Emission radiation quantities

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. 

To summarise, there are in total four radiation quantities for the characterisation of the emission of radiation from an area ... 

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 description of the direction and wavelength distribution of the radiation flow is provided by radiation quantities that are defined analogous to those for the emission of radiation. For the radiation flow d3in, from a solid angle element dee in the direction of the angles / and

surface element d/1, and which only contains the radiation in a wavelength interval dA, we can make a statement analogous to (5.4)... 

Just as for the emission of radiation, cf. 5.1.2, four radiation quantities are used for the characterisation of the incident radiation flow on a surface ... 

According to Kirchhoff s law a black body emits the maximum radiation energy at every wavelength in every direction in the hemisphere. It therefore suggests itself to relate the four radiation quantities, used to characterise the emission of any... 

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... 

Most areas of research and appHcations involving the use of radioisotopes require a knowledge of what radiations come from each isotope. The particular apphcation determines what type of information is needed. If the quantity of a radionuchde in a particular sample or at a particular location is to be deterrnined and this value is to be deterrnined from the y-ray spectmm, the half-life of the nucHde and the energies and intensities or emission probabiUties of the y-rays of interest must be known. Usually it is preferable to use the y-rays for an assay measurement because the d- and P-rays ate much more readily absorbed by the source material, and may not reach the sample surface having their original energies. Once these energies are altered they caimot be used to identify the parent radionuchde. 

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] ... 

Although conventional electron-probe microanalysis appears to be unsuitable for analysis of the exposed surface layer of atoms in an alloy catalyst, recent developments have shown that X-ray emission analysis can still be used for this purpose (89, 90). By bombarding the surface with high energy electrons at grazing incidence, characteristic Ka radiation from monolayer quantities of both carbon and oxygen on an iron surface was observed. Simultaneously, information about the structure of the surface layer was obtained from the electron diffraction pattern. 

The emission of radiation by an atom results in a change in the nature of the atom, which is said to have decayed. The rate at which a quantity of an isotope decays is proportional to the number of unstable atoms present and a graph of... 

In atomic spectroscopy, a substance is decomposed into atoms in a flame, furnace, or plasma. (A plasma is a gas that is hot enough to contain ions and free electrons.) Each element is measured by absorption or emission of ultraviolet or visible radiation by the gaseous atoms. To measure trace elements in a tooth, tiny portions of the tooth are vaporized (ablated) by a laser pulse1 and swept into a plasma. The plasma ionizes some of the atoms, which pass into a mass spectrometer that separates ions by their mass and measures their quantity. 

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