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Item Open Access The clusters growth and evaporation rate constante calculation by using of molecular dynamics method for condensation behind the shock front(Matem. Mod., 1993) Insepov, Z.; Karatajev, E. M.Molecular dynamics model of calculation of the growth and evaporation rate constants of dusters is proposed. Calculations for small clusters are carried out. On the basis of the chemical mechanism the characteristic time of condensation is achieved, which is in available agreement with experiment on condensation of iron vapors behind the shock front.Item Open Access Molecular-dynamics simulation of thin-film growth by energetic cluster impact(Physical Review B, 1995) Haberland, H.; Insepov, Z.; Moseler, M.Langevin-molecular-dynamics simulations of thin-film growth by energetic cluster impact were carried out. The impact of a Mo 1043 cluster on a Mo(001) surface was studied for impact energies of 0.1, 1, and 10 eV/atom using the Finnis-Sinclair many-body potential. The characteristics of the collision range from a soft touchdown at 0.1 eV/atom, over a flattening collision at 1 eV/atom, to a meteoric impact at 10 eV/atom. The highest energy impact creates a pressure of about 100 GPa in the impact zone and sends a strong shock wave into the material. The cluster temperature reaches a maximum of 596 K for 0.1 eV/atom, 1799 K for 1 eV/atom, and 6607 K for 10 eV/atom during the first ps after the touchdown. For energies of 1 and 10 eV/atom the cluster recrystallizes after 20 ps. The consecutive collision of 50 Mo 1043 clusters with a Mo(001) surface at T=300 K was simulated for the three impact energies. The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.Item Open Access Proposal for a hardness measurement technique without indentor by gas-cluster-beam bombardment(Physical Review B, 2000) Insepov, Z.; Manory, R.; Matsuo, J.; Yamada, I.Large gas-cluster-ion bombardment has been shown to be a unique tool for generating a variety of bombarding effects over a broad range of acceleration energies. A hardness measurement technique is proposed in this paper based on the use of the effect of crater formation by large gas-cluster beams. The cluster impact leaves a hemispherical crater on a surface, the size of which varies with surface hardness and cluster parameters ~which can be predetermined!. As shown in this paper, the crater depth h ~or diameter d! and Brinell hardness B are correlated through the formula h;(E/B)1/3, where E is the cluster acceleration energy. The material hardness, binding energy, and the crater size have also been correlated with the sputtering yield Y, and hence this correlation can also be experimentally applied for measuring hardness. The proposed method is based entirely on surface effects which depend only on the surface material and not on the substrate and therefore should be particularly suitable for measuring hardness of thin deposited films. This technique also eliminates the need for indentors that are harder than the material measured.Item Open Access Craters on silicon surfaces created by gas cluster ion impacts(Journal of applied physics, 2002) Allen, L. P.; Insepov, Z.; Fenner, D. B.; Santeufemio, C.; Brooks, W.; Jones, K. S.; Yamada, I.Atomic force microscopy ~AFM! and high-resolution transmission electron microscope ~HRTEM! cross section imaging of individual gas cluster ion impact craters on Si~100! and Si~111! substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O2 gas sources is shown. Results for low fluence (1010 ions/cm2) 24 kV Ar individual cluster impacts onto a Si~100! and Si~111! substrate surfaces are compared with hybrid molecular dynamics ~HMD! simulations. A HMD method is used for modeling impacts of Arn (n5135, 225! clusters, with energies of 24–50 eV/atom, on Si~100! and Si~111! surfaces. On a Si~100!, craters are nearly triangular in cross section, with the facets directed along the close-packed ~111! planes. The Si~100! craters exhibit four-fold symmetry as imaged by cross-sectional HRTEM, and AFM top view, in agreement with modeling. In contrast, the shape of craters on a Si~111! shows a complicated six-pointed shape in the modeling, while AFM indicates three-fold symmetry of the impact. The lower energy 3 kV individual cluster impacts reveal the same crater shape in HRTEM cross section for both Ar and O2 gas clusters, but with shallower crater depth than for the higher-energy impacts. The kinetics of the Ar and O2 crater impacts may explain the