110m Ag Research Articles

Multiscale, mechanistic modeling of irradiation-enhanced silver diffusion in TRISO particles

Tristructural isotropic (TRISO) particles are under consideration for use in several proposed advanced nuclear reactor concepts. The silicon carbide (SiC) layer in TRISO acts as a barrier to prevent the release of the fission products. However, despite remarkable retention, silver (Ag) release has been observed from intact particles, which requires investigation since the Ag isotope (110m Ag) has a long half-life. Previous work focused on developing a multiscale, mechanistic model for Ag diffusion accounting for temperature and microstructure effect and has been successfully validated. In this work, we expand the previous model to account for irradiation-enhanced Ag diffusivity in SiC and improve its accuracy over a wider grain size and temperature ranges relevant for advanced reactor conditions. A temperature, grain size, and flux dependent diffusivity is therefore derived using the mesoscale code MARMOT and implemented in the fuel performance code BISON. The irradiation-enhanced Ag diffusivity in SiC is compared against experimental data and validated using BISON against Ag release measurements from the Advanced Gas Reactor Fuel Development and Qualification Program (AGR-1 and AGR-2). Herein, we quantify the impact of SiC grain size, irradiation, and temperature on Ag release. In agreement with previous studies, we find accounting for SiC grain size improves agreement between BISON predictions and experimental observations for most cases. We also find that accounting for irradiation improves agreement for cases where Ag release was underestimated, but the impact was less significant than accounting for microstructure.

Preliminary investigation of the shutdown radioactivity for EAST based on gamma ray spectrometry

• The HPGe spectrometer system was placed inside the vacuum vessel to measure the characteristic γ-rays emission from radionuclides after EAST shutdown. • The identification and pathway analysis of radionuclides were discussed based on structural materials and radiation sources of EAST. • Activity of radionuclides and time evolution of dose rate, preliminary activation results, were discussed. Experimental Advanced Superconducting Tokamak (EAST) is capable of operating with long-pulse deuterium plasma, which will generate a lot of radiation such as fusion neutrons, gamma rays and hard X-rays. Since the structure material of the device was activated, work around and inside the tokamak would be limited from a radiation protection point of view after shutdown. Identification of radionuclides and evaluation of dose rate inside the vacuum vessel are needed to develop a guiding principle for radiation protection during maintenance. In this paper, a gamma ray spectrometer based on high purity germanium (HPGe) detector and digitizer was placed inside the vacuum vessel to measure the characteristic gamma ray emission from radionuclides. 7 Be, 46 Sc, 51 Cr, 54 Mn, 58 Co, 60 Co, 59 Fe, 88 Y, 91 Y, 91m Nb, 99 Mo, 124 Sb and 110m Ag produced by photonuclear reactions and neutron-induced reactions were identified. The activities of radionuclides was calculated respectively with the uncertainty not exceed 6.05 %. The dose rate for 10 days after shutdown was mainly contributed by 60 Co, 58 Co, 54 Mn, 110m Ag, 59 Fe, 51 Cr, 88 Y, 99 Mo, 7 Be and 124 Sb, total dose rate were 3.62 × 10 −9 Sv/h(Port E) and 3.40 × 10 −9 Sv/h(Port I).

