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Sample records for 35-mev helium ions

  1. Exotic Ions in Superfluid Helium

    NASA Astrophysics Data System (ADS)

    Wei, Wanchun; Xie, Zhuolin; Cooper, Leon N.; Maris, Humphrey J.

    2016-11-01

    Exotic ions are negatively charged objects which have been detected in superfluid helium-4 at temperatures in the vicinity of 1 K. Mobility experiments in several different labs have revealed the existence of at least 18 such objects. These ions have a higher mobility than the normal negative ion and appear to be singly charged and smaller. We summarize the experimental situation, the possible structure of these objects, and how these objects might be formed.

  2. Excitation of helium ion by positron impact

    SciTech Connect

    Khan, P.; Ghosh, A.S.

    1986-01-01

    Three (1s,2s,2p) and five (1s,2s,2p,3s-bar,3p-bar) -state close-coupling methods have been employed to calculate the n = 2 excitation cross sections of helium ion by positron impact. The effect of pseudostate is found to be very pronounced in the case of 1s-2s excitation.

  3. Helium-ion-induced human cataractogenesis

    NASA Technical Reports Server (NTRS)

    Blakely, E. A.; Daftari, I. K.; Meecham, W. J.; Alonso, L. C.; Collier, J. M.; Kroll, S. M.; Gillette, E. L.; Lee, A. C.; Lett, J. T.; Cox, A. B.

    1994-01-01

    Retrospective and ongoing analyses of clinical records from 347 primary intraocular melanoman patients treated with helium ions at Lawrence Berkeley Laboratory (LBL) will allow examination of the exposure-response data for human cataract; which is a complication of the therapy from incidental exposure of the lens. Direct particle beam traversal of at least a portion of the lens usually is unavoidable in treatment of posterior intraocular tumors. The precise treatment planned for each patient permits quantitative assessment of the lenticular dose and its radiation quality. We are reporting our preliminary results on the development of helium-ion-induced lens opacifications and cataracts in 54 of these patients who had 10% or less of their lens in the treatment field. We believe these studies will be relevant to estimating the human risk for cataract in space flight.

  4. Helium ion microscopy of Lepidoptera scales.

    PubMed

    Boden, Stuart A; Asadollahbaik, Asa; Rutt, Harvey N; Bagnall, Darren M

    2012-01-01

    In this report, helium ion microscopy (HIM) is used to study the micro and nanostructures responsible for structural color in the wings of two species of Lepidotera from the Papilionidae family: Papilio ulysses (Blue Mountain Butterfly) and Parides sesostris (Emerald-patched Cattleheart). Electronic charging of uncoated scales from the wings of these butterflies, due to the incident ion beam, is successfully neutralized, leading to images displaying a large depth-of-field and a high level of surface detail, which would normally be obscured by traditional coating methods used for scanning electron microscopy (SEM). The images are compared with those from variable pressure SEM, demonstrating the superiority of HIM at high magnifications. In addition, the large depth-of-field capabilities of HIM are exploited through the creation of stereo pairs that allows the exploration of the third dimension. Furthermore, the extraction of quantitative height information which matches well with cross-sectional transmission electron microscopy measurements from the literature is demonstrated. PMID:21796646

  5. Hydrogen recycling control by helium ion bombardment onto carbonized surfaces

    NASA Astrophysics Data System (ADS)

    Sugai, H.; Toyoda, H.; Ohshita, S.; Yoshida, S.; Sagara, A.

    1989-04-01

    A strong pumping effect was observed in a hydrogen recycling simulation experiment in a carbonized toroidal device at room temperature. The pumping effect was induced by conditioning the carbon-thin-film deposited wall with a short (~10 min) helium glow discharge. A large amount of hydrogen (~10 16cm-2) was desorbed from carbon films with helium ion bombardment at 200 eV. After conditioning, the recycling coefficient was drastically reduced from about 2 to a value close to zero. Furthermore, an advanced (multilayer) coating was developed with use of helium ion induced desorption, where a short burst of methane was admixed at regular intervals in a helium glow discharge. A fairly large wall pumping was realized by the multilayer coating when the thickness of each layer and the helium bombarding time were optimized.

