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One of the most effective ways of gaining user experience and minimizing user effects on modelling and simulation is benchmarking. Currently (2022) a new experimental workplace, the so called ‘Mini Labyrinth’ is being developed at Slovak University of Technology in Bratislava (STU). It is a simple neutron and gamma shielding benchmark, inspired by the ALARM-CF-AIR-LAB-001 ICSBEP experiment. The latest V2 setup consists of a PuBe neutron source, several NEUTRONSTOP C5 shielding blocks, H2O filled polylactic acid (PLA) tank, plastic source holder and detectors placed inside and outside the Mini Labyrinth. This paper is focused on the monitoring of the radiation doses around the workplace using the NuDET neutron detector and on the comparison of the measured quantities with ones simulated by SCALE 6 MONACO. The influence of the size of the model and the definition of the detector is studied in this analysis. The achieved results are presented and some discussions on further needed development are also included.

6H-SiC samples have been implanted by 4 MeV C and Si ions in the (0001) channeling direction to the sets of multiple implantation fluences. These samples were analyzed via Elastic Backscattering Spectroscopy in the channeling mode (EBS/C) using 1.725 MeV proton beam, from which SiC amorphization depth profiles and averaged integral 6H-SiC amorphization have been obtained. The averaged integral 6H-SiC crystal amorphization vs implanted fluence dependence has been determined for both types of implanted ions. From these dependences, the 6H-SiC integral crystal amorphization vs. implanted fluence/type of implanted atom assessment model have been proposed.

In this work the crystal rainbow effect is described. Its application for determination of the ion-solid interaction potential, which is one of basic problem in ion-solid interaction, is presented. The crystal rainbow effect occurs in transmission of ions through channels of a crystal. We show that it is possible, by measuring the angular distribution of transmitted channeled ions, to establish a novel analytical method for determination of the ion-solid interaction potential.

To extend the research possibilities of the nuclear research group at Brno University of Technology, a gamma radiation shielding measurement benchmark assembly was designed and built. Experimental device will be used for fine attenuation coefficient and build-up factors measurement and for easy validation of theoretical simulation and calculation of shielding properties of selected materials. Many different radioactive emitters can be used in the assembly, as well as many different detectors and materials, which might be tested, and results compared to understand well measurement results. A theoretical model was also created for the benchmark assembly and simulated in MCNP. Initial results show identical trends of values obtained by simulation and practical experiment.

This paper presents a new two-step method for the synthesis of NiO/TiO2–CeO2 semiconductors, which implies, the first, the mechanochemical synthesis of TiO2–CeO2 support, and the second is the doping of different NiO contents by chemical precipitation in an aqueous medium in an ambient atmosphere. Structural, optical, electrochemical and photocatalytic properties of NiO/TiO2–CeO2 semiconductors were examined. The influence of different NiO contents on the electrocatalytic activity of NiO/TiO2–CeO2 samples was investigated in the oxygen evolution reaction and the results showed that the samples with the lowest NiO content have the highest electroactivity. The photocatalytic activity was determined during the phenol decomposition process over the samples with different NiO:TiO2–CeO2 ratios and the best photocatalytic activity is observed for the sample with 4.1 mol% NiO. The sample with the lowest NiO content obtained by a relatively simple method is suitable for use both as an electrode material in the oxygen evolution reaction and as a photocatalyst in the phenol decomposition process.

Quantifying rock weathering processes, especially in ways of nondisturbance and on-site investigation, is one of the most critical tasks in predicting rocks erosion rates and understanding the sediment transportation. We proposed a more reproducible approach to test how image analysis can quantify the changes in the size and shape of fragments during the weathering process. Four artificial models were designed to select suitable metrics among over 20 parameters. To validate the efficiency of image analysis, we analyzed rocks from badlands in Nanxiong Basin, Southeast China, under three different ranges of temperature differences (TD) during cyclic wetting and drying (WD). Our results show that TDs can accelerate the disintegration rate, and even if there is only a 20°C difference in the range of TDs, an apparent difference in fragment size was observed. Moreover, the shape of fragments became more round as the increasing number of cyclic treatments, and for samples that went through the same number of treatments, the larger the temperature difference, the more round the shape became. All that serves as another evidence for landscape evolution response to climatic warming.