Activation analysis for the reference low-activation vanadium alloy NIFS-HEAT-2

• Activation analysis was performed for a NIFS-HEAT2 (V-4Cr-4Ti) sample. • The sample was irradiated in Japan Material Testing Reactor (JMTR) ~15 years before. • Detected impurities were 0.41 wppm Co and 0.71 wppm Nb. • Ag impurity concentration was estimated to be <0.034 wppm. • Results are supporting the superior low activation properties of NIFS-HEAT-2. Activation analysis of impurities was performed on a test specimen of the reference low-activation vanadium alloy NIFS-HEAT-2 (V-4Cr-4Ti) which has been irradiated in Japan Materials Testing Reactor (JMTR) ~16 years before. Since the radioactive nuclides from V, Cr and Ti are produced with short half-lives, intense peaks of 60 Co (T 1/2 = 5.27 years) were dominant in the measured gamma-ray energy spectra and peaks of 94 Nb (2.03 × 10 4 years) were also observed. The concentrations were evaluated to be 0.41 wppm and 0.71 wppm respectively from comparison with results of radioactivity calculation using the FISPACT-2005 code. In the analysis, detection of 108m Ag (418 years), which would have a considerable influence on the material recycling after the usage in a fusion reactor, was intense motivation. Although the peaks of 108m Ag has not been detected, the concentration of Ag was estimated to be <0.034 wppm from analysis of detection limit in gamma-ray peak count. Gamma-ray peaks originated from other impurity elements were not observed in the spectra, and the present analysis are supporting the superior low activation properties of NIFS-HEAT-2.

Route of exposure has a major impact on uptake of silver nanoparticles in Atlantic salmon (Salmo salar).

The potential impact of silver nanoparticles (Ag NPs) on aquatic organisms is to a large extent determined by their bioavailability through different routes of exposure. In the present study juvenile Atlantic salmon (Salmo salar) were exposed to different sources of radiolabeled Ag (radiolabeled 110m Ag NPs and 110m AgNO3 ). After 48 h of waterborne exposure to 3 μg/L citrate stabilized 110m Ag NPs or 110m AgNO3 , or a dietary exposure to 0.6 mg Ag/kg fish (given as citrate stabilized or uncoated 110m Ag NPs, or 110m AgNO3 ), Ag had been taken up in fish regardless of route of exposure or source of Ag (Ag NPs or AgNO3 ). Waterborne exposure led to high Ag concentrations on the gills, and dietary exposure led to high concentrations in the gastrointestinal tract. Silver distribution to the target organs was similar for both dietary and waterborne exposure, with the liver as the main target organ. The accumulation level of Ag was 2 to 3 times higher for AgNO3 than for Ag NPs when exposure was through water, whereas no significant differences were seen after dietary exposure. The transfer (Bq/g liver/g food or water) from exposure through water was 4 orders of magnitude higher than from feed using the smallest, citrate-stabilized Ag NPs (4 nm). The smallest NPs had a 5 times higher bioavailability in food compared with the larger and uncoated Ag NPs (20 nm). Despite the relatively low transfer of Ag from diet to fish, the short lifetime of Ag NPs in water and their transfer to sediment, feed, or sediment-dwelling food sources such as larvae and worms could make diet a significant long-term exposure route. Environ Toxicol Chem 2018;37:2895-2903. © 2018 SETAC.

Bioconcentration of Ag, Cd, Co, Mn and Zn in the Mangrove Oyster (Crassostrea gasar) and Preliminary Human Health Risk Assessment: A Radiotracer Study.

Bioaccumulation kinetics of five dissolved metals were determined in the mangrove oyster Crassostrea gasar, using corresponding radiotracers ((54)Mn, (57)Co, (65)Zn, (109)Cd and (110m)Ag). Additionally, their bioaccessibility to human consumers was estimated. Results indicated that over a 14-day exposure (54)Mn and (57)Co were linearly concentrated in oysters whereas (109)Cd, (65)Zn and (110m)Ag were starting to saturate (steady-state not reached). Whole-body concentration factors at 14days (CF14d in toto) ranged from 187±65 to 629±179 with the lowest bioconcentration capacity for Co and the highest for Ag. Depuration kinetics were best described by a double-exponential model with associated biological half-lives ranging from 26days (Ag) to almost 8months (Zn and Cd). Bioaccessible fraction of the studied elements was estimated using in vitro digestions, which suggested that oysters consumed seasoned with lemon enhanced the accessibility of Cd, Mn and Zn to human consumers, but not Ag and Co.

