The killing effectiveness of electron beam irradiation has not been completely characterized. The type of microorganisms and the composition of food have a direct effect on the efficiency of this technology. The objectives of this study were to select a surrogate suitable for use in electron beam irradiation studies of fruits and to evaluate the effect of sugar content on the kinetics of microbial damage and recovery. A 2.0 MeV Van de Graaff linear accelerator was used to apply irradiation (up to 5.0 kGy), using different configurations, on gelatin-based systems with the addition of sugars. The systems were inoculated with pathogenic and non-pathogenic bacteria strains (surrogates). Initial studies showed that Escherichia coli K-12 MG1655 is a suitable surrogate that represents the damage induced to common fruit pathogens by irradiation. The reduction in bacteria population can be maintained by storing samples at 4°C. An increase in temperature up to 20°C was enough for the damaged population to recover in 48 hours. Gelatin-based systems proved to be a simple and inexpensive medium to evaluate the effects of irradiation (up to 5.0 kGy) on selected bacteria. Reduction of the system dimensions and their positioning related to the beam source were key factors in increasing the killing effectiveness of irradiation. The sugar levels (up to 8 %) used to mimic the maturity of cantaloupes had no effect on the radiation D10 values and the recovery of the surrogate population quantified as Generation Times. The resistance of the surrogate to irradiation was validated in an optimum configuration and in cantaloupes. Temperature and sugar content caused significantly higher changes to the physical structure of the gel-based systems than irradiation (1.0 kGy). Plate counts and light microscopy techniques demonstrated that the structure of the gelatin-based systems allow for motility of the bacteria in a 3-D array (length, width and depth). When little information was available about the effectiveness of using a low energy linear accelerator, the inoculation of gelatin-based systems proved to be a reliable method to select a suitable surrogate and to predict the effects of irradiation on bacteria as a function of sugar content.

Reproduction de : Thèse doctorat : Chimie : Lyon 1 : 2003. / Titre provenant de l'écran titre. 87 Réf. bibliogr.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 102-108).

Harvested rainwater is an alternative water resource that can be utilized to help meet the world's growing demand for fresh water. Although harvested rainwater is often considered to have adequate physical and chemical qualities, its microbial quality has been found lacking. This study sought to better understand the effect of common treatment processes on the quality of harvested rainwater for potable use by examining two treatment processes: (1) batch chlorination followed by filtration, and (2) filtration followed by ultraviolet (UV) irradiation. The batch chlorination studies used rainwater harvested from four pilot-scale roofs in Austin, Texas with different roofing materials: concrete tile, green, Galvalume[Trademark] metal, and asphalt-fiberglass shingle. Chlorine tends to react with natural organic matter and produce disinfection byproducts (e.g., trihalomethanes (THMs)) that are harmful to human health. Chlorinating rainwater harvested from the metal and concrete roofs achieved adequate disinfection (total coliforms less than 1 colony forming unit per 100 mL) without forming THMs that exceed the United States Environmental Protection Agency (USEPA) limit of 80 [mu]g/L for public water systems. Chlorinating rainwater harvested from the shingle roof achieved adequate disinfection but had the potential to form excessive THMs. Chlorinating rainwater harvested from the green roof, which had the highest concentration of dissolved organic carbon, did not achieve adequate disinfection and formed THMs that were four times higher than the USEPA limit. Filtering the chlorinated rainwater from every roofing material with a block activated carbon filter generally resulted in increased bacteria concentrations and decreased THM concentrations. To study the effect of UV irradiation, cistern-stored and treated rainwater were sampled from a full-scale residential system in Austin, Texas, where the owner uses rainwater as his primary potable water supply. UV irradiation at the full-scale system effectively disinfected rainwater when the turbidity and total coliform concentrations were low, but disinfection was compromised as these two parameters increased as the drought progressed in 2011 and the ambient temperature increased. This research suggests that under certain conditions, treatment by either chlorination or UV irradiation can improve the quality of harvested rainwater so that it conforms to drinking water standards for public water systems. / text

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This thesis investigates the application of low energy electron irradiation to 1,3,5-trimethylbenzene films to test whether site-selective C–H bond cleavage can be achieved in a molecule presenting both aliphatic and aromatic target sites. IRRAS was used to characterize the orientation of vapour-deposited 1,3,5-trimethylbenzene on Au(111) and alkanethiolated gold under UHV and cryogenic conditions. On both substrates, the disordered as-deposited films were transformed by thermal treatment, producing two film structures – within the first 4-monolayers, aromatic rings lie nearly parallel to the metal surface, while molecules in additional layers are more upright. Low energy electron irradiation (0-10 eV) produced no dissociations in 1,3,5-trimethylbenzene; however, low energy electron transmission spectra indicate charge accumulates at interstitial sites in the mesitylene film, decelerating subsequent incident electrons. These decelerated electrons traverse the charged film and are reaccelerated, inducing dissociations in the underlying SAM. Contrary to literature claims, 1,3,5-trimethylbezene is a poor molecule for adsorption studies such as BET as the initial adsorption is disordered and thermodynamically unstable.

