Читать книгу X-Ray Fluorescence Spectroscopy for Laboratory Applications - Michael Haschke, Jörg Flock - Страница 17

Absorption will be understood merely as the attenuation of the incident X-ray radiation by the ionization of atoms. This process is described by the element- and energy-dependent photoionization coefficient. It increases with higher atomic number and decreases with increasing energy as can be seen in Figure 2.5. This energy dependence can be approximated by τ ≈ E⁻³. The curve does show discontinuities that manifest themselves as jumps. They occur when the energy of the absorbed radiation is sufficient to ionize a new electron shell, i.e. a new interaction mechanism is added. In the diagrams in Figure 2.5, this applies to Pb for the excitation of M, L, and K radiation at energies of approximately 3, 15, and 88 keV, respectively. The energy of the K-absorption edge of C, on the other hand, is 0.283 keV and is therefore not displayed in the diagram.

Table 2.2 Comparison of line designations for the main X-ray lines.

Siegbahn	IUPAC	Siegbahn	IUPAC	Siegbahn	IUPAC
Kα1	K–L3	Lα1	L3–M5	Mα1	M5–N7
Kα2	K–L2	Lα2	L3–M4	Mα2	M5–N6
Kß1	K–M3	Lß1	L2–M4	Mβ	M4–N6
Kß2	K–N3	Lß2	L3–N5	Mγ	M3–N5
Kß3	K–M2	Lß3	L1–M3	Mξ	M4,5–N2,3
Kß4	K–N5,4	Lß4	L1–M2
Kß5	K–M4,5	Lß5	L2–O4,5
		Lß6	L3–N1
		Lγ1	L2–N4
		Lγ2	L1–N2
		Lγ3	L1–N3
		Lγ4	L1–O3
		Lγ5	L2–N1
		Lγ6	L2–O4
		Lη	L2–M1

Figure 2.5 Contributions to the attenuation coefficient for X-radiation of (a) carbon and (b) lead.