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A study of transient molecular ions using a resonant microwave cavity as a probe

Description: The microwave-resonant-cavity technique was employes as a probe to determine the presence of molecular ions of helium in a d.c.-discharge, helium-plasma filament placed coaxially in a TM010 mode cavity. The cavity-resonance profile was displayed on an oscilloscope, and the nature of the perturbation of this resonance was used to determine the nature of the ions present in the plasma stream.
Date: December 1973
Creator: Congleton, Michael William
Partner: UNT Libraries

The Recombination Rate Coefficient of Molecular Helium Ions in a Pulsed Afterglow at 1.86 Torr

Description: The recombination rate coefficient for molecular helium ions has been measured in a pulsed afterglow at 1.86 Torr as a function of electron temperature and electron density without making a priori assumptions about the functional dependence. The concentrations of the molecular ions and electrons were measured and the source terms for the molecular ions were included in the rate equation.
Date: August 1972
Creator: Hicks, Helen Segrave
Partner: UNT Libraries

The Formation of U232 by Helium Ions of Thorium

Description: The production of U{sup 232} by the sum of {alpha},4n and {alpha},p 3n reactions on thorium has been studied. The cross section at an average energy of 37.5 Mev was 0.013 barns and the threshold for the reaction was about 30 Mev.
Date: April 14, 1948
Creator: Newton, Amos S.
Partner: UNT Libraries Government Documents Department

Products of High-Energy Deuteron and Helium Ion Bombardments of Copper

Description: The identity and relative yields of about twenty of the radioisotopes produced by the bombardment of natural copper with 190 Mev deuterons and 380 Mev helium ions have been determined. Two previously unreported isotopes were detected: Zn{sup 62}, decaying by orbital electron capture with a 9.5-hour half-life, and Fe{sup 52}, decaying by positron emission with a 7.8-hour half-life.
Date: March 1, 1948
Creator: Miller, D.R.; Thompson, R.C. & Cunningham, B.B.
Partner: UNT Libraries Government Documents Department

Depth-independent hardness improvements in ion irradiated polystyrene

Description: Polystyrene (PS) was irradiated with 2 MeV He{sup +} ions to a fluence of 3.3 {times} 10{sup 9} ions/m{sup 2}. A cross-section of the irradiated layer was subjected to hardness measurements across the section using a nanoindentation technique. Results showed that hardness increased as a function of irradiation depth and showed a maximum value of 12 GPa at a depth of approximately 6.5 {mu}m, for a total ion penetration range of 9 {mu}m, as compared to a hardness of 0.45 GPa for unirradiated PS. The hardness variation with depth followed the trend for Linear Energy Transfer (LET) for ionization from the energetic ions to substrate atoms. This investigation showed for the first time how hardness varies as a function of depth for ion-irradiated polymers; this variation approximately follows the ionization LET profile, suggesting that cross-linking in the polymers could be proportional to ionization.
Date: December 31, 1994
Creator: Rao, G.R.; Riester, L. & Lee, E.H.
Partner: UNT Libraries Government Documents Department

On the unexpected oscillation of the total cross section for excitation in He{sup 2+} + H collisions

Description: Recent calculations and measurements have revealed unexpected oscillations of the total cross section for excitation in low- to intermediate-energy He{sup 2+} + H collisions. A physical explanation of this behavior is given here stemming from analysis of classical trajectory Monte Carlo simulations, molecular orbital close coupling calculations, and solution of the time-dependent Schroedinger equation on a numerical lattice. These results indicate that the observed behavior should be characteristic of a wide range of reactions in ion-atom collisions.
Date: October 1, 1996
Creator: Schultz, D.R.; Reinhold, C.O. & Krstic, P.S.
Partner: UNT Libraries Government Documents Department

The role of implantation damage in the production of silicon-on-insulator films by co-Implantation of He{sup +} and H{sup +}

