Irradiation dose required

Examples of Irradiation Dose Requirements for Food Applications... 

It is clear from this discussion that the dose requirement and unit cost will be lower if the material has a higher molar mass M and the reaction has a high G value. Thus, the best candidates will be a polymeric material and a chain reaction. Quite often, a free-radical irradiation is used. The radiation source of choice is usually a 60Co - y facility, although electron beam irradiation is also used. Since most radiation-chemical reactions used in industry can also be brought about by other conventional means such as thermal, or photochemical processes, the processing cost must be below 10irradiation cost one has to include the cost of operation, maintenance, and the like. (Danno, 1960). 

Some sensitivities with 364 nm irradiation are as follows DMA/PEMA, 0.0059 DPA/PEMA, 0.0057 DPA/PPSQ, 0.0092 cm2/mJ. (This value is the initial rate dA/dt divided by the intensity see ref. 15.) A comparable datum for DMA/PPSQ is not available, but by comparing the doses required to reach a specified absorbance, one finds that DMA/PPSQ is slightly faster than DMA/PEMA the ratio is about 1.5 (+/-20%). These numbers are a little smaller than those for conventional positive resist (49). With deep UV irradiation, however, they will be 7-20 times larger due to the larger extinction coefficient, which helps fulfill one of the key prerequisites of a CEL (or PIE) material for the deep UV. 

The technological feasibility of a food irradiation treatment depends on how much irradiation the food withstands without adversely changing its qualities, i.e., how much useful effect can be achieved without significant change to the chemical composition, nutritional value, and sensory properties of the product. Generally, there is a minimum dose requirement. Whether every mass element of a food requires irradiation will depend... 

The dose required to inhibit sprouting of onions, shallots, and garlics is 0.03-0.12 kGy. For good sprout control of tubers such as potatoes and yams, somewhat higher doses, 0.08-0.14 kGy, are required. Because of decreased wound-healing ability after irradiation, doses in excess of 0.15-0.2 kGy may induce increased microbial rot in storage [24]. 

In the field of muscle foods, the use of marination before irradiation reduced the dose necessary to eliminate Salmonella in poultry [113]. Some antimicrobial additives, especially the natural ones (e.g., bacteriocins) [94] and GRAS (generally recognized as safe) preservatives [114] can be usefully combined with irradiation to reduce dose requirements. Some antioxidants have also been used to prevent the undesirable oxidative effects in irradiated foods. 

Extender oils were foxmd to cause a considerable increase in the dose required to attain the optimum cure. This can be explained by reaction of transienf infermediafes formed on the irradiated polymer chain with the oil and with the energy transfer, which is particularly effective when the oil contains aromatic groups. Thus, the ranking of oils as to their cure inhibition is aromatic > naphtenic > aliphatic. This aspect is very important because many carbon-black-reinforced EPDM compounds contain frequently 100 phr or more oil. 

It should be noted that AM is only a measure of an apparent crosslink density of compounds. It is beyond the scope of the present work to investigate in detail the effective crosslinking (physical and chemical). However, for a qualitative assessment it can be concluded that the apparent crosslink density decreases or is influenced by the E-beam irradiation of PTFE powder. PTFE500kGy-EPDM composites show much lower AM and hence lower apparent crosslink densities. It can be inferred that the state of cure and crosslinking efficiency are strongly dependent on irradiation dose. Table 3 shows the optimum curing time (f90, time required to reach 90% of the AM) as a function of PTFE loading and irradiation dose for different PTFE-filled EPDM composites. 

Chlorinated Novolak Resins. Mixtures of a cresol formaldehyde Novolak resin and a photoactive compound cross-link at electron doses far smaller than the dose required for the Novolak resin alone (11). The reason for this accelerated cross-linking is the reactions between the ketene (an intermediate formed from the photoactive compound upon irradiation) and the Novolak resin. This reaction may be reduced by using a Novolak resin modified for this purpose, or by using certain additives. The rationale for developing a halogen-substituted Novolak resin is the control of the reaction between the intermediate ketene and the Novolak. 

The time required to raise or lower the source is 1.5 minutes, comparable to an irradiation dose in the irradiation position of approximately 35,000 rads (transient dose). The dose rate in the irradiation position is approximately 60,000 rads per minute. Calibration of the ferrous-cupric dosimeter is determined by comparison with the Fricke dosimeter, when irradiated at a position in the cell having a lower dose rate. The dose rate in the calibration position is approximately 5 X 103 rads per minute with a transient dose of approximately 3 X 103 rads. Calibrations made at such a position when using a G(Fe3+) = 15.6 for the Fricke dosimeter gave a G(Fe3+) of 0.66 for the ferrous-copper dosimeter. 

Analytical methods for the determination of malonaldehyde are particularly well developed. 2-Thiobarbituric acid in the presence of trifluoroacetic acid reacts with malonaldehyde to give a product whose absorption at 530 nm is proportional to the irradiation dose up to 400 rads. This reaction is proposed as a test for determining the absorbed dose, provided that the humidity of the sample, date of irradiation, and the temperature of storage are known.152 168 173 An alternative method is the reaction of malonaldehyde with 2-methylindole.174 The same reaction has also been used for the determination of deoxy sugars, but this requires oxidation with periodate to give malonaldehyde.175,176... 

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