Crystal spectrometer

In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiate a specimen, and the emitted fluorescent X rays are analyzed with a crystal spectrometer and scintillation or proportional counter. The fluorescent radiation normally is diffracted by a crystal at different angles to separate the X-ray wavelengths and therefore to identify the elements concentrations are determined from the peak intensities. For thin films XRF intensity-composition-thickness equations derived from first principles are used for the precision determination of composition and thickness. This can be done also for each individual layer of multiple-layer films. 

X-Ray Fluorescence analysis (XRF) is a well-established instrumental technique for quantitative analysis of the composition of solids. It is basically a bulk evaluation method, its analytical depth being determined by the penetration depth of the impinging X-ray radiation and the escape depth of the characteristic fluorescence quanta. Sensitivities in the ppma range are obtained, and the analysis of the emitted radiation is mosdy performed using crystal spectrometers, i.e., by wavelength-dispersive spectroscopy. XRF is applied to a wide range of materials, among them metals, alloys, minerals, and ceramics. 

Before the development of semiconductor detectors opened the field of energy-dispersive X-ray spectroscopy in the late nineteen-sixties crystal-spectrometer arrangements were widely used to measure the intensity of emitted X-rays as a function of their wavelength. Such wavelength-dispersive X-ray spectrometers (WDXS) use the reflections of X-rays from a known crystal, which can be described by Bragg s law (see also Sect. 4.3.1.3)... 

Fig. 7-12. The curved-crystal spectrometer of Adler and Axelrod, showing a polished ore specimen in position. (1) Microscope stage (2) polished ore sample (3) crystal support block (4) Geiger counter and scatter slits. (Courtesy of Adler and Ayelrod and the U. S. Geological Survey.)...

The apparatus as modified for x-ray emission spectrograph is also shown in Figure 11-1. The proportional counter may be used alone (pulse-height analysis Section 2.13) or a curved-crystal spectrometer can be employed to achieve better resolution. Analytical results were comparable to those quoted above, but localization of the area analyzed was considerably less sharp than the micron-diameter spot achieved in differential absorptiometry. 

In a WDS, the X-radiation coming from the specimen is filtered by means of a curved crystal spectrometer, which employs diffraction to separate the X-rays according to their wavelength. A typical arrangement for the spectrometer is shown in Figure 5.5. 

A typical instrument is equipped with four computer controlled crystal spectrometers, as well as an EDS system for preliminary qualitative analysis. A light microscope is provided for examining the specimen and also for ensuring that the specimen height is adjusted until it is on the Rowland circle. The drawing of... 

This point analysis is employed to analyse a selected region of chemically homogeneous composition, such as a phase. The electron beam is stopped and positioned carefully on the point selected on the SEM screen, and the composition of the sampling volume is determined by a crystal spectrometer. 

X-Ray Absorption Spectroscopy (XAS). The XAS measurements were similar to those described elsewhere.Grazing incidence (GI)-XAS measurements were performed at beamline 11-2 at Stanford Synchrotron Radiation Laboratory (SSRL). A double Si(220) crystal spectrometer was used to select the energy of the synchrotron X-rays, and the beam size was set to 400 pm x 2 mm. The bandwidth of the spectrometer was about 1 eV. Routine procedures were used to optimize the positions of the samples so that the angle of incidence was about 0.17°, with the X-ray... 

Fig. 7, Geometry of a fully focusing diffracting crystal spectrometer...

An optical diagram of a Johansson curved-crystal spectrometer is given in Fig 9. F.ach spectrometer of an x-ray qnantometer may be equipped with optimum crystal-detector combinations for specific determinations in a wide variety of matrixes, including steel, aluminum, copper-base materials, ores, cement, and slags—in both liquid and solid states. 

Fig. 9. Optical diagram of Johansson curved-crystal spectrometer...

Neutron capture as well as charged particle reactions produce in general very dense y-ray spectra. The high resolution electron [MAM78] and curved crystal spectrometers [K0C80] at ILL in Grenoble present excellent... 

Fig. 4. Portion of the 165Ho(a,3ny)166Tm spectrum observed with the on-line bent crystal spectrometer and with a good resolution germanium detector in the inset (the corresponding region is represented with open circles). Transitions are identified by their approximate energy in keV.

Detail tests on nuclear models require not only a knowledge of energy, spin and parity of many levels, but also the determination of transition multipolarities and branching ratios. Precise intensities are thus needed. The well shielded anti-Compton spectrometer offers a rather simple solution especially for accurate angular distribution measurements. When the spectra are very complex, like in the case of final doubly odd nuclei, intensities cannot be determined without use of high resolution instruments. The curved crystal spectrometer provides a powerful solution at, unfortunately, non negligible cost. 

Blasco F, Stenz C, Salin F, Faenov AYa, Magunov AI, Pikutz TA, Skobelev IYu (2001) Portable, tunable, high-luminosity spherical crystal spectrometer with an X-ray charge coupled device, for high-resolution X-ray spectroscopy of clusters heated by femtosecond laser pulses. Rev. Sci. Instrum. 72 1956-1962... 

We determined the absorption of the laser pulse by recording the scattered and specularly rehected laser light with 47r-arranged calorimeters. In front of the calorimeters, a 2-mm thick quartz plate was installed to block charged particles and X-rays. In some experiments, low-order harmonics of the laser beam were analyzed using a monochromatic meter. Crystal spectrometers were used to record the plasma self-emission of X-rays, from which the ionization states of the target materials were obtained. 

To use the LEAR beam efficiently, the crystal spectrometer was set up as a twin system for the pH experiment. Three independent spherically-bent quartz crystals of 100 mm (Fig. 2) were used. Each of the crystals was directed to its own CCD detector in order to avoid any reduction of resolution from the matching of reflections. About 30 Balmer a events per hour were recorded per crystal-detector system in the case of hydrogen. For antiprotonic deuterium with a single crystal-detector system a count rate of about 60 per hour was achieved in spite of the smaller sensitive area of the detector (Table 2) because of less absorption. 

Table 1. Calculated electromagnetic energies and line widths of the antiprotonic transitions measured with the crystal spectrometer. The energy resolution AEexp of the Bragg spectrometer was determined from narrow transitions of antiprotonic noble gases. Ob stands for the Bragg angle...

Fig. 2. Set-up of cyclotron trap, crystal spectrometer, and CCD detectors in LEAR, experiment PS207. For the pH measurement, the two-arm crystal spectrometer was equipped in total with 3 spherically-bent quartz crystals each reflecting to a separate X-ray detector. Further CCD detectors installed in the second bore hole of the cyclotron trap were used for direct measurements of antiprotonic X-rays...

For the first time, evidence was found for the pD Lyman a transition [23]. The low yield (Fig. 3) and the width of the transition are in line with the strong annihilation from the 2p levels in hydrogen and deuterium as observed in the experiment using the crystal spectrometer. A simple scaling relation, based on the geometrical overlap of wave functions, yields rfj — 2.3 0.3meV [21], a value which is consistent with the direct measurement. 

Fig. 4. Position spectra of silicon and sulphur Ka fluorescence lines, the transitions p3He and pNe used to determine the crystal spectrometer response function, and the Rainier a lines from the hydrogen isotopes. For p3He, the parallel transition (5/ — 4d) is well resolved from the circular transitions (5g — 4f)...

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