Absorption radiation induced

WJ Jusko, DR Conti, A Molson, P Kuritzky, J Giller, R Schultz. Digoxin absorption from tablets and elixir the effect of radiation-induced malabsorption. J Am Med Assoc 230 1554-1555, 1974. 

In the preceding ten chapters of this book, we have described various important chemical and physical changes brought about by the absorption of ionizing radiation in gaseous and condensed media. Wherever possible, we have tried to elucidate the underlying mechanism with a discussion of the properties and reactivities of the intermediate species. However, the book would remain incomplete without discussion of some of the various uses that have been found for radiation-induced reactions in science and industry. 

Radiation absorbed dose (rad) Radiation-induced damage to biological tissue results from the absorption of energy in or around the tissue. The amount of energy absorbed in a given volume of tissue is related to the types and numbers of radiations and the interactions between radiations and tissue atoms and molecules. The fundamental unit of the radiation absorbed dose is the rad 1 rad = 100 erg (absorbed)/g material. In the latest nomenclature, 100 rad = 1 gray (Gy). 

RADIATION-SENSITIVE GROUPS. Although the absorption of radiation energy is dependent only on the electron density of the substrate and therefore occurs spatially at random on a molecular scale, the subsequent chemical changes are not random. Some chemical bonds and groups are particularly sensitive to radiation-induced reactions. They include COOH, C-Hal, -SO2-, NHz, C=C. Spatial specificity of chemical reaction may result from intramolecular or intermolecular migration of energy or of reactive species -free radicals or ions. 

For radiation induced chemical reaction, a distinction is often made between single-photon and multiple-photon events. The differentiation is based on the intensity (flux) of the photon source. For single photon events, the maximum energy of mid-IR photons is ca. 2.4kj mole and near-IR photons ca. 48 kj mole [25, 26]. Therefore, single photon mid-IR irradiation is normally considered non-destructive. However, intense irradiation and hence multiple photon absorption in mid-IR is known to promote chemical transformations [27, 28]. As an example of NIR pro-... 

The colors are clear, yellow, orange, red, blue and green, while the main color centers are radiation induced. Violet and violet-red colors in Cr-containing topaz are generated by two absorption bands in the visible part of the spectriun, which are connected with Cr + substituting for AP". Yellow topaz besides Cr +... 

Figure 3 Left Optical absorption spectrum and STM image of radiation-induced oligomers Agv at partial reduction and stabilized by PA [85,86]. Right Absorption spectrum of radiation-induced silver clusters Ag in the presence of EDTA. (a) After partial reduction (10 krad), (b) after 4 days, (c) after 8 days. Inset TEM micrographs of (a), (b), (c), and electron diffraction pattern of sample c. (From Ref 145.)...

Understanding of the mechanism of radiation degradation of polymer molecules is essential for development of improved and new industrial processes, for radiation-induced modification of polymer properties, and for selection of polymers for use in radiation environments. This means that the detailed chemical reactions resulting from absorption of radiation must be known. This fundamental understanding must enable us to relate the chemical structure of a polymer to changes in its chemical, physical and material properties. Such structure-property relationships require a great deal of research work, but they are the key to further advancement on a scientific basis. 

Pentavalent Chromium. The radiation-induced formation of unstable lower oxidation states is not limited to the cations. As an example of the anions, Cr04-2 or Cr207 2 have been investigated. In acid media, the presence of dichromate markedly decreases the H atom yields, while in alkali hydroxide solutions an absorption band (Xmax = 585 m/x) and a characteristic ESR signal both attributable to the trapped... 

Studies on irradiated solutions of phenolase showed that the enzyme was inactivated. The radiation-induced changes were found to be different from those reported to occur upon denaturation of proteins. Infrared absorption spectra revealed that deamination had occurred. Acid- and basebinding groups were reduced in number rather than increased, and the optical rotation became more dextrorotatory than levorotatory. It was fur-... 

