X-ray Wavelength Range Research Articles

Determination Of Nitrogen and Other Elements in Plant Material By X-Ray Fluorescence

In the early years, the element range covered by the Wavelength Dispersive X-Ray fluorescence (WDXRF) technique was restricted by the quality of vacuum, crystals and detectors in the system. The lightest element detectable was Aluminium (Z = 13). The area of light element analysis had obvious potential for extension over the years. It created the barrier for XRP coverage of the Periodic Table because the naturally softer radiations lay out of range of the technique. In the middle of the 1980's, new technology became available for the manufacture of synthetic crystals with artificially created 2d spacings to suit the X-ray wavelength range of interest. These hyered synthetic microstructures (also called “multilayer crystals”) allowed more sensitivity to be achieved in this part of the spectrum, and the bottom element limit soon moved down towards lighter elements.

Monochromatic spatial resolution in the soft X-ray wavelength range

The author suggests a new method which make use of glass capillary arrays to diagnose isoelectronic laser plasma ions. This new set up includes a fiber-like array, located close to the soft-X-ray source, to generate a quasi parallel polychromatic beam which is then diffracted by a grating. This quasi parallel beam is then diffracted by a plane grating; use of a holographic grating with a nonuniform groove distribution and focusing properties increases the spatial resolution as well as the luminosity of the set up. Rough approximation shows that diffracted images may be obtained in a single shot.

Superconducting wiggler for adone: Design and present status

A superconducting wiggler has been designed and built at Laboratori Nazionali INFN in Frascati, Italy, in collaboration with Ansaldo Componenti-Genova, to be used as an insertion device in the Adone storage ring. It will be used as a light source on the 1.5 GeV, 100 mA electron beam of the accelerator, to produce about 1012 photons/s/mrad in 0.1% band width, in the short X-ray wavelength range. In order to minimize the electron beam orbit disortion and to obtain the best phase space distribution of the generated synchrotron radiation (a single bright spot), a superconducting dipole, producing a sharp vertical field peak (6 T, 12 cm FWHM), between two normal conducting side dipoles (0.8T), to compensate the field integral, has been manufactured. The s.c. dipole is made up of 2NbTi coils, separated by a central plate and kept together by two 356 kg total weight iron yokes. The magnet gap is 6 cm and the design current is 360A. The system is contained in a warm bore cryostat and cooled by boiling helium at 4.6K. The static cryostat helium consumption is of 41/h and, when the cryomagnet is energized, it is cooled by a 1430S Koch liquefier/refrigerator on line with it through transfer lines. The stored energy is 184 kJ. This paper describes the latest status of the facility and the verification tests.

Synthesized multilayer Fresnel X-ray optics (abstract)

The paper considers a diffraction model of a new type of focusing elements for x-ray optics based on profiled multilayer reflection structures. The characteristics of the focusing properties of synthesized Fresnel structures (SFS) were compared to those of conventional ‘‘transparent’’ zone plates. The latter were shown to exhibit fundamental resolution limits caused by the effects of volume diffraction in structures of real thickness. SFS x-ray optical elements are free from such limitations and display the properties of volume holographic lattices, namely, absence of chromatic aberrations, high efficiency and spatial resolution. The first experimental results of the investigation of SFS focusing properties in the soft x-ray wavelength range are reported. It is most advantageous to use SFS elements for controlling powerful synchrotron radiation beams, since they combine the temperature stability of multilayer mirrors with the possibility to obtain resolution below 0.1 μm.

Soft x-ray reflection from SiC, TiC, and WC mirrors

The optical constants of SiC, TiC, and WC in the soft x-ray region (80–1200 eV) derived from the incidence-angle dependence of the specular reflectance are reported. The angular dependence of the specular intensity can be explained by simple scattering theory with a Gaussian distribution of the surface roughness in the soft x-ray wavelength range.

Improved excitation rate coefficients for the N = 2 and N = 3 levels of CA XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Determination of the bulk emittance of a laser plasma in the x-ray wavelength range

An analysis is made of a method for numerical determination of the bulk emittance of a laser plasma from experimental results obtained by contactless diagnostic methods (such as camera obscura, x-ray crystal-diffraction microscope, etc.). The main problem in an analysis of the experimental results obtained using such diagnostic apparatus is to find a stable solution of the Abel equation since it represents an incorrectly posed problem for a pair of naturally used classes of functions (metric spaces), in particular in the space of continuous functions with a uniform metric. The attention is concentrated on the problem of selection of regularizing counting parameters. It is desirable to use a counting scheme with a regularizing parameter variable over a grid of values of the required function. The results are given of test calculations and, by way of illustration, an analysis is given of experimental results.

