X-ray Intensity Measurements Research Articles

Radiation Measurement with a Solid-State-Matrix Camera

A solid-state-matrix camera containing 32 X 32 photodiode array served as the output device on an image intensifier tube. The resulting images had poor spatial resolution but permitted precise measurement of x-ray intensity. Transmission differences of 1% were detectable.

Determination of strain distribution in elastically bent materials by X-ray intensity measurement

A method for quantitative determination of local curvature in elastically bent perfect crystals is described. The method is based on X-ray intensity measurements, and a comparison of experimentally determined values with those derived from diffraction theory gives satisfactory agreement. The method was applied to determine the strain gradient and strain concentration in the vicinity of the notch of an elastically bent crystal. The experimental results were compared with those derived from a similar model based on continuum mechanics. Possible applications of the X-ray method are discussed to obtain experimental solutions to strain analyses which, when approached by continuum mechanics, pose formidable mathematical obstacles.

Extinction in sodium fluoride

X-ray intensity measurements for a single crystal of sodium fluoride obtained at four wavelengths by Howard & Jones [Acta Cryst. (1977). A33, 776-783] have been reanalysed using both the Cooper-Rouse and Becker-Coppens extinction formalisms in order to study the wavelength dependence of the extinction in this crystal, since the original analysis was unable to account for the wavelength dependence of the intensities of the strong reflections. The results indicate that the crystal is intermediate between type I and type II in nature and are consistent with the wavelength dependence predicted by the theories, although the extinction is not large enough at the shorter wavelengths to provide a useful test of the validity of the theoretical wavelength dependence. The analysis also demonstrates some of the possible consequences of the use of unbalanced weighting schemes and of inappropriate models for the scattering factors.

Quantitative analysis of carbides formed during the tempering of tungsten and molybdenum steels

The variation in composition of carbides formed during the tempering at 700°C of complex medium-carbon steels containing tungsten or molybdenum has been followed by analytical electron microscopy. Quantitative analysis of carbides containing tungsten has been achieved using L α X-ray intensity measurements. Direct measurement of carbide compositions has meant that chemical as well as structural observations can be made during the tempering of alloy steels.

The electron stationary picture method for high-speed measurement of reflection intensities from crystals with large unit cells

A method for measuring X-ray intensity data from crystals with large unit ceils is presented. The method takes full advantage of the capabilities of the multiwire area detector diffractometer. This diffractometer is a high-speed data collection system utilizing a multiwire proportional chamber that can detect photons from all simultaneously occurring reflections and record the diffraction pattern as a two-dimensional histogram in a computer mass core memory. In the electronic stationary picture method of data collection, reflection intensities are extracted from a sequence of electronic pictures each of which is exposed while the crystal is stationary. Between successive pictures the crystal is rotated about a fixed axis by a small constant angle of approximately 0.05°. Because the integrated intensity of each reflection is extracted from several consecutive pictures, advance prediction of detector coordinates and picture number is required for all reflections and the data-extraction computer program is necessarily complex. Expressions are derived for reflection detector coordinates and setting angles, the system hardware and software are described, the data collection procedure is outlined, and the quality of 7 × 105 reflection intensities measured during six months of operation is analyzed.

Direct observation of population inversion between Al +11 levels in a laser-produced plasma

Measured X-ray intensities of the resonance line series of Al +11 in a laser-produced plasma shows population inversion between the n = 4,5 levels and the n =3 level at a plasma density N e∼10 20 cm -3. The cooling of the expanding plasma leading to inversion is enhanced by a special target configuration. The gain coefficient in the 4 → 3 transition at 129.7 Å is estimated to be ∼ 10 cm -1, using both measured line intensities and numerical simulation.

Smectic C-to-Nematic Transition in p-n-Heptyloxybenzylidene-p-aminobenzoic Acid

Abstract The results on the phase transitions in p-n-heptyloxybenzylidene-p-aminobenzoic acid are reported. The microscopic and X-ray studies show that the compound goes over from smectic C to nematic phase directly. The transition entropies and specific heat are determined using differential scanning calorimetry. The translational order parameter is determined using low angle X-ray intensity measurements. The tilt angle in smectic C phase is found to be 56° and is independent of temperature. The X-ray data also lead to the conclusion that the compound exists as a dimer.