successful use of higher-energy cluster impacts for etching material of higher initial surface roughness followed by the lower energy impacts as an effective finishing step to achieve smoother surfaces.Item Open Access New mechanism of cluster-field evaporation in rf breakdown(Physical Review Special Topics-Accelerators and Beams, 2004) Insepov, Z.; Norem, J. H.; Hassanein, A.Using a simple field evaporation model and molecular dynamics simulations of nanoscale copper tip evolution in a high electric field gradient typical for linacs, we have studied a new mechanism for rf-field evaporation. The mechanism consists of simultaneous (collective) field evaporation of a large group of tip atoms in high-gradient fields. Thus, evaporation of large clusters is energetically more favorable when compared with the conventional, ‘‘one-by-one’’ mechanism. The studied mechanism could also be considered a new mechanism for the triggering of rf-vacuum breakdown. This paper discusses the mechanism and the experimental data available for electric field evaporation of field emission microscopy tips.Item Open Access Effects of surface damage on rf cavity operation(Physical Review Special Topics-Accelerators and Beams, 2006) Hassanein, A.; Insepov, Z.; Norem, J.; Moretti, A.; Qian, Z.; Bross, A.; Seidman, D. N.We describe a model of damage in rf cavities and show how this damage can limit cavity operation. We first present a review of mechanisms that may or may not affect the ultimate fields that can be obtained in rf cavities, assuming that mechanical stress explains the triggers of rf breakdown events. We present a method of quantifying the surface damage caused by breakdown events in terms of the spectrum of field enhancement factors, , for asperities on the surface. We then model an equilibrium that can develop between damage and conditioning effects, and show how this equilibrium can determine cavity performance and show experimental evidence for this mechanism. We define three functions that quantify damage, and explain how the parameters that determine performance can be factored out and measured. We then show how this model can quantitatively explain the dependence of cavity performance on material, frequency, pulse length, gas, power supply, and other factors. The examples given in this paper are derived from a variety of incomplete data sets, so we outline an experimental program that should improve these predictions, provide mechanisms for comparing data from different facilities, and fill in many gaps in the existing data.Item Open Access Requirements for advanced simulation of nuclear reactor and chemicalseparation plants(Argonne National Laboratory, 2006) Palmiotti, G.; Cahalan, J.; Pfeiffer, P.; Sofu, T.; Taiwo, T.; Wei, T.; Willamson, M.This report presents requirements for advanced simulation of nuclear reactor and chemical processing plants that are of interest to the Global Nuclear Energy Partnership (GNEP) initiative. Justification for advanced simulation and some examples of grand challenges that will benefit from it are provided. An integrated software tool that has its main components, whenever possible based on first principles, is proposed as possible future approach for dealing with the complex problems linked to the simulation of nuclear reactor and chemical processing plants. The main benefits that are associated with a better integrated simulation have been identified as: a reduction of design margins, a decrease of the number of experiments in support of the design process, a shortening of the developmental design cycle, and a better understanding of the physical phenomena and the related underlying fundamental processes. For each component of the proposed integrated software tool, background information, functional requirements, current tools and approach, and proposed future approaches have been provided. Whenever possible, current uncertainties have been quoted and existing limitations have been presented. Desired target accuracies with associated benefits to the different aspects of the nuclear reactor and chemical processing plants were also given. In many cases the possible gains associated with a better simulation have been identified, quantified, and translated into economical benefits.Item Open Access Surface erosion and modification by highly charged ions(Physical Review A, 2008) Insepov, Z.; Terasawa, M.; Takayama, K.Analyses were conducted of various models and mechanisms of highly charged ion HCI and swift-heavy ion energy transfer