Irradiation dose

The neutron dose to graphite due to irradiation is commonly reported as a time integrated flux of neutrons per unit area (or fluence) referenced to a particular neutron energy. Neutron energies greater that 50 keV, 0.1 MeV, 0.18 MeV, and 1 MeV were adopted in the past and can be readily foimd in the literature. In the U.K., irradiation data are frequently reported in fluences referenced to a standard flux spectrum at a particular point in the DIDO reactor, for which the displacement rate was measured by the nickel activation [ Ni(np) t o] reaction [equivalent DIDO nickel (EDN)]. Early on, neutron irradiation doses to the graphite moderator were reported in terms of the bum-up (energy extracted) from imit mass of the adjacent nuclear fuel, i.e., MW days per adjacent tonne of fuel, or MWd/Ate. 

Table 7 reveals that the grafting of TAC onto PE decreases the equilibrium contact angles of water and formamide from 92° to 65° and from 75° to 53°, respectively. This decrease is a function of the monomer level and the irradiation dose. At a fixed irradiation dose of 15 Mrad, variation of the TAC level from 0.5 to 3 parts causes a reduction in the contact angles of water by 13° (from 88° to 75°) and of formamide by 11° (from 72° to 61°). This is due to the fact that the concentration of... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

With the increase in irradiation dose, however, there is an optimum value of the surface energy at 10 Mrad irradiation. In order to explain these results, the grafting levels calculated from the IR spectra [30] are... 

IR studies of irradiated samples without TAC indicate absorbance peaks at 1140 and 1732 cm due to the generation of —O—CH2— and >C=0 functionalities. The ratio of the peak at 1732 cm with respect to that at 1470 cm was calculated for all samples. On introduction of TAC, the ratio increases by four- to eightfold depending on the amount of TAC and the irradiation dose. 

Figure 3 (a) Core level spectra of polyethylene (TO/0). (b) Core level spectra of polyethylene grafted with 2 parts TAC at an irradiation dose of 15 Mrad (T2/15). (c) Cls, Nls, and Ols peaks for polyethylene grafted with 1 part TAC at an irradiation dose of 10 Mrad (Tl/10). 

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. 

Compound A was affected most by the irradiation, Compound B least, and Compound C intermediate. The effect of the irradiation on cohesion increased with increasing irradiation dose and temperature. The iso-butylene-isoprene copolymer in Compound A and Compound C degrades during irradiation (9), becoming softer after irradiation. Since the seam of a can is formed before irradiation, some softening of the compound in the seam is not detrimental to the integrity of the seam. 

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.

The metallurgical experiments showed that the beta-alpha transition of the tin coating did not occur at irradiation doses of 3-5 Mrad and 6-7.5 Mrad at 5, —30, and —90°C and that the tensile properties, impact ductility, peel strength of soldered lap joints, and microstructure of commercial tinplate and solder were not affected by the irradiation conditions that are used in the sterilization of meat products. 

FIGURE 31.3 Plot of (a) grafting level versus irradiation dose having constant level of triaUyl cyanurate (TAC), (b) grafting level versus TAC level at constant irradiation dose of 50 kGy. (From Datta, S.K., Bhowmick, A.K., and Chaki, T.K., Radiat. Phys. Chem., 47, 913, 1996. With permission.)... 

FIGURE 31.4 Absorbance of control and EPDMs modified with different trimethylolpropane triacrylate (TMPTA) levels at an irradiation dose of 100 kGy. (From Sen Majumder, P. and Bhowmick, A.K., J. Adhesion Set Technol., 11, 1321, 1997. With permission.)... 

It is also interesting to note from the IR results described earlier that the absorbance at 1730 cm increases with irradiation dose up to 50 kGy. Similarly, Ai26o> An2o, and A1019 also increase with irradiation. There is also a rise in A1450 and A1379 with irradiation dose. The maximum oxygen... 

IR-ATR absorptions at 1730, 1260, and 1019 cm have been observed to rise up to the 50 kGy level beyond which there is a slight drop in the values. With increase in the radiation dose, the generation of active radicals on the EPDM backbone increases and so also that of the carbonyl and ether groups due to aerial oxidation of these radicals as noted in the earlier sections. However, at higher irradiation doses above 50 kGy, the chain scission of the EPDM molecules predominates as a... 

While the minimum irradiation dose (MID) to achieve a 10" probability of sterility assurance may be calculated by Eq. (2) ... 

Nonaqueous liquids, semi-solids, and dry powders dry heat at 160°C/120 minutes then dry heat under alternative conditions of time and temperature to achieve a sterility assurance level of 10 6 then an alternative to dry heat, e.g., ionizing radiation with a minimum absorbed dose of not less than 25 kGy then a validated alternative irradiation dose (according to ISO 11137) then aseptic filtration and aseptic processing and then the use of presterilized components and aseptic compounding or filling... 

Figure 34 Left (a) equilibrium storage modulus G as a function of y-irradiation dose determined from DMA experiments on exposed PU samples (b) 1/T2ave as a function of G. Right BC CPMAS NMR measurements on non-irradiated PU sample (a) 3 ms, (b) 0.5 ms, and (c) 100 pis. SS denotes soft segment HS denotes hard segment. Reprinted from Maxwell [87], Copyright 2003, with permission from Elsevier.

The first sample is a reactive poly(tetrafluoroethylene)/polyamide 6 (PTFE/ PA) blend [43]. When mixing PTFE micro-powder and PA in an extruder at about 280°C, relatively large PTFE particles occur in the final product because of immiscibility. By irradiation with electrons in air reactive groups in the PTFE powder are formed. These functionalised particles react with the molten PA in the extruder, and graft copolymers are formed, improving the compatibility of the components. At the same time a decrease in PTFE particle size proportional to the irradiation dose can be observed, and a PTFE/PA compound with better properties is produced. 

The chain length is therefore adversely afFected by the irradiation dose rate being inversely proportional to its square root. Wagner (1969) lists a large class of unsaturated compounds in which addition reactions can be induced by irradiation. Typical examples involving long chain lengths are for the addends HC1, Cl2, and HBr in ethylene, benzene, toluene, and so on. where the products are telomers or hexachlorides. 

The optimum processing conditions are at temperatures -50 °C, pH -7-8 and an irradiation dose around 5 KGy. Irradiation of dewatered sludge can reduce irradiation costs. 

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