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Description: A search was made for a resonant, final-state interaction between carbon ions produced in the reactions {sup 12}C + {sup 16}O {yields} a + {sup 12}C + {sup 12}C and {sup 13}C + {sup 16}O {yields} {alpha} + {sup 12}C + {sup 13}C at E{sub lab} = 140 MeV. However, the {alpha}-{sup 12}C coincidence spectra for both {sup 12}C and {sup 13}C targets were instead found to be dominated by the excitation and subsequent {alpha} decay of states in the projectile.
Date: June 1, 1980
Creator: Rae, W.D.; Stokstad, R.G.; Harvey, B.G.; Dacal, A.; LeGrain, R.; Mahoney, J. et al.
Partner: UNT Libraries Government Documents Department

L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions

Description: Article discussing research on L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions.
Date: October 15, 1987
Creator: Andrews, M. C.; McDaniel, Floyd Del. (Floyd Delbert), 1942-; Duggan, Jerome L.; Miller, P. D.; Pepmiller, P. L.; Krause, H. F. et al.
Partner: UNT College of Arts and Sciences

Precise measurements of the energy losses of heavy ions

Description: Accurate measurements of the energy loss of all charged particles are needed to determine the reliability of the Bethe theory of stopping power. Few measurements have been made for particles with energies greater than 20 MeV/u. A first step to accurate measurements is to establish the precision of an experimental method. The authors report here about the recent energy loss measurements for 290 MeV/u carbon ions from the HIMAC. They have been made with the method used for 70 MeV protons. The ion beam traverses an absorber of thickness t and the residual range of the ions is measured with a water container of adjustable thickness (``range gauge``).
Date: December 31, 1995
Creator: Bichsel, H. & Hiraoka, T.
Partner: UNT Libraries Government Documents Department

Carbon implanted in optical grade fused silica: annealing effects in reducing and oxidizing atmospheres

Description: Carbon is implanted into fused silica with doses of 1, 3, 6, 10X10{sup 16} ions/cm{sup 2}. Infrared spectroscopy identified the formation of CO and CO{sub 2} molecules in the implanted glasses. Relations among concentrations of carbon dioxide, carbon monoxide, and carbon doses are established by the infrared measurements. Annealing under different atmospheres have dramatic effects on CO and CO{sub 2} concentrations.
Date: January 1, 1997
Creator: Tsung, Y.S.; Mu, R.; Ueda, A.; Henderson, D.O.; Wang, P.W.; White, C.W. et al.
Partner: UNT Libraries Government Documents Department

Neutron and proton therapy in the treatment of cancer

Description: Several decades of clinical research have established that neutron and proton therapy constitute useful and practical additions to the radiation oncologist`s treatment modalities. This paper discusses the rationale for using these therapies and describes practical solutions to their implementation.
Date: August 1, 1996
Creator: Lennox, A.J.
Partner: UNT Libraries Government Documents Department

Growth and mechanical and tribological characterization of multi-layer hard carbon films

Description: Vacuum-arc deposition is used to deposit multilayer C films by modulating the sample bias during deposition. Effect of varying the sublayer thickness in multilayer films consisting of alternating layers of ``hard`` (68.4 GPa, -100 V bias) and ``soft`` (27.5 GPa, - 200 V bias) was investigated. Films consisting of equal thickness layers of hard and soft material and an individual layer thickness varying from 10 to 35 nm were deposited. Mechanical property measurements were obtained by finite element modeling of nanoindentation load-displacement curves. The film hardness values were about 20% below the average of the component layers and relatively independent of the layer thickness. TEM revealed deterioration of the multilayer structure when the sublayer thickness was below 15 nm due to implantation damage of the hard layers caused by the energetic C{sup +} ions of the soft layers (-2000 V bias) deposited over them. Pin-on-disk wear tests show that the wear rate drops when sublayer thickness is decreased below 20 nm and remains constant with further decreases in the layer thickness.
Date: December 31, 1996
Creator: Ager, J.; Brown, I.; Monteiro, O.; Knapp, J.A.; Follstaedt, D.M.; Nastasi, M. et al.
Partner: UNT Libraries Government Documents Department

