Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Nuclear bomb?

  1. Jul 18, 2006 #1
    Nuclear bomb!?!?!?!?

    Today my freind sent me a vid showing nuclear explosions and I was wondering what makes the huge explosion...

    I kind remember something from NOVA about how its the nuclear bond that connects the protons and nutrons that is realzed and thats what makesthe huge explotions and the cause of all the raditation

    So am I right or is it for some other reason...

    Here is the vid [MEDIA=youtube]6Xb-u4wQuCw[/MEDIA]&search=nuclear bomb
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Jul 18, 2006 #2
    Nuclear Fission (splitting), Uranium-235 or Plutonium-239 is shot with a slow neutron and fast neutron respectively then they become to large for the nuclear forces to hold them together, the atoms split into 2 smaller elements and let off more neutrons (1-3, 2.6 is the average, mostly 2 and 3) overall there is a mass lost, those neutrons can hit other Plutonium or Uranium atoms and set them off too, if there is enough of the stuff there and it is a decent shape then the number of Plutonium and Uranium atoms splitting will increase and eventually become explosive (very quickly, in the nano-seconds of time).

    The energy given off is = to the mass times the speed of light squared (E = mc²) since the speed of light is 3.0 x 10^8 (really big) and then it is squared, even very small masses (like that of an atom) becomes massive amounts of energy. A sphere is usually used (less surface area, so less neutrons going into the air) and the weight where it becomes critical (going to go boom) is about 20kgs.

    In a nuclear bomb you'll usually have 2 half spheres of 10kgs each and they'll be pushed together with explosives as the bomb hits the ground (or is detonated otherwise).

    The other elements that the Uranium and the Plutonium turn into are radioactive, so when the bomb explodes it sends the radioactive material all over the place.

    More powerfull bombs (Hydrogen Bombs) work on Nuclear Fusion (joining), 1 Deuterium (Hydrogen with an extra neutron) and 1 Tritium (Hydrogen with 2 extra neutrons) join together under extreme amounts of heat (100,000,000°c) to form 1 Helium and a lone neutron. The only way to obtain the massive amounts of heat to cause fusion is through a normal nuclear bomb exploding. So a normal nuclear bomb is just the trigger for a hydrogen bomb! The process of fusion with hydrogen doesn't give off any radiation, but a Hydrogen bomb is still radioactive since you need a normal nuclear bomb to set it off.

    I hope this answers your question.

  4. Jul 19, 2006 #3


    User Avatar

    Staff: Mentor

    Gelsamel is more or less correct, however fusion bombs using DT do give off radiation in the form of high energy neutrons, and even with DD, one produces either T + p or n + He3 - T is radioactive and n is a high energy neutron, which can damage tissue or make other material radioactive. If a thermonuclear device uses a U tamper, then the fast neutrons will cause fissions in some of the U.

    Also, nuclear weapons are prompt supercritical, which means the fissions are induced by fast prompt neutrons, without thermal or delayed neutrons. There is no moderator, and insufficient time to slow fast neutrons down.
    Last edited: Jul 19, 2006
  5. Jul 19, 2006 #4
    K thx dudes
  6. Jul 20, 2006 #5
    Thanks, I just wrote down what I learnt 2 years ago in Year 11 Highschool physics (I'm in year 12 now and finnished year 12 physics last year, I hate how they dumb down stuff D:)
  7. Jul 20, 2006 #6


    User Avatar

    Staff: Mentor

    Yeah, I guess they don't feel the need to provide the details on nuclear weapons in high school. In fact, I doubt many, if any, teachers would know the detailed physics behind nuclear weapons. :rolleyes:

    When I was in high school, I had to teach myself a lot of what I learned in astrophysics and nuclear/particle physics, because I couldn't get the information at school. :rolleyes:

    I spent a lot of time at unversity libraries. :tongue2:
  8. Jul 20, 2006 #7
    Nice, astrophysics was removed from the ciriculum (yay spelling) the year I would've done it! :(

    I loved Nuclear physics and motion, didn't like light but I absolutely hated electricity. I liked Special and General Relativity though, but that isn't much past remembering lorentz factor and then understanding concepts. Problem with me is I do no work at all! :( I pick up concepts and understand everything extremely quickly but I'm too damn lazy and I don't revise questions or do homework or anything. 38/50 (which is then marked up because physics is "hard") for my physics course. Not sure how it works outside Australia but I guess that isn't bad (though I hoped for over 40).
  9. Jul 20, 2006 #8
    Just as a quick question on this topic. How long after the seperate pieces of fissile material are combined will the full explosion take place. Will the chain reaction have to build up for several seconds or minutes, or is the reaction more rapid?
  10. Jul 20, 2006 #9


    User Avatar

    Staff: Mentor

    Modern nuclear weapons use implosion of a subcritical mass into a supercritical state. The objective is to make it happen as fast as possible - on the order of microseconds - i.e. pretty darn fast.

    Once the fissile mass passes the critical configuration, fissions are already starting to occur.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Nuclear bomb?
  1. Nuclear bomb (Replies: 4)

  2. Nuclear Bomb explosion (Replies: 3)