Bent crystal monochromators

Figure 3.36 gives a schematic layout of such a system. The white beam from a synchrotron source is focused by a bent-crystal monochromator,... 

Fig. 23. Schematic design of a double focussing mirror-monochromator camera at DORIS The middle of the mirror is at 20 m from the source point. A bent, triangular monochromator crystal is used for horizontal focussing and a segmented mirror (quartz) for vertical focussing. The ionization chamber is designated by-I-...

Figure 5.7 Reflection from an asymmetrically cut crystal monochromator. The width of the reflected beam is compressed relative to that of the incident beam. The asymmetrically cut single crystal when bent to the Guinier setting (figure 5.6(b)) provides a minimum 6XIX and a foreshortened focussing distance (equation (5.7)).

Workstations for protein crystallography have been set up by the Departments of Chemistry and Biology at the Brookhaven National Laboratory. The optical system design for the Chemistry beam line is based on a spherical collimating mirror, followed by a two-crystal ( +, —) monochromator and finally by a bent cylindrical mirror (Hastings et al 1983). The instrument combines a liquid helium cryostat Huber diffractometer, for work on valence electron density studies of small molecules, with an oscillation camera for protein crystallography. The diffractometer may be upgraded to include a multichannel electronic area detector. 

The Biology Department beam line includes a station for protein crystallography (with Supper oscillation camera and FAST TV diffractometer) and a station for small angle diffraction (with a three-circle goniostat and MWPC electronic area detector). The latter station may be available for optimised anomalous dispersion crystallographic studies. The optical design for each consists of a bent pre-mirror, double crystal monochromator and bent post-mirror the mirrors have rhodium coatings (Wise and Schoenborn 1982). 

Participating research teams Naval Research Laboratory At the NSLS a large number of participating research teams (PRTs) have established beam lines on the NSLS and a number of instruments use diffractometers as well as oscillation cameras. One of these, for instance, is the Naval Research Laboratory (NRL) and National Bureau of Standards PRT as part of this effort, NRL is constructing a materials analysis X-ray beam line. The beam optics design consists of a platinum coated copper pre-mirror dynamically bent to approximate a parabolic cylinder, followed by a fixed-exit double crystal monochromator and a platinum coated fused silica cylinder bent to approximate an ellipsoid. The hutch contains a six-circle diffractometer (Kirkland, Nagel and Cowan 1983). 

Table 6.1. Instrument smearing effects Example instrument settings based on a bent triangular monochromator (section 5.2.3) focussing in the horizontal plane and a horizontal rotation axis of the crystal sample. 

This experimental system has enabled us to perform picosecond timc-resolvcd x-ray diffraction experiments. One of the earliest experi-ments consist of a Ge (HI) crystal bent for maximum reflection of 8 keV x-ray photons, ilai to a sensitive double-crystal monochromator. The x-ray diffraction spectra are recorded before excitation. This diffraction exhibiu the normal diffraction pattern characteristic of this surface. In... 

To reduce the half-width of the characteristic X-ray lines. X-ray monochromators have been designed in which bent crystals are used to disperse the radiation. The method depends on the dispersion of X-rays by diffraction, as predicted by the Bragg equation... 

Figure 8.3 An X-ray monochromator using a bent quartz crystal Q T is the target chamber...

---