Irradiation temperature

The third term in Eq. 7, K, is the contribution to the basal plane thermal resistance due to defect scattering. Neutron irradiation causes various types of defects to be produced depending on the irradiation temperature. These defects are very effective in scattering phonons, even at flux levels which would be considered modest for most nuclear applications, and quickly dominate the other terms in Eq. 7. Several types of in-adiation-induced defects have been identified in graphite. For irradiation temperatures lower than 650°C, simple point defects in the form of vacancies or interstitials, along with small interstitial clusters, are the predominant defects. Moreover, at an irradiation temperatui-e near 150°C [17] the defect which dominates the thermal resistance is the lattice vacancy. 

Fig. 11. Neutron irradiation-induced changes in the coefficient of thermal expansion of GraphNOL N3M at irradiation temperatures of 600 and 875 C [61].

Irradiation Conditions. The gamma (cobalt-60) radiation facility and the source calibration are described by Holm and Jarrett (4). Irradiation doses were 3-4 Mrad and 6-7.5 Mrad at 9 X 102 rads per second for the screening study. Irradiation temperatures were 5, —30, and — 90°C. The gamma source was calibrated with the ferrous sulfate-cupric sulfate dosimeter. 

Table IV shows the data on rigidity changes of the end-sealing compounds at two dose levels. Rigidity was determined by torsional braid analysis (5). These data indicate that the blend of cured and uncured isobutylene-isoprene copolymer was softened most by the irradiation treatment, the blend of polychloroprene and butadiene-styrene copolymer softened the least, and the blend of polychloroprene and the uncured isobutylene-isoprene copolymer was intermediate. Increasing the irradiation dose from 3-4 Mrad to 6-7.5 Mrad decreased the rigidity of the three end-sealing compounds. The irradiation temperature did not significantly influence rigidity.

Following the same procedures described in the above-mentioned study, additional extractive data were obtained for the epoxy phenolic enamel that was irradiated at 4.7-7.1 Mrad at 25 and — 30 °C in the presence of distilled water, 3% acetic acid, and n-heptane. The changes in the amount of extractives resulting from the irradiation treatment are shown in Table IX. In the case of the water and acetic acid extractives, there was no change in either the chloroform-soluble fractions or the chloroform-insoluble fractions. In the case of the n-heptane extractives, the amount of extractives decreased when the irradiation temperature was reduced from +25 to — 30°C. Infrared spectra of the chloroform-soluble residues from the water and acetic acid extractives of the unirradiated and irradiated enamel were identical to the chloroform-soluble residues from the solvent blanks. In other words, the epoxy phenolic... 

Studying in addition the effect of irradiation temperature, presence or absence of air, gamma irradiation, and thermal annealing, Grossmann found results which can be summarized as follows ... 

In a number of instances it has been shown that the irradiation temperature is important to control. Here it is clear that normal chemical reactions are proceeding in the target compound which will, of course, obliterate evidence of earlier reactions. Short irradiations may be done at low temperatures. Dry ice is perhaps the simplest refrigerant to use for this purpose. Even though the exact temperature of the sample may not be known, such a temperature seems to quench thermal reactions during the irradiation itself, so that these reactions may be studied later. 

Of these radioactive atoms, a fraction Fj are produced in a specified form the value of Fj may depend on the irradiation temperature, T, the y-flux, and consequently on the irradiation time, t. This fraction may be altered by subsequent thermal treatment and by a variety of spurious reactions, to an extent expressible as T, y. ..). Thus, the activity of a given species, i, can be expressed as... 

Effects of wavelength of irradiating light and irradiation temperature 134... 

It should be emphasized that, in all the topochemical photoreactions without exception, an apparent reaction rate at the initial stage increases with increase in the irradiation temperature, as long as the temperature is sufficiently low to maintain the molecular orientation in the crystal. 

Ultrasound irradiation —> temperature increase —> release of drug... 

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