into a solid target, such as hollow atom formation, charge screening, neutralization, shock wave generation, crater formation, and sputtering. A plasma model of space charge neutralization based on impact ionization of semiconductors at high electric fields was developed and applied to analyze HCI impacts on Si and W. Surface erosion of semiconductor and metal surfaces caused by HCI bombardments were studied by using a molecular dynamics simulation method, and the results were compared with experimental sputtering data.Item Open Access A model of rf breakdown arcs(Fermilab, 2008) Insepov, Z.; Bross, A.; Qian, Z.; Norem, J.; Huang, D.; Veitzer, S.; Torun, Y.This paper presents a rst iteration of a model that attempts to describe all aspects of breakdown in rf cavities and provides some estimates of the parameters and parameter ranges involved, as an aid to producing more precise models and more useful experiments. The model describes how breakdown events can be triggered, how they grow, it identi es the power source for their rapid growth, mechanisms that limit their growth, how they are extinguished and how they can be mitigated. We also discuss applications to superconducting rf and high pressure gas structures. The model relies heavily on previous experiments with 805 and 201 MHz warm copper cavities, and pre-liminary plasma modeling using the code OOPIC Pro. We compare estimates from the model with experimental data where this is possible. Because of the geometrical dependence of all parameters, the wide range of experiments being performed, the wide range of experimental parameters in a given breakdown event and the lack of extensive systematic parameter searches at this stage in our studies, it is diffcult to present precise results. We are constrained to showing what mechanisms are involved, the strength of these mechanisms and how they interact to produce the experimental data. We are primarily interested in the development and dynamics of the arc, magnetic and gas effects and insights on how to avoid arcing in all environments.Item Open Access A New Multiscale Approach to Nuclear Fuel Simulations: Atomistic Validation of Kinetic Method(Transactions of the American Nuclear Society, 2010) Insepov, Z.; Rest, J.; Hofman, G. L.; Yacout, A.; Norman, G. E.; Starikov, S. A.; Stegailov, V. V.A key issue for fuel behavior codes is their sensitivity to values of various materials properties, many of which have large uncertainties or have not been measured. Kinetic mesoscale models, such as those developed at Argonne National Laboratory within the past decade, are directly comparable to data obtained from in-reactor experiments. In the present paper, a new multiscale concept is proposed that consists of using atomistic simulation methods to verify the kinetic approach. The new concept includes kinetic rate-equations for radiation damage, energetics and kinetics of defects, and gas/defect-driven swelling of fuels as a function of temperature and burnup. The quantum and classical atomistic simulation methods are applied to increase our understanding of radiation damage and defect formation and growth processes and to calculate the probabilities of elemental processes and reactions that are applicable to irradiated nuclear materials.Item Open Access MECHANISTIC INSIGHT INTO THE ROLE OF POLY(ADP-RIBOSYL)ATION IN DNA TOPOLOGY MODULATION AND RESPONSE TO DNA DAMAGE(Mutagenesis, 2010) Matkarimov, Bakhyt T.; Zharkov, Dmitry O.; Saparbaev, Murat K.Genotoxic stress generates single- and double-strand DNA breaks either through direct damage by reactive oxygen species or as intermediates of DNA repair. Failure to detect and repair DNA strand breaks leads to deleterious consequences such as chromosomal aberrations, genomic instability and cell death. DNA strand breaks disrupt the superhelical state of cellular DNA, which further disturbs the chromatin architecture and gene activity regulation. Proteins from the poly(ADP ribose) polymerase (PARP) family, such as PARP1 and PARP2, use NAD+ as a substrate to catalyse the synthesis of polymeric chains consisting of ADP-ribose units covalently attached to an acceptor molecule. PARP1 and PARP2 are regarded as DNA damage sensors that, upon activation by strand breaks, poly(ADP-ribosyl)ate themselves and nuclear acceptor proteins. Noteworthy, the regularly branched structure of poly(ADP-ribose) polymer suggests that the mechanism of its synthesis may involve circular movement of PARP1 around the DNA helix, with a branching point in