  6. Scanning reflection ion microscopy in a helium ion microscope

    PubMed Central

    Vyvenko, Oleg F

    2015-01-01

    Summary Reflection ion microscopy (RIM) is a technique that uses a low angle of incidence and scattered ions to form an image of the specimen surface. This paper reports on the development of the instrumentation and the analysis of the capabilities and limitations of the scanning RIM in a helium ion microscope (HIM). The reflected ions were detected by their “conversion” to secondary electrons on a platinum surface. An angle of incidence in the range 5–10° was used in the experimental setup. It was shown that the RIM image contrast was determined mostly by surface morphology but not by the atomic composition. A simple geometrical analysis of the reflection process was performed together with a Monte Carlo simulation of the angular dependence of the reflected ion yield. An interpretation of the RIM image formation and a quantification of the height of the surface steps were performed. The minimum detectable step height was found to be approximately 5 nm. RIM imaging of an insulator surface without the need for charge compensation was successfully demonstrated. PMID:26171289

  7. Modification on graphite due to helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Dutta, N. J.; Mohanty, S. R.; Buzarbaruah, N.

    2016-07-01

    This paper studies the influence of helium ion irradiation on morphological and structural properties of graphite samples. The helium ions emanated from a plasma focus device have been used to irradiate graphite samples by varying the number of ion pulses. The effect of radiation induced changes in morphology and structure are examined by using optical microscopy, atomic force microscopy, transmission electron microscopy along with selected area electron diffraction and x-ray diffraction. A distinct change in the surface topography is marked in the case of the ion irradiated samples when viewed under the optical microscope. The micrographs of the ion irradiated samples confirm mostly rounded and sparely elongated type of structures arising due to intense melting and local ablation accompanied with ejection of graphite melts that depends upon the ion fluence. The atomic force microscopy images also reveal the formation of globules having sizes ∼50-200 nm which are the agglomeration of small individual clusters. Transmission electron micrographs of the ion irradiated samples furnish that the diameter of these individual small clusters are ∼10.4 nm. Moreover, selected area electron diffraction patterns corroborate that the ion irradiated sample retains its crystalline nature, even after exposure to larger helium ion pulses. It is noticed from the x-ray diffraction patterns that some new phases are developed in the case of ion irradiated sample.

  8. Helium Ion Microscope-Assisted Nanomachining of Resonant Nanostrings

    PubMed Central

    Zheng, Wei; Li, Peng; van den Hurk, Remko; Evoy, Stephane

    2016-01-01

    Helium ion microscopy has recently emerged as a potent tool for the in-situ modification and imaging of nanoscale devices. For example; finely focused helium ion beams have been used for the milling of pores in suspended structures. We here report the use of helium ion milling for the post-fabrication modification of nanostrings machined from an amorphous SiCN material. The modification consisted of milling linear arrays of holes along the length of nanostrings. This milling results in a slight decrease of resonant frequency while increasing the surface to volume ratio of the device. The frequency decrease is attributed to a reduction of the effective Young’s modulus of the string, which in turn reduces the tension the string is under. Such experimental observations are supported by the finite element analysis of milled and non-milled strings. PMID:27420070

  9. Focal depth measurement of scanning helium ion microscope

    SciTech Connect

    Guo, Hongxuan; Itoh, Hiroshi; Wang, Chunmei; Zhang, Han; Fujita, Daisuke

    2014-07-14

    When facing the challenges of critical dimension measurement of complicated nanostructures, such as of the three dimension integrated circuit, characterization of the focal depth of microscopes is important. In this Letter, we developed a method for characterizing the focal depth of a scanning helium ion microscope (HIM) by using an atomic force microscope tip characterizer (ATC). The ATC was tilted in a sample chamber at an angle to the scanning plan. Secondary electron images (SEIs) were obtained at different positions of the ATC. The edge resolution of the SEIs shows the nominal diameters of the helium ion beam at different focal levels. With this method, the nominal shapes of the helium ion beams were obtained with different apertures. Our results show that a small aperture is necessary to get a high spatial resolution and high depth of field images with HIM. This work provides a method for characterizing and improving the performance of HIM.

  10. Helium Ion Microscope-Assisted Nanomachining of Resonant Nanostrings.

    PubMed

    Zheng, Wei; Li, Peng; van den Hurk, Remko; Evoy, Stephane

    2016-01-01

    Helium ion microscopy has recently emerged as a potent tool for the in-situ modification and imaging of nanoscale devices. For example; finely focused helium ion beams have been used for the milling of pores in suspended structures. We here report the use of helium ion milling for the post-fabrication modification of nanostrings machined from an amorphous SiCN material. The modification consisted of milling linear arrays of holes along the length of nanostrings. This milling results in a slight decrease of resonant frequency while increasing the surface to volume ratio of the device. The frequency decrease is attributed to a reduction of the effective Young's modulus of the string, which in turn reduces the tension the string is under. Such experimental observations are supported by the finite element analysis of milled and non-milled strings. PMID:27420070

