Peak-to-background ratio

WDSs have excellent resolving power, and the peak-to-background ratio of each line is much higher than can be achieved with a crystal detector. With a suitable crystal of large lattice spacing it is possible to detect and count X-rays as soft as boron K or even beryllium K , and this type of spectrometer is widely used when... 

Three orders of the 1010 reflection were measmed. Peak-to-background ratio was 100 or more for the first peak so a computer routine was used to create a polynomial fit to the background. For peaks of second and third order, the peak-to-background ratio was less than 3 so the data were smoothed manually and then the background was subtracted. ... 

Measurements were taken on 158Er at a total of 14 target-stopper distances. A portion of the total-projected spectra taken at four of the target-stopper separations is shown in Fig. 1. These spectra are of excellent statistical quality and reveal a favorable peak-to-background ratio in the 0° detector as a result of using the Compton suppression shield. 

The results using CCDs for the direct measurement of X-rays from pH [22] were consistent with the values obtained from the earlier experiments mentioned above. The superior background-suppression capabilities of the pixel devices led to an improvement of the peak-to-background ratio (Fig. 3). The new world-average values for the strong-interaction effects are listed in Table 3 together with typical results from model calculations. 

The various spectra were fit with Gaussian shapes and linear backgrounds by least-squares techniques. Spectra showing typical data and fitted curves are illustrated in Figure 1. The peak to background ratio was about 5 to i. 

Figure 6. II. The observed and calculated powder diffraction patterns of LaNi4.85Sno.15 after a second phase (solid solution of Sn in Ni) was included in the refinement. Considering the low background (the peak-to-background ratio exceeds 200 for the strongest Bragg reflection at 20 = 42.3°), the final residuals are excellent.

Within the last few years high resolution data collected either from synchrotron or neutron sources has allowed new structures to be solved from powder samples. Powder data from these new sources are superior to that collected from a conventional x-ray source both in resolution and peak to background ratio these improvements in data quality have the capability of making the determination of new molecular sieve topologies easier but not necessarily routine. Synchrotron radiation has possible future capabilities of being used to collect data from crystals that are only a few microns in size. At that time most newly synthesized molecular sieve materials will be solved by single crystal techniques instead of powder techniques. At the present time an acceptable structure refinement can be obtained from a crystal with a... 

COLLECTION OF DATA. It should be emphasized that the correct choice and preparation of the sample combined with careful collection of data will greatly aid in the total process. It is extremely important that the sample is pure, or if not, that all the impurity phases are known. Figure 1 shows a comparison of data collected from a typical 1970 s diffractometer, a modern computer controlled diffractometer and a high resolution diffractometer using synchrotron radiation at the National Synchrotron Light Source. The excellent resolution and high peak to background ratio (typically 1000 1) obtained from the synchrotron data enable very weak peaks to be easily observed. 

The applied detection systems can be characterized by the energy resolution, the maximum throughput, the peak-to-background ratio, and other parameters. 

If a direct excitation geometry is used for the analysis of automotive fuels, a Ti X-ray tube can be used. Typically those tubes use a power of maximum 30 W. Figure 2 shows an example spectrum for a sample with a sulfur content of 100 mg/kg. The peak-to-background ratio achieved in the example finm Fig. 2 is 2.5 1,... 

If the X-ray tube power is increased to 400 W and a Pd target tube is used in the geometry shown in Fig. 3 together with a HOPG (highly oriented pyrolithic graphite) crystal, Pd L-lines can be used for the excitation. This will lead to an improvement in the sensitivity, which can be seen in Fig. 4, where a spectrum, measured with a sample with sulfur content of 100 mg/kg, was analyzed. The peak-to-background ratio is improved to 3.7 1 the intensity of the S fluorescence line is increased by a factor of 3 in comparison to the example of direct excitation from above. 

By reflecting and focusing the X-ray beam, a higher flux of excitation radiation is transmitted to the sample. This increases the sensitivity, and lower power X-ray (less than 50 W) tubes can be utilized. A spectrum with a sulfior in oil sample at a sulfur concentration of 100 mg/kg is displayed in Fig. 6. The peak-to-background ratio is improved to 5.5 1, and the intensity of the sulfur fluorescence line is increased by a factor of 2 in comparison to the example of polarization excitation and by a factor of 6 in comparison to the example of direct excitation fi om above. 

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