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Nuclear power constitutes a major pillar on the global energy market, and it will most probably increase in importance as fossil fuels are gradually phased out. The main problem connected to nuclear power is the generation of highly radiotoxic spent nuclear fuel (95% UO2 and 5% radioactive fission products and heavier actinides). Many countries plan to place the spent nuclear fuel in geological repositories where the hazardous material will be protected by engineered and natural barriers for periods exceeding 100 000 years. Given the extremely long time periods, groundwater intrusion is a potential scenario that must be considered in safety assessments of geological repositories. In this thesis, the stability of UO2in either solutions containing HCO3- or saline waters under exposure to radiolytic oxidants has been studied. In addition, the stability of uranyl peroxide minerals, which are common secondary phases on UO2 surfaces, in either solutions containing HCO3- or saline waters has been studied. The solution chemistry was also investigated in the two systems mentioned above with the focus on uranyl speciation. It was shown that oxidants such as O2, H2O2, and other radiolytic oxidants can oxidize UO2 to UO2.33 in either HCO3- solution or saline solutions. The hyper stoichiometric UO2 surface was not expected to form in HCO3- solution, since UO2was expected to oxidize to U(VI) which is highly soluble in HCO3- solution. XPS results illustrate that the oxidized surface was dominated by U(V) and no U(VI) was observed. The accumulation of U(V) on the surface resulted in the decrease ofUO2 reactivity towards oxidants. The dissolved U(VI), in the form of UO22+, is a good electron acceptor in solution, which will interact with the anions in aqueous solutions forming highly soluble complexes. In addition to complexes, UO22+ can also interact with H2O2 and precipitate uranyl peroxides, i.e., studtite UO2O2.4H2O and meta-studtite UO2O2.2H2O. We have found that studtite forma, Kärnkraften utgör en viktig del av den globala energimarknaden och kommer sannolikt att öka i betydelse i takt med att fossila bränslen gradvis fasas ut. Huvudproblemet kopplat till kärnkraft är genereringen av mycket radiotoxiskt utbränt kärnbränsle (95 % UO2). Många länder planerar att placera det utbrända kärnbränslet i geologiska förvar där det farliga materialet kommer att isoleras med hjälp av tekniska och naturliga barriärer under perioder som överstiger 100 000 år. Med tanke på de extremt långa tidsperioderna är grundvattenintrång ett potentiellt scenario som måste beaktas i säkerhetsanalyser av geologiska förvar. I denna avhandling har stabiliteten av UO2 i antingen lösningar innehållande HCO3- eller saltvatten under exponering för radiolytiska oxidanter studerats. Dessutom har stabiliteten hos uranylperoxider, som är vanliga sekundära faser på UO2-ytan, studerats i lösningar innehållande HCO3- eller salt (NaCl/NaBr). Lösningskemin undersöktes även i de ovannämnda systemen med fokus på uranylspeciering. Det visades att oxidanter som O2, H2O2 och andra radiolytiska oxidanter kan oxidera UO2 till UO2.33 i antingen bikarbonatlösning eller saltlösning. Den UO2.33-ytan förväntades inte bildas i HCO3- lösning, eftersom UO2 förväntades oxidera till U(VI) som är mycket lösligt i HCO3- lösning. XPS-resultat visar att den oxiderade ytan dominerades av U(V) utan att observera U(VI). Ansamlingen av U(V) på ytan resulterade i en minskning av UO2-reaktiviteten mot oxidanter. Lösta U(VI), i form av UO22+, är en bra elektronacceptor i lösning, som kommer att interagera med anjonerna i vattenlösningar och bilda mycket lösliga komplex. Förutom komplex kan UO22+ också interagera med H2O2 och fälla ut uranylperoxider, dvs studtite UO2O2.4H2O och meta-studtit UO2O2.2H2O. Vi har funnit att studtitbildning i lösningar innehållande UO22+ och H2O2 påverkades av anjonkoncentrationer (andra än O22-), pH och jonstyrka. Bildandet av (meta)-studtite observerades på ytan av UO2 efter exp, QC 2023-09-04

In this work, the impact of groundwater constituents and irradiation conditions on radiation induced corrosion of copper have been studied using numerical simulations based on the recently published mechanism. The simulations show that the amount of corrosion at a given total absorbed radiation dose will increase with decreasing dose rate. Furthermore, hydroxyl radical scavengers in general have a very marginal effect on the rate of corrosion while scavengers of the hydrated electron almost double the rate of corrosion. Sulfide present under relevant conditions has a significant effect on the corrosion rate and reduces the rate by 80% already at the lowest expected concentration and flux. Fe2+ present under relevant conditions does not influence the rate of corrosion significantly. Also initially dissolved oxygen has a very marginal effect on the process. Dissolved organic material scavenge hydroxyl radicals upon formation of C-centered radicals which in turn react with molecular oxygen. In systems where peroxyl radical recombination is not dominating, i.e., where there are solutes reactive towards peroxyl radicals, the presence of dissolved organic material can reduce the rate of corrosion by almost 99%. The pH and the presence of Cl-, HCO3- and SO42-have relatively small effects. In general, radiation induced corrosion is 20-40% slower at pH = 9 as compared to pH = 7.4 and the presence of HCO3- increases the rate of corrosion somewhat at pH = 9 as compared to pure water at the same pH., QC 20230706

The core of a BWR constitutes a highly complex radiational and chemical environment. Nuclear fission is utilized to generate power and as a consequence, large quantities of ionizing radiation are produced. Gamma and beta-particles along with neutrons have the sufficient ranges to escape the fuel rods and deposit energy in the reactor coolant. By doing so, radiolysis is initiated. The radiolysis species present in the coolant can interact chemically with the fuel rod cladding and cause corrosion. Different forms of corrosion are found on BWR fuel, with some effects being very local. This thesis work outlines a method developed to investigate local corrosion phenomena, with a high spatial resolution. The purpose was to study Zircaloy corrosion and more particularly, to investigate an observed jump in corrosion thickness around the lower enrichment step on BWR fuel rod cladding. The corrosion thickness jump is a very local effect, hence the need for high spatial resolution. Monte-Carlo simulations were performed in a GEANT4-model of an inoperation reactor, to study the energy deposited from ionizing radiation in the coolant, around the low enrichment-step of the fuel rods. The energy dose data was then used as input to lwrChem to compute electrochemical potential and equilibrium concentrations of radiolysis species. These are the quantities needed to compute an equivalent corrosion rate on the cladding surface, although this was not performed within this project. The main focus was to successfully develop the two-program method using GEANT4 and lwrChem and this was achieved. The project was performed Uppsala University with financial contribution from Vattenfall Nuclear Fuel AB and scientific contribution from Studsvik Nuclear AB.

