Radiation chemistry energy

Comparative Terms and Units in UVA s Photon and High-Energy Radiation Chemistry Energy Deposition by Ionizing Radiation Sources of High-Energy... 

Ton-molecule reactions are of great interest and importance in all areas of kinetics where ions are involved in the chemistry of the system. Astrophysics, aeronomy, plasmas, and radiation chemistry are examples of such systems in which ion chemistry plays a dominant role. Mass spectrometry provides the technique of choice for studying ion-neutral reactions, and the phenomena of ion-molecule reactions are of great intrinsic interest to mass spectrometry. However, equal emphasis is deservedly placed on measuring reaction rates for application to other systems. Furthermore, the energy dependence of ion-molecule reaction rates is of fundamental importance in assessing the validity of current theories of ion-molecule reaction rates. Both the practical problem of deducing rate parameters valid for other systems and the desire to provide input to theoretical studies of ion-molecule reactions have served as stimuli for the present work. 

Because of these limitations to both the conventional internal ionization and external ionization techniques it has been impossible to obtain accurate kinetic data for the reactions of thermal energy ions. Such thermal energy data are desirable for applications in such areas as radiation chemistry, discharge and combustion phenomena, and upper atmosphere research. 

The first complication to be considered is the presence of an electrostatic field during the mass spectrometric study of the reaction. Only few quantitative studies have allowed for the possible contribution of hard collisions to cross-section (25), and the possibility that competitive reactions of the same ion may depend on ion energy is generally neglected in assigning ion-molecule reaction sequences. These effects, however, do not preclude qualitative application of mass spectrometric results to radiation chemistry. 

The electron itself is frequently used as a primary source of radiation, various kinds of accelerators being available for that purpose. Particularly important are pulsed electron sources, such as the nanosecond and picosecond pulse radiolysis machines, which allow very fast radiation-induced reactions to be studied (Tabata et al, 1991). Note that secondary electron radiation always constitutes a significant part of energy transferred by heavy charged particles. For these reasons, the electron occupies a central role in radiation chemistry. 

X-rays, often used in radiation chemistry, differ from y-rays only operationally namely, X-rays are produced in machines, whereas y-rays originate in nuclear transitions. In their interaction with matter, they behave similarly—that is, as a photon of appropriate energy. Other radiations used in radiation-chemical studies include protons, deuterons, various accelerated stripped nuclei, fission fragments, and radioactive radiations (a, /, or y). 

Track theory starts with localized energy loss. On the other hand, attention has been frequently drawn to the role of delocalized energy loss in radiation chemistry. Fano (1960) estimated from the uncertainty relation that an energy... 

Table 2.1 summarizes some of the events that occur in radiation chemistry through the various stages. The earliest discernible time, obtained from uncertainty principle, AE At - fi, is 1CH7 s, which accounts for the production of fast secondary electrons with energy > 100 eV Times shorter than these are just computed values. It has been suggested that, following ionization in liquid water, the dry hole H20+ can move by exact resonance until the ion-molecule reaction H20+ + H20 — H30+ + OH localizes the hole. The... 

The areas where the use of the track model has been found particularly expedient are (1) LET variation of product yields in the radiation chemistry of liquids (2) the yield of escaped ions and its variation with particle LET (3) energy loss in primary excitations and ionizations (4) radiation-induced luminescence and (5) particle identification. 

International Atomic Energy Agency (1968), Radiation Chemistry and Its Applications, Technical Ser. 84, Vienna. 

The first application of quantum theory to a problem in chemistry was to account for the emission spectrum of hydrogen and at the same time explain the stability of the nuclear atom, which seemed to require accelerated electrons in orbital motion. This planetary model is rendered unstable by continuous radiation of energy. The Bohr postulate that electronic angular momentum should be quantized in order to stabilize unique orbits solved both problems in principle. The Bohr condition requires that... 

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