The hexagonal silicon carbide (6H-SiC) is one of materials used in nuclear applications, and as such is exposed to crystal damage inducing by variety of energetic particles like neutrons. In this article the 6H-SiC crystal lattice damage was introduced by the 4 MeV C3+ and 4 MeV Si3+ channelling ion implantation at the room temperature. The implantation of C and Si ions (so called self-ions) to the set of different fluences, achieves a 6H-SiC crystal lattice damage more similar to what the exposure to neutrons would produce. The 6H-SiC crystal damage has been investigated by the Elastic Backscattering spectra taken in the channeling orientation (EBS/C). EBS/C spectra of the implanted 6H-SiC samples were taken with 1.725 MeV and 1.860 MeV protons. By fitting the EBS/C spectra, the quantitative 6H-SiC crystal damage depth profiles were obtained. Further, the cross section of crystal's implanted region has been scanned with the micro-Raman (μR) technique for a comparison. In this way, the qualitative analysis of a non-crystalline phase as a function of the crystal depth was independently determined. Additionally, a scanning electron microscopy (SEM) image was taken of the implanted crystal cross sections. The comparison of the crystal damage profiles obtained by fitting EBS/C spectra with the corresponding ones obtained with the μR and SEM techniques shows very good consistency between them.

The Mini Labyrinth experiment is a simple neutron and gamma shielding experiment developed at STU, inspired by the ALARM-CF-AIR-LAB-001 ICSBEP benchmark experiment. The STU Mini Labyrinth is approximately ten times smaller and consists of NEUTRONSTOP shielding blocks. This paper describes the second version of the Mini Labyrinth experiment and presents the results of the neutron and gamma fields simulation and measurement. The PuBe neutron source with the emission rate of 1.0E7 n.s-1 was utilized in the experiment. The measurement of gamma ambient dose equivalent H*(10) and neutron count rates is performed by the Thermo Scientific RadEye portable survey meter. The simulation part was carried out using the state-of-the-art MCNP6 and SCALE6 MONACO stochastic calculation tools taking into account the detailed geometry of the labyrinth and a combined neutron and gamma source of particles. The comparisons were performed between codes and an experiment, based on the dose rate in the unique detection positions and using a 2D map of neutron and photon fluxes. The propagation of cross-section uncertainties was investigated through the shielding analysis. Partial agreement between codes and measurement was achieved, however serious discrepancies near the PuBe source were identified.

The Mini Labyrinth experiment is a simple neutron and gamma shielding experiment developed at STU, inspired by the ALARM-CF-AIR-LAB-001 ICSBEP benchmark experiment, originally constructed in the former Soviet Union in 1982. Compared to the original Labyrinth, which was made from concrete blocks and had dimension of several meters, the STU Mini Labyrinth is approximately ten times smaller and consists of NEUTRONSTOP shielding blocks. The purpose of this experiment is to validate the computer codes of STU and partners involved in the APVV-DS international project “Experimental and simulation shielding studies of materials used in radiation protection”. This paper gives a brief overview of the experimental workplace and brings the first experimental results and their comparison with computer simulation. The very first experiment performed in the Mini Labyrinth experimental workplace was focused on the measurement of neutron and gamma count rate inside the Mini Labyrinth using the Thermo Scientific RadEye dose meter. The experimental setup also consisted of a PuBe radioisotope neutron source and light water moderator placed in a plastic tank between the neutron source and the detector. The simulation part was carried out using the state-of-the-art MCNP6 and SCALE6 MONACO stochastic calculation tools taking into account the detailed geometry of the labyrinth and a combined neutron- gamma source of particles. The comparisons were performed between codes, based on dose rate in the unique detection positions and using a 3D map of neutron and photon fluxes, using the so called meshtallies. The comparison between the simulated and measured data was performed based on the measured neutron count rate.

A precise surface decoration technique, ion implantation, was examined for tuning the p-type gas sensing properties of CuO nanowires. To understand the effects of ion size, ion beam energy and ion beam fluence, heavy Fe and light N ions were implanted with two different ion beam energies (60, 100 keV) and fluences (1 × 1013, 2.5 × 1016 ions/cm2). The morphological changes after ion bombardments have been tracked by a scanning electron microscope (SEM), revealing massive destruction of the nanowires on Fe ion-implanted samples with high energy and fluence values. Transmission electron microscopy (TEM) provided a closer look on single ion-implanted nanowires, highlighting the different size and mass effects of Fe and N ions. The reduction of CuO peaks intensities registered in GI-XRD profiles and the shifts of Cu 2p peaks in X-ray photoemission spectra (XPS) suggest that the monoclinic crystal structure of the CuO nanowires was transformed to amorphous Cu2O and Cu(OH)2 after ion implantations. All ion-implanted sensors improved their sensing abilities compared to pristine CuO nanowires towards various concentrations of target gases (hydrogen, ethanol, and acetone) at 400 °C in dry air flows. In the presence of humid air, sensors showed different characteristics related to outcomes of surface-ion beam interactions.

