Entrance aperture

Electron lens systems between each component serve a number of fiinctions. A lens following the source focuses electrons on the entrance aperture of the premonocliromator and decelerates these electrons to the pass energy required... 

Thus, for a set K, an inverse relationship between pass energy, and sht width, w, exists. Retardation with a CFIA can either be in the CAE or CRR modes. This retardation is accomphshed by planar retarding grids placed across the entrance aperture of the CFIA. 

If the tube is short, the conductance of the entrance aperture cannot be neglected formulas (1.9) and (1.11) give overestimated values of C [1],... 

The geometrical and/or electrical entrance apertures of mass spectrometers are very small. 

One might think that quadrupole mass spectrometers would be less susceptible to this limitation because of their much larger entrance apertures. Unfortunately, this is only marginally true, and only for ions of low mass. This is because the electrical entrance aperture of the quadrupole Is usually considerably smaller than the physical entrance aperture. By "electrical entrance aperture" we mean that area of the physical entrance aperature through which ions must travel if they are to be transmitted through the quadrupole rod structure. The radius of this aperture, r, is small and mass-dependent as seen by the following equation... 

DIP Gun In-Line on a Quadrupole A standard DIP Gun, described above, was fitted with a special tip for testing1 on a Finnigan 4500 Mass Spectrometer which has the vacuum lock inlet in line with the quadrupole analyzer. Requirements are imposed that the primary beam not impinge directly on the analyzer entrance apertures and that the secondary ions leaving the target be directed toward the analyzer. Figure 13 shows a configuration that satisfies these requirements. 

Cesium Gun In-Line on a Magnetic Sector A cesium gun was mounted in the source manifold oriented so that the ion beam just misses the entrance aperture of an MS-50 (37). The target, coated with sample, is the inside of a truncated cone. The grazing angle of incidence was also advantageous in producing more secondary ions. 

The second example employs the near grazing primary ion incident on the target which faces the analyzer entrance aperture of a magnetic sector. The scattered ions leave nearly parallel to the surface and the slow molecular ions are drawn out using an immersion lens (37). 

Systematic effects arising from the disappearance of ortho-positronium through the cavity entrance aperture, and the rate of annihilation by collisions with the cavity walls, were taken into account by expressing the measured annihilation rate as... 

An array of circular or elliptical microlenses made of photoresist was constructed on a chip, as shown in Figure 7.7. The microlenses were fabricated on both the bottom glass plate (for focusing the excitation beam), and on the top glass plate (for collecting the emission). In addition, an array of entrance apertures was formed around the focusing microlenses to limit the excitation beam another array of exit apertures was formed around the collecting microlenses to block off... 

Fig. 4. Extrapolation of the decay rate to determine the effect of the entrance aperture (from ref. [9]). The arrow labeled theory should now be moved to 7.04 [2]...

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