  11. Helium Ion Microscope-Assisted Nanomachining of Resonant Nanostrings.

    PubMed

    Zheng, Wei; Li, Peng; van den Hurk, Remko; Evoy, Stephane

    2016-07-13

    Helium ion microscopy has recently emerged as a potent tool for the in-situ modification and imaging of nanoscale devices. For example; finely focused helium ion beams have been used for the milling of pores in suspended structures. We here report the use of helium ion milling for the post-fabrication modification of nanostrings machined from an amorphous SiCN material. The modification consisted of milling linear arrays of holes along the length of nanostrings. This milling results in a slight decrease of resonant frequency while increasing the surface to volume ratio of the device. The frequency decrease is attributed to a reduction of the effective Young's modulus of the string, which in turn reduces the tension the string is under. Such experimental observations are supported by the finite element analysis of milled and non-milled strings.

  12. The Helium Atom and Isoelectronic Ions in Two Dimensions

    ERIC Educational Resources Information Center

    Patil, S. H.

    2008-01-01

    The energy levels of the helium atom and isoelectronic ions in two dimensions are considered. The difficulties encountered in the analytical evaluation of the perturbative and variational expressions for the ground state, promote an interesting factorization of the inter-electronic interaction, leading to simple expressions for the energy. This…

  13. Radiolysis of cyclooctane with [gamma]-rays and helium ions

    SciTech Connect

    Wojnarovits, L.; LaVerne, J.A. )

    1994-08-18

    Iodine scavenging techniques have been used to examine the role of the cyclooctyl radical in the radiolysis of cyclooctane with [gamma]-rays and with 5-20-MeV helium ions. In [gamma]-radiolysis about 70% of the total yield of 6.6 cyclooctyl radicals/100 eV are scavenged with 10[sup [minus]4] M iodine, which agrees well with other studies on cycloalkanes that show most of the radicals produced in these systems react in the bulk medium at times longer than 1 [nu]s. However, it is found that 2.5 radicals/100 eV (38%) are produced by H atom precursors as compared to a value of 1.5 cyclohexyl radicals/100 eV (25%) in cyclohexane. With 10-MeV helium ions (average LET of 106 eV/nm), only 8% of the cyclooctyl radicals survive longer than a few microseconds due to the increased initial radical concentration in the helium ion track. The yield of the cross-bridged product bicyclo[3.3.0]octane (pentalane) was found to be independent of iodine concentration up to 0.03 M with both types of radiation. However, the pentalane yield found with 10-MeV helium ions was only one-third of that found in [gamma]-radiolysis. The most likely reason for this result is the decreased yield of singlet-state formation due to the enhanced probability of cross combination reactions of electron-cation pairs in the high-density region of the helium ion track. 29 refs., 4 figs., 1 tab.

  14. Helium-ion-induced release of hydrogen from graphite

    SciTech Connect

    Langley, R.A.

    1987-01-01

    The ion-induced release of hydrogen from AXF-5Q graphite was studied for 350-eV helium ions. The hydrogen was implanted into the graphite with a low energy (approx.200 eV) and to a high fluence. This achieved a thin (approx.10-nm), saturated near-surface region. The release of hydrogen was measured as a function of helium fluence. A model that includes ion-induced detrapping, retrapping, and surface recombination was used to analyze the experimental data. A value of (1.65 +- 0.2) x 10/sup -16/ cm/sup 2/ was obtained from the detrapping cross section, and a value of (0.5 to 4) x 10/sup -14/ cm/sup 4//atoms was obtained for the recombination coefficient. 11 refs., 4 figs.

  15. Investigation of Cellular Interactions of Nanoparticles by Helium Ion Microscopy

    SciTech Connect

    Arey, Bruce W.; Shutthanandan, V.; Xie, Yumei; Tolic, Ana; Williams, Nolann G.; Orr, Galya

