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While outreach has long been considered an important component of counseling center efforts, the increasing demands for clinical services, along with increased severity and acuity of presenting con...

The radiation resistance of single-phase high entropy alloys has been reported to be superior to conventional alloys, due to their high lattice distortion and sluggish diffusion kinetics. The current study combines the beneficial effects of a concentrated multi-component solid solution and chemical ordering on the parent lattice of a candidate alloy, Al0.3CoFeNi, to enhance proton radiation resistance. The strong ordering tendency in this alloy results in the formation of Ni-Al-rich short-range ordered (SRO) domains when it is annealed in a single FCC phase field and water quenched. The irradiation of these microstructures with high-fluence MeV-energetic protons aids the transformation of the prior metastable single FCC solid-solution with SRO domains toward a more stable condition with L12 long-range ordered (LRO) domains embedded within the FCC solid solution matrix. Potentially, the creation of radiation-induced vacancy cascades within the FCC solid-solution enhances local diffusivity aiding the transition from SRO domains to LRO L12 domains. Therefore, this can be considered as a recovery mechanism, since the radiation-induced damage is not allowed to accumulate and is minimized via nanometer-scale precipitation of the ordered intermetallic phase. Additionally, preferential Co segregation to defect clusters or dislocation loops was also observed. In comparison, purely thermal activation via annealing at 500 °C for 30 min induces a similar transformation from SRO to LRO in this alloy, driving the system closer to equilibrium.

A synthesis process is presented for experimentally simulating modifications in cosmic dust grains using sequential ion implantations or irradiations followed by thermal annealing. Cosmic silicate dust analogues were prepared via implantation of 20–80 ​keV Fe−, Mg−, and O− ions into commercially available p-type silicon (100) wafers. The as-implanted analogues are amorphous with a Mg/(Fe ​+ ​Mg) ratio of 0.5 tailored to match theoretical abundances in circumstellar dusts. Before the ion implantations were performed, Monte-Carlo-based ion-solid interaction codes were used to model the dynamic redistribution of the implanted atoms in the silicon substrate. 600 ​keV helium ion irradiation was performed on one of the samples before thermal annealing. Two samples were thermally annealed at a temperature appropriate for an M-class stellar wind, 1000 ​K, for 8.3 ​h in a vacuum chamber with a pressure of 1 ​× ​10−7 torr. The elemental depth profiles were extracted utilizing Rutherford Backscattering Spectrometry (RBS) in the samples before and after thermal annealing. X-ray diffraction (XRD) analysis was employed for the identification of various phases in crystalline minerals in the annealed analogues. Transmission electron microscopy (TEM) analysis was utilized to identify specific crystal structures. RBS analysis shows redistribution of the implanted Fe, Mg, and O after thermal annealing due to incorporation into the crystal structures for each sample type. XRD patterns along with TEM analysis showed nanocrystalline Mg and Fe oxides with possible incorporation of additional silicate minerals.

An electrostatic quadrupole doublet lens system has been designed and constructed to provide strong, mass-independent focusing of 1–3 MeV ions to a 1 µm2 spot size. The electrostatic doublet consists of four sets of gold electrodes deposited on quartz rods that are positioned in a precision machined rigid frame. The 38 mm electrodes are fixed in a quadrupole doublet arrangement having a bore diameter of 6.35 mm. The coating process allows uniform, 360° coverage with minimal edge defects. Determined via optical interferometry, typical surface roughness is 6 nm peak to valley. Radial and coaxial alignment of the electrodes within the frame is accomplished by using a combination of rigid and adjustable mechanical supports. Axial alignment along the ion beam is accomplished via external manipulators. COMSOL Multiphysics® v5.2 and Propagate Rays and Aberrations by Matrices (PRAM) were used to simulate ion trajectories through the system.

Dilute alloys of bismuth in gallium (98-99% at.) are known from theoretical calculations and x-ray scattering to display a strong segregation of bismuth atoms at the surface, a monatomic layer of bismuth appearing because of the lower surface tension of the Bi compared to the Ga. Rutherford backscattering (RBS) spectra from 2 MeV He+ and 2 MeV C+ on a dilute alloy of Ga(99.8% at.):Bi(0.2% at.) have been measured. A distinct peak in the RBS spectra, corresponding to scattering from the surface of the alloy, is consistent with a monatomic layer of bismuth on the alloy over a range of temperatures for which the alloy is a liquid to room temperature where it is a solid. The peak is not observed when the alloy is cooled to a solid state and this observation is thought to be due to the irregular surface structure of the alloy. Bismuth is also observed to be uniformly distributed throughout the gallium host for the depths studied at these beam energies. Some oxide may be present due to the 10-7 Torr vacuum and the long spectral integration times.

