Initial Period Of Irradiation Research Articles

Probing the facet-dependent intermediate in the visible-light degradation of RhB by carbon-coated anatase TiO2 nanoparticles

The Facet-dependent photocatalytic process related to the degradation of organic pollutants by semiconductor catalysts is of great significance for understanding the photocatalytic mechanism of nanomaterials and improving their catalytic performance. Herein, the titanium dioxide catalysts with {001} or {101} dominant exposed facets coated with carbon (TiO2(001)/C and TiO2(101)/C) were synthesized by a hydrothermal method, and the photo-degradation research of rhodamine B (RhB) was analyzed by using UV–visible absorption spectroscopy, fluorescence spectroscopy and time-resolved fluorescence spectroscopy. The results demonstrated that the degradation of RhB was the competition for both N-deethylation and the destruction of aromatic ring reactions. The N-deethylation of RhB molecules dominated the reaction in the TiO2(001)/C system during the initial irradiation period. Whereas, both N-deethylation and cleavage of the aromatic ring occurred simultaneously in TiO2(101)/C/RhB system. The results of the fluorescence spectra and fluorescence lifetime analysis also suggested that the degradation rate of the intermediate product (Rh-110) is faster for TiO2(001)/C than TiO2(101)/C. We proposed a possible explanation that the carbonaceous species on the surface of TiO2 can absorb visible light to assist the degradation of RhB. The difference in surface properties and energy band structures lead to the different degradation processes and facet dependent features. Our findings presented the intermediate evidences for revealing the relation between the photocatalytic activity and exposed facets of TiO2 nanoparticles.

Gold nanorod reshaping in vitro and in vivo using a continuous wave laser.

Gold nanorods (GNRs) are increasingly being investigated for cancer theranostics as they possess features which lend themselves in equal measures as contrast agents and catalysts for photothermal therapy. Their optical absorption spectral peak wavelength is determined by their size and shape. Photothermal therapy using GNRs is typically established using near infrared light as this allows sufficient penetration into the tumour matrix. Continuous wave (CW) lasers are the most commonly applied source of near infrared irradiation on GNRs for tumour photothermal therapy. It is perceived that large tumours may require fractionated or prolonged irradiation. However the true efficacy of repeated or protracted CW irradiation on tumour sites using the original sample of GNRs remains unclear. In this study spectroscopy and transmission electron microscopy are used to demonstrate that GNRs reshape both in vitro and in vivo after CW irradiation, which reduces their absorption efficiency. These changes were sustained throughout and beyond the initial period of irradiation, resulting from a spectral blue-shift and a considerable diminution in the absorption peak of GNRs. Solid subcutaneous tumours in immunodeficient BALB/c mice were subjected to GNRs and analysed with electron microscopy pre- and post-CW laser irradiation. This phenomenon of thermally induced GNR reshaping can occur at relatively low bulk temperatures, well below the bulk melting point of gold. Photoacoustic monitoring of GNR reshaping is also evaluated as a potential clinical aid to determine GNR absorption and reshaping during photothermal therapy. Aggregation of particles was coincidentally observed following CW irradiation, which would further diminish the subsequent optical absorption capacity of irradiated GNRs. It is thus established that sequential or prolonged applications of CW laser will not confer any additional photothermal effect on tumours due to significant attenuations in the peak optical absorption properties of GNRs following primary laser irradiation.

Microwave-assisted and conventional hydrothermal synthesis of potassium merlinoite from K-feldspar

Potassium merlinoite was successfully synthesized from K-feldspar powder by microwave-assisted as well as conventional hydrothermal methods. Effects of aging, H2O/Al2O3 molar ratio, crystallization temperature, crystallization time, and mixed heating strategy on potassium merlinoite formation were systemically studied. It was observed that aging was not a necessary factor to the formation of merlinoite, and merlinoite was the unique crystalline product at a wide range of H2O/Al2O3 molar ratio, crystallization temperature and time. The reaction rate of microwave-assisted hydrothermal synthesis was 2–3 times as much as conventional method. The acceleration effect of microwave was proved to work only at the initial period of irradiation, and a mixed heating method was considered as an appropriate strategy to prepare merlinoite. A simple and economical chemical process has been proposed to convert the natural K-feldspar powder into merlinoite-type eco-fertilizer in this paper.

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.

New models for UO 2 fuel structure evolution under irradiation in fast reactors

On the base of analysis of experimental observations and critical assessment of existing models for oxide fuel structure evolution under operation conditions of fast reactors, new models for fuel restructuring and coring are proposed. The restructuring model describes coherent motion in the temperature gradient of various voids (gas bubbles, sintering pores and large lenticular pores) and grain boundaries, to which the voids are attached. As a result, the model explains elongation of thermally growing equiaxed grains and formation of columnar grains, and predicts a rapid formation of extended columnar grain zone during a relatively short initial period of fast reactor irradiation. The coring model describes formation and growth of the central void in the fuel pellet, activated by mass transport from the inner to the outer zone of the pellet under stresses induced by inhomogeneous fuel densification in the initial period of irradiation.

