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Q & A: fission bombs

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Most recent answer: 10/22/2007
Q:
Another question( don’t worry, none of these are homework questions... yet) I know that if you split an atom, it would cause an explosion. This is how atomic bombs work. a.) Why is this? How does this work? b.) What is the ratio of atoms:size of the explosion? How many atoms are split in an atomic bomb?
- Tom (age 11)
A:
It's not really true that splitting some atoms causes an explosion. In many cases, when the nucleus splits it ends up with lower binding energy, so that the extra energy gets released. An explosion results only when the fission products (specifically the neutrons) stimulate more splitting, and that stimulates still more, etc, in a chain reaction. That only happens if enough material is packed together tightly, otherwise the neutrons released by one splitting escape before they are likely to trigger another one.

There are different types of atom bombs, which split somewhat different numbers of atoms. I'll give only a very rough estimate based on how much energy is released and my dim memory of about how much energy is released per atom: around 10^23 or 10^24 nuclei split. The bomb has to have around 10^26 atoms in it, because most of the nuclei don't split.

Mike W.

(published on 10/22/2007)

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