Current prevailing practices maintain a priority on treating the individual students, typically in a medical paradigm that relies on licensed professionals to intervene.Many of the issues that indi...

Sociologists have examined how structural economic change affects household social organization and generation of household income from different sources. The introduction of elements of a market economy into rural Russia in the early 1990s provides a unique opportunity to examine these relationships. Much of the work on this topic, however, has been conducted in black earth zone, agriculturally dependent regions. Less attention has been given to non-black-earth zone, forest resource dependent regions. This article addresses this limitation by comparing the relationships between household income generation strategies and household social organization in a 2009 survey of villages in three forest resource dependent regions in northwest Russia with findings from a 2006 survey of households in nine agricultural regions of Russia. Income generated from enterprises based on household social organization—household labor and social helping networks—is substantially greater in agriculturally dependent than in forest resource dependent regions. We discuss the implications of these findings for understanding intranational regional differences in the relationship between economic systems, household social organization, and rural household economies as well as the obstacles facing policymakers and environmentalists who attempt to shift household income generation strategies away from an environmentally harmful lumber industry to income generation activities that are less harmful to the environment.

TiO2 based nanostructures have been widely explored as photoanodes for dye-sensitized solar cells (DSSCs) because of their favourable band gap and corresponding compatibility with various sensitizers (dye molecules). Various morphologies and textures of titanium oxide have been thoroughly investigated to find the best efficiency in DSSCs. In this work, a detailed study of a nanocomposite of titanium dioxide partly derived from hydrogen titanate precursor has been reported. The current structure is realized in order to achieve optimal photogenerated charge carrier transport and reduced charge recombination. Among many combinations of the composites, the best photoanode showed power conversion efficiency (η) of 8.61% and corresponding open circuit voltage was 0.69 V and short circuit current 17.22 mA cm−2. The efficiency enhancement for the nanorod-nanoparticle composite photoanode is explained by structural, optical, and morphological properties and corroborated with electrochemical impedance spectroscopy.

Meso- and microscale sheet metal forming represents new and attractive solutions to many manufacturing problems for product miniaturization. Larger organizations are utilizing commercially available microscale digital image correlation systems to measure the strains on these scales. The cost of these systems is preventing smaller research and development organizations from entering this challenging area or they are sacrificing the ability to determine strains and evaluate material behavior at the microscale. However, microscale strain grid measurement has the advantage over digital image correlation when the researchers wish to avoid polishing and etching the surface of the sheet metal to make the grain structure visible for digital image correlation and where tooling interferes with obtaining images of the workpiece in real time. This article evaluates the strain measurement and strains resulting from multiscale sheet metal hydroforming operations for annealed 0.2-mm-thick ASTM 304 stainless steel using a simple method for producing microscale grids that has been previously described. The gridding methodology was shown to be accurate with high repeatability. In addition, a strain grid measurement method using an optical microscope and digital camera is described and an error analysis was performed. Provided reasonable care is taken, the inherent error in undeformed parts is 0.76% of true strain for samples with 127 µm grids using the strain measurement system described. The maximum variation in the mesoscale and microscale strain measurement static bulge testing was ±2.4% and more typically ±1.3% of true strain. With care, the errors were reduced to less than 1% of strain. Microscale strains from sheet bulge hydroforming experiments for 11, 5, and 1 mm diameter dies are used to show that the strains measured are reasonable and consistent.

Ion beam analysis (IBA) has been a powerful, non-destructive tool for archaeological research worldwide for over four decades, yet its full potential is seldom realized in North American archaeology. Herein the potential of particle induced X-ray emission spectrometry (PIXE) as a tool for future Ozarks chert provenance studies is evaluated based on its ability to facilitate (1) discrimination of Ozarks chert materials from different geological formations and (2) identification of discrete groups of artifacts from the same geological formation. In addition, PIXE was also used to evaluate the elemental heterogeneity of Ozarks chert materials. Thirty chert (microcrystalline quartz) artifacts were visually sorted and classified according to macroscopic features characteristic of certain chert resources from particular Ozarks geological formations. The elemental concentrations obtained from PIXE analysis underwent multivariate statistical analyses in order to gain insight from the data. The results indicate that PIXE could be a useful tool for assigning Ozarks chert materials to their respective geological formations, and possibly for determining regional or sub-regional provenance.