The influence of weathering conditions on the properties of poly(vinyl chloride) for outdoor applications. An analytical study using surface analysis techniques

In the present work, four different PVC formulations, designed for outdoor applications, were submitted to artificial accelerated ageing under xenon light, without and with spray of water, and to natural exposure. The influence of the combined action of water and radiation was evaluated by means of surface analysis using XPS, SEM and colourimetry, permitting comparison of the results obtained under different exposure conditions. Results show that a long preliminary period of irradiation (∼2000 h) before the exposure to water increases the resistance of PVC surfaces to weather conditions. The role of that initial irradiation period is to create an erodable layer made of shrunk “PVC” that had lost most of its chlorine atoms and, thence, creating a network of cracks. That layer loses easily adhesion to deeper layers due to erosive action of water spray. The more perfect uncovered surface is better at resisting the effect of radiation.

Effect of X-ray Irradiation on the Chemical and Physical Properties of a Semifluorinated Self-Assembled Monolayer

The effect of X-ray irradiation on the chemical and physical properties of a semifluorinated self-assembled monolayer (CF-SAM) derived from 1H,1H,2H,2H-perfluorodecanethiol (CF3(CF2)7(CH2)2SH) adsorbed on gold and copper substrates was studied using X-ray photoelectron spectroscopy. During the initial period of irradiation, the effects of electron-stimulated C−F, C−C, and S−X (X = Au, Cu) bond breaking are responsible for changes in the chemical composition of the CF-SAM. Furthermore, the evolution of the C(1s) X-ray photoelectron spectral region indicates that C−F rather than C−C bond cleavage dominates desorption within the CF-SAM. Except for fluorine desorption, irradiation-induced changes to the chemical and structural properties of the CF-SAM were most pronounced during the initial stages of irradiation, prior to the development of a highly cross-linked carbonaceous overlayer. X-ray irradiation of CF-SAMs adsorbed on Au also resulted in the production of new irradiation-induced sulfur species. A comparison with experiments carried out on a n-hexanedecanethiol (CH3(CH2)15SH)-based SAM revealed that the concentration and distribution of these irradiation-induced sulfur species were both sensitive to the SAM's initial chemical composition. On Cu substrates, native CF-SAMs formed an effective barrier to oxygen diffusion although the film's permeability to oxygen increased for CF-SAMs pre-exposed to X-ray irradiation.

Irradiation Behavior of Large Grain UO2 Fuel Rod by Active Powder

The internal pressures in the large and normal grain UO2 pellet rods irradiated at a linear heat rate of <29 kW/m up to 21 GWd/t U were studied to clarify the effect of in-pile densification and fission gas release. The large grain (grain size: 23 μm) pellets were manufactured from the active powder produced by the new ADU (ammonium diuranate) process. The pore structure of the large grain pellets mainly consisted of coarse pores that were formed by adding a poreformer. The pore structure of the normal grain (8 μm) pellets made from the current powder consisted of fine pores. In-pile and out-of-pile densification of the large grain pellets were smaller than those of the normal pellets and occurred owing to the disappearance of fine pores as fabricated. The increase in free volume of the large grain fuel rod did not occur significantly owing to its smaller densification during the initial irradiation period. The fuel stack length change during irradiation was predicted with the in-pile densification and swelling model. The increase in grain size decreased fission gas release by diffusion. As a result, it was found that the internal pressure of the large grain fuel rod was reduced after 10 GWd/t U.

Fluorescence Photobleaching of ALA‐induced Protoporphyrin IX during Photodynamic Therapy of Normal Hairless Mouse Skin: The Effect of Light Dose and Irradiance and the Resulting Biological Effect

The photobleaching of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was investigated during superficial photodynamic therapy (PDT) in normal skin of the SKH HR1 hairless mouse. The effects of light dose and fluence rate on the dynamics and magnitude of photobleaching and on the corresponding PDT-induced damage were examined. The results show that the PDT damage cannot be predicted by the total light dose. Photobleaching was monitored over a wide range of initial PpIX fluorescence intensities. The rate of PpIX photobleaching is not a simple function of fluence rate but is dependent on the initial concentration of sensitizer. Also, at high fluence rates (50-150 mW/cm2, 514 nm) oxygen depletion is shown to have a significant effect. The rate of photobleaching with respect to light dose and the corresponding PDT damage both increase with decreasing fluence rate. We therefore suggest that the definition of a bleaching dose as the light dose that causes a 1/e reduction in fluorescence signal is insufficient to describe the dynamics of photobleaching and PDT-induced damage. We have detected the formation of PpIX photoproducts during the initial period of irradiation that were themselves subsequently photobleached. In the absence of oxygen, PpIX and its photoproducts are not photobleached. We present a method of calculating a therapeutic dose delivered during superficial PDT that demonstrates a strong correlation with PDT damage.

