Wide-range radiolysis source

The Radiolysis of Methane in a Wide-Range Radiolysis Source... 

We designed a novel three-compartment source (wide-range radiolysis source) for our research mass spectrometer, which was first used to study the radiolysis of methane. The present technique, employing flow, low pressure, localized ionization, and electric fields appears to be a straightforward approach to the problem, and we hoped that this technique would resolve some of the above discrepancies. Our objectives were to (a) determine the percent abundance of the various reactive primary species—ionic and neutral (b) ascertain the percent abundance of stable products under conditions that would minimize subsequent reactions of reactive stable products (c) calculate G values for these products (d) measure the relative contribution of ion-molecule reactions to the formation of stable products (e) obtain the threshold energies and yield curves for such products to assign their precursors and (f) postulate, from the above information and pressure studies, a mechanism for the production of the radiolytic products from methane. 

The wide-range radiolysis source shown schematically in Figure 1 consisted of three separate stainless steel compartments (A, B, C) in series, each with its own electron beam (designated hereafter as EB— e.g., EB-B means electrons beam in Compartment B). The energy and intensity of each EB emitted from a thoria-iridium filament could be varied independently by a versatile emission regulator (22) to suit the particular phase of the problem under study. The EB s were magnetically collimated to ensure localized ionization, and their intensities were usually about 10 fiA. 

Figure I. Schematic of the three-compartment mass spectrometer (wide-range radiolysis) source for studying gaseous...

Figure 2. Detailed sketch of the electric-field compartment or radiation cell (Compartment A) of the wide-range radiolysis source.

In all experiments, steady-state conditions were established (usually less than 5 minutes were required) before data were taken. Since the modus operandi of the wide-range radiolysis source was varied as different phases of the problem were investigated, the specific experimental techniques will be discussed individually in conjunction with the corresponding results. 

The wide-range radiolysis source gives direct evidence of the relative role of ion-molecule reactions, initial stable products, the radiolytic yield, and the ionic precursors of these products by using flow, low pressure, localized ionization, and electric fields. 

Although this study of the radiolysis of methane was exploratory, it illustrated the usefulness of the wide-range radiolysis source, and our results contribute to the understanding of the radiolytic process which has been so controversial. Further development of the apparatus and techniques are contemplated, and the methane system will be studied further and in more detail. 

C. E. Melton, Jr., Study by mass spectroscopy of the decomposition of ammonia by ionizing radiation in a wide-range radiolysis source, J. Chem. Phys. 45(12), 4414-4424 (1966). 

The radiolysis of propane has been studied extensively in experiments that have included a wide range of techniques. The gas-phase radiolysis in the absence of inhibitors yields the products hydrogen, ethane, propene, 2,3-dimethylbutane, methane, ethylene, isobutane, acetylene, isopentane and n-butane as well as small quantities of butene-1, -pentane, 2-methylpentane and -hexane ° ° . At high conversions the yield of ethylene, propene, 2,3-dimethylbutane and isobutane are all reduced. The reduction in ethylene arises from hydrogen atom addition, while the reduction in the other products may arise from the reaction of propyl ions with propene to remove both C3H6 and the source of isopropyl radicals. 

Termination rate coefficients can be measured using the y-radiolysis relaxation method. This involves initiation using y-radiation, followed by removal of the reaction vessel from the y-source. Conversion during the relaxation period is monitored by dilatometry, and the decay in polymerization rate over time is related to the rate of radical loss. When large particles are used, radical loss is dominated by intraparticle termination, rather than exit into the aqueous phase, and the rate coefficient for termination can be determined from the decay curve. By using multiple insertions and removals, the termination rate coefficient is determined over a wide range of polymer mass fraction (wp). 

In designing pulse radiolysis experiments, the fundamental physics and chemistry of radiolysis must be kept in mind. The properties of the accelerators and other radiation sources described in this chapter vary over a wide range. A certain kind of experiment may call for a particular type of accelerator, whereas others may be accomplished by using almost any equipment. Equally important, of course, is the variety of experimental detection systems that are available at accelerator facilities. Some of the available methods include dc or microwave... 

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