Ett problem vid byggandet av nya kärnkraftverk för elproduktion är de stora investeringskostnaderna samt den långa tiden det att få tillstånd för en reaktor och bygga den. Nyligen färdigställdes den tredje reaktorn vid Olkiluoto I Finland, den tog 18 år att färdigställa exklusive tiden att få tillstånd för reaktorn. Små modulära kärnkraftsreaktorer, SMR är mindre reaktorer med en lägre elektrisk effekt har föreslagits vara en lösning på problemet. Det behövs inte lika stora investeringar för att uppföra en reaktor och de ska också gå snabbare att bygga. Det finns flera fördelar med SMR, de kommer att tillverkas i fabriker vilket minskar konstruktionstiden. Samma reaktormodell behöver bara ett tillstånd för licensering medan stora reaktorer som byggs idag behöver ett nytt för varje reaktor. Det är dessutom billigare att serieproducera reaktorer då kostnaden går ned för varje producerad reaktor. De flesta reaktorer idag använder lättvatten som en moderator och för att kyla ned reaktorn, reaktorerna kallas för lätt vatten reaktorer, LWR. Det finns två vanliga designer, en där vatten kokas inuti reaktorn och driver sedan en turbin, reaktorn kallas för kokvattenreaktor, BWR. Den andra vanliga reaktordesignen är tryckvattenreaktorn, PWR där det är ett högre tryck som gör att vattnet inte kokar i reaktorn, i stället kokar det varma vattnet från reaktorn vatten i en sekundär vattenloop i en ånggenerator. Det är ångan i sekundär loopen som sedan driver turbinen. Det finns även flera reaktorkoncept som inte använder lättvatten. De SMR koncept som är närmast att påbörja konstruktion är alla LWR eftersom det är där den största erfarenheten från tidigare reaktordesigner finns. Genom att undersöka sju SMR koncept, sex PWR och en BWR är bilden att många är väldigt lika reaktorerna som finns idag, däremot så har många tagit bort komplicerade system och infört passiva säkerhetssystem som bland annat naturlig cirkulation för att få en passiv kylning. Materialen som används är också m, One problem with building new nuclear reactors for electricity production is the large investment costs and the long time needed for permissions and construction. Most recently is the Olkiluoto nuclear power plant in Finland where a third reactor was built, it took 18 years to finalize the reactor, and this is not including the time of handling the licencing application. Small modular nuclear reactors, SMR which is a smaller reactor with a reduced effect has been proposed to reduce the cost of investment and the time it takes from license application to finalized reactor. The SMR reactors have many advantages. It will be fabricated in factories reducing the time of construction, since reactor units are the same, the same reactor design only needs one licencing for all reactors. Compared to large reactors built today, where every single reactor needs a new licencing. Smaller reactors lead to shorter construction times and lower investment. It is also less expensive to produce reactors in series where the cost per unit decreases for every unit produced. Most reactors in operation today use light water as a moderator and coolant and are called light water reactors, LWR. Two designs are common, one where the water is boiled in the reactor and goes directly to the turbine, this reactor is called a boiling water reactor, BWR. The other common reactor is a pressurized water reactor, PWR where a higher pressure does not allow the water to boil. Instead, it is heated and boils water in a steam generator that then turns the turbine blades. There are other reactor concepts which do not use light water as a moderator and coolant, The SMR concepts that are the closest to construction are all LWR because it is where most experience from previous reactor designs is. By investigating seven SMR reactor concepts, six PWR and one BWR, it was concluded that they are similar to reactors operating today, but with some simplification and passive safety systems like natural circulation for

Nuclear energy is one of the most demanded low-carbon energy sources in this era of climate change. The “Generation IV International Forum” has selected the concept of supercritical water-cooled reactors as one of the six innovative reactor concepts to be the subject of international collaborations in terms of research and development. It is difficult to make direct experimental measurements of the primary radiolytic products of supercritical water (SCW) (e_aq^-, OH–, H+, H•, •OH, H2, H2O2, HO_2^•/O_2^(• -),…), which are corrosive for materials under extreme conditions of temperature (~350 to 650°C), pressure (25 MPa) and mixed radiation field inside the reactor core. In this study, we have developed Monte Carlo simulation programs of the chemistry involved in the trajectories in order to explore the effect of temperature and pressure (density) in the radiolysis of SCW, to calculate the yields of radiolytic species (oxidizing and reducing ) and to reveal the reaction mechanisms involved. To our knowledge, we are the first to have studied the effects of radiation dose rate in Generation IV reactors or small modular reactors cooled with supercritical water, under conditions normal operation or in an emergency or accidental situation (where the dose rate may exceed 10^10 Gy/s). For this, we irradiated the water with single pulses of N incident protons of 300 MeV kinetic energy (which mimic the ⁁ rays of cobalt-60) and varies N to study the dose rate effect. In addition, we have developed a model of water radiolysis in a cell-like environment to examine the mechanism of radiolytic oxygen depletion by e_aq^- and H• produced by radiolysis, which has been proposed to explain the protection of healthy tissue in FLASH radiotherapy (which uses instantaneous dose rates of ~10^6-10^7 Gy/s). We have shown that this radiolytic depletion of O2 is considerably attenuated in the presence of cellular components having the property of being excellent sensors of e_aq^- and •O, L'énergie nucléaire est l'une des sources d'énergie à faible émission de carbone les plus demandées en cette ère de changement climatique. Le « Forum International Génération IV » a sélectionné le concept de réacteurs refroidis à l'eau supercritique comme l'un des six concepts de réacteurs innovants devant faire l'objet de collaborations internationales en matière de recherche et développement. Il est difficile d'effectuer des mesures expérimentales directes des produits radiolytiques primaires de l'eau supercritique (SCW) (eaq−, OH–, H+, H•, •OH, H2, H2O2, HO2•/O2•−,…), qui sont corrosifs pour les matériaux dans les conditions extrêmes de température (~350 à 650 °C), de pression (25 MPa) et de champ mixte de rayonnement à l'intérieur du coeur du réacteur. Dans cette étude, nous avons développé des programmes de simulation Monte Carlo de la chimie intervenant dans les trajectoires afin d’explorer l'effet de la température et de la pression (densité) dans la radiolyse de SCW, de calculer les rendements des espèces radiolytiques (oxydantes et réductrices) et de révéler les mécanismes réactionnels mis en jeu. À notre connaissance, nous sommes les premiers à avoir étudier les effets de débit de dose du rayonnement dans les réacteurs de Génération IV ou petits réacteurs modulaires refroidis à l’eau supercritique, dans des conditions normales de fonctionnement ou dans une situation d'urgence ou accidentelle (où le débit de dose peut dépasser 1010 Gy/s). Pour cela, nous avons irradié l'eau avec des impulsions uniques de N protons incidents de 300 MeV d’énergie cinétique (qui mimiquent les rayons ⁁ de cobalt-60) et fait varier N pour étudier l'effet de débit de dose. En outre, nous avons développé un modèle de radiolyse de l’eau dans un environnement qui se rapproche de celui d’une cellule pour examiner le mécanisme de l'appauvrissement radiolytique de l'oxygène par eaq− et H• produits par radiolyse, qui a été proposé pour expliquer la protection des tissus sains dans la ra

Liquid cell transmission electron microscopy (LC-TEM) is a unique technique that permits in situ observations of various phenomena in liquids with high spatial and temporal resolutions. One difficulty with this technique is the control of the environmental conditions in the observation area. Control of the temperature ranging from room temperature to minus several tens of degrees Celsius, is desirable for controlling the supersaturation in various materials and for observing crystallization more easily. We have developed a cooling transmission electron microscopy specimen holder that uses Peltier devices, and we have combined it with a liquid cell to realize accurate temperature control in LC-TEM. We evaluated this system by using water as a specimen. Motionless bubbles, shown to be voids containing pressurized gas, formed in the specimen sometime after the temperature had reached -12 degrees C. An electron diffraction pattern showed that the specimen turned into ice Ih after the formation of these bubbles, confirming that our system works properly and can induce crystallization. In addition, we analyzed the behavior of bubbles formed in the ice Ih, and we discussed the formation of these bubbles and their internal pressure.