The spray pyrolysis is fast and simple method for deposition of CeO2 – rutile TiO2 coatings on stainless steel substrate. The coatings were deposited on stainless steel substrate and characterized by XRD, AFM, XPS, Raman, DRS and photoactivity test for methyl orange decolorization. Photoactivity of CeO2 – rutile TiO2 coatings increase with increasing CeO2 content up to 5 wt% and further increase of CeO2 content leads to decrease of photoactivity. Improvements of photoactivity originate from close contact between CeO2 and rutile TiO2 particles which create numerous centers able to produce very reactive radical species. Besides, the close contact between the CeO2 and rutile TiO2 provides easier charge transfer facilitating the formation of electron/hole pairs that is a necessary step in the overall photocatalytic process.

Pt-Ba-Al 2 O 3 coatings were obtained by spray pyrolysis deposition on stainless steel foil. The XRD results showed that the coatings consisted from Ba carbonate and Pt (fcc) phases. SEM micrographs demonstrated that the coatings are smooth and compact. The XPS data confirmed that Ba and Pt are in close contact. Pt crystallite size is only slightly influenced by the order of Pt and Ba deposition and the dispersion of Pt is in the narrow range from 28 to 33% for all samples. Catalyst component deposition order affects NOx storage capacity. Simultaneous deposition of Ba and Pt on already formed Al 2 O 3 substrate produces the most efficient catalyst. Pt deposited on top of the Ba layer results in slightly reduced NOx storage capacity, while deposition of Pt on the separated layer with Ba layer on top significantly reduces the ability for NOx storage.

A 6H-SiC single crystal implanted in channeling mode by 4-MeV C+3 and Si+3 ions at various doping levels has been examined by scanning electron microscopy (SEM) and micro-Raman spectroscopy in order to study the lattice distortions inflicted by the impinging ions. C ions create zones of strongly damaged regions, parallel to the front face of the wafer with width increasing with the amount of doping. As expected, Si has induced considerably more lattice distortions than C, and more than one order of magnitude less doping induces apparently the same effect as C. Despite the large laser spot size compared with the boundaries of the distorted regions, micro-Raman data provided results agreeing with the SEM pictures and the Monte Carlo calculations using the SRIM-2013 software. From the evolution of the crystalline peaks in the Raman spectra obtained across the damaged area, one can conclude that the impinging ions do not accommodate as defects in the lattice but mostly displace the ions breaking the bonds and destroying the long range order. The spatial correlation model that takes into consideration the intensity variation at the laser spot and the anticipated from Monte Carlo calculations for the collision events can reproduce the trend of the strong transversal optical phonon width indicating nanocrystallites of a few nanometers size in the most damaged area. © 2019 John Wiley & Sons, Ltd.

In this paper, the relationship of structure, type of oxygen defects, valence states of Cr and Ru, and electro- chemical properties of La0.7Sr0.3Cr1-XRuXO3 (0 < x < 0.1) perovskite-type oxides were studied. The samples were synthesized by a conventional solid-state reaction method and characterized by powder X-ray diffraction, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and electron paramagnetic resonance spectroscopy. The electrochemical performance of these samples was evaluated towards the detection of 4-nitrophenol and strongly depends on the concentration of ruthenium incorporated in the crystal lattice. A new La0.7Sr0.3Cr0.925Ru0.075O3 electrocatalyst with a wide linear concentration range (25–5000 mM) and a detection limit of 8 mM was obtained. These results provide an opportunity for its application in the analysis of real water samples.