IMITATION OF STANDARD VOLUMETRIC ACTIVITY METAL SAMPLES

Due to the specific character of problems in the field of ionizing radiation spectroscopy, the R&amp;D and making process of standard volumetric activity metal samples (standard samples) for calibration and verification of spectrometric equipment is not only expensive, but also requires the use of highly qualified experts and a unique specific equipment. Theoretical and experimental studies performed have shown the possibility to use imitators as a set of alternating point sources of gamma radiation and metal plates and their use along with standard volumetric activity metal samples for calibration of scintillation-based detectors used in radiation control in metallurgy. Response functions or instrumental spectra of such spectrometer to radionuclides like 137 Cs, 134 Cs, 152 Eu, 154 Eu, 60 Co, 54 Mn, 232 Th, 226 Ra, 65 Zn, 125 Sb+ 125m Te, 106 Ru+ 106 Rh, 94 Nb, 110m Ag, 233 U, 234 U, 235 U and 238 U are required for calibration in a given measurement geometry. Standard samples in the form of a probe made of melt metal of a certain diameter and height are used in such measurements. However, the production of reference materials is costly and even problematic for such radionuclides as 94 Nb, 125 Sb+ 125m Te, 234 U, 235 U etc. A recognized solution to solve this problem is to use the Monte-Carlo simulation method. Instrumental experimental and theoretical spectra obtained by using standard samples and their imitators show a high compliance between experimental spectra of real samples and the theoretical ones of their Monte-Carlo models, between spectra of real samples and the ones of their imitators and finally, between experimental spectra of real sample imitators and the theoretical ones of their Monte-Carlo models. They also have shown the adequacy and consistency of the approach in using a combination of metal scattering layers and reference point gamma-ray sources instead of standard volumetric activity metal samples. As for using several reference point gamma-ray sources with radionuclide like 152 Eu, 232 Th, 226 Ra etc, they allow, in a combination of metal scattering layers, to compensate for the absorption of low energy gamma rays in the metal and to generate the desired response in the backscatter peak range, and finally to get the correct amplitude distribution that is equivalent to interaction effects that occur in the volumetric standard sample with radionuclide uniformly distributed in it.

The EWGRD Round Robin Measurement Exercise

This paper presents the results of a round robin exercise carried out to compare specific activity measurements performed by eight European organisations on a set of ten neutron activation detectors containing the radio-nuclides 110m Ag, 60 Co, 54 Mn, 46 Sc and 94 Nb. The purpose of the exercise was to demonstrate the level of consistency between the participating organisations in blind tests of measurements relevant to reactor metrology. The samples used were selected from a stock of pre-existing irradiated material held at SCK•CEN. Taking turns over a period of approximately 9 months, the participating organisations received the samples, measured them and provided their results to an independent referee who collated and compared the data. The inter-comparison has demonstrated good agreement between the participants with standard deviations for each dosimeter varying between 1.6% and 3.1%. The paper provides results of the EWGRD Round Robin in an anonymised form together with discussion and conclusions which may be drawn from the exercise.

Trophic transfer of radioisotopes in Mediterranean sponges through bacteria consumption.

Numerous field studies highlighted the capacities of marine sponges to bioaccumulate trace elements and assessed their potential as biomonitors of the marine environment. Experimental works demonstrated that dissolved metals and radionuclides can be taken up directly by sponge tissues but, to the best of our knowledge, little is known on the contribution of the dietary pathway through the consumption of contaminated bacteria considered as one of the trophic source in sponge diet. Objectives of this work are to study trophic transfer of radiotracers (110m)Ag, (241)Am, (109)Cd, (57)Co, (134)Cs, (54)Mn and (65)Zn from the marine bacteria Pseudomonas stutzeri to the Mediterranean sponges Aplysina cavernicola and Ircinia oros. P. stutzeri efficiently bioaccumulated trace elements in our culture experimental conditions with CF comprised between 10(5) and 10(7) after 48 h of growth in radiolabeled medium. When fed with these radiolabelled bacteria, A. cavernicola took up around 60% of radiotracers accumulated in trophic source except (134)Cs for which only 8% has been transferred from bacteria to sponge. Contrasting to this, I. oros retained only 7% of (110m)Ag, (109)Cd and (65)Zn counted in bacteria, but retained 2-fold longer accumulated metals in its tissues. The sponge inter-specific differences of accumulation and depuration following a trophic exposure are discussed with respect to the structure and the clearance capacities of each species.

