Chamber irradiation tests

Contamination of the reaetor by leaks and permeation of laboratory air contaminants is minimized by continuously flushing the enclosure that houses the reactors with purified air. NOx and formaldehyde levels in the enclosure before or dining irradiations were generally less than 5 ppb and PM coneentrations are below the detection limits of oin instrumentation. Introduction of contaminants into the reactor is also minimized by use of pressure control to assure that the reactors are always held at slight positive pressines with respect to the enclosure, so leaks are manifested by reduction of the reactor volume rather than dilution of the reaetor by enelosure air. The leak rate into the chamber was tested by injecting —100 ppm of CO into the enelosure and monitoring CO within the reactor. No appreciable CO (below the 50 ppb deteetion limit) was obtained for this experiment. 

Mechanical Property Testing. Mechanical tests were performed on both unirradiated and irradiated materials at -157°C, 24°C, and 121°C. Specimens were kept dry prior to testing in an environmental chamber mounted in a tensile testing machine. Tensile test specimens of [0]4, [10]4, [45]4, and [90]4 laminates were cut from 4-ply composite panels. All specimens were straight-sided coupons. For tension and shear tests the length/width aspect ratio was 8. For the compression tests the aspect ratio was 0.25 and the unsupported length was 0.64 cm. The [0]4 laminates were used to measure the ultimate tension and compression strength, Xit the axial... 

The spectral dependence of the light sensitivity (as indicated by yellowing) of free films of Parylene-C was determined. A Heraeus Sun-Test chamber, equipped with a xenon arc lamp filtered to yield a simulated solar spectrum, was used for the irradiation. An additional infrared filter minimized sample heating. The irradiance at the sample location was originally 0.83 W/m2 at 340 nm, but the output decreased approximately 20% after 1500 hours use. Long band-pass optical filters with nominal cut-offs of 305 nm, 345 nm, 385 nm and 400 nm were inserted between the xenon lamp and the Parylene-C film samples to determine the wavelength threshold for yellowing. The sample temperature was maintained at 30+ 2 °C with a water-cooled... 

The output from the lamps can vary between the tubes and also along the length of the tubes. The UV and VIS levels should therefore be mapped across the test chamber to ensure that the samples are placed at points of equal irradiance, 10%. The specimens should be placed only in the exposure area where the irradiance is at least 90% of the maximum irradiance unless the exposure time is increased. It can also be useful to reposition the samples during the exposure period to ensure that each specimen receives an equal amount of radiant exposure. If a combination of UV and VIS is used (i.e.. Option 2, also allowed in Option 1), it is important to make sure that the sample is exposed to both radiation components independent of its location in the chamber. 

How is one to proceed if the sample shows no change after exposure to the 200Wh/m UV dose but is decomposed after the 1.2 million lux hours in a test chamber designed according to Option 1 (e.g., xenon lamp) One possibility is to rerun the test using a filter to eliminate the UV irradiation in excess. Another possibility is to rerun the exposure to 1.2 million lux hours using a cool white fluorescent tube. If the sample is stable to this VIS exposure, it meets the ICH guideline. 

Radiation intensity mapping of the test chamber is essential to ensure that samples are placed at points of equal irradiance. Sample presentation is of great importance and the containers employed should be of known transmittance. 

Testing for photoallergy is similar to patch testing for allergic contact dermatitis. Duplicate allergens are placed on the back under occlusion with stainless steel chambers. Approximately 24 h later, one set of patches is removed and irradiated with UVA. All patches are removed and clinical assessments of patch test sites are made 48 h and then 1 week following placement. A reaction to an allergen solely on... 

However, the new UCR EPA chamber dataset also includes experiments where the effect of adding CO to aromatics - NOx irradiations was determined. These experiments were carried out because model calculations indicated that the addition of CO would cause a significant enhancement in O3 formation, due to die NO to NO2 conversions caused when CO reacts with the radicals produced in the aromatic photooxidation reactions, and we wanted to test this prediction. In this regard, CO acts as a radical amplifier , enhancing the effects of radicals on ozone formation. CO addition is also useful because CO has the simplest possible mechanism to represent other VOCs present in ambient mixtures its reactions only cause NO to NO2 eonversions and its reactions result in formation of no other products or direct radical sources or sinks. Therefore, added CO experiments should provide a test of an aspect of the aromaties mechanisms that is applicable to its effects in ambient simulations, and that is different than the tests provided by aromatic NOx experiments in the absence of other VOCs. 