(Scanning) transmission electron microscopy, (S)TEM, offers a powerful characterization tool based on electronmatter interactions, highly valuable in materials science. However, the possible electron beam induced damage during (S)TEM measurements hinders the analysis of soft materials, such as acrylic resins. Importantly, acrylic resins offer an appealing playground for the development of novel composites with customized properties and convenient processing capabilities for 3D-printing technologies, including Stereolithography (SLA). There are several factors preventing the optimal performance of TEM measurements applied to acrylic resins, among which we focus on the quality of the analyzed specimen (i.e., compromise between thickness and robustness, to achieve electron transparency while keeping the material integrity), particularly challenging when working with soft materials; the electrostatic charging/discharging effects, resulting in sample drift and related noise/artefacts; and the radiolysis and knock-on electron-induced damage, which directly degrade the material under study. We explore and compare different methodologies to obtain resin specimens suitable for (S)TEM analysis, employed for the subsequent study of the electron–beam damage induced during STEM-EELS measurements. Furthermore, we propose likely underlying mechanisms explaining the acrylic resin degradation based on the different EELS monitored signals. On one hand, we assess the evolution of the carbon and oxygen content, as well as the material thinning as a function of the accumulated electron dose. On the other hand, we extract meaningful information from the spectral shape of carbon and oxygen K-edges upon increasing electron doses, unraveling likely degradation pathways. The earned understanding on the electron-beam induced damage and the determination of critical doses provide a useful framework for the implementation of (S)TEM techniques as useful tools to help in the smart engineering of

(Scanning) transmission electron microscopy, (S)TEM, offers a powerful characterization tool based on electron-matter interactions, highly valuable in materials science. However, the possible electron beam induced damage during (S)TEM measurements hinders the analysis of soft materials, such as acrylic resins. Importantly, acrylic resins offer an appealing playground for the development of novel composites with customized properties and convenient processing capabilities for 3D-printing technologies, including Stereolithography (SLA). There are several factors preventing the optimal performance of TEM measurements applied to acrylic resins, among which we focus on the quality of the analyzed specimen (i.e., compromise between thickness and robustness, to achieve electron transparency while keeping the material integrity), particularly challenging when working with soft materials; the electrostatic charging/discharging effects, resulting in sample drift and related noise/artefacts; and the radiolysis and knock-on electron-induced damage, which directly degrade the material under study. We explore and compare different methodologies to obtain resin specimens suitable for (S)TEM analysis, employed for the subsequent study of the electron–beam damage induced during STEM-EELS measurements. Furthermore, we propose likely underlying mechanisms explaining the acrylic resin degradation based on the different EELS monitored signals. On one hand, we assess the evolution of the carbon and oxygen content, as well as the material thinning as a function of the accumulated electron dose. On the other hand, we extract meaningful information from the spectral shape of carbon and oxygen K-edges upon increasing electron doses, unraveling likely degradation pathways. The earned understanding on the electron-beam induced damage and the determination of critical doses provide a useful framework for the implementation of (S)TEM techniques as useful tools to help in the smart engineering of

Understanding the behaviour of nuclear materials in the event of exposure to water, is an essential element for improving efficiency, reliability and safety throughout the nuclear fuel cycle. The most radioactive of these materials is irradiated nuclear fuel, so much so that after use in a reactor it will remain highly radioactive for thousands of years. In order maintain safe containment of these materials over this timeline, great effort is being made to understand these materials and the interactions they have with their surroundings. A particular interest of the nuclear industry is the reaction between spent nuclear fuel and water. The highest risk of this occurring is during interim storage and, over time, in a Geological Disposal Facility (GDF). Although GDF sites are designed to be watertight, when considering the timescales required to sustain safe containment, the risks may become significant. A significant characteristic of a spent fuel / water interface is the chemical altering of the water molecules due to radiation (radiolysis) that occurs at and near the fuel surface. This process causes oxidising species to form that can cause oxidative dissolution of the fuel material. This process can be seen in the degradation of legacy fuel which is still held in wet storage at Sellafield. These fuels have degraded into particulate sludges alongside cladding and structural materials forming complex waste forms, creating huge decommissioning challenges for the UK nuclear industry. In order to understand the risks posed by each scenario involving these waste forms in water, modelling tools are required to aid our understanding of the likely mechanisms taking place, especially when considering events potentially thousands of years into the future. Due to the large quantity of chemical reactions, radionuclides, geometries and external conditions that influence these interactions the computational demand is high, and many assumptions are often require

Enhanced degradation of organic dye was achieved using two different kinds of waste materials: waste tire granules and spent sealed radioactive sources. Waste tire granules were used as raw material for the production of waste tire char (WTC), which was further utilized as an adsorbent matrix for synergetic adsorption/irradiation degradation of organic dye. The spent radioactive sources were radiographic sealed sources that originate from the industry which generate the high energy radiation. Methylene Blue (MB) was used as an organic model compound. Synthesized WTC has turbostratic structure, irregular shaped particles and developed mesoporous surface. Complete degradation of 0.02 dm3 of 100 mg dm−3 MB solution, having WTC dose of 1.25 g dm−3, was achieved with delivered doze of only 60 Gy. The applied doses were 100 times smaller than those presented in the literature. Degradation pathway was determined: OH radicals that originate from radiolysis of water and from the surface of WTC played the crucial role in the radiocatalytic degradation of MB. Breakage of the aromatic ring of MB appeared by the scission of the double C‒S+˭C bond as a result of the attack of OH species on adsorbed and electronically reorganized MB molecule. © 2020 Elsevier B.V.

Lead halide perovskites have become a leading material in the field of emerging photovoltaics and optoelectronics. Significant progress has been achieved in improving the intrinsic properties and environmental stability of these materials. However, the stability of lead halide perovskites to ionising radiation has not been widely investigated. In this study, we investigated the radiolysis of lead halide perovskites with organic and inorganic cations under X-ray irradiation using synchrotron based hard X-ray photoelectron spectroscopy. We found that fully inorganic perovskites are significantly more stable than those containing organic cations. In general, the degradation occurs through two different, but not mutually exclusive, pathways/mechanisms. One pathway is induced by radiolysis of the lead halide cage into halide salts, halogen gas and metallic lead and appears to be catalysed by defects in the perovskite. The other pathway is induced by the radiolysis of the organic cation which leads to formation of organic degradation products and the collapse of the perovskite structure. In the case of Cs0.17FA0.83PbI3, these reactions result in products with a lead to halide ratio of 1 : 2 and no formation of metallic lead. The radiolysis of the organic cation was shown to be a first order reaction with regards to the FA+ concentration and proportional to the X-ray flux density with a radiolysis rate constant of 1.6 × 10-18 cm2 per photon at 3 keV or 3.3 cm2 mJ-1. These results provide valuable insight for the use of lead halide perovskite based devices in high radiation environments, such as in space environments and X-ray detectors, as well as for investigations of lead halide perovskites using X-ray based techniques., QC 20220318