A new large-volume metal reference standard for radioactive waste management.

A new large-volume metal reference standard has been developed. The intended use is for calibration of free-release radioactivity measurement systems and is made up of cast iron tubes placed inside a box of the size of a Euro-pallet (80 × 120 cm). The tubes contain certified activity concentrations of 60Co (0.290±0.006 Bq g−1) and 110mAg (3.05±0.09 Bq g−1) (reference date: 30 September 2013). They were produced using centrifugal casting from a smelt into which 60Co was first added and then one piece of neutron irradiated silver wire was progressively diluted. The iron castings were machined to the desirable dimensions. The final material consists of 12 iron tubes of 20 cm outer diameter, 17.6 cm inner diameter, 40 cm length/height and 245.9 kg total mass. This paper describes the reference standard and the process of determining the reference activity values.

Prediction of Self-Decontamination of Contaminated Territory Near the Fukushima-1 NPP (Japan)

A method is proposed for analyzing and evaluating the dynamics of self-decontamination of the region of the Fukushima-1 NPP contaminated by radioactive substances. The activity flux into the sea and average self-decontamination time of the territory due to decay and wash-off of the radionuclides 137 Cs and 134 Cs in the region of the NPP are obtained. The wash-off time constant of 137 Cs for the contaminated territory is determined from the experimental data. It is significantly greater than for the basins of the other rivers studied. This is due to the hydrological particularities of the rivers in Japan. It is shown that the maximum dose rate in the region of contamination will decrease to the background level in approximately 200 years. It is determined that the 137 Cs concentration in suspension does not depend on the water flow rate in the river; the 137 Cs flux is proportional to this flow rate, including in floods. Accidents at objects using nuclear power which are accompanied by the emission of radioactive substances, as a rule, lead to long-time contamination of the environment, which ultimately determines the radioactive effect on humans. In this connection, it is important to make a well-grounded quantitative prediction of the redistribution of radionuclides between different natural objects and the associated changes in the strength of the effect. The results of such a prediction for the region of radioactive contamination near the Fukushima-1 NPP are presented in this article. The prediction takes account of specific features, the main one being the intense wash-off of radionuclides by surface runoff from a river basin into the sea. The most complete data on the radioactive contamination of the region of the Fukushima-1 NPP are presented in [1], where the discharge into the atmosphere, deposition on the soil, density of the soil contamination by 137,134 Cs, 131 I, 129m Te, 110m Ag, 90 Sr, and 238‐240 Pu are indicated. For some of these isotopes, the depth distribution in the soil, the concentration in the water along the sea coast and the banks of the Abukuma River, flowing through the contaminated territory in the region of the NPP, as well as the bottom deposits in the sea and river are presented. Compared with the Chernobyl accident, the discharge and maximum density of the 137 Cs contamination were almost 10 times less, 22% of the 137 Cs discharged was on dry land, and the remainder was carried into the ocean [1]. The high level of radioactive contamination raises the question of the need to predict the reduction in the density of radioactive contamination and the total content of radioactive elements on this territory. The reduction in the radioactive contamination of the territory in time is due to decay and wash-off of the radionuclides by the surface run-off into the river and then into the sea. In [1, 2], the question of the need to solve such problems is raised, but steps to solving it are not mentioned. Methodological Basis of Prediction. A prediction of contamination can be based on a model of the transport of radionuclides in the river‐river-basin system as described in [3] by an equation for the density of the radioactive contamination of the basin σ = σ(y, t), which is a function of the time t and the coordinate y measured from the external boundary or a section of it:

Chromatographic separation of 65Zn from radioactive tellurium waste solution using alumina column

