Recording X-ray Diffraction Patterns Research Articles

A method for recording X-ray diffraction patterns of milligram quantities of particulates

A method for recording X-ray diffraction patterns of milligram quantities of particulates has been developed. The resulting diffraction patterns are similar to patterns obtained by standard methods. Application of this method to analysis of airborne particulates in the vicinity of a lead smelting operation has demonstrated the practical use of the method. Sample sizes as low as 1.1 mg have produced useful diffraction patterns.

Structure of the wall of Halobacterium halobium gas vesicles

The gas vesicles of Halobacterium halobium have been studied by recording X-ray diffraction patterns from both intact and collapsed vesicles. The wall is found to be remarkably thin; the average thickness is no more than 20 Å. Electron microscopy indicates that the wall consists of ribs, and the X-ray data confirm this. The thickness is therefore greater than 20 Å at some points and less at others. The X-ray data also indicate that the ribs on the two sides of the collapsed vesicle are intermeshed. Our data indicate a large amount of β-sheet in the wall. The β-sheet consists of parallel (or anti-parallel) polypeptide chains which are regularly hydrogen-bonded to one another. This bonding locks the presumed subunit proteins into the wall, which is important for its function at the gas-liquid interface. The β-sheet is in two layers, one on top of the other. The two layers together can stiffen the wall and hence strengthen the vesicle against collapse.

X-ray diffraction from outer segments of visual cells in intact eyes of the frog.

X-RAY diffraction patterns have been obtained from the light receptor membranes of frog retinal rod outer segments (of Rana temporaria and pipiens)1,2 and a one dimensional electron density profile across the membrane has been derived1. Until now the closest approach to studying the membranes in physiological conditions has been to pass X-rays through the outer segment layer of a strip of retina dissected from an eye and placed in a chilled glucose-supplemented Ringer solution1. To obtain a higher resolution electron density profile and minimize the possibility of artefact production, I have recorded X-ray diffraction patterns from photoreceptor layers in intact isolated whole eyes and also from eyes in a pithed frog with its heart beating throughout the experiment. Insofar as the respiratory system keeps functioning and the choroid and retina adjacent to the outer segments are intact, this experiment approaches an in vivo study.

New Developments in Gas-Filled Image Intensifier Detectors for X and Gamma Rays

In spark operation, with short-circuit electronics having a triggering delay of ⩽ 40 ns and yielding a peak current of 15 amperes, the detector, which is filled with xenon (720Torr) and diethylamine (40 Torr) has a counting plateau equal to 4% of the mean operating voltage. The electronic short-circuit is more effective when diethylamine replaces methylal. It is shown that this vapour produces a delay in the triggering of the spark. The life is improved. Study of electron avalanches has shown that, in the case of detection of X-rays of a mean energy of 27 keV, the number of carriers which they contain may reach 108 and that the probability is then less than 10-4 for triggering sparks. These avalanches also make it possible to obtain completely proportional amplitude spectra of excellent resolution (9% for 27 keV). When the detector is used in avalanche operation, the light emitted by the latter enables an image of the X-ray emitting source to be recorded. The quantity of light emitted can be increased by increasing the number of carriers in the avalanche but at the risk of creating a spark. This risk is eliminated by a short-circuit system similar to that operating for spark conditions but with a triggering threshold corresponding to about 105 electrons. The possibility of using this detector for recording X-ray diffraction patterns on biological molecules is discussed.

Apparatus for simultaneously recording X-ray diffraction patterns, thermograms, and electrical resistance curves of solid materials at high temperatures

Apparatus for simultaneously recording X-ray diffraction patterns, thermograms, and electrical resistance curves of solid materials at high temperatures

An X-Ray Small-Angle Scattering Instrument

AbstractAn X-ray small-angle scattering instrument is described which is used for recording X-ray diffraction patterns or small-angle X-ray scattering curves in an angular region very close to the direct beam. The measurement of X-ray intensity is accomplished with standard geiger or scintillation counter techniques. The instrument is designed for use with a spot-focus or vertical-line X-ray source, In essence, it is a multiple-reflection double-crystal diffractometer, based on a concept developed by Bonse and Hart, employing two grooved perfect germanium crystals arranged in the parallel position. Multiple diffraction from these crystals produces a monochromated X-ray beam which can be several millimeters wide while still exhibiting extremely high angular resolution. As a result, effective sample volumes can be employed with maximum volume-to-thickness ratios. The principal features of the instrument are discussed with emphasis on the advantages of this device over those employing complex slit systems and film-re cording techniques, Data are presented to illustrate the operation, intensity, and resolution of the unit.

X-ray Diffraction in Liquids

TWO questions are considered in this paper: the correct interpretation of the inner (secondary) ring familiar in many liquid diffraction patterns, and a brief survey and evaluation of the possibilities of the photographic method of recording X-ray diffraction patterns of liquids. When X-rays are transmitted through the alcohols or fatty acids or certain other long-chain compounds two diffraction maxima are produced. According to Stewart,1 the outer ring, corresponding to the smaller spacing, is a measure of the cross-section of the molecule, while the inner one is associated with the length of the molecule. On this interpretation is based his theory of cybotaxis. Recently Thibaud and Trillat have stated2 that only the outer ring is dependent on the size of the molecule while the inner ring is in every case due to general radiation and bears no relation to the length of the molecule. Obviously the question is of vital importance and should be settled before further studies of X-ray diffraction in liquids a...