Description: Recent work has demonstrated that the process of silicon thin film separation by hydrogen implantation, as well as the more basic phenomenon of surface blistering, can occur at a much lower total dose when H and He are co-implanted than when H is implanted alone. Building on that work, this paper investigates the role of implantation damage in this process by separating the contributions of gas pressure from those of damage. Three different experiments using co-implantation were designed. In the first of these experiments, H and He implants were spatially separated thereby separating the damage from each implant. The second experiment involved co-implantation of H and He at a temperature of 77 K to retain a larger amount of damage for the same gas dose. In the third experiment, Li was co-implanted with H, to create additional damage without introducing additional gas. These experiments together show that increasing the implantation damage itself hampers the formation of surface blisters, and that the increased efficiency observed for He co-implantation with H is due to the supplementary source of gas provided by the He.
Date: January 1, 1998
Creator: Venezia, V.C.; Agarwal, A.; Haynes, T.E.; Holland, O.W.; Eaglesham, D.J.; Weldon, M.K. et al.
Partner: UNT Libraries Government Documents Department

The New ELement Mendelevium, Atomic Number 101

Description: We have produced and chemically identified for the first time a few atoms of the element with atomic number 101. Very intense helium ion bombardments of tiny targets of 99{sup 253} have produced a few spontaneously fissionable atoms which elute in the eka-thulium position on a cation resin column.
Date: April 4, 1955
Creator: Ghiorso, A.; Harvey, B.G.; Choppin, G.R.; Thompson, S.G. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Formation of cavities in Si and their chemisorption of metals

Description: Nanometer-size cavities formed in Si by He{sup +} implantation and annealing are examined with cross-section TEM. During annealing at 700 C or above, He degasses from the specimens, leaving uhv cavities with reactive Si bonds on their walls. Cavity microstructures have been characterized in detail for an implanted fluence of 1 {times} 10{sup 17} He/cm{sup 2}: cavity volume remains approximately constant (0.75 lattice sites/He) for anneals from 700 to {approximately}1000 C, while surface area (3 to 7 times the wafer area) decreases with temperature as the cavities coarsen. The cavities are found to getter up to {approximately}1 monolayer of Cu or Au from solution in Si without second-phase formation, thus identifying the trapping mechanism as chemisorption on the cavity walls.
Date: December 31, 1994
Creator: Follstaedt, D.M. & Myers, S.M.
Partner: UNT Libraries Government Documents Department

Cavity nucleation and evolution in He-implanted Si and GaAs

Description: The criteria for forming stable cavities by He{sup +} implantation and annealing are examined for Si and GaAs. In Si, implanting at room temperature requires a minimum of 1.6 at. % He to form a continuous layer of cavities after annealing at 700{degrees}C. The cavities are located at dislocations and planar defects. Implanting peak He concentrations just above this threshold produces narrow layers of cavities at the projected range. In GaAs, room-temperature implantation followed by annealing results in exfoliation of the surface layer. Cavities were formed instead by implanting Ar followed by overlapping He, both at 400{degrees}C, with additional annealing at 400{degrees}C to outgas the He. This method forms 1.5--3.5 nm cavities that are often on [111] planar defects.
Date: December 1, 1995
Creator: Follstaedt, D.M.; Myers, S.M.; Petersen, G.A. & Barbour, J.C.
Partner: UNT Libraries Government Documents Department

MHD-Induced Alpha Particle Loss in TFTR

Description: MHD-induced increases in alpha particle loss to the wall were observed for both coherent modes and transient reconnection events using an array of scintillator detectors near the wall of Tokamak Fusion Test Reactor (TFTR). The magnitude of the coherent MHD-induced alpha loss as seen by these detectors was normally comparable to the MHD-quiescent first-orbit or toroidal-field ripple loss, but the magnitude of the alpha loss during reconnection events was up to 1000 times higher than this for a short time. Modeling suggest that the coherent MHD loss mechanism will be even less significant for future reactor-scale deuterium-tritium tokamaks due to the smaller ratio of the alpha gyroradius to minor radius.
Date: March 1, 1999
Creator: Darrow, D.S.; Fredrickson, E.D.; Taylor, G.; White, R.B.; Zweben, S.J. & von Goeler, S.
Partner: UNT Libraries Government Documents Department

