Channel-cut crystal

Thus the commonly used channel-cut crystal with two reflections has the notation (+ n, - n). The formal duMond diagram notation is as follows ... 

The beam conditioner has two jobs to condition the beam in angle and in wavelength. The angular conditioning may be improved by using channel-cut crystals thus reducing the streak in reciprocal space discussed in section 7.7. In practice, four reflections are required to make the streak scarcely noticeable. Variation of wave-length also affects the resolution, since all the important... 

The channel-cut monochromator is the simplest type employed experimentally. A channel is cut in a perfect crystal (e.g.. Si) to provide two parallel reflecting surfaces that have a particular crystal plane [e.g., the Si (220)] parallel to the surface. The Bragg condition is used to select a particular wavelength and the reflected beam emerges parallel to the incident beam but is vertically displaced by 2D cos d, where D is the distance between the two faces and 0 is the angle between the beam and the Bragg planes. The accuracy of data collected using channel-cut crystal monochromators may be limited due to harmonic con-... 

The USAXS instrument uses a 6-reflection symmetric Si (111) channel cut crystal before and another 6-reflection channel cut after the sample to... 

The first SAXS observations on amorphous materials, including colloidal solutions and liquid mixtures, were reported in late 1920 (Krishnamurti 1929). Over the years, there have been several X-ray collimation system designs the four pinhole (or slit) systems, the Kratky collimation system (Kratky 1954), and the use of Bonse-Hart (Bonse and Hart 1965) channel-cut crystals for very small scattering angles. 

Figure 8 Experimental resolution after single-single and triple-triple reflections within the channel-cut crystal.

Figure 2.15 The rocking curves produced from one, two, three and four successive reflections in a channel-cut Si 220 crystal for CuK radiation. The inset shows that little intensity is lost near the peak, but the tails are greatly reduced...

Figure 3 shows one of our photoacoustic cell for X-ray spectroscopy of solid samples The cylindrical cell has a sample chamber at the center with volume of 0.16 cm which has two windows of beryllium (18 mm x 0.5 mm thickness). A microphone cartridge is commercially available electret type (10 mm ) and the electronics of preamplifier for this microphone is detailed elsewhere Figure 4 shows the typical experimental setup for spectroscopic study X-ray was monochromated by channel cut silicon double crystal (111) and ion chamber was set to monitor the beam intensity. Photoacoustic signal intensity was always divided by the ion chamber current for the normalization against the photon flux. X-ray was modulated by a rotating lead plate (1 mm thick) chopper with two blades. 

The monochromatic X-ray was obtained by silicon (111) channel cut double crystal using white X-ray (at Beam Line 4A (PF)). The ion chambers were set at the both side of the photoacoustic cell, in order to compare the sp trum of photoacoustic X-ray absorption spectroscopy (PAXAS) with usual absorption spectrum, simultaneously. The chopper at chopping frequency of 10 Hz was t at the up-stream of these detectors. Copper foil (5 pm thick) was used as a sample. 

Comparison between the core-level X-ray absorption spectroscopy (XAS), emission (XES), and X-ray photoemission spectroscopies (XPS) usually shows that the spectral edges rarely coincide with each other and with the Fermi level. It is common practice, however, to place F at the emission threshold which corresponds to a fully relaxed ion core (16). For defining the structure of the edge, an energy resolution of at least 1-2 eV is required in the range of 5-20-keV X-ray photons. This can be achieved with Bonse-Hart channel-cut silicon monochromator crystals. 

We used channel-cut Si 220 or Si 400, or double crystal Si 311 monochromators, and air ionization chambers detectors. Most of the spectra were recorded with a step of 2 eV on a range of 800 to 1000 eV. 

The monochromator is a Ge(220) channel cut. A focussing double crystal monochromator is under development (Goulon and Lemonnier, unpublished work, see section 5.2.4.2). Multiple wavelength data have been collected on terbium parvalbumin at the Lm absorption edge of terbium (Kahn et al 1985) and the structure solved (see 9.7.4). 

Figure 11. Side-view schematic of optical table setup used for XSW experiments at undulator beamlines 5ID-C and 12ID-D at the Advanced Photon Source (Bedzyk et al., unpubhshed). The postmonochromator used for single-crystal XSW experiments has two separate rotary stages for tuning the Bragg reflections of the Si channel-cut (CC) crystals, and ion chambers (IC) for monitoring the X-...

The inclusion of the extra optical elements (e.g., the four extra bounces from the two detuned channel-cut postmonochromator crystals) in the optical path while producing the desired effect of increasing the XSW phase (or atomic positional) resolution, come at the cost of reducing the X-ray intensity incident on the sample. Using Figure 12a one can visually estimate this effect by comparing the emittance from the second Si(004)... 

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