PAR corresponding to one complete 360° turn. We propose that PARP1 stays bound to a DNA strand break end, but rotates around the helix displaced by the growing poly(ADP-ribose) chain, and that this rotation could introduce positive supercoils into damaged chromosomal DNA. This topology modulation would enable nucleosome displacement and chromatin decondensation around the lesion site, facilitating the access of DNA repair proteins or transcription factors. PARP1-mediated DNA supercoiling can be transmitted over long distances, resulting in changes in the high-order chromatin structures. The available structures of PARP1 are consistent with the strand break induced PAR synthesis as a driving force for PARP1 rotation around the DNA axis.Item Open Access Modeling Vacuum Arcs(arXiv preprint arXiv:1006.3770, 2010) Insepov, Z.; Norem, J.; Proslier, T.; Huang, D.; Mahalingam, S.; Veitzer, S.Item Open Access Modification on surface oxide layer structure and surface morphology of niobium by gas cluster ion beam treatments(Physical Review Special Topics-Accelerators and Beams, 2010) Wu, A. T.; Swenson, D. R.; Insepov, Z.Recently, it was demonstrated that significant reductions in field emission on Nb surfaces could be achieved by means of a new surface treatment technique called gas cluster ion beam (GCIB). Further study as shown in this paper revealed that GCIB treatments could modify surface irregularities and remove surface asperities leading to a smoother surface finish as demonstrated through measurements using a 3D profilometer, an atomic force microscope, and a scanning electron microscope. These experimental observations were supported by computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics. Measurements employing a secondary ion mass spectrometry found that GCIB could also alter Nb surface oxide layer structure. Possible implications of the experimental results on the performance of Nb superconducting radiofrequency cavities treated by GCIB will be discussed. First experimental results on Nb single-cell superconducting radiofrequency cavities treated by GCIB will be reported.Item Open Access Modeling RF breakdown arcs(arXiv preprint arXiv:1003.1736, 2010) Insepov, Z.; Norem, J.; Proslier, T.; Huang, D.; Mahalingam, S.; Veitzer, S.We describe breakdown in 805 MHz rf accelerator cavities in terms of a number of self-consistent mechanisms. We divide the breakdown process into three stages: (1) we model surface failure using molecular dynamics of fracture caused by electrostatic tensile stress, (2) we model the ionization of neutrals responsible for plasma initiation and plasma growth using a particle-in-cell code, and (3) we model surface damage by assuming a process similar to unipolar arcing. We nd that the cold, dense plasma in contact with the surface produces very small Debye lengths and very high electric fields over a large area, consistent with unipolar arc behavior, although unipolar arcs are strictly de ned with equipotential boundaries. These high elds produce strong erosion mechanisms, primarily self-sputtering, compatible with the crater formation that we see. We use the OOPIC model to estimate very high surface electric elds in the dense plasma and measure these elds using electrohydrodynamic arguments to relate the dimensions of surface damage with the applied electric eld. We also present a geometrical explanation of the large enhancement factors of field emitters.This is consistent with the apparent absence of whiskers on surfaces exposed to high elds. The enhancement factors we derive, when combined with Fowler-Nordheim analysis, produce a consistent picture of breakdown and eld emission from surfaces at local elds of 7{10 GV/m. We show that the plasma growth rates we obtain from OOPIC are consistent with growth rates of the cavity shorting currents using x-ray measurements. We believe the general picture presented here for rf breakdown arcs should be directly applicable to a larger class of vacuum arcs. Results from the plasma simulation are included as a guide to experimental veri cation of this model.Item Open Access Radiation-induced damage and evolution of defects in Mo(Physical Review B, 2011) Starikov, S. V.; Insepov, Z.; Rest, J.; Kuksin, A. Y.; Norman, G. E.; Stegailov, V. V.; Yanilkin, A. V.The formation of defects in bcc Mo lattice as a result of 50-keV Xe bombardment is studied via atomistic simulation with an interatomic potential developed using the force-matching ab initio based approach. The defect evolution in the