Multichannel Densitometry of Gas Electron Diffraction Patterns

Abstract

The use of a multichannel linear photodioide array in obtaining diffraction intensities from photographic gas electron diffraction (GED) records is described. A commercially available RETICON 1024-channel linear array together with its programmable controller (EG & G models 1412 & 1218) combined with a MINC DECLAB-23 have been tested in this novel procedure of GED plate densitometry. One complete radial intensity distribution (plate image) is obtained every 16 ms from either a spinning or manually adjusted plate and can be dynamically viewed on an oscilloscope or digitally graphed on the DEC system monitor. This rapid data acquisition presents powerful and efficient means whereby plate centering, curve averaging, parametric refinement, and other data management can be conveniently conducted. Test analyses document that results obtained by this method are accurate and reproducible. The success of this new approach suggests the use of photodiode arrays in dynamic data acquisition systems of GED requiring no photographic intermediary, either by direct exposure of the diode array to scattered electrons, or by immediate acquisition of optical intensities from a fluorescent screen illuminated by electron impact.