On the electron microscopy of fission fragment damage

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Abstract
The damage which is produced in a single crystal by the excited electrons energized by a fission fragment is explained on the basis of a simple classical model. An ‘average’ primary electron, or delta particle, possesses a typical energy of some 80 ev and this is communicated to the lattice, first by electron/electron interactions and then by electron/phonon interactions. A critical parameter is the effective range x s traversed by a typical secondary electron, and the magnitude of x s is a function of the nature of the lattice vibrations excited. In polar crystals both polar and acoustic modes are important, but in non-polar crystals only acoustic modes need be accounted for. Optical modes are relatively unimportant. The nature of the fission fragment damage observed by electron microscopy is shown to depend also upon the rate at which the secondary electrons are produced by the primaries, on the activation energies for defect-creating and defect-migrating processes, and on whether the crystal is an element or a compound.

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