In this article, the energy loss distributions of relativistic protons axially channeled in the bent 〈1 1 0〉 Si crystal are studied. The crystal thickness is equal to 1 mm, which corresponds to the reduced crystal thickness, Λ, equal to 1.22, whereas the bending angle, α, was varied from 0 to 30 μrad. The proton energy of 7 TeV was chosen in accordance with the concept of using the bent crystals as a tool for selective deflection of the beam halo particles from the LUA9 experiment at LHC. For the continuum interaction potential of the proton and the crystal the Moliere’s expression was used and the energy loss of a proton was calculated by applying the trajectory dependent stopping power model. Further, the uncertainness of the scattering angle of the proton caused by its collisions with the electrons of the crystal and the divergence of the proton beam were taken into account. The energy loss distribution of the channeled protons was obtained via the numerical solution of the proton equations of motion in the transverse plane and the computer simulation method. The analysis of the obtained theoretical data shows that the shape of the energy loss distribution strongly depends on the horizontal or vertical direction of the curvature of the crystal. The number of dechanneled protons as a function of the bending angle also strongly depends on the direction of the crystal’s curvature. As a result, the dechanneling rates and ranges, obtained from the Gompertz type sigmoidal fitting functions, have different sets of values for different bending orientations. We have also studied the influence of the proton beam divergence on the energy loss distribution of channeled protons.

Nanocrystalline TiO2-CeO2 powders were synthesized from their TiO2 and CeO2 oxides using mechanical ball milling process. The response surface method is applied to identify optimal parameters for the synthesis of TiO2-CeO2 photocatalyst. Analysis of variance and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. Regression analysis showed good agreement of experimental data with the second-order polynomial model with a coefficients of determination: R2 = 0.991, R2Adj. = 0.940 and R2Pred. = 0.983. Under optimal experimental conditions of TiO2:CeO2 weight percentage ratio 71:29, milling speed 200 rpm, and milling time 115 min the highest photodegradation efficiency was achieved. On the basis of the above statistical analysis, it was found that the band gap energy of TiO2-CeO2 nanoparticles decreases with the increase of the milling speed and milling time with constant TiO2:CeO2 weight percentage ratio. Obtained results suggest that mechanical ball milling process is a rapid, efficient and low energy consumption method to synthesize TiO2-CeO2 photocatalyst.

The desorption behavior of β-carotene from a bentonite adsorbent under microwave irradiation in isopropanol was studied as a function of temperature and different initial loading concentrations. A first-order, two-component, three-parameter model described the desorption kinetics with a coefficient of determination R2 > 0.9932, and the β-carotene desorption process under microwave irradiation was controlled by both rapid and slow desorption. The activation energies of β-carotene desorption for the rapid and slow desorption processes were 19.61 and 53.04 kJ mol–1, respectively. It was observed that the desorption equilibrium data fitted well to both the Freundlich and Langmuir isotherms. The data obtained from the desorption-isotherm model were used to determine the thermodynamic parameters. The positive value of free energy indicates the non-spontaneity of β-carotene desorption. The change in entropy relative to the enthalpy of desorption reveals that the reaction is physical in nature.

This chapter is devoted to the rainbows occurring in channeling of positrons of incident kinetic energy of E0 = 1 MeV in (11, 9) chiral single-wall carbon nanotubes. As it has been said and explained in Subsect. 2.3.1, the process will be treated using quantum mechanics. In this case, the mass of the projectiles is sufficiently small and their incident kinetic energy sufficiently low that they clearly exhibit their wave properties. As it has been demonstrated in Chap. 1, in such a case, each rainbow is composed of a principal rainbow and one or more supernumerary rainbows. The principal rainbow is the primary, secondary, or a higher order rainbow.

In this chapter, some of the high-resolution proton channeling measurements with a very thin (100) Si crystal conducted by the Singapore group [45–48] will be thoroughly analyzed. Those extraordinary measurements have proven to be crucial for verification of the theory of crystal rainbows as the proper theory of ion channeling in crystals. We shall present the results of three experimental and theoretical studies that were induced by those measurements and performed jointly by us and the Singapore group. The first study leads to the very accurate ion-atom interaction potentials [133]. As a continuation, we shall additionally explore the process that is inverse to the transmission process under consideration, and, thus, fully answer the question of its multiplicity, which is directly connected to the essence of the crystal rainbow effect, being the ion focusing along a line reflecting the symmetry of the illuminated crystal. The second study is devoted to the effect of superfocusing of channeled ions, which is the effect of spatial focusing occurring in the middle of each rainbow cycle [134]. The third study contains the proof that the doughnut effect in ion channeling, occurring with tilted crystals, which has been seen and measured many times, is in fact a crystal rainbow effect [130]. Before presenting the results of the second and third studies, we shall describe in detail the superfocusing and doughnut effects, respectively.