Development of ion sources for ion projection lithography

Description: Multicusp ion sources are capable of generating ion beams with low axial energy spread as required by the Ion Projection Lithography (IPL). Longitudinal ion energy spread has been studied in two different types of plasma discharge: the filament discharge ion source characterized by its low axial energy spread, and the RF-driven ion source characterized by its long source lifetime. For He{sup +} ions, longitudinal ion energy spreads of 1-2 eV were measured for a filament discharge multicusp ion source which is within the IPL device requirements. Ion beams with larger axial energy spread were observed in the RF-driven source. A double-chamber ion source has been designed which combines the advantages of low axial energy spread of the filament discharge ion source with the long lifetime of the RF-driven source. The energy spread of the double chamber source is lower than that of the RF-driven source.
Date: May 1, 1996
Creator: Lee, Y.; Gough, R.A.; Kunkel, W.B.; Leung, K.N. & Perkins, L.T.
Partner: UNT Libraries Government Documents Department

The effect of displacement cascades on small helium bubbles in aluminum and gold

Description: The evolution of individual helium bubbles in thin foils of gold and aluminum irradiated with 400 keV Ar+ and 200 keV Xe+ has been followed with in-situ transmission electron microscopy for a comparison between the effects of dilute (Al) and dense (Au) collision cascades. Bubble shrinkage in Al has been attributed to direct displacement of the gas out of the bubbles. Effects in Au, include the disappearance and Brownian motion of bubbles under irradiation, and are consistent with thermal spike processes seen in molecular dynamics simulations.
Date: December 1, 1994
Creator: Donnelly, S.E.; Valizadeh, R.; Vishnyakov, V.; Birtcher, R.C. & Templier, C.
Partner: UNT Libraries Government Documents Department

Surface studies and implanted helium measurements following NOVA high-yield DT experiments

Description: This paper presents the results of three March 6, 1996 direct-drive high-yield DT NOVA experiments and provides `proof-of-principal` results for the quantitative measurement of energetic He ions. Semiconductor quality Si wafers and an amorphous carbon wafer were exposed to NOVA high-yield implosions. Surface damage was sub-micron in general, although the surface ablation was slightly greater for the carbon wafer than for the Si wafers. Melting of a thin ({approx} 0.1{mu}) layer of Si was evident from microscopic investigation. Electron microscopy indicated melted blobs of many different metals (e.g. Al, Au, Ta, Fe alloys, Cu and even Cd) on the surfaces. The yield measured by determining the numbers of atoms of implanted {sup 4}He and {sup 3}He indicate the number of DT fusions to be 9.1({plus_minus}2.3) X 10{sup 12} and DD fusions to be 4.8({plus_minus}1.0) x 10{sup 10}, respectively. The helium DT fusion yield is slightly lower than that of the Cu activation measurement, which was 1.3({plus_minus}0.l) x 10{sup 13} DT fusions.
Date: February 18, 1997
Creator: Stoyer, M.A. & Hudson, G.B.
Partner: UNT Libraries Government Documents Department

Ion irradiation damage in ilmenite at 100 K

Description: A natural single crystal of ilmenite (FeTiO{sub 3}) was irradiated at 100 K with 200 keV Ar{sup 2+}. Rutherford backscattering spectroscopy and ion channeling with MeV He{sup +} ions were used to monitor damage accumulation in the surface region of the implanted crystal. At an irradiation fluence of 1 {times} 10{sup 15} Ar{sup 2+} cm{sup {minus}2}, considerable near-surface He{sup +} ion dechanneling was observed, to the extent that ion yield from a portion of the aligned crystal spectrum reached the yield level of a random spectrum. This observation suggests that the near-surface region of the crystal was amorphized by the implantation. Cross-sectional transmission electron microscopy and electron diffraction on this sample confirmed the presence of a 150 nm thick amorphous layer. These results are compared to similar investigations on geikielite (MgTiO{sub 3}) and spinel (MgAl{sub 2}O{sub 4}) to explore factors that may influence radiation damage response in oxides.
Date: October 1, 1997
Creator: Mitchell, J.N.; Yu, N.; Devanathan, R.; Sickafus, K.E.; Nastasi, M.A. & Nord, G.L. Jr.
Partner: UNT Libraries Government Documents Department