Context. The simultaneous detection of organic molecules of the form C2HnO, such as ketene (CH2CO), acetaldehyde (CH3CHO), and ethanol (CH3CH2OH), toward early star-forming regions offers hints of a shared chemical history. Several reaction routes have been proposed and experimentally verified under various interstellar conditions to explain the formation pathways involved. Most noticeably, the non-energetic processing of C2H2 ice with OH-radicals and H-atoms was shown to provide formation routes to ketene, acetaldehyde, ethanol, and vinyl alcohol (CH2CHOH) along the H2O formation sequence on grain surfaces in translucent clouds. Aims. In this work, the non-energetic formation scheme is extended with laboratory measurements focusing on the energetic counterpart, induced by cosmic rays penetrating the H2O-rich ice mantle. The focus here is on the H+ radiolysis of interstellar C2H2:H2O ice analogs at 17 K. Methods. Ultra-high vacuum experiments were performed to investigate the 200 keV H+ radiolysis chemistry of predeposited C2H2:H2O ices, both as mixed and layered geometries. Fourier-transform infrared spectroscopy was used to monitor in situ newly formed species as a function of the accumulated energy dose (or H+ fluence). The infrared spectral assignments are further confirmed in isotope labeling experiments using H218O. Results. The energetic processing of C2H2:H2O ice not only results in the formation of (semi-) saturated hydrocarbons (C2H4 and C2H6) and polyynes as well as cumulenes (C4H2 and C4H4), but it also efficiently forms O-bearing COMs, including vinyl alcohol, ketene, acetaldehyde, and ethanol, for which the reaction cross-section and product composition are derived. A clear composition transition of the product, from H-poor to H-rich species, is observed as a function of the accumulated energy dose. Furthermore, the astronomical relevance of the resulting reaction network is discussed. © K.-J. Chuang et al. 2021.

In situ liquid cell transmission electron microscopy (LC-TEM) is an innovative method for studying the processes involved in the formation of crystals in liquids. However, it is difficult to capture early stages of crystallization because of the small field of view and the unfavorable changes in sample composition resulting from electron-beam radiolysis. Nevertheless, if the radiolysis required to induce the crystallization of a sample could be controlled in LC-TEM, this would be advantageous for observing the crystallization process. Here, we examined this possibility by using a mixture of sodium chlorate (NaClO3) and acetone in the LC-TEM. The electron beam induced the formation of dendritic crystals in a saturated acetone solution of NaClO3; moreover, these crystals consisted of sodium chloride (NaCl), rather than NaClO3, suggesting that chloride ions (Cl-), which were not present in the initial solution, were generated by radiolysis of chlorate ions . As a result, the solution then supersaturated with NaCl because its solubility in acetone is much lower than that of NaClO3. The combination of radiolysis and a solvent in which a solute is much less soluble is potentially useful for establishing crystallization conditions for materials that are difficult to crystallize directly in LC-TEM experiments.

A significant portion of cancer patients receive radiotherapy as part of their curative or palliative treatment plan. Radiotherapy is however greatly limited by radiation induced toxicities in healthy tissue surrounding the tumour, which can lead to long-term or acute complications for a patient. In response to this issue, recent studies have considered a new technique called FLASH radiotherapy, where ultra-high dose rates have been shown to effectively reduce toxicity in normal cells whilst maintaining a tumour response equivalent to conventional dose rates. However, the exact mechanism for this effect is not yet well understood. This project seeks to investigate if certain dose delivery patterns exist where there is an increase or reduction of concentration of the toxic radical hydroxyl, which is known to play a key role in the damage of DNA in the cell, for unchanged total dose. This was done by simulating the chemical reactions which take place when water is irradiated with ionizing radiation using a simple model system consisting of water with free oxygen dissolved into it, called RadChemModel. Using basic reaction laws from chemistry, the concentration of each chemical species involved was solved for from a system of linear and non-linear ordinary differential equations. The concentration of hydroxyl was calculated as a function of time for a range of irradiation beam patterns. This model supports that there could be a difference in toxicity between FLASH and conventional beam parameters. Furthermore, a shift in the behaviour of hydroxyl suggesting reduced toxicity was observed at FLASH dose rates with very high beam pulse frequencies. However, the results obtained do not provide enough information to confirm that the concentration of hydroxyl is reduced with FLASH beam parameters., En stor andel cancerpatienter får strålterapi som läkande eller palliativ behandling. Strålterapi kan ge upphov till allvarliga skador i den friska vävnaden i närheten av tumörområdet. För att förebygga omedelbara så väl som långsiktiga skadliga effekter av strålterapi, har nyligen pulicerade studier undersökt en ny teknik som kallas för FLASH strålterapi. Man har påvisat att ultra-höga doshastigheter kan minska strålskadorna i friska celler samtidigt som tumörkontrollen bevaras. Emellertid finns ännu ingen tillräcklig förklaring för den exakta mekanismen bakom fenomenet. Målet med detta projekt är att undersöka om en ökning eller minskning av koncentrationen hos radikalen hydroxyl, som är känd för att spela en kritisk roll i framkallandet av DNA skador, kunde upptäckas för särskilda doseringsmönster med en oförändrad total dos. Detta studerades med en enkel matematisk modell (RadChemModel) för vatten med upplöst syre. Med denna modell simulerades de kemiska reaktioner som äger rum när vatten bestrålas med joniserande strålning. Från fundamentala kemiska reaktionslagar, kunde koncentrationen av hydroxyl som funktion av tid fås genom att lösa ett system av linjära och icke-linjära ordinära differentialekvationer. Den här modellen visar att det kan finnas en skillnad i strålinducerade skador mellan FLASH och vanlig strålterapi. Resultaten från väldigt höga pulsfrekvenser med FLASH antydde också att mindre hydroxyl producerades och därmed att strålskador kan vara beroende av både doshastighet och pulsfrekvens. Däremot är resultaten inte tillräckliga för bekräfta att koncentrationen av hydroxyl är reducerad för FLASH.

In a geological repository for spent nuclear fuel, studtite (UO2)O-2(H2O)(4) may form on the fuel surface when in contact with groundwater under certain conditions. Studtite has a very low solubility and could thereby reduce the reactivity of spent nuclear fuel toward radiolytic oxidants. This would inhibit the dissolution of the fuel matrix and thereby also the spreading of radionuclides. It is therefore important to investigate the stability of studtite under conditions that may influence its stability. In this work we have studied the kinetics of studtite dissolution in aqueous suspensions containing no added HCO3- and with 10 mM HCO3-. The same type of experiment was performed also with solutions containing 0.2 mM H2O2. The solubility of studtite in the suspensions containing no added HCO3- is very low as expected, while the solubility in solutions containing 10 mM HCO3- is significantly higher. This is attributed to the formation of uranyl-carbonate and uranyl-peroxo-carbonate complexes. In 0.2 mM H2O2 and 10 mM HCO3- the observed solubility of U(VI) seems unaffected by the presence of H2O2. Again, this can be rationalized by the formation of uranyl-peroxo-carbonate complexes. It is interesting to note that H2O2 appears to be catalytically decomposed in solutions containing uranyl-carbonate complexes. In addition, gamma-radiation-induced dissolution of studtite in HCO3- deficient solutions and in 10 mM HCO3- was studied. The dissolution rate was found to be extremely high in HCO3- under gamma-irradiation. This is attributed to a combination of radiolytic degradation of H2O2 and the formation of uranyl-peroxo-carbonate complexes keeping the concentration of free H2O2 at a very low level and thereby driving the dissolution process., QC 20200321

Alkaline fuel cells are a promising technology, with their sturdy design and many applications they are held back mostly by their cost. By introducing a catalyst, the activation energy of the cell can be reduced to an overcomable amount. Unfortunately, due to the high cost and sparse availability of the most used catalyst metal today, platinum, it has become apparent that a new suitable catalyst must be found in order to make the fuel cells economically feasible. Silver and palladium have been proposed as promising alternatives, sharing a majority of the traits but with a fraction of the cost. The original aim of this project was to study the performance of electrodes in an alkaline electrolyte loaded with different ratios of palladium and silver. However, due to the COVID-19 situation the project was not able to be completed and the aim of the project changed. The new aim was divided into two parts. The first one being to study how the initial concentration of silver ions affects the size of the obtained particles. This was achieved by a radiolysis-based method of synthesis in an aqueous solution. The second aim was to study the performance of the electrodes loaded with different amounts of silver and different average particle size. However, this part was not possible to conduct either. Therefore, results from a previous study performed by I. L. Soroka et al. was used for discussion. The results point towards a lower initial concentration achieving a smaller average particle size and a lower loading of catalyst on the electrode can be compensated by a smaller average particle size of the catalyst.

