Detection efficiencies

From this relation one gets for the probability W of the ejection of one or more secondary electrons 

The same arguments hold for the detection efficiency of a channelplate detector as for the channeltron, but in addition the ratio ropenarea of the area channel openings to the total plate area has to be included also. As a rough estimate one gets 

The quantitative evaluation of relative intensities for selected photo- or Auger processes requires information about both the relative kinetic energy dependence of the analyser transmission T (see Fig. 4.15) and the accompanying detection efficiency e of the electron detector. The relative magnitude for the desired product Te can be determined directly if, for example, non-coincident electron and ion spectrometry are combined with helium as target gas, the Is photoline is recorded as a function of the photon energy and yields the dispersion corrected area AD (electron) see equ. (2.39)  

In this expression the product Te may change with the kinetic energy. (For kinetic energies approaching zero, the relative spectrometer resolution A sp/ °in will also change (see Fig. 4.14), but this change can be measured by means of electron spectrometry.) The number N+on of He+ ions can be recorded simultaneously by the ion spectrometer  

The quantities in the brackets on the right-hand side are constant (energy-independent), and the relative instrumental resolution of the electron spectrometer can be measured. Therefore, the dependence of Te on the kinetic energy can be established on a relative scale. An example is shown in Fig. 4.30. 

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Easily interpretable patterns are observable the first one is an horizontal pattern, located around 15 Hz, and is due to Pilgrim noise. Four regularly spaced vertical patterns are also observable, and shows the detection efficiency. They are due to the presence of the 4 inner circonferential notchs of successive 60%, 40% 20% and 10% deepness notchs. 

Classical ion trajectory computer simulations based on the BCA are a series of evaluations of two-body collisions. The parameters involved in each collision are tire type of atoms of the projectile and the target atom, the kinetic energy of the projectile and the impact parameter. The general procedure for implementation of such computer simulations is as follows. All of the parameters involved in tlie calculation are defined the surface structure in tenns of the types of the constituent atoms, their positions in the surface and their themial vibration amplitude the projectile in tenns of the type of ion to be used, the incident beam direction and the initial kinetic energy the detector in tenns of the position, size and detection efficiency the type of potential fiinctions for possible collision pairs. 

Metastable and collisionally induced fragment ions can be detected efficiently by a triple quadrupole instmment. By linking the scanning regions of the first and third quadrupoles, important information about molecular structure is easily obtained. 

Metastable ions can be detected efficiently by using three quadrupoles in tandem, a QQQ instrument. 

LEIS the energies of the ions are too low for PIPS detectors and would lead to a sig-nal-to-noise ratio less than unity. A stack of microchannel plates is, therefore, used to detect the ions in LEIS. The detection efficiency of the microchannel plates is included in the experimental transmission factor Tin Eq. (3.34). 

SIMS has superb surface sensitivity since most of the secondary ions originate within a few nanometers of the surface and since high detection efficiency enables as little as 10 " of a monolayer to be detected for most elements. Because of its very high surface sensitivity, SIMS can be used to obtain depth profiles with exceptionally high depth resolution (<5 nm). Since the beam of primary ions can be focused to a small spot, SIMS can be used to characterize the surface of a sample with lateral resolution that is on the order of micrometers. Elements with low atomic numbers, such as H and He, can be detected, isotope analysis can be conducted, and images showing the distribution of chemical species across... 

The PECD measurement clearly takes the form of a cosine function with an amplitude given entirely in terms of the single chiral parameter, b. It therefore provides exactly the same information content as the y asymmetry factor dehned above [Eq. (8)]. Experimental advantages of examining the PECD rather than the single angular distribution /p(0) are likely to include some cancellation of purely instrumental asymmetries (e.g., varying detection efficiency in the forward-backward directions) and consequent improvements in sensitivity. 

