Analog counting

FIGURE 21.4 The detector electronics must be able to switch fast enough to detect isotope ratios that require both pulse and analog counting modes (data copyright 2003-2007, all rights reserved, PerkinElmer Inc.). 

This final point is exemplified in Figure 21.5, which shows the measurement of a flow injection peak of NIST 1643C potable water CRM, using an automated simultaneous pulse/analog EDR system. It can be seen that the K and Ca are at ppm levels, which requires the use of the analog counting circuitry, whereas the Pb and Cd are at ppb... 

Before the analog count rate data can be used in further calculations, they need to be converted into an equivalent pulse-counting count rate. This is done by using the following equation ... 

After the conversion of the analog count data to equivalent pulse count rates, the data can be integrated. The integration technique for peak jump is slightly different from that used for scan. 

The two detector modes should be calibrated to generate the conversion factor from analog counts to equivalent pulse counts. 

Analogous methods are used to calculated the measuring error related to inexact measuring of voltage Ur and/or Up. It is counted that the value of U is determined with measuring error 5%. The measuring error 5hu-, Shut at too low and high value of U are separately analyzed. 

Cayley s equation (1) rewritten in the form of (1") serves, with proper interpretation of the group theoretical aspects, as model for any number of counts defined analogously to and... 

With dote(Tors that count x-ray quanta, the time to a given number of counts is often used in the calculation of result s in stead of ihe number of counts iV, which is analogous to an output current,/.)... 

Chemists report numbers of atoms, ions, and molecules in terms of a unit called a mole. A mole is the analog of the wholesaler s dozen. A dozen could be defined as the number of soda cans in a twelve pack carton supplied by a wholesaler. Even if you could not open the carton to count the number of cans inside, you could find out how many cans are in a dozen by weighing the carton and dividing the mass of the carton by the mass of one can. A similar approach is used to define a mole (abbreviated mol) ... 

When the electrochemical potential of the electrons in the metal is counted from the point of reference just outside the metal, then at the electrode potential = 0 V it should also be equal to the value of A. At other potentials it wiU be determined by an equation analogous to Eq. (29.5) ... 

Mossbauer Spectral Analysis and Analog Measurements. Mossbauer spectra were obtained in the temperature range between 200 and 270 K and in two different energy windows (14.4 and 6.4 keV), which provide depth selective information about a sample [346]. To compensate for low counting statistics due to limited integration time, all available spectra were summed for the integrations on the undisturbed and brushed surface, respectively. In addition to kamacite (a-(Fe,Ni)) ( 85%) and small amounts of ferric oxide (see Fig. 8.38), all spectra exhibit features indicative for an additional mineral phase. Based on analog measurements... 

We can also count the total number of donor-emitted photons, or measure the corresponding analog intensity, in the presence and absence of energy transfer. From these intensities we can calculate the efficiency of energy transfer. The fluorescence intensity of the donor is proportional to the rate constant through the fluorescence pathway divided by the sum of the rates of leaving the excited state by all pathways. That is,... 

SPC techniques offer the advantage of low noise detection, providing / -values of 1-2 times lower than in analog detection. Although this can in principle result in four times faster acquisition speed this gain in speed is not realized in practice. In SPC, the comparatively high dead-times of detectors and electronics limits the acquisition speed. SPC system should be operated at count rates below the inverse of the dead-time of the system (electronics... 

Dust is probably present in the DLA and significantly affects the observed abundances. I counted 55 systems for which both Fe and Zn are measured, which are plotted in Fig. 1. The abundance of Fe is always found below that of Zn. By analogy with the interstellar medium, this behaviour is interpreted as the effect of some Fe being locked into dust grains. Other indicators for the presence of dust... 

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