Sunday, June 21, 2009

The Fermi Chronicles - Part 8: Neutron Interaction


OK, before getting into nuclear reactions and nuclear fission, I have to talk about the enabling mechanism for such. For nuclear fission to occur, there must be a neutron that comes into the nucleus of an atom. I already covered neutron radiation before, and won't repeat myself here (see prior entries on that subject). In any case, necessary for a self-sustained nuclear reaction is a neutron hitting the nucleus and emitting another neutron that will hit another nucleus etc. This is known as neutron scattering. Without the self-sustained neutron generation, no sustained nuclear reaction will occur.




Now, the scattering can be elastic or non-elastic (inelastic). An elastic scattering occurs when the neutron strikes a nucleus with some exchange of kinetic energy as the same neutron is redirected elsewhere, like billiard balls. In an inelastic collision, the neutron is actually absorbed by the nucleus and then a new neutron is discharged but with less kinetic energy, leaving the target nucleus 'excited' (yes, there are puns all over the place here). The 'excited' nucleus then releases the extra energy by means of gamma radiation. Here is an animation of neutron scattering on YouTube. Note the low-energy neutrons emitted now and again in the animation:








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