There exists a critical need to understand the flow and accumulation of metallic ions, both naturally occurring and those introduced to biological systems. In this paper the results of fabricating thin film elemental biological standards containing nearly any combination of trace elements in a protein matrix are presented. Because it is capable of high elemental sensitivity, particle induced X-ray emission spectrometry (PIXE) is an excellent candidate for in situ analysis of biological tissues. Additionally, the utilization of microbeam PIXE allows the determination of elemental concentrations in and around biological cells. However, obtaining elemental reference standards with the same matrix constituents as brain tissue is difficult. An excellent choice for simulating brain-like tissue is Norland® photoengraving glue which is derived from fish skin. Fish glue is water soluble, liquid at room temperature, and resistant to dilute acid. It can also be formed into a thin membrane which dries into a durable, self-supporting film. Elements of interest are introduced to the fish glue in precise volumetric additions of well quantified atomic absorption standard solutions. In this study GeoPIXE analysis package is used to quantify elements intrinsic to the fish glue as well as trace amounts of manganese added to the sample. Elastic (non-Rutherford) backscattered spectroscopy (EBS) and the 1.734 MeV proton-on-carbon 12 C(p,p) 12 C resonance is used for a normalization scheme of the PIXE spectra to account for any discrepancies in X-ray production arising from thickness variation of the prepared standards. It is demonstrated that greater additions of the atomic absorption standard cause a viscosity reduction of the liquid fish glue resulting in thinner films but the film thickness can be monitored by using simultaneous PIXE and EBS proton data acquisition.

Micro and multiscale sheet metal forming processes represent new and attractive solutions to many manufacturing problems. However, evaluating the strains in these products is a difficult endeavor. Larger organizations are utilizing commercially available microscale digital image correlation systems to measure the strains in microscale parts or on macroscale parts with critical microscale features. The cost of these strain measurement systems is preventing smaller research and development organizations from entering this challenging area or they are forgoing the ability to determine strains. The present paper describes the development of a method for creating microscale grids and measuring strains on microscale parts or microscale locations on larger parts. The method developed was able to measure true strains up to 0.618 for square grids that are 127 μm measured from center-to-center. Microscale strains resulting from sheet bulge hydroforming experiments using 11 mm, 5 mm, and 1 mm diameter dies were evaluated and material properties of the sheet metal were estimated based upon the strains measured in conjunction with FEA simulations and compared to analytical solutions and microscale tension tests. The material properties determined using the strains and FEM approach were consistent with the other methods.

Producing fuel cells bipolar plates and other devices such as microscale heat exchangers for electronics requires both macroscale and microscale forming processes. At the macroscale, typically, mechanical properties of sheet metal are determined by performing tensile tests. In addition, it has long been recognized that bi-axial tension tests, dome tests, and hydroforming or viscous bulge tests provide the basis for improved understanding of the mechanics of sheet metal forming. At the microscale strain gauges are too large for measuring strains in small regions and membrane theory is only valid at the poles of the bulge. Continuum mechanics models are useful but require tedious thickness measurements for multiple work pieces, requiring extensive sample preparation and analysis. In this paper experimental results from hydroforming tests for 0.2-mm thick annealed ASTM 304 stainless steel sheet in 11 mm, 5 mm, and 1 mm diameter open dies at various pressures were evaluated. The height of the bulge at the pole and strains based upon measurements of 127 micron strain grids were determined. These dies represent the transition from a small macroscale process to a microscale forming process. Two methods were used to estimate material properties: an analytical model and an iterative method which compared experimental strain results with the strains from a finite element model where the Holloman constitutive properties of the sheet were varied. The problems estimating material properties based upon grid strain measurement, membrane theory, and the iterative finite element approaches were investigated and the results were compared. This study indicates that membrane theory will provide adequate predictions for Holloman constructive properties provided the assumptions for membrane theory are not violated. However, using measured microscale grid deformation strains does not produce very good agreement estimates of the Holloman constitutive model when comparing experimental results with FEA strains. It is believed that while the grid strain measurement method used results in strain measurement errors of less than 1.5% of strain, this error is sufficient to result in enough uncertainty to produce results that are inconsistent with other methods.

