so much of the energy was in the form of neutrons that escaped through the surroundings that neutrons were transparent to.

    Would you like to know why “kitchen table cold fusion” isn’t possible? Very simply the fusion of two deuterons results in a compound super heavy 4Helium nucleus that splits into a 2.5 Mev neutron and a 0.76 Mev 3Helium nucleus. The problem is that the neutron leaves the vicinity of the reaction and travels for an average lifetime of about 1000 seconds (the half-life of this process is about 700 seconds). If not captured by a nucleus in its path it ultimately disintegrates into a proton-electron pair and its energy is unharvested unless it is utilized by a large light-element reservoir surrounding the reaction. In the case of deuteron-triton fusion, the liberated neutron escapes with 14 MeV of energy and a 4He atom with a little over 3MeV energy and a steady state fusion “chain” is likewise frustrated.

    More later if I haven't lost you already, Cheers, Jim
     
  12. Mar 23, 2003 #11
    Yeah I forgot to put sustained in there. :wink:
     
  13. Mar 23, 2003 #12

    drag

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    Greetings !
    NEOclassic

    Help me ?
    This is certainly general info for me and
    I'm no expert, but I do not believe I asked
    questions - I answered those of Selnex if
    you read my response, and as ignorant as I
    may be I am aware of everything that was said
    here prior to your message.
    "Cold" fusion as I understand it is a theoretical
    proccess the purpose of which (in the real world)
    is not to produce a sustained reaction, but rather
    to produce a special material with hydrogen and/or
    its isotopes spread around and contained within
    that meterial and then contract this material
    to force some of the nuclei to fuse and release
    energy in a sporadic manner. I'm not sure, but I
    think the contraction is supposed to be achieved
    through pietzo-electric proccesses or chemical
    proccesses.

    I've never been intrested in particular in cold
    fusion because it seems that the mainstream of
    fusion researchers deny it's possible. So, the
    above is just some very general stuff I read.

    Me and others - I'm sure, would be happy if you could
    provide some more expert info.
    Thanks !

    Live long and prosper.
     
  14. Mar 24, 2003 #13
    YES YOU!

    You're ticked because I didn't buy the profile you registered a week ago. When I see your birthday labeled N/A, I'm reminded that you might be obfuscating the reality that you are under 13 years, and when I look further your trite labels tend to show your intention to hide behind anonymity. Get honest with PF if you want to be respected!
     
  15. Mar 24, 2003 #14

    LURCH

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    On the subject of cold fusion;

    I recall seeing a method by which a thin wafer of "some metal" was lpaced in water, supplied with a small ellectrical charge, and returned a much greater charge. At the time, the researchers involved were calling this "cold fusion" because they claimed that the amount of energy being returned was too great to be explained by any process other than nuclear fusion.

    Others said that the process could not be fusion because of the absence of fusion byproducts. This was countered by the statement that if there were fusion byproducts, it wouldn't be "cold", and a debate raged on. I remember being disgusted and frustrated because, while the scientist in me wanted very much to know if cold fusion were possible, the pragmatist in me kept screaming "it puts out more energy than you put into it, and produces no polution, who caresif it's technically fusion or not, let's use it!"

    The cold fusion debate went on for some time, then faded quietly. I've heard very little about it in recent years. However, about the same time as that debate dropped out of popular public view, fuel cells appaered on the scene. I've allways wonderd, is this a coincidence, or was the feul cell what the "cold fusion" researchers had actually discovered?

    Does anyone know?

    BTW; I may not even have my chronologies correct, does anyone even remember the debate to which I am reffering, and whether it coincided with the appearence of feul cell tech?
     
  16. Mar 24, 2003 #15
    Hi Lurch,
    In the previous PF-2 you knew me as Jim Osborn and in MSN forums my "moniker" was Evarte Galois. A few weeks ago I addressed a post to you concerning my experience of trying to "peer review" an exploding polythene "macaroni-doped-filament" that failed when I discovered that poly used in the early "successful experiment" was not deuterated, meaning that their claimed yield of a million neutrons could not be supported with a total deuteron population of a mere million deuterons.
    Because I have found you, here and there, in other forums and have long ago been aware that your posts show you as being quiet, pragmantic, and of intellect sufficient to parry with others without being bandied about as a "stupid arm-waving quack"; I have listed you as a "buddy".

