Incident Radiation

AH bodies other than blackbodies reflect or transmit some portion of the radiation incident upon them. The fractions of the incident radiation that are absorbed, transmitted, and reflected by a body are caHed the absorptivity, a, the reflectivity, p, and the transmissivity, T, respectively. These must add up to... 

Blackbody Radiation Engineering calculations of thermal radiation from surfaces are best keyed to the radiation characteristics of the blackbody, or ideal radiator. The characteristic properties of a blackbody are that it absorbs all the radiation incident on its surface and that the quality and intensity of the radiation it emits are completely determined by its temperature. The total radiative fliix throughout a hemisphere from a black surface of area A and absolute temperature T is given by the Stefan-Boltzmann law ... 

Considering Figure 1, radiation incident on a surface (light, X rays, or neutrons) will be reflected and refracted at the interface between the two media provided there is a difference in the index of refraction. In the case of neutrons and X rays, the refractive index of a specimen is slightly less than unity and, to within a good approximation, is given by... 

A non-uegligible fraction of the solar radiation incident on the earth is lost by reflection from the top of the atmosphere and tops of clouds back into outer space. For the radiation penetrating the earth s atmosphere, some of the incident energy is lost due to scattering or absorption by air molecules, clouds, dust and aerosols. The radiation that reaches the earth s surface... 

The radiation emitted by a real surface is less than the radiation emitted by a blackbody, and the absorption of radiation by a real surface is incomplete. Many surfaces are excellent approximations to a blackbody, but some are not. Of the radiation incident upon a real surface, I(k, 9), a portion is reflected, some is... 

The solar radiation incident on the atmosphere and the Earth s surface represents the largest external energy contribution. The optical irradiation at the upper boundary layers of the atmosphere is 4,435 kJ/cm2/year, of which around 1,108 kJ/cm2/year reaches the Earth s surface. 

Optical background, n - the spectrum of radiation incident on a sample under test, typically obtained by measuring the radiation transmitted through or reflected from the spectrophotometer when no sample is present, or when an optically thin or non-absorbing standard material is present. 

Figure 2 demonstrates the principles of reflectometry and reffactometry by using a waveguide with a refractive index that is higher by n2 than that of the environment (ni). Radiation incident to an interface between media with different refractive indices is reflected in part most penetrates the medium. The radiation is reflected and refracted in dependence on the angle of incidence and the ratio of refractive indices in the two media according to Snellius law... 

Fig. 7-8. Solar radiation incident on a horizontal surface (insolation) as a function of time at various latitudes in the Southern Hemisphere.

In such decompositions the rate of decomposition mainly depends on the intensity and wave length of radiation and not much on temperature. Solvent plays an important role in this type of decomposition as it controls the intensity of the radiation incident on the initiator molecule. 

Visible light or other electromagnetic radiation incident on a solid, liquid, or gas can liberate electric charges. This is called photoelectricity. Ejection of electrons from the surface is usually called photoemission. Electrons or positive ions formed in a gas as the result of such radiation is called photoionization. Such a process, however, cannot charge a particle directly. The charging process in that case is a direct result of subsequent diffusion. 

Contemporary radiation protection systems (ICRP, 1977a 1991 NCRP, 1987 1993) include dose limits expressed in such a quantity. To obtain the quantity, absorbed doses are first multiplied by a quality factor (ICRP, 1977a) or a radiation weighting factor (ICRP, 1991), selected for the type and energy of the radiation incident upon the body, yielding, respectively, the dose equivalent in the tissue (ICRP, 1977a) or equivalent dose in the tissue (ICRP, 1991). Therefore ... 

The primary act in a photochemical reaction is absorption of a quantum of radiation by the photoactive molecule. In a quantitative study, therefore, a radiation source of known intensity and frequency a suitable cel for the photolyte and an appropriate detector of light intensity are absolutely necessary for the determination of rates of reaction. To avoid experimental error due to geometry of the reaction cell, the best arrangement is to have a plane parallel beam of monochromatic radiation, incident upon a flat cuvette with proper stirring arrangement, as given in Figure 1.2. 