Ion irradiation damage in ilmenite under cryogenic conditions

Description: A natural single crystal of ilmenite was irradiated at 100 K with 200 keV Ar{sup 2+}. Rutherford backscattering spectroscopy and ion channeling with 2 MeV He{sup +} ions were used to monitor damage accumulation in the surface region of the implanted crystal. At an irradiation fluence of 1 {times} 10{sup 15} Ar{sup 2+} cm{sup {minus}2}, considerable near-surface He{sup +} ion dechanneling was observed, to the extent that ion yield from a portion of the aligned crystal spectrum reached the yield level of a random spectrum. This observation suggests that the near-surface region of the crystal was amorphized by the implantation. Cross-sectional transmission electron microscopy and electron diffraction on this sample confirmed the presence of a 150 mm thick amorphous layer. These results are compared to similar investigations on geikielite (MgTiO{sub 3}) and spinel (MgAl{sub 2}O{sub 4}) to explore factors that may influence radiation damage response in oxides.
Date: November 1, 1996
Creator: Mitchell, J.N.; Yu, N.; Devanathan, R.; Sickafus, K.E.; Nastasi, M.A. & Nord, G.L. Jr.
Partner: UNT Libraries Government Documents Department

Segregation gettering by implantation-formed cavities and B-Si precipitates in silicon

Description: The authors show that Fe, Co, Cu, and Au in Si undergo strong segregation gettering to cavities and B-Si precipitates formed by He or B ion implantation and annealing. The respective mechanisms are argued to be chemisorption on the cavity walls and occupation of solution sites within the disordered, B-rich, B-Si phase. The strengths of the reactions are evaluated, enabling prediction of gettering performance.
Date: January 1, 1998
Creator: Myers, S.M.; Petersen, G.A. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Anomalous Loss of DT Alpha Particles in the Tokamak Fusion Test Reactor

Description: Princeton's Tokamak Fusion Test Reactor (TFTR) is the first experimental fusion device to routinely use tritium to study the deuterium-tritium (DT) fusion reaction,allowing the first systematic study of DT alpha particles in tokamak plasmas. A crucial aspect of alpha-particle physics is the fraction of alphas that escape from the plasma, particularly since these energetic particles can do severe damage to the first wall of a reactor. An escaping alpha collector probe has been developed for TFTR's DT phase. Energy distributions of escaping alphas have been determined by measuring the range of alpha-particles implanted into nickel foils located within the alpha collector. Results at 1.0 MA of plasma current are in good agreement with predictions for first orbit alpha loss. Results at 1.8 MA, however, show a significant anomalous loss of partially thermalized alphas (in addition to the expected first orbit loss), which is not observed with the lost alpha scintillator detectors in DT plasmas, but does resemble the anomalous "delayed" loss seen in DD plasmas. None of the candidate explanations proposed thus far are fully consistent with the anomalous loss observations. An experiment designed to study the effect of plasma major radius shifts on alpha-particle loss has led to a better understanding of alpha-particle dynamics in tokamaks. Intuitively, one might suppose that confined marginally passing alpha-particles forced to move toward higher magnetic field during an inward major radius shift (i.e. compression) would mirror and become trapped particles, leading to increased alpha loss. Such an effect was looked for during the shift experiment, however, no significant changes in alpha loss to the 90 degree lost alpha scintillator detector were observed during the shifts. It is calculated that the energy gained by an alpha-particle during the inward shift is sufficient to explain this result. However, an unexpected loss of partially thermalized alpha-particles ...
Date: June 1, 1997
Creator: Herrmann, Hans W.
Partner: UNT Libraries Government Documents Department

Summary of Alpha Particle Transport

Description: This paper summarizes the talks on alpha particle transport which were presented at the 5th International Atomic Energy Agency's Technical Committee Meeting on "Alpha Particles in Fusion Research" held at the Joint European Torus, England in September 1997.
Date: August 19, 1998
Creator: Medley, S.S.; White, R.B. & Zweben, S.J.
Partner: UNT Libraries Government Documents Department

