Soller collimators

In order to collimate a beam of larger cross section in one dimension, within a reasonable L, Soller-type collimators have to be applied. Such a collimator is composed of a number of equidistant neutron-absorbing blades, separated by spaces. Blades should be as flat and as thin as possible. The theoretical maximum value for the transmission of a Soller collimator with 10 divergence is 96%. 

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

Diffiactometer 1) monochromator, 2) monitor, 3) Soller collimator, 4) sample table 5 detector(multi-detector, desirable) 6) andllaiyfciyostat, etc.) 0.5 M, IMS (including multi-detector) Cryostat, Magnetic pressure cell ciyogen Ancillary equipmerrt Computer system... 

All of the above experiments were performed at a wavelength of 1.3 A. Experiments (1) to (3) were performed with an open collimator, so that counting times were 7.5 hours each. Experiment (4) was performed with a Soller collimator, so that the total counting time at each temperature was 12 hours. 

A beam from an actual sample will require a more elaborate slit S3rstem for collimation if the sample is broad. The Soller slit (Figure 4-7), a stack of thin parallel plates, is such a system. The reasoning that supports this construction is as follows. Were the sample a point or a line source, a slit between sample and crystal or a slit between crystal and detector would be enough for satisfactory collimation. With a two-dimensional sample, both slits would be needed to get this done. But this arrangement is wasteful of emitted intensity because the detector sees the sample as a line source. To use all the sample area effectively, a system of parallel slits is needed. To eliminate the divergent rays in such a system, the slits must be extended in the direction of the beam, and this leads to the parallel-plate construction in the Seller slit system. 

Fig. 4-7. Diffraction of a divergent beam from a broad sample by a large crystal. Collimation of this beam requires the Soller slit system shown. This system is equivalent to simple slits at A and B with separators provided to make certain that only parallel rays leave the exit slit.

Spectrographs sometimes have two Soller slits. The first, whose function it is to collimate the desired x-ravs, is then placed between crystal and detector. The second and wider-angled slit is interposed... 

In this second class of spectrometers, X-ray radiation emitted by the sample, after it has been filtered by a sheet collimator (Soller slits), impacts on a crystal analyser... 

Figure 13.9—Schematic of a sequential, crystal-based spectrometer and the spectrum obtained using the sequential method with an instrument having a goniometer. The Soller slit collimator, made of metallic parallel sheets, collimates the primary X-ray beam emitted by a high power source (SRS 300 instrument, reproduced by permission of Siemens). A typical spectrum of an alloy, obtained by an instrument of this category, having an LiF crystal (200) with 26 angle in degrees as the abscissa and intensity in Cps as the ordinate). Model Philips PW2400 Spectrum, reproduced with permission of VALDI-France.

In its simplest form, direct X-ray scatter imaging relies on the use of simple mechanical collimation elements such as pinholes, Soller slits and the like to determine the origin coordinates of a scattered photon. They all achieve spatial resolution of the scatter field at the detector by restricting the angular range over which radiation can reach the detector. Examples of direct tomography in the explosives detection field include the... 

Figure 2.10. The schematic showing how the x-ray beam is collimated by using both the divergence and Soller slits (top). The beam, collimated in-plane by the divergence slit, is further collimated axially by the Soller slits. The coordinates in the middle of the drawing indicate the corresponding directions. The bottom part of the figure illustrates the analogy of Eq. 2.6 with Eq. 2.5.

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