This paper investigates the effects of wall thickness and geometric shape of thin-walled structures on their performance during structural analysis. Two automotive thin-walled parts, a front joint panel from a vehicle front structure and a tailgate panel from a truck pickup box were involved in this study. Three types of analyses static analysis, impact analysis, and modal analysis were performed separately on each model to find out the influences of different wall thicknesses on both models’ structural performance. Effects of geometric shape of the models on the analysis results were also discussed. The outcomes of this study provide a solid background for the design of lightweight vehicle architectures to meet the impending energy challenge and will also benefit other industrial sectors such as shipbuilding and aircraft industry.

The newly designed and constructed electrostatic quadrupole doublet (EQD) at the University of North Texas (UNT) has achieved mass independent focusing of MeV particles to a spot size of 3.3 × 3.5 μm. The EQD is compared to the Louisiana magnetic doublet which is also in use at UNT. Characteristics such as demagnification and sensitivity to aberrations are simulated by the matrix raytracing software, propagation of rays and aberrations by matrices and compared for each focusing system. Particle induced x-ray emission (PIXE) maps of a 2000 mesh Cu grid are compared and show that both doublets produce suitable spot sizes for microprobe analysis. A coarser, 200 mesh grid and incident beams of 2 MeV H+ and O+ show the EQD to be stigmatic given common aperture sizes and lens potentials.

As high energy ions travel through a crystalline semiconductor materials they produce damage along the path which results in resistance to some of the wet chemical etching. A series of preliminary experiments have been performed at the Louisiana Accelerator Center (LAC) to examine the feasibility of irradiating high energy (keV–MeV) ions such as protons, xenon and gold through microscale masked structures on crystalline (n-type) Si substrates followed by wet chemical etch with KOH for attaining deep micromachining in Si. The results of these experiments are reported.

The new generation nuclear microprobe system at the Louisiana Accelerator Center in the University of Louisiana at Lafayette consists of a 6.25 m beam line that employs the magnetic quadrupole Sextuplet lens system. This Sextuplet is a zoom system having the same demagnifications, the same focal lengths and the same positions of the focal points in (xoz) and (yoz) planes as in the case for the Russian quadruplet, It also can have the same spherical aberrations in both planes. The parameters which allow obtaining the lowest coefficients of spherical aberration are found for different geometrical configurations of electric and magnetic quadrupole lenses. Specifically, the configuration of a combined Sextuplet consisting of two magnetic and four electrostatic lenses or consisting of two electrostatic and four magnetic lenses is studied and compared with magnetic and electrostatic Sextuplets. The values of the chromatic and spherical aberrations for these combined systems are compared and the minimum spot radius and the half-widths of the corresponding slits for some optimal magnetic and electrostatic Sextuplets are given. sponding for some optimal magnetic and electrostatic Sextuplets are given.

Deep buried layered microstructures have many potential applications as sensors, micro-electro-mechanical systems (MEMS), and optical devices, but it has always been challenging to obtain a minimum number of process steps to produce these structures. A single step ion irradiation process has been used to fabricate buried tunnels with 3 MeV P-beam writing by utilizing enhanced end-of-range damage in thick polymethylmethacrylate (PMMA). Creation of the buried tunnels in PMMA with a single energy irradiation step was found to be strongly dependent on the ion fluence and chemical developing process. The fabrication of a modular large scale complex pattern involving tunneled microstructures is presented as an example of this novel technique.

The high energy focused ion beam (HEFIB) system at the Louisiana Accelerator Center (LAC) of the University of Louisiana at Lafayette, Lafayette, USA, is constructed on one of the beamlines of a National Electrostatics Corporation 1.7 MV 5SDH-2 tandem accelerator. The HEFIB system has several components, including a versatile magnetic quadrupole sextuplet lens focusing system defined as the Russian magnetic sextuplet (RMS) system having the same demagnifications, the same focal lengths and the same positions of the focal points in xz and yz planes as the Russian quadruplet and a one-piece concrete supporting base and integrated endstation with air isolation. A review of recent microlithography and HEFIB system developments at LAC are presented, as well as new results using heavy ion (HI) beam lithography on crystalline silicon.

