Cosmic X-ray observations

1969 ◽  
Vol 313 (1514) ◽  
pp. 301-315 ◽  
Keyword(s):  
Lower Limit ◽  
Short Duration ◽  
Spectral Information ◽  
X Ray ◽  
Proportional Counters ◽  
Position Data ◽  
Intense Source

In the first few years following the discovery of discrete cosmic X-ray sources, about three dozen objects were detected (Friedman, Byram & Chubb 1967; Fisher, Johnson, Jordan, Meyerott & Acton 1966; Clark et al . 1965; Gursky, Gorenstein & Giacconi 1967; Bradt, Naranan, Rappaport & Spada 1968; Cooke, Pounds, Stewardson & Adams 1967; Giacconi, Gorenstein, Gursky & Waters 1967; Chodil et al . 1967 b ). They represent a brightness range of about a thousandfold from the most intense source, Sco XR–1, ca . 5 x 10 -10 J m -2 s -1 , to the weakest sources at a few times 10 -13 J m -2 s -1 . The lower limit of detectability is inherent in the short duration of rocket flights and the limiting size of instrumentation that can be carried in vehicles like Aerobee, Skylark and Nike Apache. As a result of this instrumentation barrier, the pace of discovery has now slowed down considerably, and the next great surge in detection of new sources will have to await the use of satellites. Spectral information is still based on the relatively crude resolution of proportional counters and scintillation counters, so that no conclusive determination of thermal or non-thermal mechanisms is yet possible. Because position data are obtained with the use of mechanical collimators, accuracies of a few minutes of arc are the best that have been achieved, and only for a few sources. As a consequence, only a few X-ray objects are reliably identified with optical and radio counterparts.

Determination of Total Chlorine in Chrysotile by X-ray Fluorescence Spectrometry

1994 ◽  
Vol 48 (2) ◽  
pp. 236-240 ◽  
Author(s):  
Régina Zamojska ◽  
Jeff Sharman ◽  
Yvon Cote ◽  
Carmel Jolicoeur
Keyword(s):  
Lower Limit ◽  
Limit Of Detection ◽  
Colorimetric Method ◽  
Standard Addition ◽  
Exchange Chromatography ◽  
Water Soluble ◽  
X Ray ◽  
Limit Of Determination ◽  
A Minor

Energy-dispersive x-ray spectrometric methods have been developed for the determination of chlorine in asbestos (chrysotile) fibers. Chlorine, which is a minor constituent, is determined by a standard addition method from the ground fiber and by a standardless method in six different fibers. The lower limit of detection for a qualitative analysis and the lower limit of determination for a quantitative analysis of chlorine in the asbestos matrix are 40 ppm and 120 ppm, respectively. The water-soluble and acid-soluble chlorine have also been determined by ion-exchange chromatography and by a colorimetric method. The agreement of the three different methods is very good in all cases.

Recent advances in X-ray astronomy

1967 ◽  
Vol 31 ◽  
pp. 439-453
Author(s):  
B. B. Rossi
Keyword(s):  
Accurate Determination ◽  
Angular Size ◽  
The State ◽  
Spectral Information ◽  
X Ray ◽  
Upper Limit ◽  
Recent Advances ◽  
Visible Object

In a review written in December 1965, the author of this report has summarized the state of observational X-ray astronomy at that time. Further data that have become available since then have produced important advances in several directions. New sources have been discovered, some of which have been tentatively identified with known galactic or extra-galactic objects. Evidence has been presented for variability of the X-ray flux received from at least one of the sources. New spectral information has been obtained. New observations of the strong X-ray source in Scorpius, Sco X-1, have greatly reduced the previous upper limit for its angular size and have provided a much more accurate determination of its celestial coordinates. This determination has led to the identification of Sco X-1 with a faint visible object whose peculiar properties had, until then, escaped the attention of astronomers.