A detailed study of the energy loss distributions of the relativistic protons axially channeled in the bent Si crystals is presented in this work. The bending angle was varied from 0 to 20 μrad, while the crystal thickness was equal to 1 mm. The proton energy was chosen to be 7 TeV in accordance with the Large Hadron Collider (LHC) project, at the European Organization for Nuclear Research (CERN), in Geneva, Switzerland. The energy loss distributions of the channeled protons were generated using the numerical solution of the proton equations of motion in the transverse plane and the computer simulation method. An accurate energy loss model was used, which takes into account the trajectory dependence of the energy loss of protons during their motion through the crystal channels. Further, the dispersion of the proton’s scattering angle caused by its collisions with the electrons of the crystal and the divergence of the proton beam were taken into account. The calculated dependence of the number of dechanneled protons on the bending angle was excellently fitted by the Gompertz type dechanneling function.

Sub-\AA{}ngstr\"om focusing of megaelectronvolt (MeV) ions within axial channels was predicted over 10 years ago, but evidence proved elusive. We present experimental angular distributions of axially channeled MeV protons in a 55-nm-thick (001) silicon membrane through which multiple scattering is negligible. Fine angular structure is in excellent agreement with Monte Carlo simulations based on three interaction potentials, providing indirect evidence of the existence of the superfocusing effect with flux enhancement of around 800 within a focused beam width of $\ensuremath{\sim}20\phantom{\rule{0.16em}{0ex}}\mathrm{pm}$.

Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 2(3) experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5-21 min; acid concentration, 2-7 M; and microwave heating power, 63-172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m(2)g(-1) was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Electrochemical behavior of 12-tungstophosphoric acid (HPW)/acid-activated bentonite (AAB) powders with various loadings of HPW was investigated. The physicochemical properties of the prepared powders were examined by X-ray powder diffraction, nitrogen adsorption-desorption isotherms, atomic force microscopy and cyclic voltammetry measurements. The results indicated that the prepared powders are composed mainly of oriented domains of large rock blocks, probably resulting from a preferable deposition of bentonite particles having a face-to-face interaction. The particles had a mainly disordered mesoporous structure with a pore volume that varied according to the pore size in the range of 2-50 nm. In addition, the particles had crystallite size between 4.9 and 9.0 nm. The electrocatalytic activities of prepared HPW/Aelectrodes were studied in the oxidation of NO2-ions and the results revealed that the electrodes possessed relatively higher nitrite oxidation currents than Aelectrode. The best electroactivity was observed for HPW3/Aelectrode (AAB+20 wt. % HPW) and the limit of detection (3?) was determined as 8 ?M.

This study is devoted to the effect of superfocusing of protons having the energy of 2 MeV in a LT 1 0 0 GT channel of a Si crystal. The analysis is performed by the theory of crystal rainbows. We analyze the superfocusing effect in the first rainbow cycle. The evolution of the spatial distribution of channeled protons is examined by the numerical solution of the proton equations of motion in the transverse position plane. We demonstrate that the superfocusing effect is a reduced crystal rainbow effect, in which the rainbow line comes to a point. (C) 2009 Elsevier B. V. All rights reserved. 23rd International Conference on Atomic Collisions in Solids, Aug 17-22, 2008, Phalaborwa, South Africa

The purpose of this study was to determine the effective operating parameters and the optimum operating conditions of an acid activation process within the framework of improvement of the process. Full two-level factorial and orthogonal central composite design methods were used successively. The examined parameters were the main and interaction effects of temperature, leaching time, acid normality, solid-to-liquid ratio and stirring rate. The selected process response was the leaching yield of the MgO content because Mg is the element most readily removed from the octahedral sheet, which affects the tendency for activation. Statistical regression analysis and analysis of variance were applied to the experimental data to develop a predictive model, which revealed that temperature, leaching time and acid normality exert the strongest influence on the specific surface area of smectite, whilst the solid-to-liquid ratio and the stirring rate have a secondary effect. Furthermore, the highest leaching yield of MgO was found to be 41.86 %, which is responsible for the increase in the specific surface area of up to 221 m2 g-1.