Tuneable polarizers for X-rays and neutrons

Abstract Multiple Bragg reflections in offset grooved crystals are shown to provide highly polarized X-ray beams. Polarization ratios of 10−5 are possible throughout a wide range of X-ray wavelengths. If sufficiently perfect crystals of magnetic materials can be obtained, then the same principle will permit the selection of polarized neutrons with unprecedented purity.

X-ray laser with a distributed feedback: output power and coherence

A theoretical analysis is made of the energy and statistical characteristics of a distributed-feedback laser. Estimates are made of the output energy and times needed to establish a practically complete coherence of the output radiation in the x-ray wavelength range.

Accurate Measurement of Bijvoet X-ray Intensity Ratios

IN noncentrosymmetric crystals the anomalous dispersion of X-rays leads, in general, to a breakdown of Friedel's law, that is to unequal diffracted intensities from reflexions of the form . A measure of this effect, which for atoms with high atomic number can be appreciable throughout the commonly used range of X-ray wavelengths, is the Bijvoet intensity ratio . Accurate measurements of the Bijvoet ratios are of considerable importance for the determination of phases in structure analysis1, in tests of the theoretically calculated values of the dispersion corrections to the atomic scattering factors2 and in the determination of the absolute configuration of molecules3. Recent determinations of absolute configurations have made use of the anomalous dispersion of CuKα radiation by atoms as light as oxygen4,5.

Convex Curved Crystal X-Ray Spectrograph

The convex side of a curved crystal will diffract a continuous range of x-ray wavelengths simultaneously. Thus, it is useful for spectral analysis of flash x-ray tubes or plasmas where there is not sufficient time to scan through the spectrum with a spectrometer. It is also convenient for detecting impurities in x-ray targets and could be used for x-ray spectrochemical analysis. The choice of analyzing crystal, the particular diffracting planes, and the orientation of the bending axis allows a considerable versatility in intensity and dispersion including the recording of two or three separate spectra in a single exposure.

Point anode proportional counters for the detection of soft X rays in microanalysis

An end-window (point anode) counter is described which has been designed for detecting soft X rays in an electron-probe microanalyser. An experimental evaluation of the counter showed that it had good resolution for the X-ray wavelength range encompassing CK, OK and AlK, provided that the needle-to-window distance and the X-ray aperture size were both suitably selected. The deterioration in counter performance when the optimum geometrical settings were not used was found to be due to a spread in mean pulse energies, which could reach 40%, arising from ionizations across the counter axis. The best resolution figures achieved during practical operation of this end-window counter, and a larger model of similar design, were σ/P = 20%, 42% and 64% for AlK, OK and CK X rays respectively, as compared with 15%, 35% and 46%, measured on a standard side-window design. These values are far inferior to suggested theoretical resolutions and methods of improving the counters are considered. It is concluded that a good side-window counter, with its superior resolution, is desirable for quantitative microanalysis using the network method, but other cases are discussed where the end-window counter may be preferred on account of its convenient geometry.

Energy Spectra of a Number of Celestial X-Ray Sources in the Energy Range from 2 to 60 Kiloelectron Volts

The emission of 20 to 60 kev x-rays by an astronomical object in the constellation of Cygnus has been observed with a balloon-borne x-ray telescope flown from Hyderabad, India. The balloon data, used in conjunction with data pertaining to the flux in the wavelength range from 2 to 10 A can be fitted by a power law in photon energy varying as (h(v))-(1.7). The Cygnus object is the brightest object in the sky in the hard x-ray wavelength range and has the hardest spectrum of all observed objects that emit x-rays. The astronomical object should be capable of accelerating protons up to energies of the order of 10(18) electron volts. Upper limits to the hard x-ray fluxes from Sco XR-1, Cyg XR-2, Oph XR-1, and Ser XR-1 are established; it is shown that the Sco XR-1 spectrum is very soft.