Coincidence instruments

Because the flight time of each ion is the time interval that begins with detection of an electron released in the same ionization event, this is a coincidence instrument. The only requirement for such instruments is that ionization events occur (predom-inandy) at intervals longer than the time-of-flight measurement. 

To increase the sensitivity, direction of amplitude variation of probe output signal in defective area must coincide with the one after CCF processing. If the defect decreases the probe signal (single contact probe) A((/should be set Ai// = 0, in the opposite case (twin contact probe) it should be set Aif/= n. So the instrument should be supplied with a device to adjust A((/ and to sustain it constant. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

All MC-ICPMS instruments are equipped with a multiple Faraday collector array oriented perpendicular to the optic axis, enabling the simultaneous static or multi-static measurement of up to twelve ion beams. Most instruments use Faraday cups mounted on motorized detector carriers that can be adjusted independently to alter the mass dispersion and obtain coincident ion beams, as is the approach adopted for MC-TIMS measurement. However, some instruments instead employ a fixed collector array and zoom optics to achieve the required mass dispersion and peak coincidences (e.g., Belshaw et al. 1998). 

Figure 8. Schematic outline of a second-generation MC-ICPMS instrument (Nu Instalments Nu Plasma), equipped with a multiple-Faraday collector block for the simultaneous measurement of up to 12 ion beams, and three electron multipliers (one operating at high-abundance sensitivity) for simultaneous low-intensity isotope measurement. This instmment uses zoom optics to obtain the required mass dispersion and peak coincidences in place of motorized detector carriers. [Used with permission of Nu Instruments Ltd.]...

Thus, the region 2100-1830 cm 1 can be covered. This allows us to monitor CO(v,J) by resonance absorption and various M(CO)n [n = 3-6] as a result of near coincidences between the CO laser lines and the carbonyl stretching vibrations of these species. The temporal response of the detection system is ca. 100 ns and is limited by the risetime of the InSb detector. Detection limits are approximately 10 5 torr for CO and M(CO)n. The principal limitation of our instrumentation is associated with the use of a molecular, gas discharge laser as an infrared source. The CO laser is line tuneable laser lines have widths of ca. lO cm 1 and are spaced 3-4 cm 1 apart. Thus, spectra can only be recorded point-by-point, with an effective resolution of ca. 4 cm 1. As a result, band maxima (e.g. in the carbonyl stretching... 

The output of each power range channel is directly proportional to reactor power and typically covers a range from 0% to 125% of full power, but varies with each reactor. The output of each channel is displayed on a meter in terms of power level in percent of full rated power. The gain of each instrument is adjustable which provides a means for calibrating the output. This adjustment is normally determined by using a plant heat balance. Protective actions may be initiated by high power level on any two channels this is termed coincidence operation. 

Fortunately, our interest in micro-constituents in the seawater both from the environmental and the nutrient balance points of view has coincided with the availability of advanced instrumentation capable of meeting the analytical needs. 

With the LS-5B instrument, the printing of the sample photomultiplier can be delayed so that it no longer coincides with the flash. When used in this mode, the instrument measures phosphorescence signals. Both the delay of the start of the gate (tA) and the duration of the gate (t ) can be selected in multiples of lOps from the keyboard. Delay times may be accurately measured, by varying the delay time and noting the intensity at each value. 

The simplest instrument that finds extensive use is the strobotac which illuminates the object at varying frequencies. When the frequency of the strobotac flash coincides with that of bubble formation, the image of the bubble appears to be stationary. This method is evidently useful only when the system is transparent. 

If the economist s question is asked, it is often assumed that it is unlikely that organic farming as a fixed system coincides in respect to environmental performance with the aspiration level of society for each indicator (Alvensleben 1998). This point of view follows the Tinbergen rule of economic theory that tells us that the number of policy instruments chosen should at least equal to the number of targets set (Ahrens and Lippert 1994, Henrichsmeyer and Witzke 1994). This is theoretically sound if the following prerequisites are given ... 

The Ubbelohde viscometer is shown in Figure 24c. It is particularly useful for measurements at several different concentrations, as flow times are not a function of volume, and therefore dilutions can be made in the viscometer. Modifications include the Cannon-Ubbelohde, semimicro, and dilution viscometers. The Ubbelohde viscometer is also called a suspended-level viscometer because the liquid emerging from the lower end of the capillary flows down only the walls of the reservoir directly below it. Therefore, the lower liquid level always coincides with the lower end of the capillary, and the volume initially added to the instrument need not be precisely measured. This also eliminates the temperature correction for glass expansion necessary for Cannon-Fenske viscometers. 

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