NPL x-ray gratings for use at grazing incidence in the wavelength range of 0.05 to 20 nm have diffraction efficiencies in the first order ranging from approximately 3% at 0.1 nm to 20% at wavelengths greater than 2 nm. X-ray gratings may have either a rectangular profile produced by processing a ruled or holographic grating or may have a shallow blazed waveform. In both types of grating, the grooves are formed in a vitreous silica blank and are usually overcoated with gold.

A precision short wavelength (0.05 to 0.5 nm) Rowland circle focusing spectrometer has bee n constructed, which can cater for concave gratings of radii between 5 and 15 m.

Important data in the investigation of laser-produced plasmas will be provided by studies of the X-ray emission characteristics in the range 1-10 keV, with time resolution comparable to plasma heating times. Present techniques using conventional photomultipliers or photodiodes are not suitable for time measurements on plasma heated by short optical pulses of several hundred picoseconds or less. The development of new X-ray cameras is also necessary. Their photocathodes must be chosen with care. In this paper we describe an initial study of the characteristics of metallic photocathodes: quantum efficiency, energy distribution of emitted photoelectrons, etc. Then we worked out the provisional sensitivity, spatial and temporal resolution of cameras in the streak mode or in shutter mode.

Self-scanning photodiode arrays were tested for their ability to measure the spatial distribution of low-energy x rays in a wavelength dispersive spectrometer. X-ray spectral sensitivity was measured with a calibrated de source of nearly-monochromatic characteristic-x rays with photon energies in the range of 1.5 to 8 keV. Photodiode response was found to be linear with x-ray flux. Exposure to large doses of copper radiation did not effect sensitivity. A mathematical model that describes the experimental data is presented. We found that spatial resolving power was lowered by the dispersal of photogenerated charges. This effect was investigated with collimated beams and is described with a formula that predicts the loss of diode signals.

Photoelectric diodes with aluminum photocathod.es have been calibrated in the energy range from 0.1 keV to 1 keV with a multielement Henke X-ray tube system using regenerative monochromatic filters. The calibration is performed at six energies: (1) Be - (0.109 keV) , (2) C - Kα (0.277 keV), (3) Ti – Lα1, 2 (0.452 keV) , (4) Fe – Lα1, 2 (0.705 keV), (5) Cu – Lα1, 2 (0.930 keV), and (6) Al – Kαl, 2 (1.487 keV). Several different 99.9%, (1000 series) aluminum foils were calibrated for use as cathodes. In addition, the average energy per electron ion pair, W, has been measured for methane at these same energies.

The filled states in the surface region of a solid can be probed by monochromatic x-rays. The spectral distribution of photoelectrons near the high kinetic energy limit is related to the density of valence band states. Complementary information regarding the unoccupied states is obtained from the spectral distribution of bremsstrahlung, emitted bv radiative capture of monoenergetic electrons, near the short wavelength limit. In soft x-ray appearance potential spectroscopy, the near-threshold excitation probability of a core level is a measure of the local density of unfilled states associated with a particular element. In each case the sensitivity to the surface results from the short mean free path for inelastic scattering of electrons. Unfortunatelv this has severe consequences for the interpretation of line shapes.

Transitions from the valence electron levels into the first relatively sharp inner sub-shell levels result in characteristic x-ray emissions in the 100-200 eV region. These spectra sensitively reflect the chemical state of the atoms which are representative of the submicron thickness of the sample surface under low energy x-ray excitation and of the first few molecular layers of the sample under electron excitation.

An optimized measurement method for this 50-100 A spectral region is “based upon single crystal spectrometry using a lead stearate analyzer which has high dispersion and efficiency and an energy width of about one eV in this wavelength range. Spectra are recorded using “tuned” proportional counter detection. In the work reported here, low energy x-ray excitation is used in order to minimize the possibility of radiation damage of the sample.

Each spectrum is calibrated for both energy and instrument transmission using known, sharp M lines of elements such as molybdenum, zirconium and yttrium which will bracket the spectraj. range under measurement. A simple method has been developed for "stripping" from the measured spectra the Lorentzian crystal width and the Gaussian collimation width in order to allow an estimation to be made of the actual emission line widths as well as the relative intensities.