Energetic (MeV) Au implantation in Si(1 0 0) (n-type) through masked micropatterns has been used to create layers resistant to KOH wet etching. Microscale patterns were produced in PMMA and SU(8) resist coatings on the silicon substrates using P-beam writing and developed. The silicon substrates were subsequently exposed using 1.5 MeV Au3+ ions with fluences as high as 1 × 1016 ions/cm2 and additional patterns were exposed using copper scanning electron microscope calibration grids as masks on the silicon substrates. When wet etched with KOH microstructures were created in the silicon due to the resistance to KOH etching cause by the Au implantation. The process of combining the fabrication of masked patterns with P-beam writing with broad beam Au implantation through the masks can be a promising, cost-effective process for nanostructure engineering with Si.

The term “P-beam writing” is used to describe the technique of using focused high energy proton microbeams for micro or nanofabrication applications. The P-beam technique can be used to rapidly fabricate three-dimensional, high aspect ratio microstructures in a variety of materials without the use of masks and it is proving to be a versatile lithographic method. Recent developments in the application P-beam writing of microstructures at the Louisiana Accelerator Center are presented.

The main difference between quadrupole and axisymmetric charge particle beam focusing systems is that quadrupole systems do not produce a regular image of an object like axisymmetric systems. Because of the special symmetry in geometry and electric or magnetic fields along the axis, only the Russian quadruplet (RQ) can produce an image, however, for each geometry and given maximum field gradient of the RQ, the number of experimentally attainable focal distances in one system is limited to one or two. A new quadrupole focusing system with the same symmetry as the RQ is now under development at the Louisiana Accelerator Center that produces an image and has the possibility to vary the focal distance over a wide range by changing the excitation of the middle lenses. As a result, the magnification may be changed from 10−3 to 10+3 so that this versatile design can be adapted for several applications of high-energy focusing ion beam (HEFIB) systems, including nuclear nanoprobe, scanning microscope or transmission microscope. The configuration of this lens system consists of six quadrupole lenses and although these lenses can be combined either as magnetic (RMS) or electrostatic (RES) sextuplets, the Louisiana Accelerator Center is presently constructing an RMS system due to operational requirements. The zoom capability of the RMS is numerically investigated and the smallest beam spot size and appropriate optimal parameters of the RMS are presented for different emittances and compared with the corresponding parameters of the RQ.

Development of stable high brightness ion sources with accelerators will enhance the capabilities for micro-analysis as well as the micro-fabrication. Recently we have upgraded a Duoplasmatron ion source associated with a 1.7 MV tandem (NEC, Pelletron) accelerator to produce high brightness proton beam for nuclear microprobe application at the Louisiana Accelerator Center. This has substantially increased the ion source life time as well as the accelerator beam brightness. The beam brightness was found to be highly heterogeneous, with paraxial rays about an order of magnitude brighter than surrounding rays.

Once focused, the ion beam in a microprobe can be scanned over the sample by using a set of two orthogonal magnetic coils or electrostatic deflection plates positioned before, inside or after the focusing system. In the paper the influence of the scanner position on the beam spot shape is considered for different focusing systems such as triplet, quadruplet and sextuplet and for two different emittances of the beam. The numerous graphs show the dependence of the shape of the spot and the density distribution of the beam on the scanning radius.

A new quadrupole focusing system-magnetic sextuplet (RMS), with the same symmetry as the Russian quadruplet (RQ), has been proposed and is presently under development. The RMS has the same demagnifications and the same focal lengths as the RQ system and it can have the same spherical aberration in both planes. Its main feature, however, is the capability to change the demagnification over a wide range from 1 to greater than 1000 by changing the excitation of the middle lenses. In the RMS it is possible to obtain a point crossover between the middle lenses with a corresponding minimum sensitivity to the relative rotation of both triplets around the longitudinal axis. By changing the excitation of the middle lenses, the optimal demagnification for every emittance can be found and for every beam emittance it is possible to achieve a minimum spot size by varying the sizes of collimator diaphragms and the distance between them. All capabilities of the RMS are numerically investigated and the smallest beam spot size and appropriate optimal parameters of the system have been found for different emittances.