cascade is described. Diffusion and interaction of interstitials and vacancies are analyzed. Only small interstitial atom clusters form directly in the cascade. Larger clusters grow only via aggregation at temperatures up to 2000 K. Stable forms of clusters demonstrate one-dimensional diffusion with a very high diffusion coefficient and escape quickly to the open surface. Point vacancies have much lower diffusivity and do not aggregate. The possibility of a large prismatic vacancy loop formation near the impact surface as a result of fast recrystallization is revealed. The mobility of the vacancy dislocation loop segments is high, however, the motion of the entire loops is strongly hindered by neighbor point defects. This paper explains the existence of the large prismatic vacancy loops and the absence of the interstitial loops in the recent experiments with ion irradiation of Mo foils.Item Metadata only The influence of the Lop Nor Nuclear Weapons Test Base to the population of the Republic of Kazakhstan(Radiation Measurements, 2011-04-01) Zhumadilov, Kassym; Ivannikov, Alexander; Zharlyganova, Dinara; Stepanenko, Valeriy; Zhumadilov, Zhaxybay; Apsalikov, Kazbek; Toyoda, Shin; Endo, Satoru; Tanaka, Kenichi; Miyazawa, Chuzou; Okamoto, Tetsuji; Hoshi, Masaharu; Kassym, ZhumadilovAbstract The method of electron spin resonance (ESR) dosimetry was applied to human tooth enamel to obtain estimates of individual absorbed dose for residents of Makanchi, Urdzhar and Taskesken settlements located near the Kazakhstan–Chinese border (about 400 km to the South–East, from the Semipalatinsk Nuclear Test Site (SNTS) and about 1000 km from the Lop Nor Nuclear Weapons Test Base, China). Since the ground and atmospheric nuclear tests (1964–1981) at Lop Nor, the people residing in these settlements are believed to have been heavily exposed to radioactive fallout. Tooth samples had been extracted for medical reasons during the course of ordinary dental treatment. The village of Kokpekty, located 400 km to the South–east of the SNTS, was chosen as the control group since it has not been subjected to any radioactive contamination. The mean excess doses in tooth enamel obtained after subtraction of the contribution of natural background radiation do not exceed 62 ± 28 mGy, 64 ± 30 mGy, 49 ± 27 mGy and −19 ± 36 mGy for all ages of the residents of Makanchi, Urdzhar, Taskesken and the control village of Kokpekty, respectively.Item Metadata only ESR dosimetry study for the residents of Kazakhstan exposed to radioactive fallout on 24, August 1956(Radiation Measurements, 2011-09-01) Zhumadilov, K.; Ivannikov, A.; Zharlyganova, D.; Zhumadilov, Zh.; Stepanenko, V.; Abralina, Sh.; Sadvokasova, L.; Zhumadilova, A.; Toyoda, S.; Endo, S.; Okamoto, T.; Hoshi, M.; K., ZhumadilovAbstract The method of electron spin resonance (ESR) dosimetry has been applied to human tooth enamel in order to obtain individual absorbed doses from the population of settlements within the vicinity of the central axis of the radioactive fallout trace from the contaminating nuclear surface test of 24, August 1956. Most of the settlements (Glubokoe, Tavriya, and Gagarino) are located near Ust-Kamenogorsk city, in Kazakhstan (about 400 km to the east from the epicenter of the explosion at the Semipalatinsk Nuclear Test Site (SNTS)). It was found that the excess doses obtained after the subtraction of natural background radiation ranged up to about 120 mGy for the residents of Ust-Kamenogorsk city, whose tooth enamel was formed before 1956. For the residents of Gagarino, excess doses do not exceed 47 mGy for all ages. For the residents of Tavriya, the maximum of excess dose was determined as 54 mGy and for the residents of Glubokoe, the maximum excess dose was about 83 mGy. For the population of the Shemonaikha settlements (about 70 km from the centerline of the radioactive fallout trace) the highest excess dose is 110 mGy. Also for this study, Znamenka village (about 130 km from the epicenter) was included. The Kokpekty settlement was chosen as a control and not subjected to any radioactive contamination and is located 400 km to the Southeast from SNTS.Item Open Access Secondary electron yield of emissive materials for large-area micro-channel plate detectors: surface composition and film thickness dependencies(Physics Procedia, 2012) Jokela, S. J.; Veryovkin, I. V.; Zinovev, A. V.; Elam, J. W.; Mane, A. U.; Peng, Q.; Insepov, Z.The ongoing development of Atomic Layer Deposition (ALD) enables the use of relatively