Fusafumi Nakao

Determination of the ionization gauge sensitivity using the relative ionization cross-section

Abstract The sensitivity of an ionization gauge for many inorganic gases and hydrocarbon gases up to C10 compounds has been determined using the ionization cross-section. Results obtained indicate a linear relationship with a slope of n = 1 between the gauge sensitivity and the ionization cross-section. The ionization cross-section relative to nitrogen for both the inorganic and hydrocarbon gases shows an almost linear increase with the number of electrons per molecule as well as the gauge sensitivity relative to nitrogen. In the absence of better information the gauge sensitivity of a given gas can be determined by the relative ionization cross-sections.

Simplified methods for the calculation of partial pressure using the relative ionization cross-section

Abstract Two simplified methods for the calculation of partial pressure are discussed theoretically in conjunction with the ionization probability of producing the most characteristic ion of molecules. Ionization probabilities for twenty molecules, usually encountered in many vacuum systems, are determined from the relative ionization cross section by using a correction factor. Partial pressure values calculated from these methods are compared with those from the usual mass spectrometric method. The value can be evaluated within an accuracy of less than 10% for many molecules. The method of calculation using the ionization gauge correction factor is also developed. By these methods the partial pressure evaluation becomes possible without doing troublesome calibrations of the residual gas analyser.

Quantitative depth profiling analyses of the surface layer in Be–Cu dynodes

A programmable SIMS instrument was developed and used to perform accurate depth profiling analyses of an activated Be–Cu alloy. The instrument offers information at every 75 A under typical ion bombarding conditions, 0.3 μA of 8 keV 40Ar+. Analytical results showed that the BeO of 10 wt. % or more is formed on the surface, which is composed of a reasonably homogeneous BeO layer with a thickness of the order of 300 to 500 A. The BeO spreads out toward the inner layer and reaches 5000 A or more. The Be concentration on the surface is less than 0.2 wt. %, but at a depth of more than 3000 A it aapproximates the concentration of the mother body, about 1.9 wt. %.

Photon‐blind, high collection efficiency ion detector for a quadrupole mass spectrometer

A low noise ion detector for microimpurity analysis with a quadrupole mass spectrometer has been developed using the off‐axis technique with an electrostatic deflector plate and a channel electron multiplier. This arrangement of ion detector can greatly reduce the noise and baseline shifts caused by photons and excited neutrals, which are dependent on the emission current and pressure in the ion source. The ion collection efficiency of 100% in this arrangement is obtained at a multiplier voltage of −3 kV and a deflector voltage of 10 V. The noise count rate was on the order of 1–2 Hz. The off‐axis ion collector gives a factor of 140 increase in effective sensitivity of the mass spectrometer. The minimum detection limit of the mass spectrometer with the off‐axis detector is also determined.

A High Sensitivity Programable Mass Spectrometer

A programable quadrupole mass spectrometer has been developed to make continuous observations of gaseous species present in the high vacuum atmosphere. The equipment has a multi-channel high speed programable scanner which consists of high speed IC switching circuits and accurate mass selector controls. A detailed description of the circuit and its function are given. A maximum scan speed is 1 msec per amu in the case of 100 channels. The equipment has a reproducibility of better than 99.6% and a detection limit of 10 ppm for SO2 in the chimney flue without concentration.