Surface Engineering of Silicon and Carbon by Pulsed-Laser Ablation

Description: Experiments are described in which a focused pulsed-excimer laser beam is used either to ablate a graphite target and deposit hydrogen-free amorphous carbon films, or to directly texture a silicon surface and produce arrays of high-aspect-ratio silicon microcolumns. In the first case, diamond-like carbon (or tetrahedral amorphous carbon, ta-C) films were deposited with the experimental conditions selected so that the masses and kinetic energies of incident carbon species were reasonably well controlled. Striking systematic changes in ta-C film properties were found. The sp{sup 3}-bonded carbon fraction, the valence electron density, and the optical (Tauc) energy gap ail reach their maximum values in films deposited at a carbon ion kinetic energy of {approximately}90 eV. Tapping-mode atomic force microscope measurements also reveal that films deposited at 90 eV are extremely smooth (rms roughness {approximately}1 {angstrom} over several hundred nm) and relatively free of particulate, while the surface roughness increases in films deposited at significantly lower energies. In the second set of experiments, dense arrays of high-aspect-ratio silicon microcolumns {approximately}20-40 {micro}m tall and {approximately}2 {micro}m in diameter were formed by cumulative nanosecond pulsed excimer laser irradiation of silicon wafers in air and other oxygen-containing atmospheres. It is proposed that microcolumn growth occurs through a combination of pulsed-laser melting of the tips of the columns and preferential redeposition of silicon on the molten tips from the ablated flux of silicon-rich vapor. The common theme in this research is that a focused pulsed-laser beam can be used quite generally to create an energetic flux, either the energetic carbon ions needed to form sp{sup 3} (diamond-like) bonds or the overpressure of silicon-rich species needed for microcolumn growth. Thus, new materials synthesis opportunities result from the access to nonequilibrium growth conditions provided by pulsed-laser ablation.
Date: February 28, 1999
Creator: Fowlkes, J.D.; Geohegan, D.B.; Jellison, G.E., Jr.; Lowndes, D.H.; Merkulov, V.I.; Pedraza, A.J. et al.
Partner: UNT Libraries Government Documents Department

Carbon, nitrogen, and oxygen ion implantation of stainless steel

Description: Ion implantation experiments of C, N, and O into stainless steel have been performed, with beam-line and plasma source ion implantation methods. Acceleration voltages were varied between 27 and 50 kV, with pulsed ion current densities between 1 and 10 mA/cm{sup 2}. Implanted doses ranged from 0.5 to 3 {times} 10{sup 18}cm{sup -2}, while workpiece temperatures were maintained between 25 and 800 C. Implant concentration profiles, microstructure, and surface mechanical properties of the implanted materials are reported.
Date: December 31, 1995
Creator: Rej, D.J.; Gavrilov, N.V. & Emlin, D.
Partner: UNT Libraries Government Documents Department

MeV ion beam induced index of refraction changes in layered GaAs/AlGaAs waveguides

Description: Previously, we showed that localized optical modifications could be produced without subsequent post thermal annealing in selectively masked planar GaAs/Al{sub .4}Ga{sub .6}As waveguide structures using 10 MeV oxygen ions. In our present investigation, irradiation experiments were performed on masked GaAs/Al{sub .4}Ga{sub .6}As waveguide samples at 298 K using 10 MeV oxygen and 8 MeV carbon ions. The two ion incident energies were chosen to yield the maximum electronic stopping power near the interface separating the top cladding layer and the guiding layer. This localized modification process emphasizes the crucial role that the electronic energy transfer plays on the degree to which the refractive index of the guiding layer is altered. Propagation loss measurements on the fabricated channel waveguides were performed by end fire coupling a laser diode source at a wavelength of 1.3 {mu}m. Observation of the extracted propagation loss values reveal that further optimization of the ion beam parameters are required before practical applications can be achieved. The relative efficiency of the various ions to induce optically altered regions which serve as lateral confinement barriers of laser light shows that this fabrication process is sensitive to the ion beam current.
Date: December 31, 1995
Creator: Taylor, T.; Ila, D. & Zimmerman, R.L.
Partner: UNT Libraries Government Documents Department

