Atomic number absorption coefficient

Element Atomic Number Absorption Cross-Section O abs (10 24 Cm2) Mass Absorption Coefficient n/p (cm2/g) ... 

In thin sections natural graphite is translucent, strongly pleochroic, and uniaxial. It has a negative sign of birefringence and two extinctions per revolution under crossed Nicol prisms. The atomic number of carbon accounts for its low absorption coefficient for x-rays and electrons. 

Atomic number Atomic weight Crystal structure Melting Density Thermal Electrical resistivity (at 20°C) Temperature coefficient of resistivity Specific Thermal Standard electrode potential Thermal neutron absorption cross-section. 

The mass absorption coefficient is sometimes denoted with a subscript e.g., Hm, which will be omitted in this book. Subscripts will be used to identify ni (linear) and fj.a (atomic), m = m/p and pa — pM/N, when p = the density (in grams per cubic centimeter) of the absorbing material, M is its atomic weight, and N is Avo-gadro s number. 

The values of r and a in Table 4-2 show that photoelectric absorption generally makes the greater contribution to the mass absorption coefficient. Absorption leading to scattering, which will be discussed in the next section, gains in relative importance as atomic number Z and wavelength X decrease. 

An interesting variant of Group I is the determination of thorium in monazite concentrates.73 Here the variations that may occur in the chemical composition of the matrix leave its x-ray absorbance virtually unaltered. This simplicity is possible because the principal individual rare-earth elements present in the samples lie in the range of atomic numbers from 57 to 60, a range so small as to preclude marked variations in the over-all mass absorption coefficient. 

Ascites tumor cells, determination of dry weight of individual, 299, 300 Atomic absorption coefficient, 15 Atomic energy program, use of x-ray absorptiometry in, 96 Atomic number, significance proved by Moseley, 28, 29... 

Mass absorption increases strongly with the atomic number Z. For the 14.4 keV radiation of Fe, the coefficient follows approximately the relation k. 0.003 from oxygen to krypton. Therefore, organic solvents containing sulfur or chlorine are virtually opaque to the Mossbauer radiation. The sulfur component of a 2 mm layer of dimethylsulfoxide (DMSO) absorbs 70% of the Mossbauer radiation (/ = 1.1 g cm ) [35]. Even worse is dichloromethane (CH2CI2), having an absorption coefficient of 16.83 cm g. A layer of 0.1 g cm , which is only 0.75 mm thick (p = 1.33 g cm ), absorbs about 82% of 14.4 keV radiation. For the same reason, chlorinated polymers (PVC) or glass should not be used for... 

Both WDXRF and EDXRF lend themselves admirably to quantitative analysis, since there is a relationship between the wavelength or energy of a characteristic X-ray photon and the atomic number of the element from which the characteristic emission line occurs. The fluorescence intensity of a given element is proportional to the weight fraction. Emitted fluorescence radiation is partly absorbed by the matrix, depending on the total mass absorption coefficient ... 

X-ray mass absorption coefficient vs. atomic number at (a) 8.34 A (aluminum Ka,3 line) and (b—facing page) 13.34 A (copper Let,a line)... 

The expression for the atomic cross section a follows from mass absorption coefficient p/p of the element is given by p/p = Aa/M, where p is the density, and A and M are Avogadro s number and the atomic weight, respectively. This gives, analogously to Eq. (1.49),... 

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