Physico-chemical modifications induced by swift heavy ions on methane-water (CH4:H2O) ices at 15 K are analyzed. Ice films, at concentrations of (1:3) and (1:15), were irradiated by 40 MeV 58Ni11+ ions. Fourier transform transmission spectroscopy in the mid-range was used to monitor the evolution ices at 15 K as a function of projectile fluence. New IR bands appearing for the irradiated (CH4:H2O) (1:3) ice are attributed to the synthesized molecules: C3H8, HCO, H2CO, CO, CO2, H2O2, HCOOH, CH3OH, C2H5OH, and CH3CHO. For the irradiated (CH4:H2O) (1:15) ice, the abundances of the compounds containing two carbons atoms are lower than those for the (1:3) ice; in contrast, CH3OH and H2O2 abundances increase when compared to the values obtained with the (1:3) ice. After irradiation, the ices were warmed up until 110 K, when the IR spectra reveal features of complex organic molecules. The destruction and formation cross sections and the sputtering yields of the ice mixtures are estimated. These findings provide possible pathways for the occurrence of compounds rich in C, O, and H, which are indeed observed in the cold regions of the universe such as ices in grain mantles of the interstellar medium and circumstellar envelopes. © 2020. The American Astronomical Society. All rights reserved.

In light-water reactors the water used as neutron moderator and coolant is subjected to a constant radiation field which leads to the formation of a number of oxidizing and reducing species. In this work, the reactivity of the radiolysis product H 2 O 2 towards the 304L alloy, commonly used for structural materials in nuclear power plants, was investigated as well as oxidative dissolution of steel components as a consequence of γ-radiation and chemically added H 2 O 2 . The concentration of hydrogen peroxide as a function of time was monitored in the presence of different amounts of steel powder, and the second order reaction rate constant was determined to k 2 = (1.8 ± 0.2) × 10 −10 m s −1 . In the case of catalytic decomposition of hydrogen peroxide, hydroxyl radicals are formed which can be scavenged by methanol. In this reaction formaldehyde is formed, which can be detected spectroscopically. A high yield of formaldehyde was observed, indicating that catalytic decomposition is the main reaction path of H 2 O 2 in the current system. A significant contribution of the homogeneous Fenton reaction to both the reaction rate constant and the formaldehyde formation must however be considered, as Fe(II) will be released from the oxide layer in solution. In the case of γ-irradiation, an increased nickel content in solution compared to background experiments is seen. When the steel is subjected to chemically added hydrogen peroxide on the other hand, the chromium content in solution is increased. This indicates that the different types of exposure will impact different parts of the oxide layer characterized by different composition. © 2019, QC 20190711

BackgroundSynchrotron hydroxyl radical footprinting is a relatively new structural method used to investigate structural features and conformational changes of nucleic acids and proteins in the solution state. It was originally developed at the National Synchrotron Light Source at Brookhaven National Laboratory in the late nineties, and more recently, has been established at the Advanced Light Source at Lawrence Berkeley National Laboratory. The instrumentation for this method is an active area of development, and includes methods to increase dose to the samples while implementing high-throughput sample delivery methods.ConclusionImproving instrumentation to irradiate biological samples in real time using a sample droplet generator and inline fluorescence monitoring to rapidly determine dose response curves for samples will significantly increase the range of biological problems that can be investigated using synchrotron hydroxyl radical footprinting.

[177Lu]Lu-DOTA-PSMA-617 for PRRT is subject to radiolysis and therefore loses receptor affinity. This will be detrimental for treatment efficacy. In this study optimal quencher(s) (combinations) are determined to maintain radiochemical purity with a downscaled model. Downscaled model in terms of activity, but at similar concentrations. DOTA-PSMA-617 was labeled with [177Lu]LuCl3 with different molar- and volume activities. Either methionine, ethanol or both showed superior effects on the stabilizing radiochemical purity of [177Lu]Lu-DOTA-PSMA-617. As a consequence, radiochemical purity of [177Lu]Lu-DOTA-PSMA-617 could be maintained by the addition of methionine and/or ethanol and downscaled model was proven and complementary.

BackgroundMembrane proteins are crucial for cellular sensory cascades and metabolite transport, and hence are key pharmacological targets. Structural studies by traditional highresolution techniques are limited by the requirements for high purity and stability when handled in high concentration and nonnative buffers. Hence, there is a growing requirement for the use of alternate methods in a complementary but orthogonal approach to study the dynamic and functional aspects of membrane proteins in physiologically relevant conditions. In recent years, significant progress has been made in the field of X-ray radiolytic labeling in combination with mass spectroscopy, commonly known as X-ray Footprinting and Mass Spectrometry (XFMS), which provide residue-specific information on the solvent accessibility of proteins. In combination with both lowresolution biophysical methods and high-resolution structural data, XFMS is capable of providing valuable insights into structure and dynamics of membrane proteins, which have been difficult to obtain by standalone high-resolution structural techniques. The XFMS method has also demonstrated a unique capability for identification of structural waters and their dynamics in protein cavities at both a high degree of spatial and temporal resolution, and thus capable of identifying conformational hot-spots in transmembrane proteins.ConclusionWe provide a perspective on the place of XFMS amongst other structural biology methods and showcase some of the latest developments in its usage for studying conformational changes in membrane proteins.

Dissolution of the UO2 matrix is one of the potential routes for radionuclide release in a future deep geological repository for spent nuclear fuel. This doctoral thesis focuses on interfacial reactions of relevance in radiation-induced dissolution of UO2 and is divided in two parts: In the first part, we sought to explore the effects of solid phase composition: The impact of surface stoichiometry on the reactivity of UO2 towards aqueous radiolytic oxidants was studied. H2O2 reacts substantially faster with stoichiometric UO2 than with hyperstoichiometric UO2. In addition, the release of uranium from stoichiometric UO2 is lower than from hyperstoichiometric UO2. The behavior of stoichiometric powder changes with exposure to H2O2, approaching the behavior of hyperstoichiometric UO2 with the number of consecutive H2O2 additions. The impact of Gd-doping on the oxidative dissolution of UO2 in an aqueous system was investigated. A significant decrease in uranium dissolution and higher stability towards H2O2 for (U,Gd)O2 pellets compared to standard UO2 was found. In the second part, we sought to look at the effect of external factors: The surface reactivity of H2 and O2 was studied to understand the overall oxide surface reactivity of aqueous molecular radiolysis products. The results showed that hydrogen-abstracting radicals and H2O2 are formed in these systems. Identical experiments performed in aqueous systems containing UO2 powder showed that the simultaneous presence of H2 and O2 enhances the oxidative dissolution of UO2 compared to a system not containing H2. The effect of groundwater components such as bentonite and sulfide on the oxidative dissolution of UO2 was also explored. The presence of bentonite and sulfide in water could either delay or prevent in part the release of uranium to the environment. The Pd catalyzed H2 effect is more powerful than the sulfide effect. The poisoning of Pd catalyst is not observed under the conditions studied., QC 20170421

