UV and Visible Radiation

Ultraviolet radiation is part of the electromagnetic spectrum and shows wavelength in the range from 40 to 400 nm. It is known as nonionizing or actinic radiation. Ultraviolet radiahon is divided into the following four regions  

Vacuum UV (VUV) is strongly absorbed by quartz, which is used as the envelope material for bulbs. Because of that and because of its small penetration depth, VUV is not suitable for usual radiation curing. 

Plasma is essenhally an ionized gas, consisting of a mixture of interacting positive ions, electrons, neutral atoms, or molecules in the ground state or any higher state of any form of excitation as well as photons. Since charge 

In industrial applications, photons with energies ranging from 2.2 to 7.0 eV are used. The mercury discharge, as used in mercury arc lamps, produces a polychromatic spectium wifh intensive emission lines ranging in energy levels from 2.8 to 6.0 eV.  

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For UV and visible radiation, the simplest detector is a photomultiplier tube. The cathode of the tube is coated with a photosensitive material (such as Cs3Sb, K CsSb, or Na2KSb, etc.) which ejects a photoelectron when struck by a photon. This photoelectron is then accelerated towards a series of anodes of successively greater positive potential (called dynodes). At each dynode, the electron impact causes secondary electron emission, which amplifies the original photoelectron by a factor of 106 or 107. The result is a pulse of electricity of duration around 5 ns, giving a current of around 1 mA. This small current is fed into the external electronics and further amplified by an operational amplifier, which produces an output voltage pulse whose height is proportional to the photomultiplier current. 

A luminescent mineral is a sohd, which converts certain types of energy into electromagnetic radiation over and above thermal radiation. The electromagnetic radiation emitted by a luminescent mineral is usually in the visible range, but can also occur in the ultraviolet (UV) or infrared (IR) range. It is possible to excite the luminescence of minerals by UV and visible radiation (photoluminescence), by a beam of energetic electrons (cathodoluminescence), by X-rays (X-ray excited luminescence) and so on. A special case is so-called thermoluminescence, which is stimulation by the heating of luminescence, prehminary excited in a different way. 

Burger, J. and Edwards, G.E., Photosynthetic efficiency, and photodamage by UV and visible radiation, in red versus green leaf coleus varieties, Plant Cell Physiol, 37, 395, 1996. 

Figure 3.25 shows the results of one set of calculations of the effects of aerosol particles whose properties were judged to be characteristic of continental or urban situations, respectively, on the transmission of UV and visible radiation to the earth s surface (Erlick and Frederick, 1998). The ratio of the transmission with particles to that without is plotted in two wavelength regions, one in the UV and one in the visible. Two different relative humidity scenarios are shown. The average summer relative humidity was 70% RH in the boundary layer and 20% RH in the free troposphere. The high relative humidity case assumes 90% RH in the boundary layer and 30% in the free troposphere. (The RH in the stratosphere was taken to be 0% in both cases see Chapter 12.)... 

As pointed out in Chapter 1, ionizing radiation includes high-energy electrons (electron beam), y-rays, and x-rays. These not only are capable of converting monomeric and oligomeric liquids into solids, but also can produce major changes in properties of solid polymers. Also, in comparison to UV and visible radiation, they can penetrate considerably deeper into the material. 

Most of the work reported so far on laser-induced photopolymerization deals with near UV and visible radiation ranging from blue (—400 nm) (3,12) to red light (—700 nm) (4). We present here a kinetic investigation on the... 

Ozone forms in the upper stratosphere from molecular oxygen under the influence of UV solar radiation. In the lower stratosphere and troposphere, the source of ozone is the decomposition of nitrogen dioxide under the influence of UV and visible radiation. The formation of the vertical profile of ozone concentration is connected with its meridional and vertical transport. The general characteristic of this profile is the total amount of ozone measured by the thickness of its layer given in Dobson units (1 DU = 0.001 cm). 

Light-Induced Ageing. The sheets were subjected to accelerated light-induced ageing in an apparatus providing UV and visible radiation (3). 

Among the open problems in photobiology which may be investigated with lasers are UV and visible radiation effects on cells, photosynthesis, vision, photomove-... 

The interaction of UV and visible radiation with matter can provide qualitative identification of molecules and polyatomic species, including ions and complexes. Structural information about molecules and polyatomic species, especially organic molecules, can be acquired. This qualitative information is usually obtained by observing the UV /VIS spectrum, the absorption of UV and visible radiation as a function of wavelength by molecules. A typical UV absorption spectrum is shown in Fig. 5.1. The spectrum may be plotted as wavelength vs. absorbance, transmittance, or molar absorptivity, s. The molar absorptivity is defined subsequently. In Fig. 5.1, the absorption spectrum of pyridine dissolved in ethanol is plotted as log s vs. wavelength in angstroms (A). 

Quantitative information can also be obtained by studying the absorption or emission of UV and visible radiation by molecules or polyatomic species. As a very simple example, we can look at the absorption spectrum of a red solution such as red ink in water (Fig. 5.2). It can be seen that with a colorless sample of pure water, shown as the dotted line, all wavelengths of white light, including aU of the red wavelengths, are transmitted through the sample. If we add one drop of red ink to water, to make a solution that appears pale red, the spectrum shows that some of the blue and some of the yellow light... 

The sample can be exposed to UV and visible radiation in sequence. This might be performed in two separate chambers. One chamber could have a visible radiation source and the second a UV radiation source. 

The sample can be exposed to UV and visible radiation simultaneously. Based on the chamber design, it may be possible to balance the UV and visible radiation such that both exposures are completed at about the same time. Otherwise, when one of the exposures is reached, that radiation source can be turned off while the second exposure continues to completion. 

Ultraviolet and visible Absorption of UV and visible radiation leading to electronic excitation N, P Ligand binding sites, side chain exposure, environment. Apphcable to proteins and nucleic acids but not glycans. Quantitative analysis. DNA conformation. Anneahng and hybridization studies of nucleic acids. 

Much work has been reported on the development of carbazole derivatives and also noncarbazole photoconductive polymers. An example of the latter group is poly(bis(2-naphthoxy)phosphazene), which is intrinsically an insulator with a very low photosensitivity toward both UV and visible radiation, but when doped with trinitrofiuorenone in a 1 1 molar ratio, it is a strong photoconductor. 

Some of the UV and visible radiation striking Earth s surface is re-emitted from Earth as IR radiation, (a) True (b) False... 

Not all semiconductors can be prepared in both n- and p-types. Schottky barrier photodiodes are of special interest in those materials in which p — n junctions cannot be formed. They also find application as UV and visible radiation detectors, especially for laser receivers where their high frequency response (in the gigahertz range in many cases) is of particular usefulness. See Ahlstrom and Gartner [2.41], Schneider [2.42] and Sharpless [2.43] for more detailed descriptions. 

Absorption of UV and visible radiation takes place in organic molecules, which depends on the presence of functional groups (chromophores) that contain valence electrons with a low excitation energy. The superposition of rotational and vibrational transitions gives rise to a combination of overlapping lines appearing as a continuous absorption band. 

Metabolism of 32K as a function of light quality Degradation of 32K occurs in UV and visible radiation (fig. 1 and ref. 16,20), as well as in far red light (19). Broad-band radiation is not required for degradation as the reaction proceeds... 

UV and visible radiation are of higher energy (shorter wavelength) than infrared radiation (used in IR spectroscopy) and radio frequency radiation (used in NMR) but not as energetic as X-radiation (Fig. 13.7). 

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