Journal of X-Ray Science and Technology - Volume 6, issue 1

Authors: Gonzalez-Hernandez, J. | Chao, B. S. | Ovshinsky, S. R. | Allred, D. D.

Article Type: Research Article

Abstract: We report the effect that thermal annealing in inert and oxidizing atmospheres, and with and without encapsulating layers, has on the structure of tungsten/carbon [W/C] multilayer thin films. This study focuses on the tungsten component and deals mainly with multilayers where the ratio of thickness of tungsten layers is equal to or greater than for the carbon layers (that is, γ ≤ 0.5). This is in contrast to prior studies where the tungsten layer thickness was generally held constant and the carbon layer was varied. Thermal annealing in inert atmospheres produces reactions and other structural changes in the tungsten and …carbide layers which depend on the as-deposited multilayer structure which depends, in turn, on the thickness of the tungsten layer. In samples where both the tungsten and carbide fractions of the multilayer are completely amorphous as deposited, which is the case for thin tungsten layers (thickness of tungsten (tw ) < 4 nm/period), the reactions in the tungsten layer forming crystalline tungsten and tungsten carbide occur at annealing temperatures above 900°C. The layer pair spacing, or period, (d), in this group shows an expansion of up to 10–15% of the original value as has been reported in the past. Changes in both the tungsten and carbide layers, and their interfaces, contribute to changes in d spacing and relative thickness of the high and low Z components. When the tungsten layer thickness exceeds 4 nm per period the tungsten is partially crystallized in as-prepared samples. In such multilayers interfacial reactions, producing an oriented partially crystalline W2 C/C superlattice, occur at temperatures of 600°C and below. The fact that W2 C crystallites in one period can form a structure which is correlated to W2 C crystallites in neighboring layers is somewhat surprising, since layers are presumably still separated by amorphous carbon which is still visible via Raman. The expansion of the layer pair spacing is relatively small (<5%) in this group and, more importantly, mostly involves increases in the thickness of the high Z components. Samples annealed in air at temperatures below 300°C are progressively destroyed by the oxidation of both tungsten and carbide layers. Encapsulation of similar multilayers with a thin (30 nm) dielectric layer of any of several types can retard oxidation to 600°C. The silicon-containing encapsulants generally perform better. Failure at this temperature is seen to occur from pinhole formation. Show more

DOI: 10.3233/XST-1996-6101

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 1-31, 1996

Authors: MacDonald, C. A.

Article Type: Research Article

Abstract: The recent invention of Kumakhov polycapillary x-ray and neutron optics has expanded the ways x-ray beams can be controlled. X rays incident on the interior of glass tubes at small angles can be guided down the tubes by total external reflection. Now, arrays of curved tapered capillaries can be used to focus, collimate, and filter x-ray radiation. Extensive research is being conducted on the performance and potential applications of these optics. Potential medical applications include mammography, digital energy subtraction angiography, and focused beam therapy. Other applications are x-ray lithography, x-ray astronomy, crystal diffraction, x-ray fluorescence, and neutron prompt gamma analysis.

DOI: 10.3233/XST-1996-6102

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 32-47, 1996

Authors: Hall, C. | Kamenskikh, I. A. | Gurvich, A. M. | Munro, I. H. | Mikhailin, V. V. | Worgan, J. S.

Article Type: Research Article

Abstract: This is a review of the properties of some photostimulable phosphors for luminescent image plates as applied to digital radiography. In particular, the properties of BaFBr:Eu and other barium fluorohalides that are useful for this application are considered. The main emphasis of the review is on the effect of the preparative conditions and the origin of the photostimulated luminescence and its features under VUV excitation.

DOI: 10.3233/XST-1996-6103

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 48-62, 1996

Authors: Davis, G. R. | Munshi, P. | Elliott, J. C.

Article Type: Research Article

Abstract: A variety of teeth and bone specimens have been scanned using the constant statistics tomographic scanner developed at the London Hospital Medical College. Each data set has been reconstructed with several Hamming filters, and for a geometric resolution ranging from 20 to 50 micrometers. The reconstructions have been studied using the approximate error formula for the convolution backprojection algorithm. Some inferences are made on the relative structure of the cross sections.

DOI: 10.3233/XST-1996-6104

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 63-76, 1996

Authors: Cornille, M. | Jacquemot, S.

Article Type: Research Article

Abstract: Energy levels, radiative decay, and Auger rates have been calculated for dielectronic recombination of seven Ne-like ions, ranging from Fel7+ to Ag38+ , from the n = 2 F-like shell into the n = 3 one, by use of the multiconfiguration AUTOLSJ code in intermediate coupling. Rate coefficients have then been computed versus the electronic temperature, the nuclear charge of the involved element, the final Ne-like state, and the population distribution among the initial 3 F-like levels. Dielectronic spectra have also been obtained.

DOI: 10.3233/XST-1996-6105

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 77-82, 1996

Authors: Lehnert, U. | Zschornack, G.

Article Type: Research Article

Abstract: Analytical approximations for calculations of the luminous efficiency of Bragg crystal diffraction spectrometers with flat and focussing crystals are derived. The given approximative formulas are in good agreement with ray-tracing calculations presented in an earlier work. Influences of the geometric source dimensions on the luminous efficiency are discussed for both spectrometer types mentioned.

DOI: 10.3233/XST-1996-6106

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 83-93, 1996

Authors: Kaftandjian, V. | Peix, G. | Babot, D. | Peyrin, F.

Article Type: Research Article

Abstract: In this paper we present an original low cost acquisition system for computed tomographic imaging. On the first hand, the use of a linear detector consisting of sensitive elements 0.225 mm × 0.5 mm in size allows one to obtain a resolution of about 150 μm after magnification. Image quality has been assessed in terms of spatial resolution and contrast sensitivity by imaging test objects. The images of in vitro vertebrae acquired by this experimental system show great improvement compared to the images acquired by a conventional medical scanner. On the other hand, an even better resolution (25 μm) has …been obtained by using an x-ray sensitive Vidicon camera, and an industrial application is presented with advanced composite materials. Show more

DOI: 10.3233/XST-1996-6107

Citation: Journal of X-Ray Science and Technology, vol. 6, no. 1, pp. 94-106, 1996