The main focus of the work presented in this thesis is on experimental studies oflaser acceleration of protons and other positive ions from solid targets. The topic is explored from three different angles: firstly, the development of diagnostics adapted to the ion pulses, secondly, the characterization of the source of the energetic particles and, finally, the application of laser-accelerated protons for time-resolved radiolysis of glass and water.Detectors that can efficiently record ion pulse parameters, such as the energyspectrum and spatial profile, were developed and implemented. One of these instruments was a modified version of a Thomson parabola spectrometer. Apartfrom the typical ion energy spectra provided by such an instrument, this modifieddiagnostic tool can also provide spatial information on pulse properties and on thespectrum of laser light transmitted through the laser-plasma interaction. The other diagnostic system developed and employed made use of plastic scintillators as a position-sensitive detector, to record either proton pulse profiles, or in combination with a dipole magnet, to record proton energy spectra, in a multiple-use, real-time feedback set-up. Laser acceleration of ions is a highly non-linear process and therefore pulse-to-pulse fluctuations are commonly large. When developing the detectors emphasis was thus placed on either being able to extract information about as many proton pulse parameters as possible simultaneously, or on being able to record large amounts of data efficiently (>100s of acquisitions over a few hours). Both these measures can be used to reduce the influence of pulse-to-pulse variations when analysing experimental results. However, they fulfil different needs, as the repetition rates of high-power lasers used for ion acceleration vary, from many laser pulses per second to one per hour or less. To be able to control and optimize the processes that occur when energyis transferred in a plasma, from a high-intensit

Résumé : Les ions hydronium (H3O + ) sont formés, à temps courts, dans les grappes ou le long des trajectoires de la radiolyse de l'eau par des rayonnements ionisants à faible transfert d’énergie linéaire (TEL) ou à TEL élevé. Cette formation in situ de H3O + rend la région des grappes/trajectoires du rayonnement temporairement plus acide que le milieu environnant. Bien que des preuves expérimentales de l’acidité d’une grappe aient déjà été signalées, il n'y a que des informations fragmentaires quant à son ampleur et sa dépendance en temps. Dans ce travail, nous déterminons les concentrations en H3O + et les valeurs de pH correspondantes en fonction du temps à partir des rendements de H3O + calculés à l’aide de simulations Monte Carlo de la chimie intervenant dans les trajectoires. Quatre ions incidents de différents TEL ont été sélectionnés et deux modèles de grappe/trajectoire ont été utilisés : 1) un modèle de grappe isolée "sphérique" (faible TEL) et 2) un modèle de trajectoire "cylindrique" (TEL élevé). Dans tous les cas étudiés, un effet de pH acide brusque transitoire, que nous appelons un effet de "pic acide", est observé immédiatement après l’irradiation. Cet effet ne semble pas avoir été exploré dans l'eau ou un milieu cellulaire soumis à un rayonnement ionisant, en particulier à haut TEL. À cet égard, ce travail soulève des questions sur les implications possibles de cet effet en radiobiologie, dont certaines sont évoquées brièvement. Nos calculs ont ensuite été étendus à l’étude de l'influence de la température, de 25 à 350 °C, sur la formation in situ d’ions H3O + et l’effet de pic acide qui intervient à temps courts lors de la radiolyse de l’eau à faible TEL. Les résultats montrent une augmentation marquée de la réponse de pic acide à hautes températures. Comme de nombreux processus intervenant dans le cœur d’un réacteur nucléaire refroidi à l'eau dépendent de façon critique du pH, la question ici est de savoir si ces fortes variations d’acidité, même, Hydronium ions (H3O+) are formed within spurs or tracks of the low or high linear energy transfer (LET) radiolysis of pure, deaerated water at early times. The in situ radiolytic formation of H3O+ renders the spur and track regions temporarily more acid than the surrounding medium. Although experimental evidence for an acidic spur has already been reported, there is only fragmentary information on its magnitude and time dependence. In this work, spur or track H3O+ concentrations and the corresponding pH values are obtained from our calculated yields of H3O+ as a function of time, using Monte Carlo track chemistry simulations. We selected four impacting ions and we used two different spur and track models: 1) an isolated “spherical” spur model characteristic of low-LET radiation and 2) an axially homogeneous “cylindrical” track model for high-LET radiation. Very good agreement was found between our calculated time evolution of G(H3O+) in the radiolysis of pure, deaerated water by 300-MeV incident protons (which mimic 60Co gamma/fast electron irradiation) and the available experimental data at 25 °C. For all cases studied, an abrupt transient acid pH effect, which we call an “acid spike”, is observed during and shortly after the initial energy release. This acid-spike effect is virtually unexplored in water or in a cellular environment subject to the action of ionizing radiation, especially high-LET radiation. In this regard, this work raises a number of questions about the potential implications of this effect for radiobiology, some of which are briefly evoked. Our calculations were then extended to examine the effect of temperature from 25 to 350 °C on the yield of H3O+ ions that are formed in spurs of the low-LET radiolysis of water. The results showed an increasingly acidic spike response at higher temperatures. As many in-core processes in a water-cooled nuclear reactor critically depend on pH, the question here is whether these variations in acidity

The process of radiation induced corrosion of copper is not well understood. The most obvious situation where the knowledge of this process is crucial is in a deep repository for high level spent nuclear fuel where the fuel will be sealed inside copper canisters. The radiation will penetrate the canisters and be absorbed by the surrounding environment. In this study gamma irradiations of polished and pre-oxidized copper cubes in anoxic pure water, air of 60-100 % RH and in humid argon were performed. The copper surfaces were examined using IRAS, XPS, cathodic reduction, SEM, AFM, and Raman spectroscopy. The concentration of copper in the reaction solutions was measured using ICP-OES. Also the formation of oxidative species caused by radiation absorption of water was studied by numerical simulations using MAKSIMA software. The corrosion of copper during gamma irradiation vastly exceeds what is expected. The production of oxidative species caused by radiation absorption of water is hundreds of times too low to explain the amount of oxidized copper. A possible explanation for this mismatch is an enhanced radiation chemical yield of HO· on the copper surface. Another one is an increased surface area due to oxidation of copper. One speculation is that HO· interacting with the copper oxide can cause oxidation of the metal. If the thermodynamic driving force is large enough then electrons can be conducted from the metal through the oxide to the oxidant. A dramatic increase in surface area together with an increased interfacial yield of HO· might explain the radiation enhanced corrosion process., QC 20151022

Membrane proteins, such as receptors, transporters and ion channels, control the vast majority of cellular signalling and metabolite exchange processes and thus are becoming key pharmacological targets. Obtaining structural information by usage of traditional structural biology techniques is limited by the requirements for the protein samples to be highly pure and stable when handled in high concentrations and in non-native buffer systems, which is often difficult to achieve for membrane targets. Hence, there is a growing requirement for the use of hybrid, integrative approaches to study the dynamic and functional aspects of membrane proteins in physiologically relevant conditions. In recent years, significant progress has been made in the field of oxidative labelling techniques and in particular the X-ray radiolytic footprinting in combination with mass spectrometry (MS) (XF-MS), which provide residue-specific information on the solvent accessibility of proteins. In combination with both low- and high-resolution data from other structural biology approaches, it is capable of providing valuable insights into dynamics of membrane proteins, which have been difficult to obtain by other structural techniques, proving a highly complementary technique to address structure and function of membrane targets. XF-MS has demonstrated a unique capability for identification of structural waters and conformational changes in proteins at both a high degree of spatial and a high degree of temporal resolution. Here, we provide a perspective on the place of XF-MS among other structural biology methods and showcase some of the latest developments in its usage for studying water-mediated transmembrane (TM) signalling, ion transport and ligand-induced allosteric conformational changes in membrane proteins.