High-purity 65Zn was separated from a mixture containing 121,121m,123m,127Te, 65Zn, 54Mn, 60Co, 110m Ag, 125Sb, and 134Cs using a small chromatographic alumina column. Samples of aged radioactive tellurium waste were dissolved in alkali solutions (1 and 5 M NaOH) and fed into preconditioned 1.0 g alumina columns at ∼50°C. The columns were washed with 1 M NaOH or successively with 5 and 1 M NaOH. 65Zn was quantitatively retained in the alumina column in the course of feeding and washing the column with 1 M NaOH. Solutions of NH4Cl-NH3, NH4Cl-HCl, and HCl were studied as eluents for 65Zn from the alumina column. 2 M HCl ensured the highest elution yield (88.7 ± 1.7%) with the 65Zn radionuclidic purity of 99.4 ± 0.02%.

Redox Decomposition of Silver Citrate Complex in Nanoscale Confinement: An Unusual Mechanism of Formation and Growth of Silver Nanoparticles

We demonstrate for the first time the intrinsic role of nanoconfinement in facilitating the chemical reduction of metal ion precursors with a suitable reductant for the synthesis of metal nanoparticles, when the identical reaction does not occur in bulk solution. Taking the case of citrate reduction of silver ions under the unusual condition of [citrate]/[Ag(+)] ≫ 1, it has been observed that the silver citrate complex, stable in bulk solution, decomposes readily in confined nanodomains of charged and neutral matrices (ion-exchange film and porous polystyrene beads), leading to the formation of silver nanoparticles. The evolution of growth of silver nanoparticles in the ion-exchange films has been studied using a combination of (110m)Ag radiotracer, small-angle X-ray scattering (SAXS) experiments, and transmission electron microscopy (TEM). It has been observed that the nanoconfined redox decomposition of silver citrate complex is responsible for the formation of Ag seeds, which thereafter catalyze oxidation of citrate and act as electron sink for subsequent reduction of silver ions. Because of these parallel processes, the particle sizes are in the bimodal distribution at some stages of the reaction. A continuous seeding with parallel growth mechanism has been revealed. Based on the SAXS data and radiotracer kinetics, the growth mechanism has been elucidated as a combination of continuous autoreduction of silver ions on the nanoparticle surfaces and a sudden coalescence of nanoparticles at a critical number density. However, for a fixed period of reduction, the size, size distribution, and number density of thus-formed Ag nanoparticles have been found to be dependent on physical architecture and chemical composition of the matrix.

Ionic and electronic transport in AgI–As2Te3 glasses

Abstract 108m Ag tracer diffusion, ac impedance measurements and Wagner dc polarization experiments show that x AgI⋅(1 − x )As 2 Te 3 glasses (0 ≤ x ≤ 0.8) prepared either by traditional thermal synthesis in vacuum or by mechanical milling exhibit drastic changes in electronic and ionic conductivity as a function of silver iodide content x . The ionic transport increases monotonically by 9 orders of magnitude while the electronic conductivity decreases by a factor of 10 4 with increasing x . The x − 8 ≤ t Ag + x ≤ 0.8, belong to superionic glasses with the residual electronic conductivity of n -type, 10 − 5 ≤ t n ≤ 0.01.

Distribution of Artificial Radionuclides in Abandoned Cattle in the Evacuation Zone of the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (FNPP) accident released large amounts of radioactive substances into the environment. In order to provide basic information for biokinetics of radionuclides and for dose assessment of internal exposure brought by the FNPP accident, we determined the activity concentration of radionuclides in the organs of 79 cattle within a 20-km radius around the FNPP. In all the specimens examined, deposition of Cesium-134 (134Cs, half-life: 2.065 y) and 137Cs (30.07 y) was observed. Furthermore, organ-specific deposition of radionuclides with relatively short half-lives was detected, such as silver-110m (110mAg, 249.8 d) in the liver and tellurium-129m (129mTe, 33.6 d) in the kidney. Regression analysis showed a linear correlation between the radiocesium activity concentration in whole peripheral blood (PB) and that in each organ. The resulting slopes were organ dependent with the maximum value of 21.3 being obtained for skeletal muscles (R2 = 0.83, standard error (SE) = 0.76). Thus, the activity concentration of 134 Cs and 137Cs in an organ can be estimated from that in PB. The level of radioactive cesium in the organs of fetus and infants were 1.19-fold (R2 = 0.62, SE = 0.12), and 1.51-fold (R2 = 0.70, SE = 0.09) higher than that of the corresponding maternal organ, respectively. Furthermore, radiocesium activity concentration in organs was found to be dependent on the feeding conditions and the geographic location of the cattle. This study is the first to reveal the detailed systemic distribution of radionuclides in cattle attributed to the FNPP accident.