Irradiation Behavior of Large Grain UO2 Fuel Rod by Active Powder.

The internal pressures in the large and normal grain UO2 pellet rods irradiated at a linear heat rate of <29 kW/m up to 21 GWd/t U were studied to clarify the effect of in-pile densification and fission gas release. The large grain (grain size: 23 μm) pellets were manufactured from the active powder produced by the new ADU (ammonium diuranate) process. The pore structure of the large grain pellets mainly consisted of coarse pores that were formed by adding a poreformer. The pore structure of the normal grain (8 μm) pellets made from the current powder consisted of fine pores. In-pile and out-of-pile densification of the large grain pellets were smaller than those of the normal pellets and occurred owing to the disappearance of fine pores as fabricated. The increase in free volume of the large grain fuel rod did not occur significantly owing to its smaller densification during the initial irradiation period. The fuel stack length change during irradiation was predicted with the in-pile densification and swelling model. The increase in grain size decreased fission gas release by diffusion. As a result, it was found that the internal pressure of the large grain fuel rod was reduced after 10 GWd/t U.

Radiation induced CO 2 reduction in an aqueous medium suspended with iron powder

Radiation induced CO 2 conversion to CO and hydrocarbon has been studied using a solution suspended with iron powder and saturated with CO 2. Due to the corrosion enhanced by γ-rays, H 2 has become the most dominant product of all. Corresponding to the rapid H 2 formation, a little hydrocarbon containing less than 4 carbon atoms has been produced in the initial period of irradiation, whereas CO yield has gradually increased to a considerable amount over a prolonged irradiation period. The CO yield has also shown a marked increase associated with introducing Ni 2+ or Cu 2+ into the solution. It is understood that 5.6 hydrogen atoms are consumed in the termination reaction of H 2 formation.

Irradiation induced dimensional changes in ceramics

Aluminum-oxide, silicon-carbide, silicon and vitreous silica specimens of thicknesses around 300 μm were irradiated with protons in the 10 MeV range at temperatures from 220°C to 600°C under uniaxial tensile stresses from 5 to 100 MPa to dose levels up to about 2 × 10−2 dpa. Straining of Al2O3 and SiC was essentially independent of stress and was therefore interpreted in terms of volume dilatation by point defect accumulation. Silicon showed a small but stress dependent dilatation, while the length of SiO2 -glass was reduced during an initial period of irradiation by up to ≈ 0.6%. Subsequently also SiO2 elongated, showing a linear stress- and dose rate dependence. Irradiation with a typical dose rate of 2.3 × 10−7 dpa/s produced a viscosity of vitreous silica corresponding to a thermal viscosity at ≈ 1200°C.

The preparation of poly[N(n‐butoxymethyl) methacrylamide] grafted silk fibers by polymerization using a low pH system

AbstractThe graft polymerizations of the N(n‐butoxymethyl) methacrylamide (BMA) monomer onto silk fibers were effected after reducing the pH of the grafting system to 2.5 by the addition of a formic acid solution. We compared the grafting efficiencies, surface characteristics, and thermal behaviors, as well as the whiteness levels and the extent of reduction of the rate of yellowing following UV irradiation, with the equivalent features of poly(BMA)‐grafted silk fibers, prepared under normal (pH 6) conditions. The grafting efficiency [as poly(BMA) weight gain] onto silk fiber that was attained was almost 100% through optimization of the pH environment in the polymerization system by the addition of formic acid. The stiffness of the silk fabrics observed, following the conventional grafting, was markedly higher than that of equivalent silks after the polymerization at pH 2.5. The rates of yellowness index increase, for these latter silk fabrics following UV irradiation were also reduced, specifically in the initial irradiation period (up to 60 h).The SEM of the grafted silk fabrics reveal the absence of granules on the surface of the grafted silk fiber, when the silk was grafted with poly(BMA), after reducing the pH of the grafting system to 2.5. These findings suggest that the BMA monomer was polymerized specifically within the silk fiber and not on the surface. It is suggested that the increase in the polymer weight gain, and the reduced adverse effect on the fabric handle, arise because of the modified polymer location. © 1993 John Wiley &amp; Sons, Inc.

