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Sophisticated Analytical Techniques for Investigation of Building Materials
Published in A. Bahurudeen, P.V.P. Moorthi, Testing of Construction Materials, 2020
The type and the quality of X-rays emitted from the anode highly depend upon the accelerating voltage (Suryanarayana & Norton, 1998). Higher the accelerating voltage, lesser will be the continuous distribution of X-ray wavelengths (i.e. less will be the white light emitted from the source). Therefore, higher the accelerating voltage, greater is the intensity of radiation emitted from the source as well as shorter will be the wavelength. Characteristic X-rays are emitted from the source (anode) when the electrons impinge on the anode. This electron impingement results in the removal of electrons from different shells of the atom in anode resulting in the transition of electrons from the outer shells to the inner shells. This transition of electrons from higher energy level (outer shell) to lower energy level (inner shell) in the anode results in the emission of characteristic X-rays from the anode. The wavelengths of the X-ray highly depend on the energy levels of the electrons involved in the transition (L – shell to K –shell or M – shell to K – shell). If E1 and E2 are two energy levels of the electrons, then the wavelength of the emitted X-rays can be given by λ=hcE2−E1
Basic Atomic and Nuclear Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Consider electrons with n = 1 (K shell). Since ℓ = 0 (s state electrons), then m = 0 and ms=±12. Hence, there are only 2 1s electrons, written as 1s2, in the K shell. In the L shell (n = 2), ℓ = 0 or 1. For ℓ = 0, there are two 2s electrons (denoted by 2s2), and for ℓ = 1 (m = −1, 0, 1), there are six 2p electrons (denoted by 2p6). Thus in the L shell there are a total of eight electrons (2s2 2p6). Electrons with the same value of ℓ (and n) are referred to as a subshell. For a given subshell, there are (2ℓ + 1) m values, each with two ms values, giving a total of 2(2ℓ + 1) electrons per subshell, and 2n2 electrons per shell. A shell or subshell containing the maximum number of electrons is said to be closed.
Hybrid x-ray luminescence and optical imaging
Published in Yi-Hwa Liu, Albert J. Sinusas, Hybrid Imaging in Cardiovascular Medicine, 2017
Raiyan T. Zaman, Michael V. McConnell, Lei Xing
SXRF is a rapidly emerging high-resolution method to image elements in biological samples. The principle of SXRF is based on the intrinsic fluorescent properties of elements. High-energy x-rays (primary radiation) are used to emit inner shell electrons (such as K- or L-shell) from atoms of an object into the continuum. Outer shell electrons fill the inner shell vacancies, thereby emitting fluorescence (secondary radiation). The energy of these secondary x-rays depends on the properties of the nucleus and the electron shell and is different for each element and/or oxidation state. X-ray fluorescent measurements of biological samples yield quantitative information about the spatial distribution of multiple elements simultaneously with high sensitivity and low background (Yun et al. 1999). No dyes are needed, and when carried out in energy scanning mode, SXRF can be used to determine the oxidation state of an element. While many x-ray synchrotron sources have focusing optics that achieve resolution in the low micrometer range (Miller et al. 2006; McCrea et al. 2008), only third-generation synchrotron sources can provide high brilliance at high photon energy that is needed to acquire 2-D elemental maps at submicron (~200 nm) resolution. To date, SXRF is the only available method for quantitative imaging of whole cells.
Review of Candidate Techniques for Material Accountancy Measurements in Electrochemical Separations Facilities
Published in Nuclear Technology, 2020
Jamie B. Coble, Steven E. Skutnik, S. Nathan Gilliam, Michael P. Cooper
X-ray fluorescence is a low-latency method based on active interrogation by an X-ray beam that can be used to determine the relative concentration of many isotopes within a UNF sample. This technique measures de-excitation X-rays emitted from ionized atoms to evaluate the relative elemental composition of the material.55 XRF relies on the fact that the electron binding energies for each shell are unique to each element. When X-rays of high enough energy to overcome the electron binding energy ionize weakly bound K-shell electrons, an electron from a higher orbital (for example, the L-shell) can drop to fill the vacancy left by the liberated electron and a characteristic X-ray is emitted whose energy is equal to the difference in the binding energies of the two electron shells.55 Because the electron binding energies are unique to each element, XRF spectra can be used to estimate elemental ratios based on the relative abundance of emitted florescence X-rays within an uncertainty of 1%. Measurement latency for XRF depends on whether the analysis is handled onsite or offsite. For onsite measurements and analysis, latency could be on the order of several hours, whereas for offsite analysis the required time could be several days.