Areas for Improvement in XRF Analysis of Low Atomic Number Elements

1992 ◽  
Vol 36 ◽  
pp. 73-80
Author(s):  
Bruno A.R. Vrebos ◽  
Gjalt T.J. Kuipéres
Keyword(s):  
Lower Limit ◽  
Atomic Number ◽  
Energy Dispersive Spectrometry ◽  
Limit Of Detection ◽  
Heavy Elements ◽  
Fluorescence Spectrometry ◽  
Accurate Analysis ◽  
X Ray ◽  
Made In

Accurate analysis of the light elements has been, from the early applications of X-ray fluorescence spectrometry a struggle compared to the determination of heavy elements in the same matrices. In contrast, there has been virtually no upper limit to the atomic number of the element that could be determined. The lower limit, however, has been continuously adjusted downward through the years. Clearly, the sensitivity as well as the lower limit of detection for the heavy elements have also been improved, but the effect is Jess striking than the advances made in the region of tight element performance. This paper deals specifically with wavelength dispersive sequential x-ray fluorescence spectrometry, although some of the observations made are equally applicable to energy dispersive spectrometry.

Determination of Wear Metals in Oil by X-Ray Spectrometry

1985 ◽  
Vol 29 ◽  
pp. 503-509
Author(s):  
Ya-Wen Liu ◽  
A.R. Harding ◽  
D.E. Leyden
Keyword(s):  
Trace Elements ◽  
Thermal Degradation ◽  
Lower Limit ◽  
Organic Material ◽  
Limit Of Detection ◽  
Spectrometric Analysis ◽  
Trace Impurities ◽  
X Ray

AbstractTrace elements in oil may be determined by adsorption of the oil sample onto maguesium oxide followed by thermal degradation of the organic material. The resulting powder is easily pressed into a pellet suitable for X-ray spectrometric analysis. The lower limit of detection depends upon the trace impurities in the MgO and is a few parts per million for most elements determined.

Determination of Uranium in Carbonate Solutions by Extraction onto a Chemically Modified Surface

1977 ◽  
Vol 21 ◽  
pp. 59-69
Author(s):  
Bruce B. Jablonski ◽  
Donald E. Leyden
Keyword(s):  
Lower Limit ◽  
Silica Gel ◽  
Limit Of Detection ◽  
X Ray ◽  
Chemically Modified ◽  
Carbonate Concentration ◽  
Carbonate Solutions ◽  
Modified Surface ◽  
Materials Used

Silica gel treated with a commercial silylation reagent (Dow-Corning Z-6020) has been found to extract uranium from carbonate solutions. The materials used are simple to prepare and once the uranium is extracted, x-ray fluorescence may be employed to determine the uranium directly on the solid. A dependence of the extraction upon carbonate concentration is observed. A lower limit of detection of 2.46 μg of 0.12 ppm uranium from a 20 ml sample is obtained.

Lateral resolution of the electron microbeam analysis

1978 ◽  
Vol 36 (1) ◽  
pp. 542-543
Author(s):  
H.J. Dudek
Keyword(s):  
Quantitative Analysis ◽  
Depth Resolution ◽  
Lateral Resolution ◽  
Cylindrical Particle ◽  
Correction Procedure ◽  
X Ray ◽  
Element Concentrations ◽  
Microbeam Analysis ◽  
The Matrix

The chemical inhomogenities in modern materials such as fibers, phases and inclusions, often have diameters in the region of one micrometer. Using electron microbeam analysis for the determination of the element concentrations one has to know the smallest possible diameter of such regions for a given accuracy of the quantitative analysis.In th is paper the correction procedure for the quantitative electron microbeam analysis is extended to a spacial problem to determine the smallest possible measurements of a cylindrical particle P of high D (depth resolution) and diameter L (lateral resolution) embeded in a matrix M and which has to be analysed quantitative with the accuracy q. The mathematical accounts lead to the following form of the characteristic x-ray intens ity of the element i of a particle P embeded in the matrix M in relation to the intensity of a standard S

