Search

The spectral density of the current fluctuations (noise) of the channel electron multiplier (channeltron) working in the analogue mode has been measured. The results for the channeltron operating in the pulse counting mode have been analysed and compared with those for the analogue mode. In both cases the existence of `flicker noise' (i.e. a spectral density function of the 1/fα (f is the frequency) type) has been observed unless the current has reached high enough values.

Absolute detection efficiencies of an ion-counting system have been examined for Li+, Rb+, Cs+, Ar+, and Ar2+ ions as a function of the incident ion-impact energy. The ion-counting system consists of a converter plate (SUS), an electrostatic-lens system, and a channel-type secondary-electron-multiplier. For all ions examined in this study, the detection efficiencies are about unity if the ion energy is greater than 5 keV. The charge-state dependence is not as high for Ar+ and Ar2+.

Photoabsorption coefficients of krypton and xenon have been measured to +or-5% accuracy in the 48-210 AA region using a synchrotron radiation source and channel electron multiplier photodetection.

Photoabsorption coefficients of molecular nitrogen have been obtained to +or-3% accuracy in the 380-700AA region using a synchrotron radiation source and channel electron multiplier photodetection. Broad structure in the continuum is clearly observed with an absorption maximum at 540AA and a shoulder at 430AA.

The efficiency vs operation voltage characteristics of a channel electron multiplier (CEM) with a negative voltage applied to the entrance cone are investigated in detail. In this negative bias operation, an abnormal increase in efficiency with operation voltage is found, arising from two main mechanisms. One is the change in potential distribution in the cone with the applied voltage. This is because the probability of secondary electrons ejected from the cone being pulled into the channel depends on the potential distribution in the cone. The other is the ionization of particles by leakage electrons from the gap between the CEM exit and the electron collector. Methods of solving these problems are also described.