The angular distributions of relativistic protons channeled in the bent 〈1 0 0〉 Si crystals are considered. The ion energy is 7 TeV, the radius of curvature of the crystal is 49.8 m and the crystal thickness is varied from 0.1 to 0.5 cm (before bending), corresponding to the bending angle range from 0.02 to 0.1 mrad. The crystal thickness range under consideration corresponds to the reduced crystal thickness range from 2.1 to 10.35. The angular distributions of transmitted protons were generated by the computer simulation method using the numerical solution of the ion equations of motion, with the Lindhard's expression for the continuum interaction potential of the ion and the crystal. The results of the analysis show that the angular distribution has a periodic behavior for the reduced crystal thickness, Λ, smaller than about 5. For variable Λ larger than 5 the angular distribution is “frozen”, i.e. its shape does not change, and this is accompanied by a slow decrease of the number of transmitted ions as Λ increases.

The theory of crystal rainbows is presented. It enables the generation and full explanation of the angular distribution of ions transmitted through thin crystals. The angular distribution of the transmitted ions is generated by the computer simulation method. Then, the rainbow lines in the scattering angle plane are determined. These lines ensure the full explanation of the angular distribution. The theory is applied to the transmission of ${\mathrm{Ne}}^{10+}$ ions through a 〈100〉 Si thin crystal. The ion energy is 60 MeV and the crystal thickness is varied from 105 to 632 atomic layers, i.e., from the beginning of the first rainbow cycle to the beginning of the second rainbow cycle.

We analyze here the energy dependence of the effect of zero-degree focusing of Ne10+ ions transmitted through the [100] channels of a Si crystal. The thickness of the crystal is 1 mu m and the ion energy is varied from 1.0 to 37 MeV per nucleon. The angular distributions of the transmitted ions were obtained by the computer simulation method using the numerical solution of the equations of motion of the ion, and two continuum interaction potentials of the ion and the crystal - Lindhards potential, and the corresponding catastrophic potential. We demonstrate that the effect of zero-degree focusing is periodic with the respect to variable E-1/2, where E is the ion energy, and that it decays with this variable. This periodicity is explained by the harmonic part of the continuum interaction potential, and the decay is attributed to the anharmonic part of the potential. 3rd International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES), Jul 22-26, 1996, Univ Surrey, Guildford, England

Summary The data on productive and technological characteristics of Victoria variety grown on two trellis systems, pergola and espalier are shown in this paper. Mechanical composition of a bunch and a berry as well as chemical composition of the must were analysed. The results of investigation show that this variety has good results on either of the trellis systems, pergola and espalier in the Strumica vine growing district, the Republic of Macedonia. The Victoria’s bunches from pergola are heavier and longer whereas the bunch and berries are wider, with uniform characteristics of berries and skin colour in comparison with bunches from espalier trellis system.

Using the theory of crystal rainbows, we prove that the well-known doughnut patterns observed in ion channeling in thin crystal membranes are manifestations of the rainbow effect. This is done by a detailed morphological study of the high-resolution experimental angular distributions of 2 MeV protons channeled in a 55-nm-thick (001) silicon crystal tilted away from the [001] direction. The inner side of the doughnut is the dark side of the rainbow, analogous to the Alexander's dark band, occurring between the primary and secondary meteorological rainbows.

The crystal rainbow effect is modeled by the catastrophe theory. It is shown that the 4X9 catastrophe can be treated as the organizing center of the crystal rainbows in the cases of square, rectangular, centered rectangular and hexagonal very thin crystals with one atomic string per primitive cell. This results in a universal, simple and accurate approximation to the continuum potential in the crystal.

Solid surfaces are neither ideally regular, that is, morphological and energetically homogeneous, nor are they fully irregular or fractal. Instead, real solid surfaces exhibit a limited degree of organization quantified by the fractal dimension, D. Fractal analysis was applied to investigate the effect of concentrations of HCl solutions on the structural and textural properties of chemically activated bentonite from southern Serbia. Acid treatment of bentonites is applied in order to remove impurities and various exchangeable cations from bentonite clay. Important physical changes in acid-activated smectite are the increase of the specific surface area and of the average pore volume, depending on acid strength, time and temperature of a treatment. On the basis of the sorption-structure analysis, the fractal dimension of the bentonite surfaces was determined by Mahnke and M?gel method. The fractal dimension evaluated by this method was 2.11 for the AB3 and 1.94 for the AB4.5 sample. The estimation of the values of the fractal dimension of activated bentonites was performed in the region of small pores, 0.5 nm < rp < 2 nm.