Wavelength dependence of detector response can also be compensated by using a fluorescent screen in front of the photocell or photomultiplier. This screen acts as a quantum counter. A concentrated solution of Rhodamin B in glycerol (3g per litre) or fluorescein in 0.01N NajCO, has been used for this purpose. Quantum counters work on the principle that whatever be the wavelength of radiation incident on the screen, if completely absorbed, the photodetector sees only the wavelength distribution of fluorescence from the dye. It requires that the fluorescence yield of the counter material be independent of wavelength of excitation and therefore that its emission intensity is directly proportional to the incident intensity. 

The unit of radiation exposure is the roentgen (R). It is a historical unit of the exposure and characterizes the radiation incident on an absorbing material without regard to the character of the absorber. The unit was formalized in 1928 as The amount of radiation which produces one electrostatic unit of ions (esu), either positive or negative, per cubic centimeter of air at standard temperature and pressure. Translated in modem units ... 

Davies. J. E. and Hay. J. E. (1980) Calculation of solar radiation incident on a horizontal surface, Ptoc. 1st Canadian Solar radiation Data Workshop. 

The term Qsh is the net solar radiant energy absorption rate on the basin bottom. It is equivalent to total radiation incident on the basin cover minus reflection from the cover, the water surface, and the basin bottom, and minus loss due to structural shadowing. Its determination from Weather Bureau records of total daily radiation on a horizontal surface is complicated by many factors such as variation in angle of incidence, and resulting transmissivity of cover, hourly and seasonally, intensity change due to cloudiness, and different properties of direct and diffuse radiations. Detailed explanation of these meteorological and optical calculations is beyond the scope of this paper, but may be found in the literature (6). 

For microwave radiation incident upon a slab from a direction perpendicular to its surface, a fraction of the energy will be reflected from the surface, Pr, depending upon its complex dielectric constant e. The main contribution to the magnitude of reflection however, is from the dielectric constant e. Errors due to neglecting e" are less than 5% for virtually all foods as is indicated by the 5% line in Figure 1. Neglecting the loss factor, an approximate equation for the fraction of microwave power reflected from an infinite slab food surface is given by ... 

Fig. 4.2. Diagrammatic representation of the experimental crystal and beam geometries for p-polarized radiation incident upon the (111) crystal face as viewed (a) from the side and (b) from the top including the second atomic plane ( ). The crystal coordinates are labeled x, y, z with the Z direction along the [211] crystal direction. The beam coordinates are labeled s, k, z. From Ref. 122.

Usually, the front of the film-pack is covered with black paper and additional sheets may be introduced between the films to act as "spacers. 1 Effects due to absorption in these extra layers must also be taken into account. If the absorption coefficient for a spacer is k, a fraction N2(29) of the radiation incident at an angle 29 to the nornPal will be transmitted, where... 

In order to determine the natural structure of the Compton modified line it is necessary to first minimize an experimental cause for the breadth of the line which is ordinarily superposed upon the natural breadth so as to mask the latter. This cause is the unavoidable inhomogeneity of scattering angle. The x-radiation incident upon the scattering material... 

Radiation incident on a sample results in radiation interacting with the sample to be transmitted, reflected, refracted, absorbed or emitted. Almost any of these modes19 may be used for examining the absorbance characteristics in a microscopic configuration. Since microscopy places unique sampling demands upon an... 

Radiation incident to a detector array, which is not absorbed but reflected back into space by the detector array, is referred to as the "light signature", LS. In order to minimize the light signature of a detector array having trench walls or mesa structures, these wall-sides must be reduced to be much smaller than an optical blur diameter. The optical blur diameter is given by 1.22 times the wavelength, divided by the numerical aperture. 

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