Kinetic Theory of Plasma Adiabatic Major Radius Compression in Tokamaks

Description: A kinetic approach is developed to understand the individual charged particle behavior as well as plasma macro parameters (temperature, density, etc.) during the adiabatic R-compression in a tokamak. The perpendicular electric field from Ohm's law at zero resistivity E = -v{sub E}{times}B/c is made use of to obtain the equation for particle velocity evolution in order to describe the particle motion during the R-compression. Expressions for both passing and trapped particle energy and pitch angle change are obtained for a plasma with high aspect ratio and circular magnetic surfaces. The particle behavior near the trapped passing boundary during the compression is also studied to understand the shift induced loss of alpha particles produced by D-T fusion reactions in Tokamak Fusion Test Reactor experiments. Qualitative agreement is obtained with the experiments. Solving the drift kinetic equation in the collisional case, i.e., when the collisional frequency of given species exceeds the inverse compression time, we obtain that the temperature and the density evolution is reduced to the MHD results T {approximately} R{super -4/3} and n {approximately} R{super -2}, respectively. In the opposite case, the collisional frequency of given species is smaller than the inverse compression time, the longitudinal component of the temperature evolve like R{super -2} and perpendicular component of the temperature is R{super -1}. The effect of toroidicity is negligible in both cases.
Date: October 1, 1997
Creator: Romannikov, A.N.; Azizov, E.A.; Herrmann, H.W.; Gorelenkova, M.V. & Gorelenkov, N.N.
Partner: UNT Libraries Government Documents Department

HIGH CURRENT SOURCE OF He IONS

Description: A negative helium ion beam of 70 mA at 10.5 kV has been produced by charge exchange in sodium. The production is studied as a function of sodium line density, beam energy and background helium gas density. The characteristics of this high current He{sup -} source are analyzed to determine the design requirements for He{sup -} beam generation in the range of tens to hundred of milliamperes.
Date: March 1, 1980
Creator: Hooper, Jr., E.B.; Pincosy, P.A.; Poulsen, P.; Burrell, C.F.; Grisham, L.R. & Post, D.E.
Partner: UNT Libraries Government Documents Department

Collision cross sections for few electron systems. Final report, August 1, 2992--July 31, 1995

Description: The purpose of this project was to produce accurate cross sections for collisionally induced reactions from the ground stated and excited states of species of ions and at present in a hot fusion plasma. The collisional constituents may be divided into two categories for the purpose of calculations: Those in which a bare projectile excites a one electron or two electron ion or atom from its ground state, or excited states to higher excited states or ionized states. Those in which the projectile has one or more electrons attached to it and excites a one electron or two electron ion or atom from its ground state, or excited states to higher excited states or ionized states. During the collision the projectile itself may change its state being simultaneously excited or ionized. Cross sections are needed typically over the whole energy range from low velocities where molecular, orbitals begin to form to high velocities where first Born or more sophisticated asymptotic theories can be used. These high energy cross sections are very useful for experimentalists to check the absolute normalization of their cross sections. The theoretical tools used were therefore both analytical and numerical in character. Numerical calculations were restricted to expansions of the wavefunctions in a set of finite hilbert basis states (FHBS). The many body aspects of the problem, i.e. the important presence of the interelectron force, or correlation mandate a careful systematic approach. But this section was tempered in our strategy by the fact that many of the cross sections needed, especially from excited states, have never been calculated or measured at all. Thus any information we can provide is useful even if later work may modify our results.
Date: December 31, 1995
Creator: Reading, J.F. & Ford, A.L.
Partner: UNT Libraries Government Documents Department

Energetic particle acceleration at corotating interaction regions: Ulysses results

Description: We present here statistical properties of energetic ions (tilde 1 MeV) accelerated by corotating interaction regions observed at the Ulysses spacecraft. We have correlated the tilde 1 MeV proton intensity measured near the trailing edges of the interaction regions with their compression ratio. We interpret our results in terms of the plasma conditions experienced at Ulysses and identify a likely source of the low energy seed particles accelerated at the interaction regions.
Date: July 1, 1997
Creator: Desai, M.I.; Marsden, R.G.; Sanderson, T.R.; Balogh, A.; Forsyth, R.J. & Gosling, J.T.
Partner: UNT Libraries Government Documents Department