![]() The electron has a mass of only about 1/1837 of the proton or neutron, so almost all of the mass of the atoms is made up by the protons and neutrons. Both the proton and neutron have masses that are approximately 1 atomic mass unit, amu. The atomic number, Z, is the number of protons in the nucleus. House, in Inorganic Chemistry (Third Edition), 2020 1.7 Nuclear stability However, normal scatter process is a more efficient process than scatter, so that the Bragg diffraction of Pd L-lines from a particular orientation of a highly orientated pyrolytic graphite crystal provides a significant boost to the excitation of the low atomic number elements (Na to Cl K-lines). Polarization is inherent in the diffraction process, so that the overall benefit in this arrangement is similar to the Barkla scatter process. A few combinations of X-ray tube lines and crystalline materials cut at a particular orientation display the property of Bragg diffraction through an angle of 90 degrees. To compensate for intensity losses during the excitation process, the primary excitation source must be a higher power X-ray tube (e.g., 1–2 kW).Ī second process is capable of achieving a similar effect, but instead based on Bragg diffraction at 90°. Instruments of this design are capable of achieving detection limits in the range 1–5 μg per g in the analysis of environmental samples. This arrangement offers the benefits of direct tube excitation but using a polarization configuration that suppresses the detection of scattered tube background. The entire tube spectrum is polarized by the low atomic number secondary target and is available to excite the sample, but this polarized beam cannot (in an ideal geometric arrangement) be scattered off the sample into the detector. ![]() If, therefore, the metal target (in the secondary target ED-XRF configuration, Fig. 3) is replaced by a low atomic number target such as boron carbide (or corundum), the benefits of polarization can be achieved, without interference from nonpolarized secondary target lines. Low atomic number materials are more efficient at scattering X-rays than higher atomic materials. Potts, Kouichi Tsuji, in Encyclopedia of Analytical Science (Third Edition), 2019 ED-XRF Using Polarized Excitation Oxford: Blackwell Scientific Publications.) (1993) Quantities, Units and Symbols in Physical Chemistry, 2nd edn. (Reprinted with permission from Mills I et al. Results have been published, which show that the (111) surface has the highest hardness value ( Zhang et al., 2008b). In general, the energy of defect formation increases with the addition of Zn ( Owens et al., 2002). The incorporation of Zn into the CdTe structure strengthens the crystal lattice ( Szeles, 2004), and considering that the Zn–Te ionicity is smaller than the Cd–Te ionicity, but the Zn–Te binding energy is higher, the stability of the compound increases as well as the shear modulus, while the densities of dislocations and subgrains are reduced ( Triboulet, 2005). This property leads to higher collection efficiency ( Duff et al., 2008) as the interactions between the crystal lattice and incoming radiation are increased. Although there is some discrepancy among authors, values between 5.8 and 6.68 g cc −1 ( Lun et al., 2006 Mandal et al., 2007) have been reported for CZT. CZT materials have a density of nearly 6 g cc −1 ( Auricchio et al., 2008 Fiederle et al., 2004 Goswami et al., 2005 Horodysky et al., 2006 Mandal et al., 2007 Marchini et al., 2008), which provides greater stopping power against incoming γ-rays than competing material technologies. One advantage of using CZT as a detector for high-energy radiation is the high average atomic number of Z = 50, compared with other well-known detector materials such as silicon and germanium with Z = 14 and Z = 32, respectively.ĭensity. Diéguez, in Comprehensive Semiconductor Science and Technology, 2011 3.04.2.2.1 Structural propertiesĪtomic number.
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