Cross section effective escape

The reasons for the divergent effects of surface charge on TMB and ZnTPP photoionization yields in vesicular suspensions are unknown. Experimentally determined photoionization yields are complex quantities, which include as elementary processes primary ionization cross-section terms, dry electron escape probabilities, relatively complex electron hydration processes and recombination of various hy-... 

Fig. 4.4. A schematic cross-section of two evaporation boats showing the popcorn effect. In (a), the boat is open, and the evaporant material sublimes first at the hottest point of the assembly, which is the bottom of the material granules. This creates a vapor jet which can eject solid particles of evaporant from the boat. In a baffled arrangement (b), the source is constructed so as to prevent line of sight contact between the source and the substrate. Solid particles which are propelled are trapped, whereas material vapor can escape and deposit.

In these and the above equations, the a are cross sections per imit volume, the a in (8) is scattering cross section, the average loss in r per collision. The are used because the material may contain different types of atoms. The (Ta is the thermal absorption cross section r(r) the resonance absorption cross section per unit volume. The = qef is the multiplication constant divided by the resonance escape probability. The product of thermal utilization / and (Ta is the effective cross section of uranium per unit volume, i.e., its cross section per unit volume multiplied by the thermal neutron density in it and divided by the average thermal neutron density. One can write, therefore, (Tu for f(Ta- If one multiplies this with rj the result is the same as crfU where fission cross section for thermal neutrons per unit volume, p the number of fast neutrons per fission. As a result, the third term in (7) can be written also as e is the multiplication by fast effect)... 

The effectiveness of the moderators and the optimum moderator/fuel ratios previously presented have been based only on the use of as a fuel. On the basis of cross-sectional data for the fissile nuclides, it is to be expected that the optimum moderator/fuel ratio would be larger for Pu fuel and smaller for fuel. In addition, for heterogeneous, low-enrichment, or natural-uranium reactors it is desirable to achieve a large resonance escape probability, and, consequently, the optimum moderator/ fuel ratio is even larger than that previously indicated. Typical initial values for the C/U ratios in several gas-cooled reactors can be found in Table I. 

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