Electron irradiation, energy absorbed

The energy, or power, of electron beam induced in the flue gas is divided and absorbed by their gas components roughly depending on their electron fraction. Therefore almost all the energy is absorbed by the main components of the flue gas, namely, N2, O2, CO2, and H2O. Table 2 shows a typical concentration of the components in coal-fired flue gas in Japan. The ratio of the total number of electrons in each gas components is also listed in the same table. The energy absorbed directly by the toxic components (SO2 and NO) is negligibly small. For electron beam treatment of flue gas, ammonia gas is added to the flue gas before the irradiation. The amount of ammonia is usually set as stoichiometrically, i.e., 2A[S02] + A[NO], where A[S02] and A[NO] are the concentrations of SO2 and NO intended to be treated, respectively. The concentration of ammonia is usually higher than the initial concentration of SO2 and NO however, it is still far lower than that of the main components. 

E(keV), the energy absorbed per incident electron during electron irradiation, is given by ... 

The role of subexcitation electrons is most important when the irradiated medium contains small amounts of impurity molecules the excitation energy ha) 0j (or the ionization potential I ) of which is below h(o0l. Such additive molecules can be excited or ionized by the subexcitation electrons the energy of which is between h(o 0j and fuom, and, consequently, the relative fraction of energy absorbed by an additive will be different from what it should be if the distribution of absorbed energy were solely determined by the relative fraction of valence electrons of each component of the mixture.213 214 According to estimates of Ref. 215, this effect is observed when the molar concentration of the additive is of the order of 0.1%. This selective absorption with ionization of additives has been first pointed out by Platzman as an explanation for the increase in the total ionization produced by alpha particles in helium after small amounts of Ar, C02, Kr, or Xe were added (the so-called Jesse effect).216... 

These results serve to outline possible mechanisms for desorption as a complicating factor under radiation and give some idea as to the energies and efficiencies involved. It is clear that irradiation with heavy particles to modest doses is certain to remove adsorbed molecules as well as the outer layers of the solid itself. The effect of electrons. X-rays and y-rays will be less marked, and probably more variable, but one could expect desorption of an appreciable fraction of a monolayer for integrated electron fluxes of the order of lO i cm-. This is a reasonable bombardment to achieve directly with electrons, but an equivalent dose from X- or y-rays would require 10 to 10 minutes at usual intensities (10 to 10 r/min). One would not expect much desorption from the doses ordinarily used in catalytic studies, 10 to 10 minutes at 10 to 10 r/min, except for cases in which energy absorbed in the solid was effective for the process at the surface. On the other hand, fragments produced on the surface by radiation may account for effects on activity at fairly low doses. 

Dosimetry. The intensity of the flux at the sample site was measured periodically with a ferrous sulfate dosimeter, using GFe(iii) = 15.5. Energy absorbed in liquid samples was based on this dosimetry and was corrected for the electron density of the samples. To determine energy absorbed in the vapor samples, nitrous oxide was irradiated, at comparable electron densities, in the vessel used for the hydrocarbons the G value for nitrogen production was taken to be 11.0 (7). 

Dosimetry. The dose rate of 2.0 X 1018 e.v. grams"1 min."1 in water vapor was based on the yield of hydrogen from ethylene, using G(H2) = 1.31 (23). Using this dosimetry, the yield of nitrogen from 700 torr N20 irradiated in the same experimental set-up at room temperature was G(N2) = 10.0 0.3. The relative dose rate was checked periodically with the Fricke dosimeter. The energy absorbed by each component in a mixture was calculated, assuming it to be directly proportional to the electron density of that component. 

Irradiation Procedures. G(Fem) of 15.6 for the ferrous sulfate dosimeter was determined in our laboratory by Hochanadel and Ghorm-ley (II). G-values reported here are based on total energy absorbed by the solutions. The energy absorbed in concentrated sodium nitrate solutions relative to the ferrous sulfate dosimeter was taken to be in the ratio of electron densities since energy absorption in 60Co irradiations is caused essentially only by Compton recoil electrons. 

In the case of TC, both stages of the process are thermally activated. In the case of RTC, the first stage is radiation initiated chain carriers are created by irradiation. The absorbed electron energy, necessary for formation of radical concentration sufficient for cracking initiation is only about 0.4 kJ/mol. The propagation stage of RTC is still thermally activated. The radical mechanism of RTC assumes that radiation-induced chain initiation does not depend on temperature, and the rate of radical generation depends only on irradiation dose rate. 

Polymer-protected noble metallic colloids can be prepared by the one-step radiation-induced reduction of aqueous metallic ions with 2-propanol using y-irradiator or e-beam irradiator (see. Figures 19.1 and 19.2). In an aqueous solution, water molecules absorb the irradiation energy and generate many reactive species, such as solvated electrons (e q"), H, and OH" Equation 19.1... 

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