In this report, as an illustrative application example, S-LII, III spectra are presented for a series of sulfur compounds in "both solid, and gas states. Manne's approximate molecular orbital interpretation of the x-ray emission spectra has been adopted and extended to apply to the LII, III spectra for second row elements.

Holographically-formed X-ray reflection grating scan now be constructed with competitive groove efficiency to classically ruled types, down to a short wavelength diffracting limit of several angstroms.

The gratings can be generated on any surface capable of intersecting the interference fringe pattern without shadowing. This fact alone brings several new X-ray optical design possibilities within reach, for example, by combining plane construction waves with steep aspheric substrates. The first order imaging theory of the grazing incidence mounting is discussed and compared to measured performance for aberration corrected stigmatic types.

A new 5 meter spectrograph has also been constructed with applications in molecular chemistry, laser fusion research and synchro tronspectroscopy. The unit is available with fully prefocussed holographic and classical X-ray grating optics, and uses the precision miniature camera principle of fully interchangeable lenses, but applied, in this case to the entrance slit, grating and detector modules.

Calculations carried out to investigate the van Cittert iterative deconvolution method and the effects of random noise and truncation errors on its convergence behavior are presented. Gaussian functions are used for "both the true function W and the system, response function A. The model "observed" function S is generated from W and A. Both rms differences between the result of n iterations Wn and the true function, and between Wn*A and S are used to measure convergence. The effects of introducing errors can be measured against standards set by the convergence without such errors. These "no-error" calculations make use of true functions with widths from 2.0 to 0.67 times the response function width. The effects of random noise are investigated by adding noise to W*A before deconvolution. A small amount of random noise initially added builds up rapidly in amplitude during the iterative process and eventually dominates the rms difference calculations. To suppress the effects of random noise build-up; smoothing techniques are applied, the best of which involved smoothing both the noisy observed function, S, and the system response function, A, before deconvolution. The smoothing operation is thus taken as part of the measurement and. the divergence resulting from, the noise build-up is avoided. The results depend strongly upon, the -width of the smoothing function. Uhsymmetric system response functions, similar' to those encountered in soft x-ray appearance potential spectroscopy and in x-ray continuum, isochromat measurements, are used in investigations of truncation errors. Abrupt cut-offs of the model S and A functions before deconvolution result in the build-up of large fluctuations in W . These truncation errors become increasingly localized with continued iterations and make only minor contributions to the errors in Wn in the vicinity of the real peak if the truncations are made sufficiently far from the peak location. Alternatively, the truncation errors can be avoided by analytical continuation.

An exact knowledge of environmental particulate levels at their sources of production, geographic sites of dissemination and/or anatomic sites of deposition after they have been inhaled or ingested by the body is considered a main priority in the environmental health field. One must therefore recognize the need for rapid, accurate and sensitive means of sampling and analyzing these materials, often found in trace amounts, with little alteration from their original physical and chemical structure. A summary of the various theoretical approaches and methodologies investigated in our laboratory towards that goal are discussed with emphasis on X-ray techniques used, correction factors involved, and areas requiring further research.

The most prominent peaks of chrysotile are the 002 and 004 reflections, and in dilute mixtures of chrysotile in talc they are the only peaks that can be detected. Milling of chrysotile markedly reduces these peak heights and areas, and generates a new, sharp peak at d = 2.52 A. Milling of other serpentine minerals also results in line broadening and integrated intensity decrease of the 002 and 004 lines; a weak d = 2.52 reflection is initially present and milling causes this to increase slightly in intensity, without any detectable line broadening. The variations in relative intensities of these peaks for different size-classified fractions of the several minerals after prolonged milling confirms that the d = 2.52 A reflection is due to a phase that is different from the starting material. Investigation of specimens held at various temperatures up to 1000°C shows that the consequences of milling cannot be attributed to local heating effects. It is confirmed that chrysotile is readily attacked and dissolved by 1 M HCl, whereas the other serpentine minerals are relatively inert to this reagent. In the case of extensively milled chrysotile, the acid treatment causes the 002 and 004 peaks to weaken and eventually disappear, but the d = 2.52 A peak remains unaffected.

