High energy radiation, production

A major complication in applying radiation chemical techniques to ion-molecule reaction studies is the formation of nonionic initial species by high energy radiation. Another difficulty arises from the neutralization of ions, which may also result in the formation of free radicals and stable products. The chemical effects arising from the formation of ions and their reactions with molecules are therefore superimposed on those of the neutral species resulting from excitation and neutralization. To derive information of ion-molecule reactions, it is necessary to identify unequivocally products typical of such reactions. Progress beyond a speculative rationalization of results is possible only when concrete evidence that ionic species participate in the mechanism of product formation can be presented. This evidence is the first subject of this discussion. 

The primary product which arises from the degradation of PVC, whether induced thermally, photochemically or by high energy radiation, is a distribution of conjugated polyene sequences of various lengths produced by a dehydrochlorination process which may be written -... 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

There is evidence that both ionic and free radical species are involved in the degradation and depolymerization of poly (olefin sulfone) s by high energy radiation (70). Thus, the yields of olefins from poly (1-butene sulfone) at 30 °C (the sample was heated to 70 °C during removal of the gaseous products) are shown in Table II. The butene is not solely 1-butene, but comprises significant proportions of all three isomers, 1-butene, 2-butene and isobutene. 

I. The Production of Highly Excited States by High-Energy Radiation. 183... 

Since the ionic states formed by high-energy radiation seem to be the chemically important ones, let us consider their reactions. The reactions between ions and neutral molecules in the gas phase can be studied directly in a mass spectrometer. Under ordinary operating conditions the pressure in the ionizing chamber of the mass spectrometer is about 10 6 mm. and the ions formed have little chance to collide with a molecule during their brief lifetime (10-5 sec.) before collection. Therefore, mainly unimolecular decomposition reactions occur and it is the products of these that are detected. The intensity of these primary ions increases with the first power of the pressure in the ionization chamber. However, when the pressure becomes great enough so that ion molecule collisions can occur readily, additional secondary ions which are the products of these ion molecule Collisions appear. The intensity of these secondary product ions depends on the concentrations of both the molecules and the primary ions, and thus on the square of the pressure. 

The modification of the properties of cotton cellulosic textile products, through free radical-initiated graft copolymerization reactions with vinyl monomers, has been investigated at the Southern Laboratory for a number of years (6, 9). In this chapter, we summarize the basic mechanisms and principles involved in free radical reactions of cellulose, initiated by high energy radiation, ceric ion in acidic solution, and aqueous solutions of ferrous ion and hydrogen peroxide. Some of the properties of fibrous cotton cellulose graft copolymers are also presented. 

Another reason for an apparent, but not a true, limit to the amount of a particular product formed would be the existence of competing reactions such as chain breaking and cross-linking. Charlesby has developed equations to permit calculation of the ratio of chain breaking to cross-linking in thermoplastic polymers exposed to high energy radiation (29). These have been applied to analyze the effect of exposure of Acrylan, Mylar, nylon and polyethylene to 2537 A ultraviolet radiation (30). 

A direct synthesis of N2F2 in low yield and admixed with other nitrogen fluorides has been reported from the irradiation of N2-F2 mixtures with ra-y-radiation from a nuclear reactor admixed with other high-energy radiation from uranium fission products (85). There is also a radiochemical synthesis of N2F2 (1.5%) and NF3 (42%) when an N2-F2 mixture is irradiated with 30-MeV electrons in an electron linear accelerator (86). Reaction of fluorine diluted with N2 and NH3 also gives some N2F2 (159,213). 

Photochemistry involves the interaction of visible and ultraviolet light with cellulose whereas radiation chemistry involves its interaction with high-energy radiations, such as from y-radiation. Light promotes the deterioration of cellulosic products, particularly cotton fabrics, and certain dyes or other additives greatly accelerate this process known as phototendering. Ionizing radiation is used to sterilize medical and bioproducts many of which are cellulosic. Several authoritative reviews are available [511-514]. 

Nitric oxide is again catalytic but here its effect is to change 03 to 02. This is a potential problem because 03, which absorbs ultraviolet light, is necessary to protect us from the harmful effects of this high-energy radiation. That is, we want 03 in the upper atmosphere to block ultraviolet radiation from the sun. However, we do not want it in the lower atmosphere where we have to breathe it and its oxidation products. 

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