Scaling with radiation reflection

SCALING-UP OF A PHOTOCATALYTIC WALL REACTOR WITH RADIATION ABSORPTION AND REFLECTION... 

The required parameters for the spur diffusion model are the initial yields, G°, and the spur radii t e for eaq , and f for i = iT, H, OH, H2 and H2O2. In their treatment, Swiatla-Wojcik and Buxton [1,31] chose these parameters to fit the extensive data available for low LET radiation at ambient temperature. The values are hsted in Table 2. The values of G° were then assumed to be independent of temperature and the spur radii were scaled with temperature according to the density, with the result that t e and increased by no more than 11.5% up to 300 °C. The main factors determining the temperature dependence of the g-values, therefore, are the rate constants listed in Table 1. Thus, the significant increase in g(OH) compared with g(eaq ) reflects the fact that the spur reactions of OH (R2, R7 and R8 in Table 1) become significantly slower than the diffusion-controlled rate, whereas reactions Rl, R4, R5 and R9 are close to diffusion-controlled over the whole range of temperature. 

Figure 5.2 A (normalised) comparison between experimental and simulated rocking curves. InP specimen 004 reflection, CuK radiation, (a) Comparison without incorporation of curvature, (b) comparison with incorporation of curvature of 10 arc seconds, x-axis scale in arc seconds...

The diffractometer is a more complex apparatus than a powder camera and therefore more subject to misalignment of its component parts. A further difficulty with most commercial diffractometers is the impossibility of observing the same back-reflected cone of radiation on both sides of the incident beam. Thus, the experimenter has no automatic check on the accuracy of the angular scale of the instrument or the precision of its alignment. 

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