Several southern magnolia (magnolia grandiflora) tree samples, with known concentrations of mercury, were analyzed using particle induced x-ray emission (PIXE) and neutron activation analysis (NAA). Results from the PIXE measurements indicate that the average mercury absorption percentage was found to be 85 ± 4%. The distribution of mercury was found to be reasonably homogeneous over the sample surface. However, small variations in mercury concentration are most likely caused by the structure of cellulose in the wood. Mercury in the samples appears to be stable to a total integrated charge of 10 μC. Three mercury L-shell x-rays are easily observed in the resulting PIXE spectrum. Using PIXE, the mercury detection limit was calculated to be approximately 1 ppm. With one exception, the measured NAA mercury concentrations were larger than the corresponding mass-based values. The NAA mercury detection limit for the southern magnolia samples was estimated to be about 0.017 ppm (17 ppb).

Until recently, it was difficult to measure properties of individual fluor grains. The development of an accelerator-based nuclear microprobe, as is currently available at the Louisiana Accelerator Center, has made this type of research possible. Using ion beams as small as 1 /spl times/ 1 /spl mu/m (horizontal /spl times/ vertical extent), it is now possible to measure properties of individual fluor grains. Starting in 2000, a research program was initiated to determine the microscopic fluorescence properties for selected rare earth compounds, like Y/sub 2/O/sub 2/S:Eu. Particle-induced X-ray emission (PIXE) was used to characterize individual fluor grains. Individual Y/sub 2/O/sub 2/S:Eu grains are clearly visible in the analysis and are less than 10 /spl mu/m in extent.

Most previous research measures fluorescence properties over the macroscopic regime. Properties of individual microscopic grains could be significantly different than those measured over the macroscopic scale. Until recently, it was difficult to measure properties of individual fluor grains. Existing characterization techniques like scanning electron microscopy are not practical, since the resulting fluorescence masks the electron surface profile. Starting in September 2000, a research program was initiated at the Acadiana Research Laboratory to determine microscopic fluorescence properties for selected inorganic rare earth compounds. The initial phase of this program utilized microscopic proton induced X-ray emission (μPIXE) to characterize the elemental composition of individual fluor grains. Results show that both individual grains and small clusters of grains could be seen using μPIXE. Maps of this type can be used to estimate grain dimensions for the selected rare earth fluor. This technique is a new and innovative method to characterize a fluor material.

This paper investigates the synthesis of Ag NCs in Si(100) substrate by implanting multiple energies and fluences of Ag ions and subsequent thermal annealing.

Understanding the atomic bonding properties at the interface between thin films is crucial to a number of key modern technical devices, including semiconductor integrated circuits, magnetic recording media, batteries, and even solar cells. Semiconducting materials such as titanium nitride (TiNx) are widely used in the manufacturing of modern electronic devices, requiring a wealth of information about its electronic structure. We present data from soft x-ray emission, soft x-ray absorption, and Rutherford backscattering spectroscopy experiments involving a sample consisting of a 40 nm TiN layer on top of an aluminum film 600 nm thick. Soft x-ray emission spectroscopy and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy are tools that provide a nondestructive, atomic site-specific probe of the interface, where the electronic structure of the material can be mapped out element by element. Rutherford backscattering spectroscopy (RBS) measurements supply data on the elemental composition and dep...

Total wet mercury deposition was monitored weekly at six Upper Midwest, USA, sites for a period of six years, 1990--1995, to assess temporal and spatial patterns and contributions to surface waters. Annual wet mercury deposition averaged 7.4 {micro}g Hg/m{sup 2}{center{underscore}dot}yr and showed significant variations between sites and increased trends averaging 0.60 {micro}g Hg/m{sup 1}{center{underscore}dot}yr [8%/yr] over the period. Warm (rain) season wet mercury deposition was found to average 77% of total annual wet deposition. Warm (rain) and cold (snow) season trends showed increases of 0.31 [5.5%/yr] and 0.29 {micro}g Hg/m{sup 2}{center{underscore}dot}yr [17%/yr], respectively. Average annual precipitation depth showed a nonsignificant increase of 0.25 cm/yr [0.4%/yr] for the period. Differences in precipitation depth, mercury concentrations, and wet mercury deposition among sites were noted. Methylmercury wet deposition, measured in 36 weekly samples, averaged about 0.18 ng/L [1.5% of total mercury] in rain and strongly correlated with total mercury, major ions, and precipitation depth.

