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We have examined the properties of several isochromat detectors and selected a Galileo 4800 series channel electron multiplier/CaF 2 combination for use in IPES experiments on clean and CO covered Ru(0001). These experiments, performed at T = 300 K and at an off-normal angle of incidence, showed a bulk, a crystal-induced surface state and an image potential state for clean ruthenium with the image state being suppressed at intermediate CO coverages and re-emerging with the formation of ordered overlayers. Two new features emerge upon CO adsorption. They are attributed to a splitting of the 2π ∗ state into bonding and anti-bonding components.

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+.

Channel electron multiplier array (CEMA) amplification factors were determined for organic ions in the mass range of 31–614 amu, noble gas and Hg ions by direct comparison of the output signals of the CEMA (Mullard G 40 25 ) and a Faraday cage collector, both placed at the detector end of a mass spectrometer. Empirical formulae are discussed to represent the gain as a function of the mass, the structure, and the energy of the ion.

Pulse height distribution are measured when multiply charged ions of S, Ne, F, O, N and C are incident on a microchannel plate of chevron type (MCP) and a channel electron multiplier (CEM) in the velocity range of 3–4.5 × 105 m/s. The pulse height distributions obtained with the CEM shows no significant dependence of the gain on the energy, mass and charge state of incident ions. On the other hand, for the case of the MCP, an increase of the gain is observed with an increase of the charge state of incident ions irrespectively of ionic species. Such behavior is discussed in connection with secondary electron emission yield at the input and electron multiplication mechanism iin the channels.

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.

Some fundamental studies on the application of a continuous channel electron multiplier (channeltron) for monitoring gaseous tritium present in an evacuated vessel at low pressures below 10(-4) Torr were carried out. The results showed that at the tritium pressures lower than 10(-6) Torr the tritium counting rate measured by the channeltron increased linearly, in practice, with increasing tritium pressure, as was expected by assuming that the interactions between beta-particle emitted from tritium and the vessel wall and gaseous molecules during the migration of beta-particle to the channeltron can be ignored. However, in the range of pressures over 10(-5) Torr the measured tritium counting rate was found to be getting smaller than the expected with increase in tritium pressure. This is presumably due to the absorption and scattering of beta-particles by gaseous tritium.

A method for determining relative channel electron multiplier (CEM) detection efficiencies for low energy neutrals using the technique of direct recoiling is described. The method uses time-of-flight analysis of low-energy atoms recoiling from an energetic ion/surface collision. The system used for demonstration is 1–10 keV Ne+ scattering from a polyimide resin surface, producing H and C recoils. The behavior of the CEM detection efficiency γ can be divided into two regions: A flat plateau region is observed at high velocity while below a specific velocity, νH = 4.4 × 107 and νC = 3.2 × 107 cm/s, γ decreases linearly with velocity with slope d γ d ν = 6.4 × 10 −8 s/cm . This behavior is discussed in terms of secondary electron emission by a kinetic ejection process.

The electrons emitted when tritium β decays can be used to determine the amount of near-surface tritium in materials. A tritium contaminated sample is placed near a channel electron multiplier (CEM) in a vacuum chamber. If information is available about the depth distribution of tritium in the material, energy analysis of the electrons emerging from the surface allows an absolutely calibrated, noninvasive assay of the amount of tritium near this surface. The assay apparatus is described, and the method for relating the CEM counting rate of a given sample to its tritium content is explained. Comparisons with experiment are presented.

A vacuum apparatus suitable for measurements of conversion electron Mo¨ssbauer spectra at temperatures up to 1200 K is presented. The apparatus allows CEMS measurements and in situ heat treatment of the samples under ultra-high vacuum conditions. The detecting system is based on the channel electron multiplier used in a close-to-sample geometry. A special technique of suppressing the background due to thermally activated electrons and ions is described. Examples of measurements with a metallic iron foil above the Curie point and with crystals implanted with 57 Fe ions are given.

In this paper we review the present status of experiments that test quantum electrodynamics (QED) using the simple atoms of hydrogen (H), muonium (Mu), and positronium (Ps). Since the recent developments in QED theory are reviewed separately (see G. P. Lepage — these proceedings) we need only introduce the results of such calculations for clarity and completeness. Emphasis will be given to the experimental techniques employed, the most recent experimental results, and the outlook for future improvement in the measurements.

The Mossbauer spectra of 77.3 keV γ-transition in 197Au have been measured for the first time in the conversion electron scattering mode, with the use of a channel electron multiplier at low temperatures. The high magnitude of the resonant effect obtained makes the investigations of various phenomena in very thin gold films feasible. The application of the technique in studying other high-energy Mossbauer transitions is also possible.

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.