X-ray setup

Figure 4.1. Typical X-ray setup with 2D detector in normal-transmission geometry. The intensity of the incident X-ray beam is measured in an ionization chamber (a). Thereafter it penetrates the sample which is subjected to some process. At a distance R (cf. Table 2.1 on p. 7) behind the sample the detector is recording the scattering pattern. In its center (b) the detector is protected by a beam stop. It is equipped with a pin-diode which records the intensity of the attenuated beam...

What kind of experimental setup is required to record the diffraction patterns from the macromolecular crystals and what kind of information is usually reported about the experiment Figure 16 shows a typical X-ray setup. The main parts are the X-ray source, including the optics to focus the parallel radiation onto the crystal, a device called a goniostat, and the detector that records the diffracted radiation. X-ray sources fall into two categories conventional generators and synchrotron sources. Most data these days are collected at synchrotrons. 

In principal, the scientic questions addressed can be investigated by X-ray scattering. This fact has been well-known for decades. Therefore great, engineering efforts have been undertaken for a long time to optimize the components of X-ray setups. 

The setup as seen in Figure 1 mainly consists of a Varian Linatron 3000A linear accelerator (LINAC) as radiation source, a rotational stage for sample manipulation, and a two-dimensional high-energy x-ray detector array consisting of four amorphous silicon area detectors Heimann RIS 256. The source to detector distance is 3.7 m. 

This opens perspectives for obtaining phase contrast information in a microfocus tomographic system Recently we have developed a desktop X-ray microtomographic system [4] with a spot size of 8 micrometer (70 KeV) and equipped with a (1024) pixel CCD, lens coupled to a scintillator. The system is now commercially available [5], The setup is sketched in Figure 1 In this work we used the system to demonstrate the feasibility for phase contrast microtomography. 

The setup in Figure 1-7 becomes an effective generator of nearly monochromatic x-rays when various elements inserted in the sample position are irradiated by x-rays of energy sufficient to excite the characteristic spectra that is, when by x-ray excitation the characteristic... 

Figure 5.34. Schematic of the experimental setup for using X-ray photoelectron spectroscopy (XPS) to investigate the catalyst-electrode surface.6 Reprinted with permission from the American Chemical Society.

Figure 33. Experimental setup for X-ray standing wave measurements on an LSM.

Figure 38. Experimental setup for back-reflection X-ray standing wave...

Today, structure evolution can be tracked in-situ with a cycle time of less than a second. Moreover, if a polymer part is scanned by the X-ray beam of a microbeam setup, the variation of structure and orientation can be documented with a spatial resolution of 1 pm. For the application of X-rays no special sample preparation is required, and as the beam may travel through air for at least several centimeters, manufacturing or ageing machinery can be integrated in the beamline with ease. 

In principle every scattering pattern can be recorded using the classical X-ray diffraction setup sketched in Fig. 2.2. In the detector the scattering intensity is measured in units of counts-per-second. 

Very thin films exhibit special structure because of their confined geometry between substrate and surface. Their structure cannot be studied in a normal setup. In order to obtain enough photons on the detector, the X-ray beam must impinge on them under grazing incidence (Cf. Sects. 7.6.3.1,1.63.2, 8.8). This technique is suitably combined with microbeams. Current effort is focusing both on progress of the instrumentation and on the development of adapted analysis methods. 

Since powerful X-ray sources and sophisticated beam shaping have generally become available, point-collimated setups for the study of X-ray scattering have lost their former handicap of low intensity. Today they benefit from their simple and versatile geometry. This section is devoted to an overview of modern apparatus -beginning with the source of X-radiation and ending with the detector and the data acquisition system. 

Figure 4.2. Sketch of a laboratory setup comprising a rotating anode, conventional beam shaping optics, and an X-ray camera with the sample in normal-transmission geometry...

According to ongoing development the most powerful and versatile X-ray light source of the next generation will no longer be realized by means of an orbit for electrons. Instead, it will be based on a long linear accelerator. The key features of this novel setup are... 

The design and placement of the second beam intensity monitor demands more attention. The definition of X-ray absorption does not discriminate between primary beam, USAXS and SAXS. So the second beam intensity monitor should guide primary beam, USAXS and SAXS through its volume, whereas the WAXS should pass outside the monitor. The optimum setup for SAXS and USAXS measurements is a narrow ionization chamber directly behind the sample. For WAXS measurement a pin-diode in the beam stop is a good solution for WAXS. For USAXS and SAXS it may be acceptable, as long as the relevant part of the primary beam is caught, the optical system is in thermal equilibrium and the synchrotron beam does not jump (cf. Sect. 4.2.3.5). 

Figure 5. Experimental setup for the intensity-dependent nonlinear coupling measurement. The sample, as shown in the inset, is mounted on an x-ray spectrogoniometer and the polarized light is incident on the PDA film surface at an angle, 0.

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