• Question: what is a nuklear bomb made out of

    Asked by 767merf42 to Angus, Catherine, Jenni, Melissa, Waqar on 15 Jun 2016.
    • Photo: Melissa Ladyman

      Melissa Ladyman answered on 15 Jun 2016:

      A nuclear bomb is very different from other types of bombs. They can be much more powerful, and hurt people over much larger distances. They are so much more powerful because they use a special kind of chemical reaction called a nuclear reaction- this is when the middle part of an atom collides with another atom to create to new atoms, or parts of atoms. The reaction gives out lots of energy.

      In an atomic bomb the reaction is designed to keep on going once it starts so that the first two new atoms will react with two more to make four and so on… In a nuclear explosion lots of reactions happen almost at the same time which gives out an enormous amount of energy- that is the explosion.

      I hope this makes sense. Nuclear reactions are very complicated- perhaps some of the other scientists can correct me or explain it better!

    • Photo: Angus Cook

      Angus Cook answered on 15 Jun 2016:

      A basic nuclear bomb is designed around a weird property of some radioactive elements called ‘critical mass’.

      Uranium 235, for example is an unstable, radioactive element. An atom of Uranium may randomly decide to split itself into two smaller elements. When it does this it releases energy (the two ‘daughter’ elements fly away at really high speeds). It also releases a few particles called ‘neutrons’. These neutrons are REALLY important in nuclear reactions.

      If you throw a neutron at a uranium atom, it can make that atom even MORE unstable, and make it really likely that it will split up itself. Because these splitting reactions (called ‘decays’) produce neutrons, and these neutrons can go on and cause more decays, which produce more neutrons (and so on and so on) we call this a ‘chain reaction’ (in the same way a chain is a link leading to a link leading to a link…). Because each of these splitting reactions also releases energy, you can quickly buildup to a LOAD of energy being released.
      Example with mousetraps:

      Now, a neutron doesn’t have to hit a uranium atom and make it decay. The neutron might just pass straight through all the uranium without hitting anything, and fly straight off without causing a reaction. This can happen if there’s not much uranium about. If you keep adding uranium, there’s more and more uranium atoms about so it’s more likely that a neutron will hit one and cause a decay than it will escape the uranium.

      The ‘critical mass’ is the amount of substance you need (in this case uranium) before you start a self-sustaining chain reaction (i.e. so that the uranium is keeping enough neutrons within it to keep the reaction going). For Uranium 235 it’s about 52 kg.

      A simple nuclear bomb is based around the idea of allowing a material to reach critical mass. For uranium you might do this by making two hemispheres of uranium, each of mass 26 kg, and then using an explosion to force them together. 26 + 26 = 52 kg. The uranium goes critical, releases lots of energy at once, and you have your bomb.

      Please, please don’t try this at home…

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