    Concerning the "metal wafer", I would be inclined to dismiss any claims without some thorough overall analysis. E.g., a process that appears coulomb-wise exothermic is really worthless unless account of the temp and volume changes attending the process are also reconciled.

    I consider as cold fusion, the many methods whose purpose is merely the production of neutrons. The invention of the neutron source called a "zipper" not only makes my point but also shows the impact energies required to control a steady current of neutrons. The zipper is a pre-transistor high vacuum type "radio" tube that propels a beam of atomized tritium from a positively charged "cathode" toward a negatively charged "plate". A volage of 180 kilovolts across the gap, produced voluminous amounts of 14 MeV neutrons. Cheers, Jim
     
    Last edited: Mar 24, 2003
  17. Mar 24, 2003 #16

    LURCH

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    Well a big "Hey Howdy" there, Jim! Isn't this a coincidence, I was just reading about that neutron gun last week.

    Another idea regarding fusion that has been rolling around my grey-matter lately; what about coliding two plasma streams? So far, all the attempts I've seen to make fusion sustainable have involved maintaining containment for a longer time. But if the problem is that equal energy spread out over greater volume means lower temp, then there are two avenues to persue. A pair of TokaMaks acting as a partical collider could add energy to the expanding plasma stream(s), keeping temperature up even though expansion occurs. The obvious question is "would it be enough additional energy?"

    I'll admit, my initial gut reaction is that it would not, but that's only a hunch. Seems as though adding more energy would make the expansion more rapid, and having the energy input be greater than the temperature loss due to expansion looks (when I try to "graph it out" in my head) something like trying to achieve perpetuall motion.
     
    Last edited: Mar 25, 2003
  18. Mar 25, 2003 #17

    LURCH

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    A natural evolution of this idea: what about many streams converging on a common point? This would combine magnetic and inertial confinement, possibly iimproving confinement and putting additional energy into the system.
     
  19. Mar 25, 2003 #18

    pmb

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    There's another thread here on nuclear energy - see
    https://www.physicsforums.com/showthread.php?s=&threadid=243

    In it I gave a (very) brief outline of why hydrogen fusion releases energy an splitting plutonium releases energy. The key to understanding why hydrogen fussion yields energy whereas plutonium fission releases energy is the understanding of binding energy - which is related the potential energy of the nucleons in the nucleus of the atom.

    However what has not yet been mentioned here is the operation of a Hydrogen bomb - A Hydrogen bomb is, basically, a fusion bomb. But litterally it is really kind of fission bomb and a fussion bomb rolled into one. The fission bomb is used as a trigger in order to superheat the hydrogen.

    Microsoft Encarta explains this as follows

    "The thermonuclear bomb exploded in 1954 was a three-stage weapon. The first stage consisted of a big A-bomb, which acted as a trigger. The second stage was the H-bomb phase resulting from the fusion of deuterium and tritium within the bomb. In the process helium and high-energy neutrons were formed. The third stage resulted from the impact of these high-speed neutrons on the outer jacket of the bomb, which consisted of natural uranium, or uranium-238. No chain reaction was produced, but the fusion neutrons had sufficient energy to cause fission of the uranium nuclei and thus added to the explosive yield and also to the radioactivity of the bomb residues."

    Pete
     
  20. Mar 25, 2003 #19

    LURCH

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    Speaking of "binding energy", I just realized that no one has got around to mentioning why the two types of "nukes" use hydrogen and uranium/plutonium, which are at opposite ends of the periodic table.

    In case it has not already become obvious, fusion uses hydrogen because it is the latest element. The trick to remember is that the strong nuclear force (which binds protons together in the nucleus) is much more powerful than electromagnetic force, but has a very short range. So, in order for fusion to take place, all one must do is get to atomic nuclei close enough to one another so that they are within range of the strong nuclear force. Of course, both nuclei containing protons and therefore both having positive charge, they resist. A hydrogen atom has only one proton, and offers the least resistance possible. The nuclei of two helium atoms (with two protons each) have twice as much charge, and are therefore much more difficult to cram together.

    But a uranium/plutonium atom has a HUGE nucleus. In fact it is my understanding that these nuclei are so large, and the strong nuclear force has such short range, that two protons on opposite sides of the nucleus are almost beyond the range of that force. That makes these atoms the easiest to "split".
     
  21. Mar 25, 2003 #20

    pmb

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    Actually LURCH that was what I just explained in my previous post - although I did so by linking to my explanation from another thread - but hey! More the merrier right? :-)

    Pete
     
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