Mass Spectrometric Investigation of Barium Iodide and Caesium Iodide Vaporizations

Abstract

A MASS spectrometer (radius, 3 in. 45° sector) was used to examine Knudsen cell effusates1. Cylindrical graphite cells had orifice-to-evaporant surface area ratios of approximately 0.03 and were heated by conduction from a resistance furnace and by radiation from a grid above the furnace. The grid was necessary for maintaining axial temperature uniformity in the absence of radiation shielding2. Temperature was measured with a thermocouple attached to the cell base. A movable defining slit between the grid and water-cooled ion-source base made background correction of the ion signals possible; an electron multiplier followed the collector slit. Ionizing electron energies ranged from 7 to 20 eV. Repellers were kept at block potential and spectra were magnetically scanned. Vapour-pressure data (ion signals) were taken at random with respect to temperature; isotopic corrections of ion signals were made when necessary. Each experiment involved a fresh sample.