Raman spectroscopy of C-irradiated graphite

Description: Highly oriented pyrolytic graphite samples were irradiated with C{sup +} ions at 35 keV in a direction normal to the basal plane and subsequently annealed up to 1373 K. Substantial surface topography changes were observed at fluences of 5 {times} 10{sup 18} ions/m{sup 2} and higher using scanning electron and atomic force microscopies. Intricate networks of surface cracks and ridges developed after high dose implantation. A systematic study of the irradiation effects was conducted using Raman spectroscopy. Microstructural changes in irradiated regions were first detected at a dose of 1 {times} 10{sup 17} ions/m{sup 2} through the appearance of the Raman D-line at {approx}1360 cm{sup {minus}1}. The intensity of this line increases while that of the Raman G-line at 1580 cm{sup {minus}1} decreases as the irradiation dose is increased or the irradiation temperature is decreased. After irradiation at 280K to a fluence of 5 {times} 10{sup 19} ions/m{sup 2} or higher the first order spectrum exhibits one single line at a wavelength intermediate between the D- and G-lines. Damage recovery upon thermal annealing depends not only on the initial damage state but also on the annealing temperature sequence. Samples irradiated to a damage level where two distinct Raman peaks are no longer resolvable exhibited upon direct annealing at a high temperature two distinct Raman lines. By contrast, pre-annealing these highly irradiated specimens at lower temperatures produced less pronounced changes in the Raman spectra. Pre-annealing appears to stabilize damage structures that are more resistant to high-temperature annealing than those induced by irradiation.
Date: September 1, 1994
Creator: Hembree, D. M. Jr.; Pedraza, D. F.; Romanoski, G. R.; Withrow, S. P. & Annis, B. K.
Partner: UNT Libraries Government Documents Department

Scrape-Off Layer Transport and Deposition Studies in DIII-D

Description: Trace {sup 13}CH{sub 4} injection experiments into the main scrape-off layer of low density L-mode and high-density H-mode plasmas have been performed in the DIII-D tokamak [Luxon{_}NF02] to mimic the transport and deposition of carbon arising from a main chamber sputtering source. These experiments indicated entrainment of the injected carbon in plasma flow in the main SOL, and transport toward the inner divertor. Ex-situ surface analysis showed enhanced {sup 13}C surface concentration at the corner formed by the divertor floor and the angled target plate of the inner divertor in L-mode; in H-mode, both at the corner and along the surface bounding the private flux region inboard of the outer strike point. Interpretative modeling was made consistent with these experimental results by imposing a parallel carbon ion flow in the main SOL toward the inner target, and a radial pinch toward the separatrix. Predictive modeling carried out to better understand the underlying plasma transport processes suggests that the deuterium flow in the main SOL is related to the degree of detachment of the inner divertor leg. These simulations show that carbon ions are entrained with the deuteron flow in the main SOL via frictional coupling, but higher charge state carbon ions may be suspended upstream of the inner divertor X-point region due to balance of the friction force and the ion temperature gradient.
Date: October 27, 2006
Creator: Groth, M; Allen, S; Boedo, J; Brooks, N; Elder, J; Fenstermacher, M et al.
Partner: UNT Libraries Government Documents Department

Tune-stabilized linear-field FFAG for carbon therapy

Description: A hybrid design for a Fixed-Field Alternating-Gradient (FFAG) accelerator has been invented which uses edge and alternating-gradient focusing principles applied in a specific configuration to a combined-function magnet to stabilize tunes through an acceleration cycle which extends over a factor of 2-6 in momentum. Using normal conducting magnets, the final, extracted energy from this machine attains 400 MeV/nucleon and thus supports a carbon ion beam in the energy range of interest for cancer therapy. Competing machines for this application include superconducting cyclotrons[1], synchrotrons[2], and, more recently, scaling FFAGs. The machine proposed here has the high average current advantage of the cyclotron with smaller radial aperture requirements that are more typical of the synchrotron; and as such represents a desirable innovation for therapy machines.
Date: July 1, 2006
Creator: Johnstone, C.; /Fermilab; Koscielniak, S. & /TRIUMF
Partner: UNT Libraries Government Documents Department