Machining of PZT, PT and (Mn, Zn)Fe2O4 Ceramics by Laser-Induced Chemical Etching

Laser-enhanced chemical etching of PbTiO3, PZT and (Mn–Zn)-ferrite ceramics is reported. The KOH solution of 10 mol/1 is suitable for the laser enhanced inter-granular etching of the PbTiO3 and PZT with depth etching rate higher than 100 µm/s in the initial laser irradiation period of Ar+ laser of 1 W. The KOH and NaOH solutions are also suitable for the intergranular etching of (Mn–Zn)-ferrite. The H3PO4 solution of 6 mol/1 is suitable for the laser enhanced trans-granular etching of (Mn–Zn)-ferrite with the depth etching rate of about 10 µm/s in the initial irradiation period of an Ar+ laser of 1 W.

Spectral tailoring for fusion radiation damage studies: Where do we stand?

The Oak Ridge Research Reactor is currently being used to irradiate an experiment (MFE-4A) to simulate in stainless steel-316 the He-to-DPA ratio of 14 appm He/DPA expected at the first wall of a fusion reactor. The experimental design criterion is to remain within ±20% of this ratio after an initial irradiation period of ∼1.2 years. At present (March 31, 1981) the experiment has been in the reactor for 19 cycles corresponding to 131,543 MWh, 4.05×10 25 n/m 2 in thermal fluence, 1.21×10 26 n/m 2 in total fluence, 3.1 DPAs and 21.0 appm He. The current He-to-DPA ratio is 6.8. This paper summarizes some of the analytical calculations for this experiment and presents the current status of this work. The analytical calculations utilize the codes VENTURE, ANISN, GAS, UNFOLD, etc. and the obtained results include gas production, DPA, and heating rates, and neutron spectral modifications resulting from different reactor fuel loadings and core piece compositions.

Effect of irradiation conditions and chemical composition on radiational-damage development in steels and alloys irradiated by neutrons

The investigation of the initiation and growth kinetics of pores, dislocation structure, and particles of phase inclusions at fluxes of 1–100 dislocation/atom leads to the following conclusions. 1. The dependence of the pore concentration in steels on the flux is described by a power law; the power-law index depends strongly on the composition of the steel and the irradiation temperature. The mean pore diameter in the initial period of irradiation varies according to the law (Kt)1/2; at large fluxes, it remains almost constant. 2. In all the steels investigated, at fluxes above 5 dislocation/atom, the total dislocation density increases according to a power law; the power-law index varies from 0.4 to 1 depending on the composition of the steel and the irradiation temperature. 3. In the initial period of irradiation, a stage of accelerated inclusion-particle initiation is observed, while at high fluxes they are seen to coalesce. The correlation of the kinetics of inclusion-particle initiation and growth with the dislocation density and the irradiation temperature has been established. 4. The effect of the chemical composition of the steel, which is particularly clearly expressed at low temperature and small fluxes, is evidently due to the action of the alloying elements either on the ability of the dislocations to capture interstitial atoms or on the mechanism of the formation of new-phase inclusions.

A scanning electron microscope study of the degradation of electron channelling effects in alkali halide crystals during electron irradiation

The effects ofin-situ, 25 kV electron irradiation on SEM electron channelling patterns from alkali halide crystals at room temperature are reported. Patterns were generated using wide beam and narrow beam methods. It is observed that after an initial period of irradiation, during which well defined high resolution patterns can be generated, degradation occurs. This is marked either by channelling line difiuseness or by waviness, depending on the method of generation. After prolonged irradiations, patterns can no longer be detected. Subsequent annealing experiments on irradiated NaCl show that patterns return to their original clarity if the annealing temperature is between 285 and 325‡C. Initial distortions (i.e. diffuseness and waviness) are attributed principally to the effects on the incident beam of irradiation induced surface electric fields; pattern loss, and subsequent recovery on annealing, is attributed to lattice distortion effects arising from beam-induced defect clusters.

Effects of High Energy Radiation on Polymers III. Viscosity

It was known that solubility of irradiated polymers was not free from the effect of cyclization. On the contrary, viscosity before gel point is not affected by it and it is utilized in order to investigate the effects of high energy radiation on polymers. Intrinsic viscosity is discussed first for the case where cross-linking and degradation occur. In certain cases intrinsic viscosity decreases in the initial period of irradiation, but increases in larger radiation doses, so that it has a minimum and becomes infinite at a certain radiation dose which corresponds to gel point. It is also derived that G -value of cross-linking and degradation are calculated from the intrinsic viscosity in the initial period of irradiation. An example of polyvinylchloride gives G -values whose orders of magnitude are not unreasonable. The more accurate is the measurement, the more correct values will be obtained. Intrinsic viscosity for the case where end-linking occurs is likewise discussed, and the same properties as those in cross-linking are derived. Finally we know that the gel point determined from an asymptotic behaviour of intrinsic viscosity will be more correct than that determined from an extrapolation of solubility curve.