Platinum is deposited spontaneously on Au(1 1 1) surface from 1 mM H-2 PtCl6 + 1 M HClO4 solution using multiple deposition procedure. X-ray photoelectron spectroscopy (XPS) analysis has shown that after immersion into the Pt containing solution and rinsing with water, Pt(OH)(2) resides on the Au(1 1 1) substrate. Consecutive depositions as well as in situ scanning tunneling microscopy (STM) and electrochemical measurements are performed on previously electrochemically reduced Pt/Au(1 1 1) surfaces. Only homogeneous distribution of thus deposited Pt islands is observed by in situ STM. With subsequent depositions, the width of deposited Pt islands increases, but stays lower than 10 nm, while a significant increase of Pt islands height is observed, leading to moderate increase of the coverage. Cyclic voltammetry (CV) profiles of obtained Pt/Au(1 1 1) surfaces, and CO stripping curves are recorded in 0.5 M H2SO4 solution. CO oxidation takes place only at higher potentials shifting negatively with increasing coverage. This is discussed with respect to Pt islands width and height distributions and to the influence of the Au(I 11) substrate surface. (C) 2007 Elsevier Ltd. All rights reserved.

Active transition alumina powders were obtained by flash calcination of gibbsite in a reactor for pneumatic transport in the dilute, two-phase flow regime in the temperature interval from 883 to 943 K with a residence time between 0.4 and 0.9 s. The results of X-ray diffraction analysis confirmed that the activated alumina samples were either microcrystalline or amorphous. From nitrogen adsorption-desorption isotherms, the specific surface areas of all samples were calculated by the BET method. Using the sorption data, the fractal dimension of the surface of the alumina samples was calculated according to a modified FHH method. By application of fractal geometry, using the values of the fractal dimension of the surface and of the specific surface area, the effective surface areas of the active aluminas were calculated for the adsorption of molecules having a cross-section area greater than that of the nitrogen molecule. Kratkovremenom termičkom aktivacijom gibsita u reaktoru za pneumatski transport čestica na temperaturama u intervalu od 883 do 943 K i vremenu boravka od 0.4 do 0.9 s dobijen je aktivni prah aluminijumoksida. Rentgenska strukturna analiza pokazala je da dobijeni uzorci imaju visok stepen amorfnosti i mali procenat polaznog gibsita. Na svim uzorcima su određene adsorpciono - desorpcione izoterme azota iz kojih je po BET - metodi izračunata specifična površina. Na osnovu rezultata sorpciono - strukturne analize određene su fraktalne dimenzije površine FHH - metodom, koje su poslužile za sagledavanje efektivne površine uzoraka aktivirane alumine za adsorpciju molekula veće površine poprečnog preseka od molekula azota.

We present here a study of the effect of zero-degree focusing of C6+ ions moving along the (100) channels of a Si crystal. The ion energy is 25 MeV and the thickness of the crystal is varied from 0 to 5000 atomic layers. The angular distributions of the channeled ions were obtained via the numerical solution of the equations of motion of the ion using the Lindhards expression for the continuum interaction potential, and the computer simulation method. The analysis shows that the effect of zero-degree focusing has a periodic behaviour. It also shows that the maxima of the zero-degree yield of the channeled ions decay with the thickness of the crystal. This decay can be described by a sum of two exponential functions. 16th International Conference on Atomic Collisions in Solids (ICACS-16), Jul 17-21, 1995, Linz, Austria

The energy loss distributions of Ne10+ ions channeled in a [100] Si thin crystal are considered. The thickness of the crystal is 500 nm (921 atomic layers), while the ion energy is varied from 1 to 35 MeV per nucleon. The energy loss distributions were obtained by the computer simulation method using the numerical solution of the equations of motion of the ion. We used Lindhards continuum interaction potential of the ion and the crystal, and the Bethe formula for the stopping power of the electron gas of the crystal. The results of the calculations are explained via the effect of zero-degree focusing of the channeled ions and the crystal rainbow effect. 3rd International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES), Jul 22-26, 1996, Univ Surrey, Guildford, England