Radiotherapy of malignancies in the head and neck often involves the major and minor salivary glands in the radiation field. Adverse effects, such as dry mouth symptoms, are common after such therapy. The aim of this thesis was to study longitudinal effects of fractionated irradiation to the head and neck on salivary gland function in man and in the rat and to test radioprotection from antioxidant vitamins (retinol, a-tocopherol and ^-carotene). A sharp decrease in parotid saliva flow rate was seen after one week of irradiation in cancer patients, but in some patients recovery was seen two months after completed treatment. Loss and recovery of salivary gland function were dependent on the total dose given. Irradiation with doses of &gt;65 Gy to the parotid glands led to permanent loss of function in the majority of parotid glands, while recovery could be seen after irradiation with doses of &lt;52 Gy. Concentrations of some proteins and electrolytes in saliva were increased during irradiation but no changes remained 18 months after radiotherapy. However, large inter-individual differences were seen. The irradiation effects observed in rats did not greatly differ from those seen in humans, but no recovery of salivary gland function was seen. On the one hand the impairments of saliva flow and composition w ere dose and time dependent, but on the other hand the response pattem differed between salivary components. Morphological alterations were not seen in the rat salivary' glands after tw'O or five weeks but 26 weeks after irradiation. No single model seems to be optimal for studying all parameters. Therefore, to study effects on salivary glands after irradiation the rat model must be adjusted to meet the questions addressed. Supplementation with vitamin A provided no radioprotection, whereas it w'as found that supplementation with a-tocopherol (3.4 mg/day) and ß-carotene (6 mg/day) during irradiation reduced the degree of inflammation and partly preserved salivary gland function. It did not, however, lead to morphometrically detectable differences in proportions of acinar or ductal cells or stroma.Keywords: Irradiation, salivary glands, saliva composition, antioxidants / <p>S. 1-82: sammanfattning, s. 85-152: 6 uppsatser</p> / digitalisering@umu

High energy particle irradiation inevitably generates defects in solids in the form of collision cascades. The ballistic formation and thermalization of cascades occur rapidly and are believed to be reasonably well understood. However, knowledge of the evolution of defects after damage cascade thermalization, referred to as dynamic annealing, is quite limited. Unraveling the mechanisms associated with dynamic annealing is crucial since such processes play an important role in the formation of stable post-irradiation disorder in ion-beam-processed semiconductors and determines the “radiation tolerance” of many nuclear materials. The purpose of this dissertation is to further our understanding of the processes involved in dynamic annealing. In order to achieve this, two main tasks are undertaken. First, the effects of dynamic annealing are investigated in ZnO, a technologically relevant material that exhibits very high dynamic defect annealing at room temperature. Such high dynamic annealing leads to unusual defect accumulation in heavy ion bombarded ZnO. Through this work, the puzzling features that were observed more than a decade ago in ion-channeling spectra have finally been explained. We show that the presence of a polar surface substantially alters damage accumulation. Non-polar surface terminations of ZnO are shown to exhibit enhanced dynamic annealing compared to polar surface terminated ZnO. Additionally, we demonstrate one method to reduce radiation damage in polar surface terminated ZnO by means of a surface modification. These results advance our efforts in the long-sought-after goal of understanding complex radiation damage processes in ceramics. Second, a pulsed-ion-beam method is developed and demonstrated in the case of Si as a prototypical non-metallic target. Such a method is shown to be a novel experimental technique for direct extraction of dynamic annealing parameters. The relaxation times and effective diffusion lengths of mobile defects during the dynamic annealing process play a vital role in damage accumulation. We demonstrate that these parameters dominate the formation of stable post-irradiation disorder. In Si, a defect lifetime of ∼ 6 ms and a characteristic defect diffusion length of ∼ 30 nm are measured. These results should nucleate future pulsed-beam studies of dynamic defect interaction processes in technologically relevant materials. In particular, understanding length- and time-scales of defect interactions are essential for extending laboratory findings to nuclear material lifetimes and to the time-scales of geological storage of nuclear waste.

Graduation date: 1963