Linear selective irradiation

Figure 10. Selective irradiation of linear PE (2 X 10 mol wt, 1 — K 0.5). Spectral details are 35°C 67.9 MHz sweep width 5 KHz (quadrature detection) line broadening 9.7 Hz pulse width 35 jisec (90°C = 48 /jsec) delay = 1.0 sec, 4K data points 1024 scans accumulated 10-mm sample tube. Decoupling 7W (forward), 0.4W (reflected), broad band noise modulated decoupling.

This formation was linear as a function of time and cyclohexanol was only detected as a very minor product. Cyclooctane was similarly oxidized with the formation of cyclooctanone as a major product. Other iron(III)porphyrins involving different axial ligands, like Fe(TDCPP)Q and Fe(TPP)Cl, were much less efficient and less selective. Irradiation of Fe(TDCPP)OH in the presence of 02 and cis-stilbene failed to give any formation of stilbene epoxide, and cyclohexene was mainly oxidized on its allylic position with formation of cyclohex-2-enol and cyclohex-2-enone under such conditions. Finally, the intermediate formation of OH radicals was detected by spin trapping experiments during cyclohexane oxidation by 02 with photochemically-activated Fe(TDCPP)OH. 

Historically, the progress in radiation therapy has been linked mainly to technological developments. The physical selectivity of the irradiations was significantly increased when 200-kV x-rays were progressively replaced by cobalt-60, betatrons, and linear accelerators. As a consequence, the clinical results were dramatically improved. 

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

If ESR spectra are recorded at different microwave powers and a plot of spectrum area versus the square root of power constructed, then the spectrum shows increasing deviation from linearity above a critical "saturation" power. This is normally the maximum microwave power which should be used to record spectra. However, observation of the ESR spectra from irradiated aromatic polymers at higher power levels has shown selective saturation of the singlet produced preferentially at low doses. Thus the dose saturation behavior is mirrored by the power saturation. 

As shown in Figure 9, UV-irradiation of Mo-MCM-41 in the presence of a mixture of NO and CO leads to the formation of N2 and C02 with a linear dependence on UV-irradiation time, whereas the turnover frequency exceeds 1.0 after 2h (Tsumura et al., 2000). After 3h, NO conversion and selectivity towards N2 are close to 100%, with only a small amount of N20 formed. Figure 10 shows that there is a good correspondence between the yield of N2 produced and the yield of PL of tetrahedral molybdenum species and the amount of Mo4+ ions generated upon... 

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