Spectral quantities emissivity

The hemispherical spectral emissive power Mx(X,T) covers the wavelength dependency of the radiated energy in the entire hemisphere (hemispherical spectral quantity). 

The emission yield, Ra, defined as the radiation of the spectral line, k, of an element, i, emitted per unit sputtered mass must be determined independently for each spectral line. The quantities g, and Ry are derived from a variety of different standard bulk samples with different sputtering rates. In practice, both sputtering rates and excitation probability are influenced by the working conditions of the discharge. Systematic variation of the discharge voltage, L/g, and current, I, leads to the empirical intensity expression [4.185] ... 

Describing complex wave-packet motion on the two coupled potential energy surfaces, this quantity is also of interest since it can be monitored in femtosecond pump-probe experiments [163]. In fact, it has been shown in Ref. 126 employing again the quasi-classical approximation (104) that the time-and frequency-resolved stimulated emission spectrum is nicely reproduced by the PO calculation. Hence vibronic POs may provide a clear and physically appealing interpretation of femtosecond experiments reflecting coherent electron transfer. We note that POs have also been used in semiclassical trace formulas to calculate spectral response functions [3]. 

Here Psa is the transfer probability. Esa represents the resonance condition (in practise the spectral overlap of the emission of S and the relevant absorption of A) and occurs in both formulas. The quantity gsA comprises the optical strengths of the relevant transitions and a distance-dependence of the type rsA n=6,8, etc.). The quantity /sa, however, is proportional to the wave function overlap of S and A and comprises an exponential distance-dependence. 

Hohnium oxide occurs in nature, usually associated with small quantities of other rare-earth oxides. Commercial applications of this compound have not been explored fuUy. It is used in refractories and as a catalyst. Characteristic spectral emission lines of holmium oxide glass are used to cahbrate spectrophotometers. ... 

For most treatments, the spectral density, J(a>), Eq. 2.86, also referred to as the spectral profile or line shape, is considered, since it is more directly related to physical quantities than the absorption coefficient a. The latter contains frequency-dependent factors that account for stimulated emission. For absorption, the transition frequencies ojp are positive. The spectral density may also be defined for negative frequencies which correspond to emission. 

The radiation may be due to emissions from a hot source, or to the luminescence, fluorescence or phosphorescence of the sample. An emission spectrum consists of a number of generally very narrow peaks (called spectral lines) occurring at certain wavelengths which are characteristic of the materials contained within the source. The amplitudes of the peaks are related to the abundance or concentration of the materials present. Alternatively, radiation from a source is passed through a sample. In this case the quantity absorbed by the sample at a particular wavelength is again characteristic of the materials present in the sample. This is termed absorption spectrometry and produces spectral transmission lines in the form of equally narrow valleys—or peaks (Fig. 6.42) where the information is expressed in terms of absorbance (si) rather than transmittance (20<57>, and ... 

The optical emission spectrum of uranium, while exceedingly rich in lines, cannot be depended upon in the detection and identification of this element. None of its lines is sufficiently persistent, and unless a comparatively large quantity of uranium is present in the zone of excitation, no spectral lines will be observed. On the other hand, it is possible to make use of a simple photoluminescence reaction which will enable the chemist to detect small traces of uranium. 

In most experiments designed to measure the intensity of spectral absorption, the measurement gives the net absorption due to the effects of absorption from the lower energy level m to the upper energy level n> less induced emission from n to m. Since the populations depend on the temperature, so will the measured net absorption. This comment applies to all the quantities defined in the table to measure absorption intensity, although for transitions where hc0v kTthe temperature dependence... 

Emission spectrum Plot of the emitted spectral radiant power (spectral radiant exi-tance) or of the emitted spectral photon irradiance (spectral photon exitance) against a quantity related to photon energy, such as frequency, v, wavenumber, a, or wavelength, X. When corrected for wavelength dependent variations in the equipment response, it is called a corrected emission spectrum. 

Scattering and other forms of spectroscopy Rely on the fact that electromagnetic radiation has other interactions with matter beyond that of simple absorption and emission. These interactions generate other measurable quantities such as scattering of polarized light (e.g. circular dichroism), and changes of spectral features of chemical bonds (e.g. Raman spectroscopy). 

Note that the spectral absorptivity, transmissivity, and emissivity of a medium are dimensionless quantities, with values less than or equal to l.The spectral absorption coefficient of a medium (and tlrus Ca, cta, and Ta), in general, vary with wavelength, temperature, pressure, and composition. 

The methods range from simple, inexpensive absorption spectroscopy to sophisticated tunable-laser-excited fluorescence and ionization spectroscopies. AAS has been used routinely for uranium and thorium determinations (see for example Pollard et al., 1986). The technique is based on the measurement of absorption of light by the sample. The incident light is normally the emission spectrum of the element of interest, generated in a hollow-cathode lamp. For isotopes with a shorter half life than and Th, this requires construction of a hollow-cathode lamp with significant quantities of radioactive material. Measurement of technetium has been demonstrated in this way by Pollard et al. (1986). Lawrenz and Niemax (1989) have demonstrated that tunable lasers can be used to replace hollow-cathode lamps. This avoids the safety problems involved in the construction and use of active hollow-cathode lamps. Tunable semiconductor lasers were used as these are low-cost devices. They do not, however, provide complete coverage of the spectral range useful for AAS and the method has, so far, only been demonstrated for a few elements, none of which were radionuclides. 

The spectral intensity Lx(X,f3,p,T) characterises in a detailed way the dependence of the energy emitted on the wavelength and direction. An important task of both theoretical and experimental investigations is to determine this distribution function for as many materials as possible. This is a difficult task to carry out, and it is normally satisfactory to just determine the radiation quantities that either combine the emissions into all directions of the hemisphere or the radiation over all wavelengths. The quantities, the hemispherical spectral emissive power Mx and the total intensity L, characterise the distribution of the radiative flux over the wavelengths or the directions in the hemisphere. 

The relationships between the four quantities are schematically represented and illustrated in Fig. 5.7. The spectral intensity Lx(X,f3,tp,T) contains all the information for the determination of the other three radiation quantities. Each arrow in Fig. 5.7 corresponds to an integration on the left first over the solid angles in the hemisphere and then over the wavelengths, on the right first over the wavelengths and then over the solid angles. The result of the two successive integrations each time is the emissive power M (T). 

The distribution function Kx(X,/3,incident spectral intensity, is defined by this. It describes the wavelength and directional distribution of the radiation flow falling onto the irradiated surface element. Like the corresponding quantity Lx for the emission of radiation, Kx is defined with the projection d 4p = cos/SdAl of the irradiated surface element perpendicular to the direction of the incident radiation, Fig. 5.12. The SI units of Kx are W/(m2pmsr) the relationship to the wavelength interval dA and the solid angle element dw is also clear from this. 

The following relationships for the four radiation quantities for emission from a real body are obtained from the defining equations for the emissivities. The body s spectral intensity Lx is... 

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