Single crystal monochromator

The x-ray powder diffraction pattern of isoxsuprine HCl has been measured using a Philips PW-1710 diffractometer, equipped with a single crystal monochromator and using copper Ka radiation. The pattern thusly obtained is shown in Figure 1, and the table of scattering angles, interplanar d-spacings, and relative intensities are found in Table 1. 

There are three accessories used to produce monochromatic radiation metal foil filters, crystal monochromators, and focusing mirrors. An element with atomic number Z can be used as a selective filter for radiation produced by an element of atomic number Z+ 1. For example, a nickel (Z=28) absorption filter, may be used to cut out the Cu KjS (Z=29 for Cu) radiation, leaving only Cu Ka radiation.Not all white radiation, however, is eliminated by this method. Alternatively a single-crystal monochromator may be used. An intense Bragg reflection from the monochromator crystal is used as the incident beam for X-ray diffraction studies. Focusing mirrors, designed to produce a beam that is not only monochromatic but also convergent, may be used. In this case the incident beam is doubly deflected by two perpendicular mirrors. 

Figure 2.13. The schematic explaining the principle of monochromatization using a single crystal monochromator. Generally 3 (02 + 0 )/2. The directions of the propagation vectors are indicated by arrows.

Because of the smooth spectrum of energies available at the synchrotron (Fig. 1) a single-crystal monochromator (Fig. 2) is used to select a small spread of energies (typically with AE/E 10 ). In other respects, most of the laboratory hardware required for diffraction experiments at the synchrotron is similar to that used in the laboratory and will not be dealt with in detail here. Several excellent texts and at least one comprehensive volume (Klug and Alexander 1974), detail the requirements for powder diffractometry. 

Neutron powder diffractometers that exploit a monochromatic beam are normally situated at reactors, which have a steady-state output of neutrons, though the SINQ at the Paul Scherrer Institute in Switzerland is a continuous spallation source. As with synchrotron X-rays, neutrons of a particular wavelength are selected from the polychromatic beam using a single-crystal monochromator, and the diffraction pattern is measured as a function of angle. 

A schematic view of a generalized neutron experiment is shown in Figure 1, along with the essential quantities defining the incident and scattered neutrons. A collimated white thermal neutron beam from a reactor is impinged on a single crystal monochromator or a mechanical... 

Soller collimators are most frequently used in combination with single-crystal monochromators (see below), for defining the wavelength resolution of the instrument. 

---