A Precision Densitometer for Gaseous Electron Diffraction

Abstract
A high precision, single beam densitometer is described for gaseous electron diffraction which averages transmission by spinning the photographic plate in order to measure densities between 0.1 and 1.4 on scattering patterns with a precision approaching the limit set by electron statistics. An automatic plate reading system makes 350 digital photocurrent readings across a 10 cm diam pattern in 25 min. The precision in density values is ±0.03% in favorable cases. An error discussion includes an analysis of the effect of finite slit, density error as a function of density, and error in density resulting from averaged transmission.

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