Correlation between structure and electrical transport in ion-irradiated graphene grown on Cu foils

Description: Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra following fluences ranging from 1012 cm-2 to 1015 cm-2 indicate that the structure of graphene evolves from a highly-ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting that the Fermi level is pinned at a hole concentration near 1x1013 cm-2. A model for scattering by resonant scatterers is in good agreement with mobility measurements up to an ion fluence of 1x1014 cm-2.
Date: November 4, 2010
Creator: Buchowicz, G.; Stone, P.R.; Robinson, J.T.; Cress, C.D.; Beeman, J.W. & Dubon, O.D.
Partner: UNT Libraries Government Documents Department

Ion implantation of silicon nitride ball bearings

Description: Hypothesis for ion implantation effect was that stress concentrations reflected into the bulk due to topography such as polishing imperfections, texture in the race, or transferred material, might be reduced due to surface amorphization. 42 control samples were tested to an intended runout period of 60 h. Six ion implanted balls were tested to an extended period of 150 h. Accelerated testing was done in a V groove so that wear was on two narrow wear tracks. Rutherford backscattering, XRPS, profilometry, optical microscopy, nanoindentation hardness, and white light interferometry were used. The balls were implanted with 150-keV C ions at fluence 1.1x10{sup 17}/cm{sup 2}. The samples had preexisting surface defects (C-cracks), so the failure rate of the control group was unacceptable. None of the ion-implanted samples failed in 150 h of testing. Probability of randomly selecting 6 samples from the control group that would perform this well is about 5%, so there is good probability that ion implantation improved performance. Possible reasons are discussed. Wear tracks, microstructure, and impurity content were studied in possible relation to C-cracks.
Date: September 1, 1996
Creator: Williams, J.M. & Miner, J.R.
Partner: UNT Libraries Government Documents Department

Atomic scale enhancement of the adhesion of beryllium films to carbon substrates

Description: We have used 200 keV carbon ions to enhance the adhesion of 240-nm thick Be films to polished, vitreous carbon substrates. Adhesion of the as-deposited films was below that necessary to pass the scotch-tape test. Carbon ion fluences less than 1.6x10{sup 14} C/cm{sup 2} were sufficient to ensure the passage of the tape test without affecting the optical properties of the films. Adhesion failure of the as-deposited film was attributed to an inner oxide layer between the Be and the carbon. Because this oxide ({approximately}5 nm of BeO) was not measurably changed by the irradiation process, these results are consistent with adhesion enhancement occurring on the atomic scale at the interface between the inner oxide and the carbon substrate. This conclusion was supported by Rutherford backscattering (RBS) data, and potential adhesion mechanisms are discussed with consideration of relative contributions from electronic and nuclear stopping.
Date: December 1, 1995
Creator: Musket, R.G. & Wirtenson, G.R.
Partner: UNT Libraries Government Documents Department

Quantitative comparisons between experimentally measured 2-D carbon radiation and Monte Carlo impurity (MCI) code simulations

Description: Experimentally measured carbon line emissions and total radiated power distributions from the DIII-D divertor and Scrape-Off Layer (SOL) are compared to those calculated with the Monte Carlo Impurity (MCI) model. A UEDGE background plasma is used in MCI with the Roth and Garcia-Rosales (RG-R) chemical sputtering model and/or one of six physical sputtering models. While results from these simulations do not reproduce all of the features seen in the experimentally measured radiation patterns, the total radiated power calculated in MCI is in relatively good agreement with that measured by the DIII-D bolometric system when the Smith78 physical sputtering model is coupled to RG-R chemical sputtering in an unaltered UEDGE plasma. Alternatively, MCI simulations done with UEDGE background ion temperatures along the divertor target plates adjusted to better match those measured in the experiment resulted in three physical sputtering models which when coupled to the RG-R model gave a total radiated power that was within 10% of measured value.
Date: August 1, 1998
Creator: Evans, T.E.; Leonard, A.W.; West, W.P.; Finkenthal, D.F.; Fenstermacher, M.E. & Porter, G.D.
Partner: UNT Libraries Government Documents Department

