Ionizing radiation chemical interpretation

The DP of polymers formed by ionizing radiations is more difficult to interpret than that of polymers formed by chemical initiation, because after quite a low degree of conversion the degradation of the polymers by the radiation may become significant (Stannett et al. 1964 Deffieux et al. 1982). It is not known to what extent this fragmentation and to... 

Aqueous systems have been studied by a very large number of investigators. Economy, safety, convenience and quality of product have combined to make this the method of choice for commercial production of copolymers. The industrial importance of such end products as elastomers and acrylic fibers has been a special incentive to related fundamental studies. Furthermore, the relatively high solubility of acrylonitrile monomer in water coupled with insolubility of the polymer make it a convenient test monomer for studies of initiation by redox systems (6, 25, 102). Large numbers of homogeneous chemical initiators and some heterogeneous initiators have been studied as well as initiation by photochemical means, by ultrasonics and by ionizing radiation. It will not be possible here to review the enormous world literature. Several publications (/, 92, 117) refer in some detail to the older papers, and we shall restrict our comments to recent interpretations that have received support from several quarters. 

Although the effects of spin coherence have been mainly studied using radiation-chemical processes as an example, published are the first works on the MARY spectra of radical ion pairs produced in solutions by photoionization. Probably, there are no principle obstacles to the application of the method of quantum beats to these systems. Interpretation of results is expected to be more simple, in this case, because of the use of monochromatic sources of ionization and the absence of cross recombination effects typical of the ionization track. Another manifestation of spin coherence, observed experimentally but omitted in this review, is the beats induced by resonance microwave pumping [36-38]. The range of applications of this phenomenon for studying spin-correlated radical ion pairs has yet to be outlined. 

In arriving at this synthesis comprehensive studies were summarized of initiation by stimuli such as heat, light, shock, and nuclear radiation. In spite of earlier suggestions to the contrary (see Chapter 9), little evidence was found that tribo-chemical fracture of crystals leads to detonation. Nitrogen tri-iodide was the only substance known to explode under ionizing radiation. The failure to achieve initiation in other substances was discussed in terms of the limited-size hot spots introduced by nuclear particles. This interpretation was consistent with the observation that hot spots of 10" -10" cm diameter are necessary to produce self-sustaining decomposition. 

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