inexpensive and robust borosilicate micro-channel substrates for use as Micro-Channel Plates (MCPs). The surfaces of the channels in these glass plates are functionalized to control the conductivity as well as the Secondary Electron Yield (SEY). The extensive SEY data found in literature show significant variation for a given material depending on the apparatus, the measurement procedure, and the sample preparation and handling. We present systematic studies on the effects of film thickness and surface chemical composition on SEY. We have modified an existing ultra-high vacuum apparatus containing X-ray and Ultraviolet Photoelectron Spectrometers (XPS and UPS, respectively) by adding a modified Low Energy Electron Diffraction (LEED) module for SEY measurements. With these tools, we have characterized the secondary electron emissive properties for MgO, Al2O3, and multilayered MgO/TiO2 structures to serve as electron emissive layers in the channels of the MCPs.Item Open Access Simulation of Ion Irradiation of Nuclear Materials and Comparison with Experiment(arXiv preprint arXiv:1203.0327, 2012) Insepov, Z.; Kuksin, A.; Rest, J.; Starikov, S.; Yanilkin, A.; Yacout, A. M.; Yun, D.Radiation defects generated in various nuclear materials such as Mo and CeO2, used as a surrogate material for UO2, formed by sub-MeV Xe and Kr ion implantations were studied via TRIM and MD codes. Calculated results were compared with defect distributions in CeO2 crystals obtained from experiments by implantation of these ions at the doses of 11017 ions/cm2 at several temperatures. A combination of in situ TEM (Transmission Electron Microscopy) and ex situ TEM experiments on Mo were used to study the evolution of defect clusters during implantation of Xe and Kr ions at energies of 150-700 keV, depending on the experimental conditions. The simulation and irradiation were performed on thin film single crystal materials. The formation of defects, dislocations, and solid-state precipitates were studied by simulation and compared to experiment. Void and bubble formation rates are estimated based on a new mesoscale approach that combines experiment with the kinetic models validated by atomistic and Ab-initio simulations. Various sets of quantitative experimental results were obtained to characterize the dose and temperature effects of irradiation. These experimental results include size distributions of dislocation loops, voids and gas bubble structures created by irradiation.Item Open Access Sheath parameters for non-Debye plasmas: Simulations and arc damage(Physical Review Special Topics-Accelerators and Beams, 2012) Morozov, I. V.; Norman, G. E.; Insepov, Z.; Norem, J.This paper describes the surface environment of the dense plasma arcs that damage rf accelerators, tokamaks, and other high gradient structures. We simulate the dense, nonideal plasma sheath near a metallic surface using molecular dynamics (MD) to evaluate sheaths in the non-Debye region for high density, low temperature plasmas. We use direct two-component MD simulations where the interactions between all electrons and ions are computed explicitly. We find that the non-Debye sheath can be extrapolated from the Debye sheath parameters with small corrections. We find that these parameters are roughly consistent with previous particle-in-cell code estimates, pointing to densities in the range 1024–1025 m 3. The high surface fields implied by these results could produce field emission that would short the sheath and cause an instability in the time evolution of the arc, and this mechanism could limit the maximum density and surface field in the arc. These results also provide a way of understanding how the properties of the arc depend on the properties (sublimation energy, for example) of the metal. Using these results, and equating surface tension and plasma pressure, it is possible to infer a range of plasma densities and sheath potentials from scanning electron microscope images of arc damage. We find that the high density plasma these results imply and the level of plasma pressure they would produce is consistent with arc damage on a scale 100 nm or less, in examples where the liquid metal would cool before this structure would be lost. We find that the submicron component of arc damage, the burn voltage, and fluctuations in the visible light production of arcs may be the most direct indicators of the parameters of the dense plasma arc, and the most useful diagnostics of the mechanisms limiting gradients in accelerators.