Experimental charge density distribution in potassium azide by diffraction methods

The electron density distribution of potassium azide is determined from high-resolution X-ray intensity measurements. The calculated distributions of errors in the experimental densities are included. Refinement of high-order X-ray data yields parameters in good agreement with neutron diffraction results. The inclusion of high-order data in calculating the deformation density is found to be necessary to obtain a quantitative distribution. Densities calculated with only low-order data are qualitatively similar but lack detail in the shape as well as in the height of the bonding features.

Statistical control and optimization of X-ray intensity measurements

When used to determine the concentrations of chemical elements in samples, X-ray intensity measurements are processed by correction programmes. These measurements are now usually obtained with fully or partially automated instruments. In order to suppress useless computations on sets of results containing rogue values, statistical tests must first be applied to the original experimental data. From an economic standpoint, it may also be worthwhile to reject the outlying counts automatically rather than discard complete sets of measurements. Statistical tests permitting the detection of outliers in groups of results are described.

X-ray observation of anharmonicity in cadmium selenide

X-ray intensity measurements of selected Bragg reflections in hexagonal cadmium selenide have been interpreted within the framework of the one-particle potential. An estimate of the anharmonic parameter characterizing the thermal motion in the basal plane is obtained.

X-ray intensity measurements on large crystals by energy-dispersive diffractometry. III. Fine structures of integrated intensities and anomalous scattering factors near theKabsorption edges in GaAs

The anomalous scattering factor f' + if” of GaAs very near the K absorption edges has been investigated with the stress on the following two points. One is the determination of f' from the measured f” values through the linear absorption coefficient by calculation with the dispersion relation. The other concerns the effect of fine structures in the anomalous scattering factor on the integrated reflexion powers R555 and R{\bar 555} in the two ranges of ± 20 eV near the Ga K and As K absorption edges. The agreement between these calculations and measurements of R values is fairly good; this fact justifies the application of the dispersion relation to the determination of the f' values near the edge. Some advantages of this application are pointed out in terms of, particularly, the phase determination of reflexions from crystals with unknown structures.

Microprobe technique for determining the thickness of SiO 2 and Si 3N 4 ultra-thin film composites of fet wafers and devices

An electron microprobe technique is described for determining the thickness of SiO 2 and Si 3N 4 in wafers and devices. The technique is based on the measurement of oxygen and silicon X-ray intensities at 2.5 kV and 10 kV through the nitride overlay. At the lower accelerating voltage, both intensities decrease with increasing nitride thickness owing to absorption and silicon distribution in depth. The SiO 2 thickness, however, is obtained by measuring the oxygen X-ray intensity at the higher voltage (10 kV), because at this voltage the oxygen intensity is not dependent on the nitride thickness. Empirical relationships expressing Si 3N 4 thickness in terms of Si and O X-ray intensities and SiO 2 thickness are derived.

GaussianversusLorentzian distribution for the mosaic spread in single crystals

For accurate X-ray or neutron diffraction intensity measurements the mosaic spread of a single crystal should be small. Plots are given from which the quality of the crystal can be checked and from which the scan range can be calculated.

The problem of white radiation in the measurement of intensities with a solid-state detector

Measurement of X-ray intensities, using a solid-state detector and with pulse-height discrimination to select the characteristic wavelength, has shown that the low-angle reflections can be seriously overestimated for crystals with moderate to large mosaic spread. This is a result of the effects of mosaic spread masking the contribution of white radiation in the reflections. It is thought that similar difficulties could arise with crystal monochromators that reflect a narrow band of wavelengths of white radiation along with the characteristic line, and with balanced filters where the pass band can be quite narrow.

