Energy loss of protons channelling through very thin gold

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Abstract
The energy loss of protons channelled along the [001] direction in 500 Å thick gold is analysed as a function of emergence angle. For a given emergence angle, the energy loss can be related to a particular path along the channel and, by applying Poisson's equation to the interatomic potential, to the local electron density. The small thickness of the samples used in the present investigation, compared to prior investigations, allows a relatively simpler and more unequivocal interpretation of the experimental data than previously possible. The relative variation in the stopping power due to channelling turns out to be much smaller than the variation in the local electron density, in satisfactory agreement with recent theoretical expectations (Bonsignori and Desalvo 1969). Also, our measurements distinguish between not too different approximations to the interatomic potential : Lindhard's potential yields agreement with experiment and Nielsen's does not.