Radioisotopes Demonstrate the Contrasting Bioaccumulation Capacities of Heavy Metals in Embryonic Stages of Cephalopod Species

Cephalopods play a key role in many marine trophic food webs and also constitute alternative fishery resources in the context of the ongoing decline in finfish stocks. Most coastal cephalopod species of commercial importance migrate into shallow waters during the breeding season to lay their eggs, and are consequently subjected to coastal contamination. Eggs of common cuttlefish Sepia officinalis, European squid Loligo vulgaris, common octopus Octopus vulgaris and the sepiolid Rossia macrosoma were exposed during embryonic development to dissolved 110mAg, 109Cd, 60Co, 54Mn and 65Zn in order to determine their metal accumulation efficiencies and distribution among different egg compartments. Cuttlefish eggs, in which hard shells enclose the embryos, showed the lowest concentration factor (CF) values despite a longer duration of exposure. In contrast, octopus eggs, which are only protected by the chorionic membrane, accumulated the most metal. Uptake appears to be linked to the selective retention properties of the egg envelopes with respect to each element. The study also demonstrated that the octopus embryo accumulated 110mAg directly from the dissolved phase and also indirectly through assimilation of the contaminated yolk. These results raise questions regarding the potential contrasting vulnerability of early life stages of cephalopods to the metallic contamination of coastal waters.

Determination of iron(III) by displacement substoichiometric extraction with labeled silver–dipyridyl

A substoichiometric radiochemical displacement method has been designed for the estimation of trace quantities of iron. The method involves the displacement of spiked ((110m)Ag) silver from its dipyridyl complex in n-butanol by iron(III) owing to the greater stability of iron-dipyridyl complex compared to that of silver-dipyridyl complex. The interference effects of various closely related foreign ions on the displacement reaction were found to be negligible, thus establishing the selectivity of the proposed technique over other standard analytical techniques available for the estimation of iron(III). The validity of this method has been established by successful estimation of iron from various complex matrices. Investigations have been made.

Radiotracer Study of Synergistic Effects of Organophosphorus Compounds on the Extraction of Silver by N-(thio acetyl) benzamide into n-butanol

In the present investigation, systematic study of synergistic effects of phosphine oxides and tributyl phosphate on the extraction of Ag (I) from aqueous nitrate medium with N-(thioacetyl) bezamide into n-butanol is being reported. The ligand was synthesized and cha racter ized in our laborator y. Temperature dependence of extraction equilibrium have been studied in order to evaluate the thermodynamic parameters responsible for the extraction. Finally, IR data were used to support the extraction mechanism. 2. Experimental 2.1. Reagents and instrument. The chelating ligand (Nthio acetyl) benzamide was synthesised by the reaction of thioacetamide and benzoylchloride, derived form benzoic acid, which were obtained from Aldrich, USA. The donor reagents used in this work e.g tri-butyl phosphine oxide (TBPO), triphenyl phosphine oxide (TPPO), tri-butyl phosphate (TBP), were also collected from Aldrich; USA. The solvents were purified by standard procedures. All other reagents used were of A.R. grade. A stock solution of silver was prepared by dissolving A.R. AgNO3 in deionized water and a working stock was prepared by appropriate dilution. In order to spike the solution, an appropriate volume of stock solution of Ag(I) was mixed, with few drops of tracer solution containing, 110m Ag as

