Effective cross section, absorption

Here (Tabs,i is the cross-section for an absorption from the Si -level to higher lying states, Nt is the density of triplet excitations and (Tt is the corresponding cross-section for absorption into higher lying triplet levels. Since the first two terms on the right hand side both depend linearly on the density N xc of excited Si-states an effective stimulated emission cross-section iVsc,cn = sc- ahs,i can be defined. A quantitative treatment of the triplet absorption is more complicated since the density of molecules in the 7 -stale has to be known. 

Nuclide Half-Ufe (S = stable) Atoms per fission-product pair Effective thermal cross sections, b absorption, bams per fission-product pair... 

In resonance Raman experiments it is very important to consider the effect of the absorbed light on the sample composition. Raman scattering and absorption are independent events. Some photons are scattered, but a much larger number are absorbed. Cross sections for Raman scattering are on the order of 10" A /molecule, whereas cross sections for absorption are about 1 A /molecule. Thus, if photon absorption results in a photochemical transformation, as in the case of visual pigments, the effect of the photoalteration must be carefully considered. This situation has been analyzed in detail and rapid-flow methods devised that allow one to obtain resonance Raman spectra of even the most photolabile molecules without distortion of the sample composition. " ... 

Carbon black is a well-known stabilizer for polyolefins, but has limited utility in fibers unless a black fiber is desired. Even then, the stability of black fibers is not sufficient for many current end-uses. UV absorbers are reasonably effective in products of thick cross section but are of hmited value for products of low denier per filament. The small cross section prevents absorption from being effective. 

If the sample nuclear levels are not split and the I = 3/2 to I = 1/2 transition energy equals that of the somce, then the effective cross-section for absorption is a function of gamma energy as given by... 

The analysis of steady-state and transient reactor behavior requires the calculation of reaction rates of neutrons with various materials. If the number density of neutrons at a point is n and their characteristic speed is v, a flux effective area of a nucleus as a cross section O, and a target atom number density N, a macroscopic cross section E = Na can be defined, and the reaction rate per unit volume is R = 0S. This relation may be appHed to the processes of neutron scattering, absorption, and fission in balance equations lea ding to predictions of or to the determination of flux distribution. The consumption of nuclear fuels is governed by time-dependent differential equations analogous to those of Bateman for radioactive decay chains. The rate of change in number of atoms N owing to absorption is as follows ... 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The next step is to consider tire cross-sections of the absorption of radiation by the diatomic halogen molecules in order to decide if the relative effects result from the efficiency of the radiation photon-molecule interactions. These are reflected in the dissociation cross-sections of tlrese interactions. 

The dendritic effect evidenced for 1-8 might be useful to optimize the optical hmiting properties characteristic of fullerene derivatives. Effectively, the intensity dependant absorption of fuUerenes originates from larger absorption cross sections of excited states compared to that of the ground state [32], therefore the... 

For the application of QDs to three-dimensional biological imaging, a large two-photon absorption cross section is required to avoid cell damage by light irradiation. For application to optoelectronics, QDs should have a large nonlinear refractive index as well as fast response. Two-photon absorption and the optical Kerr effect of QDs are third-order nonlinear optical effects, which can be evaluated from the third-order nonlinear susceptibility, or the nonlinear refractive index, y, and the nonlinear absorption coefficient, p. Experimentally, third-order nonlinear optical parameters have been examined by four-wave mixing and Z-scan experiments. 

It is much more difficult to observe the Mossbauer effect with the 130 keV transition than with the 99 keV transition because of the relatively high transition energy and the low transition probability of 130 keV transition, and thus the small cross section for resonance absorption. Therefore, most of the Mossbauer work with Pt, published so far, has been performed using the 99 keV transition. Unfortunately, its line width is about five times larger than that of the 130 keV transition, and hyperfine interactions in most cases are poorly resolved. However, isomer shifts in the order of one-tenth of the line width and magnetic dipole interaction, which manifests itself only in line broadening, may be extracted reliably from Pt (99 keV) spectra. 

In (9.2), AEy is the bandwidth of the incoming radiation and Cei is the electronic absorption cross section. The exponential decay is modulated by the square of a Bessel function of the first order (/j), giving rise to the aforementioned dynamical beats. The positions of their minima and maxima (i.e., the slope of the envelope of the time-dependent intensity) can be determined with high accuracy and thus give precise information about the effective thickness of the sample. 

The coefficient of infrared light absorption by an adsorbed molecular monolayer of the surface concentration N/F depends both on the angle of incidence reckoned from a normal to the surface and on the effective absorption cross-section o(ft>) 122... 

In bulk samples, X-ray yields need to be adjusted by the so-called "ZAF" correction. Z stands for the element number (heavier elements reduce the electron beam intensity more than lighter elements, because they are more efficient back-scatterers), A for absorption (different elements have different cross sections for X-ray absorption), and F for secondary fluorescence (the effect described above). Corrections are much less important when the sample is a film with a thickness of 1 pm or less, because secondary effects are largely reduced. The detection limit is set by the accuracy with which a signal can be distinguished from the bremsstrahlung background. In practice, this corresponds to about 100 ppm for elements heavier than Mg. 

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