AUTOMATED PARTICLE ANALYSIS OF POPULATIONS OF SILVER-HALIDE MICROCRYSTALS BY ELECTRON-PROBE MICROANALYSIS UNDER CRYOGENIC CONDITIONS

An automated particle analysis routine is implemented on an electron m icroprobe for analyzing the chemical composition and projective area o f populations of individual silver halide microcrystals. An LN2 cryost age is used to prevent material degradation due to reaction with the i mpinging electron beam. The background in the EDX spectra is lowered b y depositing the microcrystals on a carbon-coated copper grid, mounted in a transmission holder. The IL-alpha/AgL-alpha net X-ray intensity ratio, obtained from a spectrum-fitting algorithm, is used to determin e the crystal composition by means of a standard-based calibration cur ve. The uncertainty on the concentration measurement of individual mic rocrystals is calculated using the uncertainties on the net X-ray coun ts and the uncertainties on the calibration curve. The area measuremen t is optimized by introducing a gray value histogram correction on eac h individual measurement. Overlapping microcrystals are scrapped from the analysis by defining a maximum shape factor, against which the sha pe factor of the microcrystal is tested. To minimize problems with dri ft of the cryostage, spectrum acquisition is carried out immediately a fter a single microcrystal has been located, based on the backscattere d electron image. Several applications are discussed.