In addition to the surface/interface selectivity, IR-Visible SFG spectroscopy provides a number of attractive features since it is a coherent process (i) Detection efficiency is very high because the angle of emission of SFG light is strictly determined by the momentum conservation of the two incident beams, together with the fact that SFG can be detected by a photomultiplier (PMT) or CCD, which are the most efficient light detectors, because the SFG beam is in the visible region, (ii) The polarization feature that NLO intrinsically provides enables us to obtain information about a conformational and lateral order of adsorbed molecules on a flat surface, which cannot be obtained by traditional vibrational spectroscopy [29-32]. (iii) A pump and SFG probe measurement can be used for an ultra-fast dynamics study with a time-resolution determined by the incident laser pulses [33-37]. (iv) As a photon-in/photon-out method, SFG is applicable to essentially any system as long as one side of the interface is optically transparent. 

In a different example, traceability in the amount-of-substance analysis of natural potassium, thorium, and uranium by the method of passive gamma-ray spectrometry was demonstrated by Nir-El (1997). For an absolute quantitative determination, accurate values of two parameters were required (i) the emission probability of a gamma-ray in the decay of the respective indicator radionuclides, and (2) the detection efficiency of that gamma-ray. This work employed a number of CRMs in the critical calibration of the detection efficiency of the gamma-ray spectrometer and the establishment of precise emission probabilities. The latter results compared well with literature values and provided smaller uncertainties for several gamma-rays that were critical for the traceabUity claim. The amount-of-substance analytical results of the long lived naturally occurring radionucHdes K, Th, and... 

The instrument MIMOS 11 is extremely miniaturized compared to standard laboratory Mossbauer spectrometers and is optimized for low power consumption and high detection efficiency (see Sect. 3.3) and [326, 327, 336-339]. All components were selected to withstand high acceleration forces and shocks, temperature variations over the Martian diurnal cycle, and cosmic ray irradiation. Mossbauer measurements can be done during day and night covering the whole diurnal temperature... 

High detection efficiency (detection of single ions)... 

Also, the distance of the injection system from the first oxidized guanine influences the product ratio Pggg/Pgu because the injection system itself can influence the water trapping rate of the nearby Gf+. Therefore, the experimentally detected efficiencies of the charge transfer (measured by the ratio of the chemical products) depend upon the special injection system and the reaction conditions. This has to be taken into account if the experimental results obtained under different reaction conditions are to be compared with each other. 

The density here refers to the spatial coordinate, i.e. the concentration of the reaction product, and is not to be confused with the D(vx,vy,vz) in previous sections which refers to the center-of-mass velocity space. Laser spectroscopic detection methods in general measure the number of product particles within the detection volume rather than a flux, which is proportional to the reaction rate, emerging from it. Thus, products recoiling at low laboratory velocities will be detected more efficiently than those with higher velocities. The correction for this laboratory velocity-dependent detection efficiency is called a density-to-flux transformation.40 It is a 3D space- and time-resolved problem and is usually treated by a Monte Carlo simulation.41,42... 

Although the absolute beam intensities, the exact size of the collision volume, and the detection efficiency are not known in a CMB experiment, they... 

Photoionization ti me-of-fli ght mass spectrometry is almost exclusively the method used in chemical reaction studies. The mass spectrometers, detectors and electronics are almost identical. A major distinction is the choice of ionizing frequency and intensity. For many stable molecules multi photon ionization allowed for almost unit detection efficiency with controllable fragmentation(20). For cluster systems this has been more difficult because high laser intensities generally cause extensive dissociation of neutrals and ions(21). This has forced the use of single photon ionization. This works very well for low i oni zati on potential metals ( < 7.87 eV) if the intensity is kept fairly low. In fact for most systems the ionizing laser must be attenuated. A few very small... 

Fig. 3.7. The detection efficiency of a system with a dead-time 350 ns as a function of the incident count rate. At high count rates the detection efficiency reduces due to pileup effects.

E represents the combined collection and detection efficiency of the system and F the intrinsic photon-economy of the technique. The factor 77 accounts for the subtractive noise, tA is the dead-time of the detector and Q the count rate of the system. 

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