Continuous Channel Electron Multiplier Research Articles

Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes

Although only a few years old, the combination of a linear ion trap with an Orbitrap analyzer has become one of the standard mass spectrometers to characterize proteins and proteomes. Here we describe a novel version of this instrument family, the Orbitrap Elite, which is improved in three main areas. The ion transfer optics has an ion path that blocks the line of sight to achieve more robust operation. The tandem MS acquisition speed of the dual cell linear ion trap now exceeds 12 Hz. Most importantly, the resolving power of the Orbitrap analyzer has been increased twofold for the same transient length by employing a compact, high-field Orbitrap analyzer that almost doubles the observed frequencies. An enhanced Fourier Transform algorithm—incorporating phase information—further doubles the resolving power to 240,000 at m/z 400 for a 768 ms transient. For top-down experiments, we combine a survey scan with a selected ion monitoring scan of the charge state of the protein to be fragmented and with several HCD microscans. Despite the 120,000 resolving power for SIM and HCD scans, the total cycle time is within several seconds and therefore suitable for liquid chromatography tandem MS. For bottom-up proteomics, we combined survey scans at 240,000 resolving power with data-dependent collision-induced dissociation of the 20 most abundant precursors in a total cycle time of 2.5 s—increasing protein identifications in complex mixtures by about 30%. The speed of the Orbitrap Elite furthermore allows scan modes in which complementary dissociation mechanisms are routinely obtained of all fragmented peptides.

Detection efficiency of a channel electron multiplier for low energy incident noble gas ions

The absolute detection efficiency of a continuous channel electron multiplier (DeTech 407-EIC) has been measured for the noble gas ions He+, Ar+, and Xe+, with energies up to 4.9 keV. For all ions, the detection efficiency initially rises linearly as a function of velocity. Our results and a reanalysis of literature data show that the threshold velocity below which a multiplier does not respond to impinging ions cannot be regarded as independent of the ion’s atomic number, Z, as previously reported. Instead, the threshold velocity is proportional to Z−c. The experimentally obtained efficiency-versus-velocity curves for our detector have been analyzed in the region of linear increase. The resulting expression for the detector efficiency, ε, is a function of the ion’s atomic number and velocity, v, and can be written as ε(v,Z)=a(v−b/Zc)Zn, with a, b, c, and n being constants.

Photoelectron spectrometer for high resolution angular resolved studies

We report on a new electron spectrometer system designed for use on storage ring light sources. The system features a large (76 cm diameter ×92 cm long) triply magnetically shielded vacuum chamber and two 10.2 cm mean radius hemispherical electron energy analyzers. One of the analyzers is fixed and the other is rotatable through about 150°. The chamber is pumped by a cryopump and a turbomolecular pump combination so as to enable experiments with a variety of gases under different conditions. The light detection includes both a direct beam monitor and polarization analyzer. The electron detection is accomplished with either a continuous channel electron multiplier or with multichannel arrays used as area detectors.

Selection criteria for continuous channel electron multipliers in space applications

Criteria for selecting continuous channel electron multipliers were applied to fifteen Mullard units without significantly affecting their overall lifetime. The gain fatigue vs accumulated counts, the change of the pulse height distribution during lifetime, the gain degradation vs count rates as well as the gain vs operating voltage and the resolution vs operating voltage have been investigated using a tritium source. The results provide several criteria to determine good, marginal and poor multipliers. From all tested devices 25% had a very low gain and did not operate satisfactory at the end of their lifetime investigations (4×109 accumulated counts). 40% of all devices could be classified as good multipliers. Their main characteristic was a gain recovery phenomenon after 3×109 accumulated counts with a progressive gain stabilizing. Multipliers classified as marginal exhibited some unexpected behaviour during the lifetime but a gain recovery phase and gain plateau region could be identified. Furthermore, the relative efficiency of the multipliers vs electron energy as a function of the operating voltage has been measured by using a near monoenergetic electron beam.

Application of a Continuous Channel Electron Multiplier for Measuring Gaseous Tritium at Low Pressures

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.

Mass-dependent channel electron multiplier operation

This paper contains the results of measurements to determine the absolute counting efficiencies and pulse height distributions of a continuous channel electron multiplier (Spiraltron) used in the detection of hydrogen, argon, and xenon ions. The technique involves the post-acceleration of 8-eV ion beams to energies between 100 and 4000 eV. The absolute counting efficiency versus effective ion energy for the ions H2+, A+, and Xe+ is given. The Spiraltron was operated in a marginally gain saturated mode to investigate the charge pulse distribution for the three ions H2+, A+, and Xe+ at ion energies of 3 keV. The pulse height distribution for the light ion H2+ peaked near an equivalent gain of 2×107, while the distributions for the heavier ions displayed no significant peaks. This study suggests that discrimination between light and heavy ions may be accomplished in the energy range E<2 keV by utilizing continuous channel electron multipliers.

Le comportement du multiplicateur tubulaire d'electrons entre 20 et 100°C

The wall current and the charge distribution of a continuous channel electron multiplier are studied between 20 and 100°C. The influence of gas desorption is minimized to find the electronic structure of the emissive layer. Conduction current is characterized by an activation energy temperature dependence while mean charge analysis leads to a saturation process based on electronic conduction in a glassy solid.

