Radiation-induced

When monochromatic radiation falls on a molecular sample in the gas phase, and is not absorbed by it, the oscillating electric field E (see Equation 2.1) of the radiation induces in the molecule an electric dipole which is related to E by the polarizability... 

Crystallinity has been studied by x-ray irradiation (85). An initial increase caused by chain scission in the amorphous phase was followed (above 3 kGy or 3 X 10 rad) by a gradual decrease associated with a disordering of the crystallites. The amorphous component showed a maximum of radiation-induced broadening in the nmr at 7 kGy (7 x 10 rad). 

Solution polymerization of VDE in fluorinated and fluorochlorinated hydrocarbons such as CEC-113 and initiated with organic peroxides (99), especially bis(perfluoropropionyl) peroxide (100), has been claimed. Radiation-induced polymerization of VDE has also been investigated (101,102). Alkylboron compounds activated by oxygen initiate VDE polymerization in water or organic solvents (103,104). Microwave-stimulated, low pressure plasma polymerization of VDE gives polymer film that is <10 pm thick (105). Highly regular PVDE polymer with minimized defect stmcture was synthesized and claimed (106). Perdeuterated PVDE has also been prepared and described (107). 

Research has focused on V—Cr—Ti—Si alloys, having 0.15 wt % Cr, 0—20% Ti, and less than 1% Si. Titanium additions above 3 wt % drastically reduce the magnitude of radiation-induced sweUing. The alloy of greatest interest is V—5Ti—5Cr (31). 

A third source of initiator for emulsion polymerisation is hydroxyl radicals created by y-radiation of water. A review of radiation-induced emulsion polymerisation detailed efforts to use y-radiation to produce styrene, acrylonitrile, methyl methacrylate, and other similar polymers (60). The economics of y-radiation processes are claimed to compare favorably with conventional techniques although worldwide iadustrial appHcation of y-radiation processes has yet to occur. Use of y-radiation has been made for laboratory study because radical generation can be turned on and off quickly and at various rates (61). 

The bismaleimide can then be polymerized by reaction with additional amine to form polyaininobismaleknide or by radiation-induced homopolymerization to form polybismaleimide (4). 

Radiation-induced degradation reactions are in direct opposition to cross-linking or curing processes, in that the average molecular weight of the preformed polymer decreases because of chain scission and without any subsequent... 

There are numerous reports of the effects of antioxidant vitamins on transformation. Vitamin C suppresses x-ray-induced transformation when CSHlOTy cells are treated daily for one week following irradiation (97), suppresses transformation by y-rays or neutrons, and prevents the promotion of radiation-induced transformation by 12-0-tetradecanoylphorbol 13-acetate (TPA), but has no effect on cell survival (98). In these studies, the continuous presence of vitamin C for a critical period appears to be necessary for suppression of transformation. Vitamin C may act on the promotion stage of... 

One vitamin E analogue, TROLOX, inhibits radiation-induced apoptosis in murine thymocytes (26). Chicks given vitamin E prior to exposure to a sublethal dose (2.25 Gy (225 rad)) of y-radiation demonstrate a more rapid recovery from damage to the thymus (100). 

Protection appears to be mediated by PKC activation. Radiation induces b-EGE production by these cells, allowing a survival-associated positive autocrine loop to develop. 

A 2-h incubation with another PGE2 analogue, nocloprost (9P-chloro-DMPG) protects normal human fibroblasts but has no effect on the survival of colon adenocarcinoma cells exposed to 10 Gy (1000 rad) (218). Nocloprost protects against radiation-induced DSBs in normal cells but not in tumor cells. Moreover, incubation using nocloprost for 2 h after irradiation enhances the rate of DSB rejoining in fibroblasts but not in adenocarcinoma cells. These data possibly reflect a different distribution of PG receptors on the plasma membrane of the two cell types. 

Radiation-Induced Polymerization. In 1956 it was discovered that D can be polymerized in the soHd state by y-irradiation (145). Since that time a number of papers have reported radiation-induced polymerization of D and D in the soHd state (146,147). The first successhil polymerization of cychc siloxanes in the Hquid state (148) and later work (149) showed that the polymerization of cycHc siloxanes induced by y-irradiation has a cationic nature. The polymerization is initiated by a cleavage of Si—C bond and formation of silylenium cation. 

The y-radiation-induced polymerization requires an extremely high purity reaction system. Trace amounts of water can terminate a cationic reaction and inhibit polymerization. Organic bases such as ammonia and trimethylamine also inhibit polymerization. The y-radiation-induced polymerization of a rigorously dried D obeys the Hayashi-WilHams equation for completely pure systems (150). 

Fusion Reactors. The development of fusion reactors requires a material exhibiting high temperature mechanical strength, resistance to radiation-induced swelling and embrittlement, and compatibUity with hydrogen, lithium and various coolants. One aUoy system that shows promise in this appHcation, as weU as for steam-turbine blades and other appHcations in nonoxidizing atmospheres, is based on the composition (Fe,Co,Ni)2V (30). 

Penicillins. Since the discovery of penicillin in 1928 as an antibacterial elaborated by a mold, Penicillium notatum the global search for better antibiotic-producing organism species, radiation-induced mutation, and culture-media modifications have been used to maximize production of the compound. These efforts have resulted in the discovery of a variety of natural penicillins differing in side chains from the basic molecule, 6-aminopenici11anic acid [551-16-6], These chemical variations have produced an assortment of dmgs having diverse pharmacokinetic and antibacterial characteristics (see Antibiotics, P-lactams). 

Radiation Effects. Alpha sihcon carbide exhibits a small degree of anisotropy in radiation-induced expansions along the optical axis and perpendicular to it (58). When diodes of sihcon carbide were compared with sihcon diodes in exposure to kradiation with fast neutrons (59), an increase in forward resistance was noted only at a flux about 10 times that at which the increase occurs in a sihcon diode. In general, it appears that sihcon carbide, having the more tightly bound lattice, is less damaged by radiation than sihcon. 

Eig. 2. Radiation-induced dimensional changes in isotropic graphite at various temperatures, nvt = neutron(density)-velocity-time. 

The experimental and theoretical aspects of the radiation and self-induced conversion kinetics and equiUbria between the ortho and para forms of hydrogen, deuterium, and tritium have been correlated (17). In general, the radiation-induced transitions are faster than the self-induced transitions. 

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