Ultraviolet radiation properties

Ultraviolet radiation in the region between 0.2 fi to 0.3 has germicidal properties. The peak germicidal wavelength is around 0.26 fi. This short UV is attenuated in air and, hence, the source must be very near the medium to be treated. The medium must be very thin as the UV will be attenuated in the medium as well. 

Acrylic is a generic name for derivatives of acrylic acid, of which methyl methacrylate is the most important. Polymerization is controlled to produce chain length of 800 to 3,000 monomer units. A small amount of plasticizer such as dibutyl phthalate may be added before bulk polymerization to assist in deep molding. The outstanding property of polymethyl metliacrylate is 0 transparency resistance to ultraviolet radiation from fluorescent lamps and ability to be... 

A particularly important property of ozone is its strong absorption in the ultraviolet region of the spectrum between 220-290 nm ( max255.3nm) this protects the surface of the earth and its inhabitants from the intense ultraviolet radiation of the sun. Indeed, it is this absorption of energy, and the consequent rise in temperature, which is the main cause for the existence of the stratosphere in the first place. 

The most stable resin for many of our purposes has proven to be a copolymer of ethyl methacrylate and methyl acrylate. This comes as little surprise the Rohm and Haas Company has for years sold a durable resin based on these two monomers, Acryloid B-72 (6,28). We have also prepared polymers of similar physical properties based on methyl methacrylate and ethyl acrylate and have found that their behavior is practically the same - the methyl and ethyl groups apparently do not become seriously involved in crosslinking. As reported elsewhere( 23), rather than crosslink, Acryloid B-72 tends to chain break under visible and near-ultraviolet radiation, although at a very slow rate. Polyvinylacetate is another polymer used in the care of museum objects that tends more to chain break than crosslink under these conditions(23), but it is not our purpose to discuss its properties at this time. 

Electromagnetic radiation can be absorbed or emitted. The absorption of ultraviolet radiation by our skin may cause sunburn. When we cook food in a microwave oven, the absorption of microwave radiation by the water in the food causes the water molecules to vibrate, generating heat that cooks the food. However, when electromagnetic radiation is absorbed or emitted by matter, it behaves more like a stream of particles than as a wave motion. These particles are called photons and so electromagnetic radiation can be considered both as a stream of photons and as waves with characteristic properties, such as wavelength (1) and frequency (/). Therefore we say that electromagnetic radiation has a dual nature wave motion and streams of photons. 

The role of CFCs in the destruction of ozone in the stratosphere was something of a surprise to some researchers because those compounds are normally quite stable. In fact, their stability is one of their most desirable properties for many industrial and commercial applications. But, when CFCs escape into the atmosphere and drift upward, they are exposed to ultraviolet radiation in sunlight and, as is oxygen itself, are dissociated by that radiation. In the case of Freon-12 (CCI2F2), photodissociation results in the formation of free chlorine atoms ... 

All fine chemicals are used for making speciality chemicals, either by direct formulation or after chemical/biochemical transformation from intermediates to active substances. Specialty chemicals are solid (e.g., tablets) or liquid (e.g., solutions) mixtures of commodities or fine chemicals and exhibit specific properties. They are sold on the basis of what they can do (e.g., protect the skin against ultraviolet radiation), rather than on what they are (e.g., molecular structure 2-ethyl-hexylmethoxycinnamate). Within specialties, pharmaceuticals and other life science products use the largest amount of fine chemicals. They are described in detail in Sections 11.1-11.3. Uses of fine chemicals outside life sciences are discussed in Section 11.4. 

Torres, 0 P. K. Bhartia, J. R. Herman, Z. Ahmad, and J. Gleason, Derivation of Aerosol Properties from Satellite Measurements of Backscattered Ultraviolet Radiation Theoretical Basis, J. Geophys. Res., 103, 17099-17110(1998). 

The initiation of polymerization by ultraviolet radiation has been of particular interest in the study of free radical processes [1,2]. The test tube demonstration described here is simple and may be used to evaluate the polymerizabil-ity of new monomers or to study some of the physical properties of a polymer. Although the method is particularly effective for acrylic and methacrylic monomers, it may also be applied to the polymerization of a wide range of vinyl -type monomers. 

The absorption of a quantum of energy by an atom or a molecule takes it from a low energy state to a higher one, and the jump will affect the different properties of the atom or molecule depending upon the amount of energy in the quantum. When absorbed, a quantum of visible or ultraviolet radiation raises an electron to a higher orbit on the other hand, a quantum of infrared radiation will alter energy levels on an atomic basis. 

As noted earlier, poly(methyl methacrylate) plastic has excellent resistance to ultraviolet radiation. Nevertheless, in long-term outdoor applications or in lighting fixtures, small amounts of ultraviolet absorbers are employed to retard the yellowing and degradation in physical properties which would otherwise occur. 

In 1918, Mellanby produced experimental rickets in dogs. In 1919, Huldschinsky ameliorated rachitic symptoms in children with ultraviolet radiation. Hess, in 1922, showed that liver oils contain the same antirachitic factor as sunlight In that same year, McCollum increased calcium deposition in rachitic rats with cod liver oil factor. In 1924. Steenbook and Hess demonstrated irradiated foods have antirachitic properties, It was in 1925 that McCollum named antirachitic factor as vitamin D. In 1931, Angus isolated crystalline vitamin D (calciferol). In 1936, Windaus isolated vitamin D3 (activated 7-dehydrocholesterol). 

The carboxyl function does absorb ultraviolet radiation, but the wavelengths at which this occurs are appreciably shorter than for carbonyl compounds such as aldehydes and ketones, and, in fact, are out of the range of most commercial ultraviolet spectrometers. Some idea of how the hydroxyl substituent modifies the absorption properties of the carbonyl group in carboxylic acids can be seen from Table 18-2, in which are listed the wavelengths of maximum light absorption (Amax) and the extinction coefficients at maximum absorption (emax) of several carboxylic acids, aldehydes, and ketones. 

Torres, O., Bhartia, P.K., Herman, J.R., Ahmad, Z and Gleason, J. (1998) Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation Theoretical basis, J. Geophys. Res., 103, pp. 17,099-17,110. 

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