Channel electron multipliers as detectors in organic mass spectrometry

The utility of continuous channel electron multipliers as detectors in combination with integrating amplifiers and with ion counting techniques for organic mass spectrometry has been investigated. They prove to be reliable and convenient detectors, suitable to replace conventional dynode multipliers.

Saturation in Continuous Channel Electron Multipliers

The steady state gain of electron space current in straight continuous channel electron multipliers is calculated. Ion feedback and space charge effects are neglected, but variation of secondary yield with primary energy and increased wall conductivity due to electron bombardment are considered. Saturation occurs when enough wall current is converted to space current so that the reduced electric field diminishes the effective secondary yield to unity. Predicted results are in good qualitative agreement with reported observations.

Ion Acoustic Wave Detection Using a Continuous Channel Electron Multiplier

First Page

Blanking Method for Continuous Channel Electron Multipliers

First Page

A far ultraviolet photometer for space research

A photometer for use in the wavelength region from 100 to 1300 Å has been developed. Specific bands within this region can be isolated by combining the spectral response of individual solar blind photocathodes with the transmission qualities of various thin metallic films. A continuous channel electron multiplier is used as a low background, high gain charge amplifier in the device. Each of these components is discussed in turn with emphasis placed on those characteristics which have special relevance to space borne instrumentation. Two examples of instruments employing these components are given, one a device to measure the resonantly scattered hydrogen and helium radiation in the upper atmosphere, and the other a device to measure the far u.v. photon flux generated in an aurora.

Ion Detection Using a Continuous Channel Electron Multiplier

A spiral type continuous channel multiplier was used for pulse counting heavy positive ions. The shape of the output pulses was studied. The pulse risetime was found to be very long and composed of numerous after-pulsing as revealed by the ``staircase'' appearance of the pulse. As a consequence, the count rate capability is greatly hampered. Detection of the positive ions by a catcher foil and collection of the secondary electrons lead to a smooth pulse clean of any after-pulsing and to a greatly improved count rate capability.

Detection of Metastable Atoms and Molecules with Continuous Channel Electron Multipliers

Detection of metastable He, H, Ne, Ar, Kr, Xe and molecular nitrogen with continuous channel electron multipliers

Pulse Counting Method in Mass Spectrometry

It was tried to obtain mass spectra in a pulse counting mode with a continuous channel electron multiplier.Two continuous channel electron multiplier were used.One of them had length of about100mm, inside diameter of1.5mm and arc of270°.The resistance was about2×108Ω. Background rate was0.2cps at an applied voltage of3.0kV, 0.04cps at2.8kV and0.002cps at2.6kV. When argon ions were injected with an accelerating voltage of1kV, counting rate attained to plateau above2.3kV, and its slope was1.2%/100V. Pulse height distribution at3.0kV showed saturation. The other, which had length of about84mm, inside diameter of1mm, arc of480°and resistance of about1.5×108Ω, was mounted on a90° Kmagnetic deflection type mass spectrometer with100mm radius of curvature. Characteristics of this multiplier were studied and mass spectra of residual gas were obtained. This multiplier had background rate of2-3cps at2.4kV. Mass spectra obtained with a12stage Cu-Be electron multiplier in the pulse counting mode were also investigated.

Transformer Coupling for the Continuous Channel Electron Multiplier

First Page

Operational analysis of the continuous dynode channel electron multiplier

A theory of operation is developed for the continuous dynode channel electron multiplier and its validity checked by comparison with experimentally measured data. Secondary emission, the multiplication mechanism inside the channel, is best described by a Maxwell distribution in energy and a Lambert distribution in direction of released electrons. Electron motion in the uniform axial field of the channel interior leads to three probability density functions describing at a fixed time interval after emission the electron's expected location. A graphical method is employed to relate the probability of being able to locate the electro with respect to the cylindrical channel geometry.

Detection Efficiency of a Continuous Channel Electron Multiplier for Positive Ions

The relative detection efficiency of a curved continuous channel electron multiplier has been measured for H+, H2+, 3He+, 3He++, He+, Ne+, and A+ ions over a 500-eV energy range. The detector's efficiency is presented as a function of the incoming ion's energy, velocity, and degree of ionization. Preacceleration was employed to reduce the falloff in efficiency for energies below 3 keV.

Continuous Channel Electron Multiplier Operated in the Pulse Saturated Mode

Peaked pulse height distributions are obtained from curved channel electron multipliers at high gain levels. They are caused by a gain saturating mechanism which limits the instantaneous output current from the multiplier. Various limiting mechanisms are considered. Experimental and theoretical evidence strongly supports the hypothesis that space charge limiting is the major cause of gain saturation.

Low Energy Charged Particle Detection using the Continuous Channel Electron Multiplier

It has been found to be possible to operate the continuous channel electron multiplier, a recently developed type of windowless electron multiplier, in a gain saturated mode such than single charged particles entering the input mouth of the channel will initiate output pulses whose amplitude and shape are both uniform and independent of the character of the excitation radiation. By suitable design of the channel this saturated pulse can be made stable against changes in such operating conditions as ambient pressure and applied voltage. Some degradation in the pulse height distribution is noted at very high count rates but operation for short periods at count rates of at least 105 per second is possible. When operated in this mode the efficiency of the channel for the detection of electrons over the energy range 250 eV to 10 keV is estimated to be greater than 50%. The channel multiplier has been used as the detector in rocket borne low energy electron spectrometers to obtain the energy spectrum of the auroral electrons. Data indicate that the operation of the detectors was as expected.