Two important applications of radiation to determine molecular structure—X-ray crystallography and magnetic resonance—were discussed in Chapters 3 and 5. In this chapter we will discuss a variety of other techniques. Microwave absorption usually forces molecules to rotate more rapidly, and the frequencies of these absorptions provide a direct measure of bond distances. Individual bonds in a molecule can vibrate, as discussed classically in Chapter 3. Here we will do the quantum description, which explains why the greenhouse effect, which overheats the atmosphere of Venus and may be starting to affect the Earth s climate, is a direct result of infrared radiation inducing vibrations in molecules such as carbon dioxide. 

Application of pulse radiolysis to polymers and polymerization was motivated at first by the success of radiation-induced polymerization as a novel technique for polymer synthesis. It turned out that a variety of monomers could be polymerized by means of radiolysis, but only a little was known about the reaction mechanisms. Early studies were, therefore, devoted to searching for initiators of radiation-induced polymerization such as radicals, anions and cations derived from monomers or solvents. Transient absorption spectra of those reactive intermediates were assigned with the aid of matrix isolation technique. Thus the initiation mechanisms were successfully elucidated by this method. Propagating species also were searched for enthusiastically in some polymerization systems, but the results were rather negative, because of the low steady state concentration of the species of interest. 

The behavior of cationic intermediates produced in styrene and a-methyl-styrene in bulk remained a mystery for a long time. The problem was settled by Silverman et al. in 1983 by pulse radiolysis in the nanosecond time-domain [32]. On pulse radiolysis of deaerated bulk styrene, a weak, short-lived absorption due to the bonded dimer cation was observed at 450 nm, in addition to the intense radical band at 310 nm and very short-lived anion band at 400 nm (Fig. 4). (The lifetime of the anion was a few nanoseconds. The shorter lifetime of the radical anion compared with that observed previously may be due to the different purification procedures adopted in this experiment, where no special precautions were taken to remove water). The bonded dimer cation reacted with a neutral monomer with a rate constant of 106 mol-1 dm3s-1. This is in reasonable agreement with the propagation rate constant of radiation-induced cationic polymerization. 

Figure 16 shows the absorption spectrum obtained by additive-free polyethylene [67], At ambient temperature the absorption observed on nanosecond time-scale increased continuously from 500 to 200 nm without showing any maximum. The absorption in UV is similar to that obtained by y-irradiation. Considering the results obtained by liquid alkanes, the absorption seems to be comprised of several different free radicals. At 95 K additional absorption due to the trapped electron was observed at wavelengths longer than 600 nm the band was observable even at ambient temperature in the picosecond time-domain [96]. The electron decays presumably by the hole-electron recombination. The decay of the trapped electron was independent of the presence of carbon tetrachloride, suggesting that the additives reacted with a mobile electron but not with the trapped electron. On adding naphthalene, the radiation-induced spectrum showed the bands due to the first excited triplet state and the radical... 

Besides spectroscopic techniques such as infrared-reflection-absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS), SFM-based stiffness imaging was applied in order to detect radiation-induced variations of surface stiffness [180]. For that purpose, when exposing the PE-film to the VUV-radiation, the film was covered with a Ni mesh. Thus, the PE-film was partially masked and exposed to the VUV radiation only within the square-shaped holes of the mesh. After having finished that treatment and having removed the mesh, the sample surface was scanned in force modula-... 

An ink must be transformed to a solid from its liquid supply form once on the substrate. This change of state is referred to as an ink drying, and can be physical (absorption or evaporation) or chemical (oxidative or photochemical radiation induced). There are several forms of radiation used to dry ink, including UV, infrared, EB, microwave, and radio frequency. 

Time-resolved microwave conductivity TRMC) Technique allowing the quantitative and qualitative detection of radiation-induced charge separation by time-re-solved measurement of the changes in microwave absorption resulting from the production and decay of charged and dipolar molecular entities. 

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