XCII. <i>The reflexion of X-rays from imperfect crystals</i>

Darwin, Charles

doi:10.1080/14786442208633940

Cited by 285 publications

(70 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Failure to take account of this effect could lead to substantial underestimation of the nominally corrected value of the structure factor. Again, in his original paper, Darwin (1922) discussed whether an imperfect crystal should best be modelled as warped or cracked. Although he leaned towards the former model as probably the more realistic, he adopted the latter as being the more tractable mathematically.…”

Section: Importance Of Extrapolationmentioning

confidence: 99%

The Experimental Value of f(220) for Copper

Mackenzie¹,

Mathieson²

1984

Aust. J. Phys.

View full text Add to dashboard Cite

Aust. J. Phys., 1984,37, 651-6 The value of the atomic form factor, /(220), for copper has been determined in recent years by a variety of methods. All the dynamical methods agree on a value in the region of 16'70-16·75. These methods include two X-ray methods, one involving measurement of intensity profiles and the other of Pendellosung beats, and also an electron diffraction measurement using a critical voltage procedure. By contrast, two recent kinematical measurements using y rays both report a distinctly different value of about 16·45. One of these determinations has already been re-examined by the present authors and the discrepancy removed by an appropriate extrapolation to zero extinction. The present paper shows that the published experimental data for the other y-ray determination should lead to a value of about 16·69. This value confirms the linearity of our extrapolation and the importance of this extrapolation in deriving experimentally based extinction-free values of structure factors.

show abstract

Section: Importance Of Extrapolationmentioning

confidence: 99%

The Experimental Value of f(220) for Copper

Mackenzie¹,

Mathieson²

1984

Aust. J. Phys.

View full text Add to dashboard Cite

show abstract

“…The crystal may have a mosaic structure, the third type of disorder, where there are several (or many) three dimensional regions of a crystal slightly misaligned to each other (Darwin, 1922). In the limit of very many small 'mosaic blocks' a crystal will have a crumbly nature (Stojanoff et al 1996).…”

Section: Quality Characterisation Of Protein Crystalsmentioning

confidence: 99%

Trends and Challenges in Experimental Macromolecular Crystallography

Chayen

Boggon

Cassetta

et al. 1996

Quart. Rev. Biophys.

View full text Add to dashboard Cite

Macromolecular X-ray crystallography underpins the vigorous field of structural molecular biology having yielded many protein, nucleic acid and virus structures in fine detail. The understanding of the recognition by these macromolecules, as receptors, of their cognate ligands involves the detailed study of the structural chemistry of their molecular interactions. Also these structural details underpin the rational design of novel inhibitors in modern drug discovery in the pharmaceutical industry. Moreover, from such structures the functional details can be inferred, such as the biological chemistry of enzyme reactivity. There is then a vast number and range of types of biological macromolecules that potentially could be studied. The completion of the protein primary sequencing of the yeast genome, and the human genome sequencing project comprising some 105 proteins that is underway, raises expectations for equivalent three dimensional structural databases.

show abstract

“…This treatment uses the Zachariasen (1967) solution to the Darwin (1922) intensity transfer equations and is valid only for secondary extinction and small absorption. In addition, it is assumed that the crystal has a uniform cross section o-(to) over the irradiated volume and that the mosaic structure is sufficiently broad that the geometrical conditions for diffraction are satisfied for all neutrons in the incident beam.…”

Section: Extinction Treatmentmentioning

confidence: 99%

“…Secondly, the flipping ratio Rob s is measured across the rocking curve and not merely at the peak (R-on-rocking) and the curve is fitted on a point-by-point basis to a function in which the secondary extinction appears as a parameter ( van Laar, Maniawski & Kaprzyk, 1979). The fitting function is derived from Zachariasen's (1967) solution to the Darwin (1922) intensity transfer equations and should be excellent for weakly absorbing specimens. Unfortunately, the mechanical treatment of the sample increases the likelihood of multiple scattering and this, in turn, changes the measured flipping ratio at some or all points on the rocking curve, so that the fitting function no longer accurately describes the intensity distribution and unrealistic values for the extinction parameters and R may result.…”

mentioning

confidence: 99%

Treatment of secondary extinction and multiple scattering in polarized neutron scattering: an improved method. I. Method

Yelon¹,

Laar²,

Kaprzyk³

et al. 1984

Acta Cryst Sect A

View full text Add to dashboard Cite

A new method for the treatment of secondary extinction in polarized neutron diffraction data has been developed. As in previous models, the Zachariasen solutions to the Darwin intensity transfer equations are used, but in this case the extinction corrections are made on a point-by-point basis across the rocking curve and the corrections are determined by the absolute reflectivity at each point. There are no adjustable parameters (other than background). Measure-* On leave from and now returned to the University of Missouri Research Reactor, Columbia, MO 65211, USA. ment of the reflectivity also provides a simple test for multiple scattering, since the sum of diffracted and transmitted intensities should equal the direct-beam intensity, corrected for absorption, if no multiple scattering is present. The present method should give more reliable results than parametrized models where the correlation between the extinction and other parameters, such as the scale factor and temperature factors, are important.

show abstract

XCII. The reflexion of X-rays from imperfect crystals

Cited by 285 publications

References 6 publications

The Experimental Value of f(220) for Copper

The Experimental Value of f(220) for Copper

Trends and Challenges in Experimental Macromolecular Crystallography

Treatment of secondary extinction and multiple scattering in polarized neutron scattering: an improved method. I. Method

Contact Info

Product

Resources

About