Sem and X-Ray Analysis of Renal and Biliary Calculi

1976 ◽  
Vol 34 ◽  
pp. 306-307
Author(s):  
R. J. Narconis ◽  
G. L. Johnson
Keyword(s):  
Chemical Constituents ◽  
Natural State ◽  
X Ray Diffraction ◽  
Chemical Methods ◽  
X Ray ◽  
Additional Dimension ◽  
Biliary Calculi ◽  
Calculus Formation ◽  
Scanning Electron

Analysis of the constituents of renal and biliary calculi may be of help in the management of patients with calculous disease. Several methods of analysis are available for identifying these constituents. Most common are chemical methods, optical crystallography, x-ray diffraction, and infrared spectroscopy. The application of a SEM with x-ray analysis capabilities should be considered as an additional alternative.A scanning electron microscope equipped with an x-ray “mapping” attachment offers an additional dimension in its ability to locate elemental constituents geographically, and thus, provide a clue in determination of possible metabolic etiology in calculus formation. The ability of this method to give an undisturbed view of adjacent layers of elements in their natural state is of advantage in determining the sequence of formation of subsequent layers of chemical constituents.

Preparation And elemental analysis of ancient fibers

1987 ◽  
Vol 45 ◽  
pp. 410-411
Author(s):  
Allen Angel ◽  
Kathryn A. Jakes
Keyword(s):  
Cross Sections ◽  
Physical Structure ◽  
Energy Dispersive ◽  
Archaeological Sites ◽  
X Ray ◽  
Long Term Storage ◽  
Backscattered Electron ◽  
Electron Imaging

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.

Determination of Stoichiometry of GaAs Component in (Gaas)Ge Epitaxially Grown Thin Films by Electron Microprobe X-Ray Analysis

1990 ◽  
Vol 48 (2) ◽  
pp. 264-265
Author(s):  
D. R. Liu ◽  
S. S. Shinozaki ◽  
R. J. Baird
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Compound Semiconductors ◽  
Energy Dispersive Analysis ◽  
X Ray ◽  
Metastable Alloys ◽  
Lower Voltage

The epitaxially grown (GaAs)Ge thin film has been arousing much interest because it is one of metastable alloys of III-V compound semiconductors with germanium and a possible candidate in optoelectronic applications. It is important to be able to accurately determine the composition of the film, particularly whether or not the GaAs component is in stoichiometry, but x-ray energy dispersive analysis (EDS) cannot meet this need. The thickness of the film is usually about 0.5-1.5 μm. If Kα peaks are used for quantification, the accelerating voltage must be more than 10 kV in order for these peaks to be excited. Under this voltage, the generation depth of x-ray photons approaches 1 μm, as evidenced by a Monte Carlo simulation and actual x-ray intensity measurement as discussed below. If a lower voltage is used to reduce the generation depth, their L peaks have to be used. But these L peaks actually are merged as one big hump simply because the atomic numbers of these three elements are relatively small and close together, and the EDS energy resolution is limited.

Polarity Determination in Sphalerite and Wurtzite Structures

1990 ◽  
Vol 48 (2) ◽  
pp. 500-501
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
Opposite Polarity ◽  
Single Domain ◽  
Polar Material ◽  
Electron Microscopic ◽  
Dynamical Interaction ◽  
X Ray ◽  
Polarity Determination ◽  
The Absolute ◽  
Microscopic Techniques

The determination of the absolute polarity of a polar material is often crucial to the understanding of the defects which occur in such materials. Several methods exist by which this determination may be performed. In bulk, single-domain specimens, macroscopic techniques may be used, such as the different etching behavior, using the appropriate etchant, of surfaces with opposite polarity. X-ray measurements under conditions where Friedel’s law (which means that the intensity of reflections from planes of opposite polarity are indistinguishable) breaks down can also be used to determine the absolute polarity of bulk, single-domain specimens. On the microscopic scale, and particularly where antiphase boundaries (APBs), which separate regions of opposite polarity exist, electron microscopic techniques must be employed. Two techniques are commonly practised; the first [1], involves the dynamical interaction of hoLz lines which interfere constructively or destructively with the zero order reflection, depending on the crystal polarity. The crystal polarity can therefore be directly deduced from the relative intensity of these interactions.

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