Titanium samples implanted with 1 MeV gold ions at doses of 8.8 × 1014ions/cm2 to 1.5 × 1016ions/cm2 were allowed to corrode freely in 20 wt% sulfuric acid solution at 40 °C while continuously measuring the open circuit potential (OCP). Inductively Coupled Plasma (ICP), was used to calculate the corrosion rates from the corrosive solutions. The time required for the OCP to drop to a value characteristic of pure titanium in this solution ( − 718 mVSCE), was related to the implant dose. Implantation of gold produced a passivating effect but the observed trend towards passivity persisted beyond the depth of implanted gold. Rutherford Backscattering (RBS) and Nuclear Resonance Scattering (NRS) spectra revealed the presence of oxygen atoms recoil-implanted slightly deeper than the gold. Scanning Tunneling Microscopy (STM) was used to study the differences in surface roughness before and after ion implantation.

Impedance spectroscopy was used to study the corrosion of a nickel implanted steel sample. The dosage was 5 x 10{sup 15} ion/cm{sup 2} and the energy of the nickel ions was 3 MeV. The data from a Simple Randles circuit (R{sub p} and C{sub d1}) were used to explain the corrosion changes observed in a NACE (National Association of Corrosion Engineers) Brine solution (used to emulate geothermal brine conditions) at pH 2.0 and 25{degrees}C in an air saturated solution. Iron concentrations measured by Induction Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) were used to calculate corrosion rates at various time intervals.

Electrostatic tandem accelerators are widely used to accelerate ions for experiments in materials science such as high energy ion implantation, materials modification, and analyses. Many applications require high beam current as well as high beam brightness at the target; thus, maximizing the beam transmission through such electrostatic accelerators becomes important. The Ion Beam Modification and Analysis Laboratory (IBMAL) at University of North Texas is equipped with four accelerators, one of which is a 9SDH-2 3.0 MV National Electrostatic Corporation (NEC) Pelletron® tandem accelerator. The tandem accelerator is equipped with three ion sources: one radio frequency-He ion source (Alphatross) and two ion sources of Cs-sputter type, the SNICS II (Source of Negative Ions by Cesium Sputtering) and a Cs-sputter source for trace-element accelerator based mass spectrometry. This work presents a detailed study of the beam transmission of hydrogen, silicon, and silver ions through the accelerator using the SNICS ion source with injection energies ranging from 20 keV to 70 keV. The beam transmission is quantified for three different terminal voltages: 1.5 MV, 2.0 MV and 2.5 MV. For a given terminal voltage, it has been found that beam transmission is strongly dependent on the ion source injector potential. Details of experiments and data analysis are presented.

The Ion Beam Modification and Analysis Laboratory (IBMAL) at the University of North Texas includes several accelerator facilities with capabilities of producing a variety of ion beams from tens of keV to several MeV in energy. The four accelerators are used for research, graduate and undergraduate education, and industrial applications. The NEC 3MV Pelletron tandem accelerator has three ion sources for negative ions: He Alphatross and two different SNICS-type sputter ion sources. Presently, the tandem accelerator has four high-energy beam transport lines and one low-energy beam transport line directly taken from the negative ion sources for different research experiments. For the low-energy beam line, the ion energy can be varied from ∼20 to 80 keV for ion implantation/modification of materials. The four post-acceleration beam lines include a heavy-ion nuclear microprobe; multi-purpose PIXE, RBS, ERD, NRA, and broad-beam single-event upset; high-energy ion implantation line; and trace-element accelerator mass spectrometry. The NEC 3MV single-ended Pelletron accelerator has an RF ion source mainly for hydrogen, helium and heavier inert gases. We recently installed a capacitive liner to the terminal potential stabilization system for high terminal voltage stability and high-resolution microprobe analysis. The accelerator serves a beam line for standard RBS and RBS/C. Another beamline for high energy focused ion beam application using a magnetic quadrupole lens system is currently under construction. This beam line will also serve for developmental work on an electrostatic lens system. The third accelerator is a 200 kV Cockcroft-Walton accelerator with an RF ion source. The fourth accelerator is a 2.5 MV Van de Graaff accelerator, which was in operation for last several decades is currently planned to be used mainly for educational purpose. Research projects that will be briefly discussed include materials synthesis/modification for photonic, electronic, and magnetic applications, surface sputtering and micro-fabrication of materials, development of high-energy ion microprobe systems, and educational and outreach activities.