Test specimens were cut from samples of commercial polymeric materials. Irradiation was carried out in Sandia s Co-60 facility which has been described elsewhere (16). A slow, steady flow of air was supplied to the sample chambers during the irradiation. Tensile tests were performed at ambient temperature using a Model 1130 Instron at a strain rate of 12.7 cm/min with an initial jaw gap of 5.1 cm. 

The presentation of samples within the test chamber can have a significant effect on the outcome of the photostability study. Factors of importance are alignment of the samples relative to the irradiation source sample form and layer thickness and selection of protective material (Table 7.2). 

The irradiance may not be homogenous or uniform throughout a test chamber. Samples placed in regions of low intensity may therefore be underexposed unless appropriate time corrections are made. Mapping of the test chamber (i.e., measure of irradiance at various locations in the chamber) should be performed every time the photolysis source is replaced. The mapping should include the UV and visible regions (see the following for calibration procedures). 

The devices used for calibration of radiation sources and test chambers are discussed in Chapter 5 and Chapter 6. Neither the UV filter radiometer nor the luxmeter provides information on the spectral power distribution (SPD, the plot of radiation intensity vs. wavelength) of sources. Upon delivery, the device should have been calibrated by the manufacturer against a standard lamp and provided with a response curve. If the meters are used as received, they are well suited for measuring evenness of irradiance across the sample area and changes in total output with time. 

Temperature and humidity conditions in the test chamber should be kept at a level to ensure that the effects of changes such as sublimation, evaporation, or melting are minimized in the physical state of the samples. Rate constants for photochemical reactions depend on the temperature because of secondary thermal reactions of the parent compound or primary products. Thermal stability of the material should independently be determined through accelerated stability testing. The ambient temperature and the temperature of the samples during irradiation are related to the photon source used for testing and the intensity and distance of the sample from the photon source. 

Changes in physicochemical properties of the drug substance (e.g., color, crystal modification) may take place upon irradiation. Efforts should be made to observe such changes during the in vitro assay. The sample absorption spectrum should be recorded before and after irradiation surface color of solid samples should be evaluated by appropriate methods and the identity of the sample crystal modification should be confirmed when the drug is irradiated in the solid state. The humidity in the test chamber can influence the photochemical stability of certain solid samples, as demonstrated for mefloquine. The photoinduced yellowing of uncoated mefloquine tablets is accelerated by an increase in humidity. These tablets are mainly used in tropical countries and the real in-use conditions will include high relative humidity. In such cases, the influence of the humidity on the photostability must be taken into account (Tpnnesen et al., 1997). 

Marvel and Chambers [80,80a] extended Coffinan s work and obtained polymers up to MW 14,000 using UV irradiation of a dimercaptan/diene solution in cyclohexane, in a closed quartz test tube. The results of Marvel and Chambers work is summarized in Table Vlll. 

Light fastness properties were measured according to ISO 105 B02. Samples were subjected, for 32 h, to artificial light at 420 nm and irradiance of 0.65 W/m. For this purpose, a Q-SUN XENON test chamber was used. 

The chloroplasts were isolated from 12-day old pea pla-nts grown in a climatic chamber under irradiance 9 and 30 W/m (LL and HL variants) and at 15°C. The isolation medium contained 50 mM trycin buffer, pH 7.5, 0.4 M sucrose and 5 niM MgClo. The chloroplast sediment was resuspended in an isolation medium that contained 0.1 M sucrose used instead of 0.4 M one. The chloroplasts were phosphorylated by incubation in white light (70 W/m ) in the presence of 0.2 mM ATP and 10 mM NaP. The degree of chloroplast protein phosphorylation was tested by radioactive labelling and the spectral methods as described earlier (3) ... 

ITER will be able to test plasma confinement and key technologies needed for a fusion reactor but will not be able to test how structirral materials behave tmder the extreme neutron dose expected in a fusion reactor. Most of the difference in the dose comes from the fact that ITER will operate in short ptrlses only, while a fusion reactor will have to have a high availability. The expected irradiation damage to structural materials in a fusion reactor will also be much higher than in present-day fission reactors for two reasons. Firstly, in a fission reaction only a few percent of the energy is taken away by the neutrons, while in a fusion one 80%. Secondly, the fusion plasma is tenuous and therefore all neutrons reach the wall of the reaction chamber. This neutron load will certainly cause serious damage to the materials, but the nature of this is largely unknown as fission reactors can simulate the fusion neutron load only to a certain extent. 

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