Understanding the fundamental mechanisms involved in the induction of biological damage by ionizing radiation remains a major challenge of todays radiobiology research. The Monte Carlo simulation of physical, physicochemical and chemical processes involved may provide a powerful tool for the simulation of early damage induction. The Geant4-DNA extension of the general purpose Monte Carlo Geant4 simulation toolkit aims to provide the scientific community with an open source access platform for the mechanistic simulation of such early damage. This paper presents the most recent review of the Geant4-DNA extension, as available to Geant4 users since June 2015 (release 10.2 Beta). In particular, the review includes the description of new physical models for the description of electron elastic and inelastic interactions in liquid water, as well as new examples dedicated to the simulation of physicochemical and chemical stages of water radiolysis. Several implementations of geometrical models of biological targets are presented as well, and the list of Geant4-DNA examples is described. (C) 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Ices (H2O, CO, CO2, NH3, ..) are omnipresent in space on comets, the moons of giant planets, dust grains in dense clouds (the birthplaces of stars and planetary systems). They are exposed to cosmic rays, which in turn induce radiolysis, i.e. fragmentation of initial molecules, formation of radicals, and subsequent synthesis of molecules. Even complex pre-biotic molecules such as amino acids can be formed. Due to their high electronic energy loss the heavy ion fraction in cosmic rays yields nonnegligible contributions to sputtering and radiolysis, even if protons and alpha particles are more abundant [1]. Heavy-ion beams from large accelerator facilities are useful to simulate the specific effects induced by the heavy ion fraction of cosmic radiation in the laboratory. We complemented the experiments (550 MeV Ti beams) reported in [2] at the UNILAC M-branch, by irradiation with 630 MeV Xe beams. On-line Fourier transform infrared absorption spectroscopy (FTIR) allowed us to follow molecule destruction and synthesis in CO2 ice deposited at approx. 20 K on a CsI substrate.

Transmission electron microscopy is undoubtedly an indispensable tool for materials characterization, which can currently reach sub-angstrom resolution down to the elemental building blocks of matter, isolated single atoms of most elements. In addition to the phenomenal image resolution, if the material is strong enough, it can be accompanied with chemical information, converting electron microscopy into a unique method for the analysis of a great variety of materials. Unfortunately, extracting all this valuable information is not simple as most materials in one way or another are affected by the strong and localized electron beam. Radiolysis is one kind of reaction between electrons and matter than can cause irreversible structural transformations in our materials. This effect is the predominant factor in zeolites, zeotypes and the majority of molecular sieves. In the present work some results, taken at high voltage (300 kV) and minimizing the exposure to the beam, are presented proving the feasibility of the technique to obtain unprecedented atomic resolution information of different zeolites and microporous solids.

We investigated the effect of ionizing radiation on organic matter (OM) in the carbonaceous uranium (U) mineralization at the Mulga Rock deposit, Western Australia. Samples were collected from mineralized layers between 53 and 58.5 m depths in the Ambassador prospect, containing <5300 ppm U. Uranium bears a close spatial relationship with OM, mostly finely interspersed in the attrinite matrix and via enrichments within liptinitic phytoclasts (mainly sporinite and liptodetrinite). Geochemical analyses were conducted to: (i) identify the natural sources of molecular markers, (ii) recognize relationships between molecular markers and U concentrations and (iii) detect radiolysis effects on molecular marker distributions. Carbon to nitrogen ratios between 82 and 153, and Rock–Eval pyrolysis yields of 316–577 mg hydrocarbon/g TOC (HI) and 70–102 mg CO2/g TOC (OI) indicate a predominantly lipid-rich terrigenous plant OM source deposited in a complex shallow swampy wetland or lacustrine environment. Saturated hydrocarbon and ketone fractions reveal molecular distributions co-varying with U concentration. In samples with <1700 ppm U concentrations, long-chain n-alkanes and alkanones (C27–C31) reveal an odd/even carbon preference indicative of extant lipids.Samples with ⩾1700 ppm concentrations contain intermediate-length n-alkanes and alkanones, bearing a keto-group in position 2–10, with no carbon number preference. Such changes in molecular distributions are inconsistent with diagenetic degradation of terrigenous OM in oxic depositional environments and cannot be associated with thermal breakdown due to the relatively low thermal maturity of the deposits (Rr = 0.26%). It is assumed that the intimate spatial association of high U concentrations resulted in breakdown via radiolytic cracking of recalcitrant polyaliphatic macromolecules (spores, pollen, cuticles, or algal cysts) yielding medium chain length n-alkanes (C13–C24). Reactions of n-alkenes with OH− radicals from wat

Interfacial reactions between H2O2 and metal oxides are important in several fields but are yet not fully understood. Recently, tris(hydroxymethyl)aminomethane (Tris) was used as a probe in detecting the intermediate hydroxyl radical (HO center dot) during such process via the formation of formaldehyde (CH2O). In this work, we evaluate two probes (methanol and Tris) for detection of surface bound HO center dot by investigating the O-2 and pH effects on the production of formaldehyde. Moreover, we also examine the pH effect on the production of formaldehyde from Tris in the catalytic decomposition of H2O2 on ZrO2. The influence of O-2 and pH on the yield of formaldehyde under homogeneous conditions was studied via gamma-radiolysis of water. The solution was either deoxygenated or saturated with gas containing 20% 02, and the pH was ranging from 7.0 to 9.0. In the gamma-radiolysis experiment, O-2 shows a strong impact on the yield of formaldehyde: 14-68% for methanol and 16-29% for Tris. However, during the catalytic decomposition of H2O2, O-2 only enables a 30% enhancement of the production of CH2O when using Tris as the scavenger. While for methanol, the O-2 effect is almost negligible, and the production of CH2O from Tris is much higher than that from methanol. For practical reasons, only Tris was studied when evaluating the pH effect. A significant increase in the production of formaldehyde is observed by increasing pH during gamma-radiolysis of water while an even more pronounced pH-dependent increase is observed in the catalytic decomposition of H2O2 on ZrO2. The former indicates that the scavenging yield is base-catalyzed while the latter indicates that the formation of HO center dot is also base-catalyzed. On the basis of the observed effects of O-2 and pH, we propose a mechanism for the production of formaldehyde from Tris. The mechanism accounts for the observed impacts of O-2 and pH on the yield of formaldehyde., QC 20140611

We investigated the molecular basis for ionizing radiation (IR) resistance in extremophiles using the halophilic archaeon Halobacterium salinarum as a model system and several thermophilic bacteria and archaea also highly resistant to IR. Oxidative damages are the main lesions from IR and result from the production of reactive oxygen species (ROS) via radiolysis of water., The original document contains color images.

The radiolysis of persulfate (S2O8 2-) aqueous solution was studied for the enhancement of electron beam process applied to water treatment. It was shown that the persulfate ion reacts with aqueous electron and produces additional radical species in aqueous solution. The oxidative radical species formed (sulfate radical SO4 -•) is a very strong oxidant able to react with various recalcitrant pollutants. A model of the evolution of persulfate concentration in solution was performed. It was shown that the presence of persulfate induces a decrease of pH and also an increase of dissolved oxygen concentration in solution during irradiation. Moreover the interest of persulfate addition for the improvement of an organic compound degradation by radiolysis was shown.

