Characteristic X-ray emission

Absorption measurements by Barkla revealed the existence of characteristic x-ray emission lines before x-ray wavelengths could be measured. There is no better evidence for the fundamental importance of the absorption process. 

Characteristic x-ray emission spectra, discovery, 11-14 from a target, 101 from electron excitation, 27, 28... 

Emission spectra, x-ray, see Characteristic x-ray emission spectra Emission spectrograph, see X-ray spectrograph... 

Such an experimental characterization is a necessary step to carry out a detailed comparison of emission properties as measured experimentally with the corresponding quantities as calculated by numerical models capable of describing transport and energy deposition of fast electrons in matter and consequent emission of characteristic X-ray emission. A possible modeling approach of fast electron transport experiments is given here, where the above results on Ka imaging were interpreted using the hybrid code PETRA [53] to... 

Figure 6. An example of the dependence of characteristic x-ray emissions on incident beam orientation for the dolomite structure.

FIGURE 4.14 Electronic transitions during characteristic x-ray emission. 

Fig. 11. A view of copper and zinc oxide crystallites with dispersed copper ions in the binary Cu/ZnO catalyst = 30/70 derived from diffraction and characteristic X-ray emission analysis in TEM and STEM.

Energy-dispersive spectrometry (EDS) composition based on characteristic x-ray emission induced by electron beam Particle recognition by BSE... 

Microprobe analysis is based on the detection of the characteristic x-ray emission from an ion with which the ion exchanger has been partially or completely loaded. Thc emission is induced by scanning the material with an elec-... 

Modern bulk analysis methods make possible non-destructive chemical identification, which means that the sample remains intact after the analysis. Such a procedure is provided by electron microprobe or X-ray fluorescence analyses, in which the sample is irradiated by electron beams or X-rays and the elemental composition is determined on the basis of induced characteristic X-ray emissions. These methods have been successfully employed to study both stratospheric (Junge, 1963) and tropospheric (Gillette and Blifford, 1971) aerosol particles. Neutron activation analysis is also widely used to identify the chemical composition of atmospheric particulate matter (e.g. Duceef ai, 1966 Rahn etal., 1971) this is also a non-destructive procedure. 

In IT decay from a metastable state to its ground state of a nucleus, an internal conversion process often occurs and as a result, characteristic X-ray emissions are observed. The chemical effect of the X-ray intensity ratio was first studied by Yoshihara and... 

Inner electron shell vacancies can be produced by electron, proton, and heavy ion bombardments. When the vacancies are filled with electrons, characteristic X-ray emissions occur. Kiss et al. > observed the K /K, X-ray intensity change due to chemical environments by bombarding various targets of titanium, chromium, and manganese with electrons. The magnitude of the chemical effect is about 6% for titanium (TiO —Ti), for measurements performed using a Si(Li) detector. 

When a chemical element is bombarded by high-energy particles, orbital electrons may be ejected creating inner orbital atomic vacancies. These vacancies may be filled by transition of outer level electrons giving rise to characteristic X-radiation. X-ray fluorescence spectrometry provides the means of identification of an element by measurement of its characteristic X-ray emission wavelength of energy. 

Charles Barkla, an early X-ray spectroscopist, introduced this terminology for electron shells in 1911. We still use it today to designate characteristic X-rays in both X-ray diffraction and in chemical analysis using electron microscopy. Barkla named the two types of characteristic X-ray emissions he observed as the K-series and L-series. He later predicted that an M-series and a J-series might exist. An M-series was subsequently discovered, but no J-series. The K shell is hence the first shell. 

Rgure 1 An X-ray energy spectrum obtained from the analysis of a freeze-dried tissue culture cell. The spectrum is essentially a histogram plot of the number of counts against the X-ray energy. The spectmm consists of peaks that correspond to characteristic X-ray emissions from different elements. The curved background under the peaks is derived from the X-ray continuum radiation. 

When an EDS detector is used, the characteristic X-ray emissions form a Gaussian peak rather than a... 

The x-ray emission spectrum is obtained by bombardment of the sample with electrons (or other x-rays) with sufficient energy to excite the characteristic x-ray emission from the P atom. When the excitation is by higher energy x-rays, the technique is usually known as x-ray fluorescence analysis (XRF). Identification is specific, and the method requires only small quantities of sample which are recoverable. 

The shortest wavelength K lines are usually used for analysis, that is, K = 6.155 A, Kp = 5.804 A and Cr K radiation (2.29 A) is a suitable source of excitation. The K lines of P are easily distinguished from those of Si or S (Table 14.5). The sensitivity of the method is generally quite high, but it varies considerably depending upon the nature of the matrix. The latter can affect the intensity of characteristic x-ray emission and appropriate corrections have to be made. In the case of an iron matrix, the limits of detection are about 300 ppm, but in mineral oils the element can be detected in... 

X-RAY FLUORESCENCE (XRF) Characteristic X-ray emission produced by iiradiating a material with photons of energy greater than the K-shell binding energy of the element irradiated. Used for chemical analysis. 

Commercially available micro-CT systems utilize X-ray sources with tungsten as the anode material, which has a characteristic X-ray emission spectram. This spectmm has a significant peak at 60 kV and a second peak at 67 kV at a typical maximum kinetic energy of the electrons of 100 kV (Fig. 6.4). Tissue absorbs X-rays better with lower energy photons (about energy dependence in regions <25 kV) (31). 

The energy levels in the inner electron shells are comparatively little affected by the chemical environment of the atoms. Thus, a spectral analysis of the characteristic X-ray emission is well suited for elemental analysis. The relation between the wavelength A of a particular X-ray line and the nuclear charge Z of the corresponding atom is given by Moseley s law... 

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