Accelerator irradiation

Photo-excitation and de-excitation are basic processes in nuclear reactions. A Japanese-Hungarian cooperation investigating these processes has yielded good results during the past few years [21-26], These studies used weighable amounts of "Tc to look at the (y, y ) reaction that leads to the production of the nuclear isomer "mTc by electron linear accelerator irradiation. 

The degree of light-induced photoyellowing measured on mechanical pulps depends to some extent on the time between the actual irradiation and the brightness measurement. For example, if a sheet is kept for a certain time after accelerated irradiation the brightness increases slowly to reach a new upper limit. If the irradiated and stared sheet is irradiated a second time, the brightness decreases again, i.e. the pulp shows a photochromic effect. The extent of the photochromic effect depends both on the type of mechanical pulp used and on the irradiation time. In this study we have tried to evaluate which factors affect the photochromic effect and to identify the chemical structures responsible. 

Figure 5. The ESR signal intensity and the brightness increase of a peroxide-bleached groundwood sample after accelerated irradiation (1 h) as a function of storage time at room temperature.

Calculation of the so-called fluence factor of the copper impact into the transition temperature shift confirms that for the value fluence about 0.0002 dpa saturation of this factor is observed already. The attempt to separate out the embitterment data into the two components of CEC and AfDg was carried out . It was found that the copper component remains unchanged already due irradiation 0.0005 dpa at 190-200°C of weld surveillance material. Similar analysis for PWR submerged-arc weld material following accelerated irradiation at temperatures in the range 255-315°C shows that copper contribution remains unchanged after irradiation with dose of 0.01 dpa. 

The time accelerated aging method for electric wires and cables requires a high dose rate irradiation, but the exposure to polymer in air results only the oxidation of surface when the dose rate is higher. I previously reported the methodology study of time accelerated irradiation of elastomer (2). The study showed two appropriate methods, one was irradiation in pressurized oxygen at room temperature the other was irradiation at 70°C in air. The article studied the effect of higher dose (up to 10 MGy) irradiation on ethylene-propylene-diene elastomer (EPDM) by using the time accelerated method. Irradiation at 70°C in air was chosen as the time accelerated irradiation condition because of the experimental convenience. 

PP/EPDM Blends To improve impact properties of PP, the resin is usually modified by incorporation of an elastomer. Since the performance depends on morphology, radiation crosslinking was used in its stabilization [van Gisbergen et al., 1989a] (Table 11.9). The blends were made either in a two-roll miU, at 185°C, then compression molded into 1-mm-thick sheets, or in a co-rotating twin-screw extruder, then pelletized. The irradiations (100 kGy) were done using a 3-MeV electron accelerator. Irradiated and non-irradiated pellets were injection-molded. Eor the DSC measurements, the samples were melted at 200°C, quenched to 110°C, and then heated at a rate of 10°C/min. 

This equation represents the basic relationship for the production of radionuclides in a reactor k is calculated according to (15.8a) for accelerator irradiation (15.8b) is used. 

Radionuclides of high specific activity are produced either through accelerator irradiation or through secondary reactions in the target ( 15.6) in a reactor. Maximum specific activity is obtained when the radioactive nuclide is the only isotope of the element. This is not possible to achieve in regular reactor irradiation through (n,y) capture processes. For example, reactor-produced Na may be obtained in specific activities of 2 X 10 Bq g while the specific activity of accelerator-produced Na may exceed 10 Bq g however, the total activities available are usually the inverse. 

A carrier-free radioactive sample is usually one in which the radionuclide is not diluted with isotopic atoms. In reactor production of Na from target Na, each Na is diluted with a large number of Na atoms. Na cannot be made carrier-free in a reactor. If a carrier-free radionuclide has been produced, e.g. through accelerator irradiation, which thm must be purified, its concentration is so low that it may not follow the normal chemical rules. A macroscopic amount of carrier, either isotopic or not, may have to be added to carry the radionuclide through the proper chemical purification steps. We discuss this further in 9.2. 

The ultraviolet resistance of poly( 1,3,4-oxadiazole) fibers can be improved, by the addition of 4,4 -azodibenzoic acid [50]. The tensile strength retention of the oxadiazole fibers containing 4,4 -azodibenzoic acid is much higher than that of the fibers without the azo groups after accelerated irradiation by an iodine-gallium lamp. Also the fibers with 4,4 -azodibenzoic acid in the molecular chain by copolymerization show a better UV stability than the fibers simply blended with the same amount of 4,4 -azodibenzoic acid. 

Absolute experiments were performed in which a 30 ns pulse of 2 MeV electrons from an accelerator irradiated the gas mixtures to initiate the radical reactions. The decay of the radicals was recorded by use of transient UV spectroscopy, for OH at 309 nm. Hydroxyl radicals were produced by irradiation of 11 Torr H2O mixed with 749 Torr Ar. Initially excited argon atoms, Ar, are formed, and OH radicals are produced through the reaction ... 

C-Mn weld data shown in Fig. 9.28. Here, there is no significant effect on the level of P segregation to boundaries at doses up to 13.4 mdpa for both surveillance samples and surveillance samples given an additional accelerated irradiation to a higher dose. 

Lack of experimental data collected for irradiated thermal conductivity (verify or disprove theoretical calculations) May be less suitable for accelerated irradiation testing since this would push the fuel into a restructuring regime... 

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