Peak counting

Another way of demonstrating currently achievable performance with the above system is shown in Table 13. Here, the peak counts/sec from a typical empty suitcase, leather attache case, and the leather attache case containing six sticks of Dynamite are compared to the background level. The attache case, in both cases, was also filled with common nitrogen-rich materials such as wool, vitamins Bj and B12t pills, rayon, saccharin, silk and other materials such as paper, cotton and brass ... 

The large amount of S in the particles suggested that S02 gas molecules or small sulfur-containing particles condense on to the surface of soil dusts during their transportation from China. Figure 4.22 illustrates an elemental map for Si distribution in coarse particles within a total scanning area of 25 pm x 25 pm. The scale bar shows the peak count of characteristic X-rays by pixel of the scan area. 

We present here the theory behind the method, which has been used on D3 for some 20 years, to achieve such optimisation. Because (+) and (-) peak count rates and peak/background ratios may differ strongly from one reflection to another and are not known a priori, the measurement is divided into a number of steps of duration T. A first flipping ratio measurement is made in predefined conditions (4+, 4-> 4+, 4-). Then, after calculating the counting-time proportions which minimise the variance of the flipping ratio, the time already spent is subtracted and the measurement is made again with times chosen to achieve these optimised proportions. The process of calculation and measurement is repeated in each step. 

The results of adsorption and desorption of CO mentioned above suggest that for the reaction at low temperature, the sites for relatively weakly chemisorbed CO are covered by the deposited carbon and the reaction occurs between molecularly adsorbed CO and oxygen on the carbon-free sites which are the sites for relatively strongly chemisorbed CO. Therefore, the definition of the turnover rate at 445 K remains as given in Equation 1. For the reaction at 518 K, however, this definition becomes inappropriate for the smaller particles. Indeed, to obtain the total number of Pd sites available for reaction, we now need to take into consideration the number Trp of CO molecules under the desorption peak. Furthermore, let us assume that disproportionation of CO takes place through reaction between two CO molecules adsorbed on two adjacent sites, and let us also assume that the coverage is unity for the CO molecules responsible for the LT desorption peak, since this was found to be approximately correct on 1.5 nm Pd on 1012 a-A O (1). Then, the number Np of palladium sites available for reaction at 518 K is given by HT/0 + NC0 LT s nce t ie co molecules under the LT desorption peak count only half of the available sites. Consequently, the turnover rate at 518 K should be defined as ... 

Can an unquenched double Gaussian be differentiated from a discrete double or triple exponential decay We fit a double Gaussian distribution (Tcenter = 5 and 15 R s = 0.2 50% intensity from each) to discrete double and triple exponentials. Even with the double exponential fit, the n sare well below the SPC noise level and the triple was essentially a perfect fit. Therefore, a discrete double or triple exponential decay would be indistinguishable from the true underlying double Gaussian distribution at 104 peak counts.(55)... 

Of course, the problem in decay time measurements is improved noticeably if the noise level can be reduced. This is possible, but expensive. SPC instruments with peak counts of 500,000 have been developed. 59 ... 

FIGURE 5 (a) Peptide digest run on a 4.8-gm particle on a traditional HPLC system. Peak count is 70, and peak capacity is 143. (b) Peptide digest run on a 1.7-gm particle on the ACQUITY UPLC system. Peak count is 168, and peak capacity is 360. (Courtesy of Waters Corp.)... 

Dry weight, grams Counts in peak Counts in background Net counts, S.D. Counting time, min. 

The deviation of the correction factor from unity measured with spectrometers with PGT 386 amplifiers is comparable with the deviations measured in [5], There the authors reported a deviation of the peak count rate of approximately 2% at 1400 keV and 0.5% at 122 keV at a total count rate of 9000 s1. The measurement with the Ortec 573 amplifier yielded superior results. At the accuracy achieved, the deviation was not measurable up to 10000 s1 with this amplifier. The difference in the performance of the measurements with different amplifiers originates, most probably, in the fact that the Ortec amplifier is of newer design. 

Figure 6 shows a typical SCOM image of single fluorescent molecules of Dil embedded in a 20 nm PMMA film on glass. The molecules show up as bright diffraction-limited spots with peak count rates as expected from our previous analysis. The dark pixels inside the molecular spots correspond to quantum jumps of the molecule into the triplet state. They become visible since the pixel integration time is comparable to the triplet relaxation rate. 

Step 1. Count the quality control source under specified conditions for a brief period (e.g., 500 s) to obtain count rates in the channels beneath the full-energy peaks. Count the radiation background for a long period (e.g., 200,000 s). 

Step 2. Measure the control source count rate of each peak and compare it to the routinely recorded counting room QA information on these source-peak count rates. 

If computation is by hand, calculate the net counts per second (c/s) of the 40K gamma-ray peak at 1.461 MeV. Examine the background count rate and subtract the background contribution from the 1.461 MeV peak count rate. Note that the background count rate includes a peak at that energy (due to potassium salt in the environment). Enter data into Data Table 3.2. 

Data Table 3.2 Hand computation of peak count rate... 

Fig. 3. First successful observation of laser resonance of antiprotonic helium, now attributed to the (n, l) = (39,35) —> (38,34) transition. (Left) Observed time spectra of delayed annihilation of antiprotons with laser irradiation of various vacuum wavelengths near 597.2nm. Spikes due to forced annihilation through the resonance transitions are seen. (Upper right) Enlarged time profile of the resonance spike. (Lower right) Normalized peak count versus vacuum wavelength in the resonance region. From Morita et al. [11]...

A mercury atom that was ionized by a weak electron beam was captured in a miniature Paul (radio frequency) trap that has internal dimensions of rQ s 466 pm and zQ s 330 pm. The rf trapping frequency was 21.07 MHz with a peak voltage amplitude of about 730 V. The ion was laser cooled by a few microwatts of cw laser radiation that was frequency tuned below the 6s Si -6p Pi electric dipole transition near 194 nm. When the Hg+ ion was cold and the 194 nm radiation had sufficient intensity to saturate the strongly allowed S-P transition, 2 x 10 photons/s were scattered. With our collection efficiency, this corresponded to an observed peak count rate of about 10 s-1 against a background of less than 50 s— -. 

The peak count-rate is thus 5 10 events sec , leading to about 5 10 counts sec , with negligible dead-time losses. 

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