The background of negative ions emitted from a cold-pressed and sintered surface ionizer was studied. The ion beams were mass analysed and their temperature dependence was measured in order to determine the origin and formation mechanism of the various ions. The predominant ions in the spectrum were BO2- and BO-; both probably originating from the interior of the ionizer. Uncondensable substances appearing in the rest gas, such as oxygen and hydrogen, were believed to be ionized by electron capture processes. The modulated voltage method was used to estimate the ionization efficiency of the ions formed by surface ionization, resulting in values for the halogens (70 to 95%) that could be expected from the Saha-Langmuir equation.

The Mass Spectrum of Negative Ions Emitted from an LaB6 Ionizer. Martenson, B.M., Wilhelmsson, S.O.: International Journal of Mass Spectrometry and Ion Processes, 1985, 67[2], 179-89