Oxygen is known to be an important factor in reducing the corrosion rate of titanium, yet small amounts of oxygen on the titanium surface are practically undetectable by standard Rutherford Backscattering Spectrometry (RBS) analysis. The 3.05 MeV nuclear scattering resonance for 4 He + on oxygen was used in this study to show that surface oxygen is recoil-implanted by collisions with 1 MeV gold ions and produces a noticeable effect on corrosion test results.

An artificially coalified Taxodium peat was used to examine the behavior of inorganic constituents in terrestrial organic matter during the early coalification process. The artificial coal is produced by subjecting the peat to incremental increases in temperature up to 60 °C and pressures to 14.48 MPa over a four-week period in a partially open reactor. A standard polished thin section 30 μm thick is then cut from the resulting disk and examined using light microscopy to select and mark areas to be cut from the polished thin section. The distribution of inorganic constituents in these areas of the solid produced during the coalification process is then studied using nuclear microscopy. Results suggest that concentrations of inorganic constituents, including silicon, are lower in the newly produced solids than in the initial material. Distributions of other inorganic elements, including aluminum, sulfur, chlorine, potassium, calcium, barium and iron are also investigated.

Most of the mercury contamination in lakes and streams of nonindustrialized regions of the United States and Canada is derived from atmospheric deposition. In order to determine the regional patterns of these inputs, seven mercury-in-precipitation monitoring sites were established in Minnesota, North Dakota, and Michigan. A 3-year study showed that the magnitude of mercury deposition was dominated by the quantity of precipitation. Regional variations of mercury concentrations in precipitation were mostly explained by precipitation rate with higher concentrations occurring in the summer. Statewide (Minnesota) annual mercury emission estimates exceeded depositions for 1990, 1991, and 1992 by a factor of approximately 2 and indicated long-range transport of mercury. Significant correlations were observed between concentrations of mercury and other ions in precipitation.

Beam focusing is understood as the result of non-linear motion of a set of particles. As a result of this motion, we have the beam spot on the target. The set has a volume (the phase volume, or emittance). For a given brightness, the phase volume is proportional to the beam current and vice versa. The beam has an envelope surface. All particles of the beam are located inside of this surface, inside of this beam envelope. For the same phase volume (or beam current) the shape of the beam envelope can be different. We say the beam envelope is optimal if the spot size on the target has a minimum value for a given emittance. The essential feature of our optimization is the matrix approach for non-linear beam motion. In this approach we obtain and use analytical expressions for the matrizant (or transfer matrix) and for the envelope matrix. This matrix technique is known as the Matrizant method.

The focusing system is an essential part of any ion microbeam system and focusing of MeV ion beams is generally accomplished using quadrupole lenses. There are two types of quadrupole lenses requiring the application of either voltage or current to provide the excitation, but there is also the possibility of utilizing lenses constructed from permanent magnets. All of these lens types have different advantages and disadvantages. Most microprobes employ electromagnetic quadrupoles for focusing, however electrostatic lenses have several advantages with respect to electromagnetic lenses, including significantly smaller size, no hysteresis effects, no heating, the utilization of highly stable voltage supplies, focusing which is independent of ion mass, and construction from industrial grade materials. The main advantage of the permanent magnetic lens is that it does not require the application of external power which can significantly reduce the overall lifetime cost. In this presentation, the short probe‐forming systems comprised from all these types of quadrupole lenses are compared and the smallest beam spot size and appropriate optimal parameters of these probe‐forming systems are determined.

The interest in assessing environmental pollution using tree ring analysis has increased in recent years. However, attempts to link metal deposition in tree rings to environmental pollution should be evaluated cautiously. In order to investigate the variation of the trace element distribution at two heights and two positions, four cores were extracted from a 60 year-old water oak (Quercus nigra). Experimental results show variations in the distribution of metals in different cores. These differences were not due to sample preparation, but possibly to differential deposition in the tree. The results indicate that caution must be exercised when attempting to link trace element studies of tree rings to pollution chronology of the surrounding environment.