In recent years, the impact of H-2 on alpha-radiation induced dissolution Of UO2-based spent nuclear fuel has been studied and debated extensively. Experimental results on the effect of H-2 on the concentration of H2O2 during alpha-radiolysis have been shown to disagree with numerical simulations. For this reason, the reaction scheme used in simulations of aqueous radiation chemistry has sometimes been questioned. In this work, we have studied the impact of H-2 on the H2O2 concentration in alpha-irradiated aqueous solution using numerical simulations. The effects of H-2 pressure, alpha-dose rate and HCO3- concentration were investigated by performing systematic variations in these parameters. The simulations show that the discrepancy between the previously published experimental result and numerical simulations is due to the use of a homogeneous dose rate (the energy is assumed to be equally distributed in the whole volume). Taking the actual dose rate of the alpha-irradiated volume into account, the simulation is in perfect agreement with the experimental results. This shows that the H-2 effect is strongly alpha-dose rate dependent, and proves the reliability of the reaction scheme used in the simulations. The simulations also show that H-2 influences the H2O2 concentration under alpha-radiolysis. The magnitude of the effect depends on the dose rate and the H-2 pressure as well as on the concentration of HCO3-. The impact of the radiolytic H-2 effect on the rate of alpha-radiation induced dissolution of spent nuclear fuel is discussed along with other (alpha- and gamma-) radiation induced processes capable of reducing the concentration of uranium in solution. The radiolytic H-2 effect is quantitatively compared to the previously presented noble metal catalyzed H-2 effect. This comparison shows that the noble metal catalyzed H-2 effect is far more efficient than the radiolytic H-2 effect. Reduction of U(VI) in solution due to low dose rate gamma-radiolysis in the pr, QC 20110210

Introduction: Microparticles derived from denatured human serum albumin (DOTA-derivatized human serum albumin microspheres, or DOTA-HSAM) are attractive carriers of radionuclides for both therapeutic and diagnostic purposes. In this article, we describe a labeling procedure for diagnostic (Ga-68) and therapeutic (Y-90, Lu-177) radionuclides and report on the results of stability studies of these products. Methods: DOTA-HSAM was labeled in 0.5 M ammonium acetate buffer, pH 5.0, containing 0.02 mg/ml detergent. After adding the radionuclide, the mixture was shaken for 15 min at 90°C. Labeling yields and in vitro stability were determined by thin-layer chromatography. For determination of the in vivo stability of Ga-68 and Y-90 DOTA-HSAM, the particles were injected intravenously in Wistar rats. Results: Labeling yields up to 95% in the case of Ga-68 and Lu-177 were achieved. Ga-68-labeled DOTA-HSAM showed high in vitro and in vivo stability. The amount of particle-bound radioactivity of Lu-177 DOTA-HSAM declines slowly in a linear manner to approximately 72% after 13 days. For Y-90, the labeling yield decreased with increasing radioactivity level. We presume radiolysis as the reason for these findings. Conclusion: The labeling of DOTA-HSAM with different radionuclides is easy to perform. The radiation-induced cleavage of the labeled chelator together with the rather short half-life of radioactivity fixation in vivo (3.7 days) is, in our opinion, opposed to therapeutic applications of DOTA-HSAM. On the other hand, the high stability of Ga-68 DOTA-HSAM makes them an attractive candidate for the measurement of regional perfusion by PET.

The impact of 2-propanol (100 mM), NaCl (0.1 - 2 M) and Fe(II)(aq) (10 mu M) on the radiation induced oxidative dissolution of UO2 is investigated experimentally by gamma-irradiating a UO2 pellet immersed in aqueous solution containing 10 mM HCO3- together with one of the studied solutes and measure the U(VI) concentration in solution as a function of irradiation time. The solution was saturated with one of the following gases; Air, N2O, inert gas (N-2 or At) in order to vary the experimental conditions and/or avoid the influence of oxygen. The results show that, in the presence of oxygen, 2 M chloride decrease the rate of UO2 dissolution whereas the dissolution rate increases somewhat in the presence of 100 mM 2-propanol. Under oxygen-free conditions both 2 M chloride, 100 mM 2-propanol and 10 mu M Fe(II)(aq) decrease the rate of UO2 dissolution. The trends in dissolution rates were reproduced by calculations based on previously determined rate constants for UO2 oxidation and oxidant concentrations obtained from numerical simulation of radiolysis in the corresponding homogeneous systems (taking reactions between the different solutes and the products of water radiolysis as well as changes in oxygen solubility into account). However, the results indicate that we cannot fully account for the G-values in 2 M chloride solution or all reactions involving CI- in the aqueous phase. This calls for further studies of the chloride system., QC 20100525

Monte-Carlo calculations are used to simulate the stochastic effects of fast neutron-induced chemical changes in the radiolysis of the ferrous sulfate (Fricke) dosimeter. To study the dependence of the yield of ferric ions, G(Fe[superscript 3+]), on fast neutron energy, we have simulated, at 25 [degree centigrade], the oxidation of ferrous ions in aerated aqueous 0.4 M H[subscript 2]SO[subscript 4] (pH 0.46) solutions when subjected to ~0.5-10 MeV incident neutrons, as a function of time up to ~50 s. The radiation effects due to fast neutrons are estimated on the basis of track segment (or"escape") yields calculated for the first four recoil protons with appropriate weighting according to the energy deposited by each of these protons. For example, a 0.8-MeV neutron generates recoil protons of 0.505, 0.186, 0.069, and 0.025 MeV, with linear energy transfer (LET) values of ~41, 69, 82, and 62 keV/[micro]m, respectively. In doing so, we consider that further recoils make only a negligible contribution to radiation processes. Our results show that the radiolysis of dilute aqueous solutions by fast neutrons produces smaller radical yields and larger molecular yields (relative to the corresponding yields for the radiolysis of water by [superscript 60]Co [gamma]-rays or fast electrons) due to the high LET associated to fast neutrons. The effect of recoil ions of oxygen, which is also taken into account in the calculations, is shown to decrease G(Fe[superscript 3+]) by about 10%. Our calculated values of G(Fe[superscript 3+]) are found to increase slightly with increasing neutron energy over the energy range covered in this study, in good agreement with available experimental data. We have also simulated the effect of temperature on the G(Fe[superscript 3+]) values in the fast neutron radiolysis of the Fricke dosimeter from 25 to 300 [degree centigrade]. Our results show an increase of G(Fe[superscript 3+]) with increasing temperature, which is readily explained by an incre

In this review the kinetics and mechanism of oxidative dissolution of UO2(s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO2 and dissolution of oxidized UO2) are used to calculate the rates of oxidative UO2(s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO3-/CO32- concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions., QC 20100908

5-Fluorouracil (5-FU) is used widely as an anticancer drug to treat solid cancers, such as colon, breast, rectal, and pancreatic cancers, although its clinical application is limited because 5-FU has gastrointestinal and hematological toxicity. Many groups are searching for prodrugs with functions that are tumor selective in their delivery and can be activated to improve the clinical utility of 5-FU as an important cancer chemotherapeutic agent. UV and ionizing radiation can cause chemical reactions in a localized area of the body, and these have been applied in the development of site-specific drug activation and sensitization. In this review, we describe recent progress in the development of novel 5-FU prodrugs that are activated site specifically by UV light and ionizing radiation in the tumor microenvironment. We also discuss the chemical mechanisms underlying this activation.