Surface Modification of AISI-4620 Steel With Intense Pulsed Ion Beams

Description: A 300-keV, 30-kA, 1-{micro}s intense beam of carbon, oxygen, and hydrogen ions is used for the surface treatment of AISI-4620 steel coupons, a common material used in automotive gear applications. The beam is extracted from a magnetically-insulated vacuum diode and deposited into the top 1 {micro}m of the target surface. The beam-solid interaction causes a rapid melt and resolidification with heating and cooling rates of up to 10{sup 10} K/sec. Treated surfaces are smoothed over 1-{micro}m scale-lengths, but are accompanied by 1-{micro}m diameter craters and larger-scale roughening over >=10 {micro}m, depending on beam fluence and number of pulses. Treated surfaces are up to 1.8 x harder with no discernible change in modulus over depths of 1 {micro}m or more Qualitative improvements in the wear morphology of treated surfaces are reported.
Date: September 1, 1996
Creator: Rej, D.J.; Davis, H.A.; Nastasi, M.; Olson, J.C.; Peterson, E.J.; Reiswig, R.D. et al.
Partner: UNT Libraries Government Documents Department

Review of ion beam therapy: Present and Future

Description: First therapy efforts at the Bevalac using neon ions took place in the 70's and 80's. Promising results led to construction of HIMAC in Chiba Japan, and more recently to therapy trials at GSI. Both these facilities are now treating patients with carbon beams. Advances in both accelerator technology and beam delivery have taken place at these two centers. Plans are well along for new facilities in Europe and Japan.
Date: June 1, 2000
Creator: Alonso, Jose R.
Partner: UNT Libraries Government Documents Department

Diode and final-focus simulations for DARHT

Description: Beam dynamics calculations for the injector and final-focus region of a 4 kA, 20 MeV linear induction accelerator are presented. The injector is a low-emittance 4 MeV thermionic or photocathode diode designed to produce four 70 ns pulses over 2 {micro}sec. Due to the long total pule length, the authors have kept the field stress to < 200 kV/cm over the cathode electrode, and to {approx} 50 kV/cm on the radial insulator stacks. The normalized edge emittance produced by the diode is only {approx} 0.019 cm-rad. In the final-focus region, the authors have modeled the effect of ion emission from the target. The intense electric field of the beam at the 1-mm-diameter focal spot produces substantial ion velocities, and, if the space-charge-limited current density can be supplied, significant focal spot degradation may occur due to ion space-charge. Calculations for the existing Integrated Test Stand, which has a larger focal spot, show that the effect should be observable for H{sup +} and C{sup +} ion species. The effect is lessened if there is insufficient ion density on the target to supply the space-charge-limited current density, or if the ion charge-to-mass ratio is sufficiently small.
Date: October 1, 1997
Creator: Hughes, T.P.; Welch, D.R. & Carlson, R.L.
Partner: UNT Libraries Government Documents Department

Effect of irradiation spectrum on the microstructure of ion-irradiated Al{sub 2}O{sub 3}

Description: Polycrystalline samples of alpha-alumina have been irradiated with various ions ranging from 3.6 MeV Fe{sup +} to 1 MeV H{sup +} ions at 650 C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructure of the irradiated specimens. The microstructure following irradiation was observed to be dependent on the irradiation spectrum. In particular, defect cluster nucleation was effectively suppressed in specimens irradiated with light ions such as 1 MeV H{sup +} ions. On the other hand, light ion irradiation tended to accelerate the growth rate of dislocation loops. The microstructural observations are discussed in terms of ionization enhanced diffusion processes.
Date: December 31, 1994
Creator: Zinkle, S.J.
Partner: UNT Libraries Government Documents Department

Strength and tribology of bulk and electroformed nickel amorphized by implantation of titanium and carbon

Description: Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and electroformed Ni and Ni{sub 80}Fe{sub 20} materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear.
Date: October 1, 1997
Creator: Myers, S.M.; Knapp, J.A.; Follstaedt, D.M.; Dugger, M.T. & Christenson, T.R.
Partner: UNT Libraries Government Documents Department