Primary internal decomposition

The decomposition of a compound labeled with a radioactive isotope can be due to one or more of four effects, as follows. (1) A primary (internal) radiation effect, wherein the decomposition of the molecules arises as a result of the disintegration of their unstable atomic nuclei. (2) A primary (external) radiation effect, in which decomposition occurs hy interaction of the molecule with a nuclear particle. (3) A secondary radiation effect, where decomposition arises from reaction with a reactive species produced hy the radiation. An example would he that of free radicals produced hy the radiolysis of residual water in freeze-dried carbohydrate samples. (4) A chemical effect, whereby decomposition arises from chemical reactions which are not connected with radiation. 

Antioxidants act so as to interrupt this chain reaction. Primary antioxidants, such as hindered phenol type antioxidants, function by reacting with free radical sites on the polymer chain. The free radical source is reduced because the reactive chain radical is eliminated and the antioxidant radical produced is stabilised by internal resonance. Secondary antioxidants decompose the hydroperoxide into harmless non-radical products. Where acidic decomposition products can themselves promote degradation, acid scavengers function by deactivating them. 

To account for this behaviour, it is generally assumed that the coal "molecule" breaks down much more drastically when very rapidly raised to decomposition temperatures, and that repoly-merlzatlon of the radical fragments Is Inhibited by their fast discharge from the coal. Some support for this thesis can be seen In the fact that. In a coke oven, "primary" tars will aromatize the more the longer they are In Intimate contact with the hot coke. But a necessary corollary Is, obviously, that the fragments must be supposed to stabilize themselves In the vapour-phase by Internal disproportionation. 

For a further decomposition, see Pomerantz et al. (2004), who hnd that patients seen by psychiatrists were most likely to receive appropriate treatment duration, patients seen by primary care and internal medicine physicians were less likely to receive appropriate treatment duration, and patients seen by specialists other than psychiatrists, primary care physicians, or internists were least Hkely to receive appropriate treatment duration. 

Clearly, the major primary decomposition processes are loss of SO and loss of CO, both of which require prior formation of a C—0 bond. This virtually demands isomerization to an internal sulphinate ester (7),... 

The goal of the MTO process is to convert methanol to light olefins, in particular ethylene, propylene and butenes. The key by-products of the reaction include the co-product water, C5+ hydrocarbons such as aromatics and heavier olefins, coke that remains on the catalyst at process conditions and light paraffins that are the primary sink for hydrogen lost during aromatic formation. Small amounts of H2 and COx are also typically observed in the MTO product, although these by-products could arise from feed and product decomposition on the reactor walls and internals at the temperatures that are typically used. 

Accepting the assumptions of Cundall and Davies , and taking their value given for 0co at 48 °C as the measure of the primary decomposition, it follows that the triplet aldehyde yield, is equal to 0.4. Consequently, the yield of the internal conversion from the first excited singlet state to the ground state has to be 0.6, since the triplet yield is still 0.4 even if decomposition does not occur. It has also been concluded that about 75 % of the triplet aldehyde molecules decompose, therefore, the quantum yield of the intersystem crossing from the triplet to the ground state can be estimated to be 0.1-0.2. 

Without going into details to be discussed elsewhere (20), we may point out the main difference between the two approaches as follows While our approach tends to emphasize the contribution gs of slow secondary electrons to the primary yields, Platzman s treatment puts generally more emphasis on the internal energy of the ionized species than we do. Consequently, his absolute values of primary yields are, in general, lower than ours, and a significant part of the observed decomposition is implicitly expected to occur in subsequent physicochemical and chemical stages of radiolysis. In contrast, our approach explains most of the observed decomposition by the primary processes of the physical stage. 

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