Radiation stability

Particle Energy range in MeV average in MeV Dose in Gy Solmin-Solmax 

The glass ceramics have densities around 2.5g/cm, therefore, the penetration depth of space electrons and protons is only a few discoloring. Network modifications resulting in changed material properties affect the performance of glass ceramics only if they are exposed directly to space and mounted on the outside of the spacecraft. However, in this case as above only the first discoloring of the glass ceramics are concerned. 

Electrons with adequate energies were provided by a Van de Graaf accelerator at the solid-state physics laboratories of Groningen University. According to the expected doses in Table 4.6, 1.3 x 10 Gy is the nominal dose for one year at mean sun activity. The realistic dose of 10 Gy produces only faint damages, if any. To investigate time dependence and the types of defects, 1, 5, 10, 10 , and 10 years in space (10 -10 Gy) were simulated. 

The dose distribution of an energy spectrum was achieved by irradiating samples in two steps. The doses of the successive monoenergetic irradiations matched the integrated real particle flux and, on the other hand, the individual stopping power of Zerodur (see Fig. 4.65). For example, the dose distribution for 1000 years in space was simulated by 20.5 Gy at 0.5 MeV and 1.3 X 10 Gy at 0.3 MeV. 

Apart from other pubhshed experiments [4.57] related to EURECA, mission radiation and recording of EPR spectra have been done at room temperature (see spectrum 3 in Fig. 4.66). Spectra 1 and 2 result from samples irradiated at 77 K, recorded at 170 K and irradiated at 77 K, annealed at 440K, and recorded at 170K, respectively (published in [4.57]). The main, quite complicated signal around consists basically of a variety of the so-called oxygen hole centers (OHCs) close to aluminum or silicon, aluminum has a natural abundance of 100% Al with I = 5/2, yielding a hyperfine coupling. In accordance with other publications it has been shown that all 

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Radiation Stability. Numerous studies have been undertaken to define the effect of radiation on all types of ion-exchange resins. As... 

Table 7-15(a) Guide to relative radiation stabilization of medical plastic devices where dose (kilogray) in ambient air and room temperature at which elongation changes by 25%... 

Polyvinyl chloride/Polyvinyl acetate Good prevent yellowing. High-molecular-weight organotin stabilizers improve radiation stability color-corrected radiation formulations are available. Less resistant than PVC. 

Polypropylene, stabilized irradiated. Radiation-stabilized grades,... 

Although each of these cyclic siloxane monomers can be polymerized separately to synthesize the respective homopolymers, in practice they are primarily used to modify and further improve some specific properties of polydimethylsiloxanes. The properties that can be changed or modified by the variations in the siloxane backbone include the low temperature flexibility (glass transition temperature, crystallization and melting behavior), thermal, oxidation, and radiation stability, solubility characteristics and chemical reactivity. Table 9 summarizes the effect of various substituents on the physical properties of resulting siloxane homopolymers. The... 

The yield of cross-linking depends on the microstructure of polybutadiene and purity of the polymer as well as on whether it is irradiated in air or in vacuum. The cross-link yield, G(X), has been calculated to be lowest for trans and highest for vinyl isomer [339]. The introduction of styrene into the butadiene chain leads to a greater reduction in the yield of cross-linking, than the physical blends of polybutadiene and polystyrene [340]. This is due to the intra- and probably also intermolecular energy transfer from the butadiene to the styrene constituent and to the radiation stability of the latter unit. 

How does the primary mechanism of stabilization differ between ultraviolet radiation stabilizers and thermal stabilizers ... 

Since icosahedral carboranes are generally viewed as 3D energy sinks as well as polymer building blocks, the thermal and radiation stability that these units impart on the base rubbery material needs to be explored. While the thermal stability of these materials has been studied and reported by a number of workers, there is little reported work on the stability of these materials to ionizing radiation. A brief account of our work within this area is detailed below. 

Another problem is degradation of the sensor due to the high UV dose. The radiation resistance of most photodiodes decreases with wavelengths. UV-enhanced Si photodiodes show a loss of 10% in sensitivity already after an accumulated dose of some hundred J/cm2 at X = 254 nm. This is the dose a sensor will have received over the lifetime of an Hg lamp. Special silicon nitride-protected photodiodes are stable up to 105 J/cm2. A filter combined with an attenuator may help to achieve the required selectivity and reduce the exposure of the detector. However, the radiation stability of the filter has to be guaranteed. 

Liquid carbon dioxide is decomposed efficiently by ionizing radiation79. The decreased radiation stability of the liquid phase compared to the gas phase has been attributed to the much smaller contribution of ion-molecule reactions to radiolysis in the condensed phase, where an efficient geminate charge neutralization process is likely to minimize the occurrence of such processes. Ion-molecule reactions are probably responsible for the rapid reoxidation observed in the gas phase. The yields of CO, 02 and 03 from the y-radiolysis of liquid C02 can be... 

The radiation stability of waste forms is determined by changes in their structure, chemical,... 

Cubic fluorite-structure (Fm3m) zirconia-based solid solution, (Zr,ACT,REE)02 x, exhibi ts significant compositional flexibility to incorporate high concentrations of Pu, neutron absorbers, and impurities contained in Pu-bearing wastes (Gong et al. 1999). The phase has excellent radiation stability. No amorphization was observed under ion irradiation at room temperature to a dose corresponding to 200 dpa, and at 20 K to a dose of 25 dpa. Irradiation with I+ and Sr+ up to 300 dpa produced defect clusters in Y-stabilized zirconia, but did not cause amorphization. Amorphization... 

Although antioxidants trap the free radicals produced by the degradation of polymers, radiation stabilizers absorb radiation prior to molecular bond breakage. 

Spices, being vegetative in origin, may be placed in this category. Their reaction however, is atypical, since they show good radiation stability, Provided the economics are favorable, this field has distinct possibilities. 

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