Activation cross-section for reactions induced by 14 MeV neutrons on natural silver

Cross-sections for (n, 2n), (n, p), and (n, α) reactions have been measured on silver isotopes at the neutron energies from 13.5 to 14.8 MeV using the activation technique in combination with high-resolution γ-ray spectroscopy. Corrections were made for the literature cross-sections of 109Ag(n, 2n) 108mAg reaction with incorrect half-life of product 108mAg. Neutrons were produced via the 3H(d, n) 4He reaction using solid TiT. The neutron fluences were determined using the monitor reaction 27Al(n, α) 24Na. The neutron energy in this measurement was determined by cross-section ratios for the 90Zr(n, 2n) 89m+gZr and 93Nb(n, 2n) 92mNb reactions. Data are reported for the following reactions: 109Ag(n, 2n) 108mAg, 107Ag(n, 2n) 106mAg, 109Ag(n, p) 109m+gPd, and 109Ag(n, α) 106mRh. The cross-sections were discussed and compared with experimental data found in the literature, and with the comprehensive evaluation data in ENDF/B-VII, JENDL-3.3, and JEFF-3.1/A libraries.

Tracer diffusion of 65Zn, 110mAg and 88Y in QE22 metal matrix composite

Tracer diffusion of 65 Zn, 110m Ag and 88 Y in QE22 metal matrix composite was measured by serial sectioning method in the temperature interval 646–728 K. The volume diffusion coefficients of Zn and Ag in the un-reinforced alloy follow Arrhenius dependences with frequency factors D 0 = 9.5 × 10 −5 and 6.0 × 10 −3 m 2 s −1 and the activation enthalpies 125.3 and 153.5 kJ mol −1 , respectively. In the case of the reinforced alloy, the effective diffusion coefficients D eff were obtained and interface diffusion coefficients D i in the interface boundaries were estimated. Both temperature dependences of D eff and D i were not Arrhenius-type. This feature was explained by the large difference in coefficients of the thermal expansion of the metal matrix and the reinforcement. In the case of 88 Y diffusion in un-reinforced QE22 alloy, it was found that yttrium diffuses along dislocations that act as paths of rapid diffusion. Diffusivity of 88 Y along dislocations, a 2 sD d , was estimated.

Antimicrobial surface functionalization of plastic catheters by silver nanoparticles

To test the antimicrobial activity and evaluate the risk of systemic toxicity of novel catheters coated with silver nanoparticles. Catheters were coated with silver using AgNO3, a surfactant and N,N,N ',N '-tetramethylethylenediamine as a reducing agent. Particle size was determined by electron microscopy. Silver release from the catheters was determined in vitro and in vivo using radioactive silver ((110m)Ag+). Activity on microbial growth and biofilm formation was evaluated against pathogens most commonly involved in catheter-related infections, and the risk for systemic toxicity was estimated by measuring silver biodistribution in mice implanted subcutaneously with (110 m)Ag+-coated catheters. The coating method yielded a thin ( approximately 100 nm) layer of nanoparticles of silver on the surface of the catheters. Variations in AgNO3 concentration translated into proportional changes in silver coating (from 0.1 to 30 microg/cm(2)). Sustained release of silver was demonstrated over a period of 10 days. Coated catheters showed significant in vitro antimicrobial activity and prevented biofilm formation using Escherichia coli, Enterococcus, Staphylococcus aureus, coagulase-negative staphylococci, Pseudomonas aeruginosa and Candida albicans. Approximately 15% of the coated silver eluted from the catheters in 10 days in vivo, with predominant excretion in faeces (8%), accumulation at the implantation site (3%) and no organ accumulation (< or = 0.1%). A method to coat plastic catheters with bioactive silver nanoparticles was developed. These catheters are non-toxic and are capable of targeted and sustained release of silver at the implantation site. Because of their demonstrated antimicrobial properties, they may be useful in reducing the risk of infectious complications in patients with indwelling catheters.