International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 6.1, pp. 165-166   | 1 | 2 |

Section 6.1.4.3. Other focusing collimators

U. W. Arndta

aLaboratory of Molecular Biology, Medical Research Council, Hills Road, Cambridge CB2 2QH, England

6.1.4.3. Other focusing collimators

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There has been very active development in recent years of tapering capillaries for focusing X-rays, either as individual capillaries (see the review by Bilderback et al., 1994[link]), or in the form of multicapillary bundles. The latter were first described by Kumakhov & Komarov (1990[link]); since then, they have undergone great improvements in the form of fused bundles (Bly & Gibson, 1996[link]) (Fig. 6.1.4.7[link]). Single capillaries have found the greatest use as X-ray concentrators, where a larger-diameter beam of X-rays enters the large end of a tapered capillary and is concentrated to a diameter of a few µm. Fused polycapillary bundles have been employed as focusing collimators for protein crystallography (MacDonald et al., 1999[link]). Both types of capillary optics are usually designed as multi-bounce devices, in which the X-rays undergo several, or many, reflections at the walls of the capillary; consequently the cross-fire half-angle at the output end has a value about equal to the critical angle for reflection at a glass surface or, perhaps, 4 mrad. This is sometimes too great for producing diffraction patterns with an optimum signal-to-background ratio.

[Figure 6.1.4.7]

Figure 6.1.4.7 | top | pdf |

A polycapillary collimator (after Bly & Gibson, 1996[link]).

Other methods of focusing X-rays, such as zone plates (Kirz, 1974[link]) and refractive optics, are being investigated, but at present none of them can compare with toroidal reflectors for data collection from single crystals of macromolecules.

References

Bilderback, D. H., Thiel, D. J., Pahl, R. & Brister, K. E. (1994). X-ray applications with glass-capillary optics. J. Synchrotron Rad. 1, 37–42.
Bly, P. & Gibson, D. (1996). Polycapillary optics focus and collimate X-rays. Laser Focus World, March issue.
Kirz, J. (1974). Phase zone plates for X-rays and the extreme UV. J. Opt. Soc. Am. 64, 301–309.
Kumakhov, M. A. & Komarov, F. K. (1990). Phys. Rep. 191, 289–350.
MacDonald, C. A., Owens, S. M. & Gibson, W. M. (1999). Polycapillary X-ray optics for microdiffraction. J. Appl. Cryst. 32, 160–167.








































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