In recent years considerable success has been achieved in the development of detectors for the localization of ionizing radiation. One dimensional position sensitive detectors have a number of uses in nuclear physics and in biological studies utilizing small-angle scattering. Detectors are now capable of providing position information of high resolution with a high count rats capability and a simple readout system. We report here on the feasibility of employing a position sensitive proportional counter (PSPC) for the measurement of residual stresses with X-rays.

Comparisons of the accuracy and time of data accumulation between a scintillation detector and a PSPC have been performed on stress relieved, shot peened steel specimens, and specimens deformed in tension.

The ability of obtaining the entire profile at once is somewhat offset by the lower efficiency of the PSPC when compared to a scintillation detector, but this is counteracted by the fact that motion of the detector is eliminated with the PSPC, It will be shown that a PSPC system provides a speed of data accumulation currently not available in any other way, while still remaining a versatile and accurate method.

The two-angle and Sin2ψ methods of x-ray diffraction, residual stress measurement have been shown to yield anomalous results When applied to samples which have been plastically deformed uniaxially in tension or by rolling. These anomalous stresses, which are not true mechanical macrostresses, have been shown to arise from a nonlinear dependence,of d, the interplanar spacing employed for stress measurement, upon Sin2 ψ. A new method of x-ray diffraction stress measurement has been developed by Marion and Cohen which aLlows the separation of the Linear and nonlinear components of the dependence of d upon Sin2 ψ.

The two-angle and the Marion-Cohen x-ray diffraction methods are applied to the measurement of residual stresses in the machined and shot peened surfaces of steel and aluminum samples. The results indicate that machining deformation results in a nearly linear dependence of d upon Sin2ψ , and onLy a slight deformation texture. The two x-ray methods yield stress values in ground, turned, and shot peened steel and aluminum samples which agree within the estimated experimental error. Previous results are sighted showing agreement between the two-angle method and a mechanical stress measurement technique. The results indicate that, at least in steels, the multiaxial plastic deformation produced by machining does not significantly effect the accuracy of the two-angle x-ray diffraction stress mea surement method.

Computer simulation of back reflection Laue patterns now provides the means to plot Laue patterns for any crystal system in any orientation. This capability makes it possible to determine, rapidly and accurately, the orientation of single crystals and large grains in polycrystalline materials even in cases where little or no symmetry is displayed in the Laue photograph. A set of standard Laue patterns is first simulated to cover the stereographic triangle of the crystal being studied. The Laue photograph obtained from the crystal, or grain, is compared with the set of simulated Laue patterns. The pattern most similar to the photograph is used to determine the (HKL) values of three Laue spots. The (HKL) values of these spots and half their angular separations from the x-ray beam, along with the lattice constants, are used by a computer program to calculate the (HKL) value of the crystallographic plane perpendicular to the x-ray beam. A simulated Laue pattern can now be obtained in exactly the same orientation and it can be drawn directly to the scale of the Laue photograph. Thus the validity of the orientation can be easily verified by direct comparison. The (HKL) value of the crystallographic plane perpendicular to the x-ray beam can also be used to plot a stereographic projection of the crystal poles. Therefore, the complete orientation of the crystal can be determined.

A fast X-ray diffraction powder method of quantitative analysis has been developed and demonstrated using mixtures of alpha and beta silicon nitride and silicon.

An analytical procedure, assuming both Gaussian and Cauchy diffracted characteristic line distributions, was used to synthesize CuKα X-ray peaks in the 2θ range 20° to 50° with peak widths from 0.1° to 0.4° 2θ. The relationship of peak height to integrated intensity was established as a function of peak width and tested using pure silicon powder with variable receiving slit widths from 0.01° to 0.40° 2θ.

Concentration calibration curves for silicon nitride and silicon were corrected for extinction and preferred orientation with statistical figures of merit to indicate the extent of preferred orientation.

Preliminary results indicate that this procedure may be used for cold-worked materials.