X-ray intensity measurements on large crystals by energy-dispersive diffractometry. II. Energy dependence of the Friedel pair intensities and their ratio near the absorption edge

It has experimentally and theoretically been confirmed that the intensity ratio rh of Friedel pair reflexions h and {\bar {\bf h}} is given by |Fh|2/|F_{{\bar {\bf h}}}2 in a perfect crystal as well as in a mosaic crystal both in the symmetrical Bragg case and in the symmetrical Laue case. The measurements have been carried out on a nearly perfect GaAs crystal plate in the energy range near the As K absorption edge by the use of the energy-dispersive diffractometer and continuous radiation. These results have shown, a reasonable agreement with the relevant theoretical curves. The limitation of the above relation in tile presence of extinction effects has been considered.

Internal strain of GaAs. II. Transverse case

The effect of internal strain in the zincblende structure was examined on a GaAs single crystal by X-ray intensity measurements under a uniaxial stress along the [1{\bar 1}0] direction. It was found that the stress changes the structure factor of the weak reflexion (006), giving the value ζ = 0.764 ± 0.009 for the bond-bending constant.

X-ray intensity measurements on large crystals by energy-dispersive diffractometry. I. Energy dependence of diffraction intensities near the absorption edge

The intensity variations of X-rays diffracted from a nearly perfect GaAs plate have been measured in symmetrical Laue and Bragg cases in the energy region near the As K absorption edge with small energy intervals, by the use of an energy-dispersive diffractometer and continuous X-rays from a sealed-off tube. The corresponding intensity variations have been calculated with the dynamical theory. These measurements and calculations have shown a good agreement. Moreover, the curve measured for the Bragg case on the same crystal, but after polishing, has shown good agreement with the corresponding curve calculated by the kinematical theory. However, there is a minor discrepancy in the energy region very near the absorption edge. This is probably due to the fact that the values of anomalous-scattering factors used for calculation are not precise enough to explain fine structures at the edge.

Determination of Atomic Scattering Factors of B.C.C. Metals by the Critical-Voltage Method

The critical-voltage effect in electron diffraction has been applied to the 400 reflexion of b.c.c. metals, V, Cr, Fe and Nb, and the X-ray atomic scattering factors f x for the first-order reflexion 200 have been determined from the measured values of critical voltages E c by many-beam calculations. The results are compared with X-ray experimental data and theoretical scattering factors for free and solid atoms, and it is shown that the theoretical values for solid atoms calculated, e.g. by Wakoh and Yamashita agree well wiht the present results for V, Cr and Fe. It is pointed out that the reproducibility of the experimental data given by the present method is superior to that of the X-ray intensity measurements, and that the accurate measurement of scattering factors such as the present study serves as a sensitive and useful test of the band calculation.

Internal strain of GaAs. I. Longitudinal case

The theory of the internal strain, which has been verified experimentally for crystals with the diamond structure, is extended here to the zincblende structure. X-ray intensity measurements were taken on GaAs under a uniaxial stress along the [111] direction. It was found that this stress causes a slight change of the structure factor of the weak reflexion 006, from which the value ζ = 0.046 ± 0.002 for the bond-bending constant was estimated. This means that in GaAs the effect of the internal strain is very weak, so that the tetrahedral bond changes its length almost according to the macroscopic strain tensor.

Short range order and the development of long range order in Ni 4Mo

The short-range ordered structure present in quenched Ni 4Mo and the initial development of the long-range-ordered structure have been studied using single crystal X-ray diffuse scattering techniques. Measurements of the diffuse X-ray intensities were made in a volume in reciprocal space for the f.c.c. alloy resulting in a quantitative determination of the three dimensional local-order parameters. The local-order parameters were used for a computer simulation of the atomic configuration. The local atomic arrangements for the quenched alloy consist of a strong preference for no molybdenum atom pairs as first neighbors. The atoms tend to satisfy the long-range-ordered structure of Ni 4Mo in which there are no Mo-Mo pairs as first neighbors, only one Mo atom as second neighbors and six or more as third neighbors. A rodlike morphology consisting of a strong preference for 200 and 400 Mo-Mo pairs exists on ordering for 5 min at 650°C. This result is similar to the rodlike morphology present in dilute Ni-W alloys and explains the [100] streaking of the short-range order peaks observed in the diffraction studies.