    2011-06-01

    The helium ion mircroscope (HIM) probes light elements (e.g. C, N, O, P) with high contrast due to the large variation in secondary electron yield, which minimizes the necessity of specimen staining. A defining characteristic of HIM is its remarkable capability to neutralize charge by the implementation of an electron flood gun, which eliminates the need for coating non-conductive specimens for imaging at high resolution. In addition, the small convergence angle in HeIM offers a large depth of field (~5x FE-SEM), enabling tall structures to be viewed in focus within a single image. Taking advantage of these capabilities, we investigate the interactions of engineered nanoparticles (NPs) at the surface of alveolar type II epithelial cells grown at the air-liquid interface (ALI). The increasing use of nanomaterials in a wide range of commercial applications has the potential to increase human exposure to these materials, but the impact of such exposure on human health is still unclear. One of the main routs of exposure is the respiratory tract, where alveolar epithelial cells present a vulnerable target at the interface with ambient air. Since the cellular interactions of NPs govern the cellular response and ultimately determine the impact on human health, our studies will help delineating relationships between particle properties and cellular interactions and response to better evaluate NP toxicity or biocompatibility. The Rutherford backscattered ion (RBI) is a helium ions imaging mode, which backscatters helium ions from every element except hydrogen, with a backscatter yield that depends on the atomic number of the target. Energy-sensitive backscatter analysis is being developed, which when combined with RBI image information, supports elemental identification at helium ion nanometer resolution. This capability will enable distinguishing NPs from cell surface structures with nanometer resolution.

  16. Investigation of cellular interactions of nanoparticles by helium ion microscopy

    NASA Astrophysics Data System (ADS)

    Arey, B. W.; Shutthanandan, V.; Xie, Y.; Tolic, A.; Williams, N.; Orr, G.

    2011-06-01

    The helium ion microscope (HIM) probes light elements (e.g. C, N, O, P) with high contrast due to the large variation in secondary electron yield, which minimizes the necessity of specimen staining. A defining characteristic of HIM is its remarkable capability to neutralize charge by the implementation of an electron flood gun, which eliminates the need for coating non-conductive specimens for imaging at high resolution. In addition, the small convergence angle in HeIM offers a large depth of field (~5× FE-SEM), enabling tall structures to be viewed in focus within a single image. Taking advantage of these capabilities, we investigate the interactions of engineered nanoparticles (NPs) at the surface of alveolar type II epithelial cells grown at the airliquid interface (ALI). The increasing use of nanomaterials in a wide range of commercial applications has the potential to increase human exposure to these materials, but the impact of such exposure on human health is still unclear. One of the main routs of exposure is the respiratory tract, where alveolar epithelial cells present a vulnerable target at the interface with ambient air. Since the cellular interactions of NPs govern the cellular response and ultimately determine the impact on human health, our studies will help delineating relationships between particle properties and cellular interactions and response to better evaluate NP toxicity or biocompatibility. The Rutherford backscattered ion (RBI) is a helium ions imaging mode, which backscatters helium ions from every element except hydrogen, with a backscatter yield that depends on the atomic number of the target. Energy-sensitive backscatter analysis is being developed, which when combined with RBI image information, supports elemental identification at helium ion nanometer resolution. This capability will enable distinguishing NPs from cell surface structures with nanometer resolution.

  17. Failure of choroidal melanoma to respond to helium ion therapy

    SciTech Connect

    Char, D.H.; Crawford, J.B.; Castro, J.R.; Woodruff, K.H.

    1983-02-01

    Helium ion irradiation is a promising alternative therapy for choroidal melanoma. In short-term follow-up (less than 5 years), more than 90% (18/19) of treated patients demonstrated tumor regression. Researchers had to enucleate five eyes after helium ion therapy either because of continued tumor growth (four patients) or other complications (one patient). Two melanomas continued to grow and seemed to be radioresistant. In two other tumors it retrospectively seemed that the entire lesion was not inside the radiation field. In one patient total retinal detachment and glaucoma developed; enucleation was performed because of a painful eye. Metastatic disease developed in no patients. The treatment failures emphasize that there are a number of unresolved issues regarding the use of charged-particle irradiation in the treatment of melanoma. Further studies must be performed to answer these questions and better delineate the use of these newer forms of therapy.

  18. Neovascular glaucoma after helium ion irradiation for uveal melanoma

    SciTech Connect

    Kim, M.K.; Char, D.H.; Castro, J.L.; Saunders, W.M.; Chen, G.T.; Stone, R.D.

    1986-02-01

    Neovascular glaucoma developed in 22 of 169 uveal melanoma patients treated with helium ion irradiation. Most patients had large melanomas; no eyes containing small melanomas developed anterior segment neovascularization. The mean onset of glaucoma was 14.1 months (range, 7-31 months). The incidence of anterior segment neovascularization increased with radiation dosage; there was an approximately three-fold increase at 80 GyE versus 60 GyE of helium ion radiation (23% vs. 8.5%) (P less than 0.05). Neovascular glaucoma occurred more commonly in larger tumors; the incidence was not affected by tumor location, presence of subretinal fluid, nor rate of tumor regression. Fifty-three percent of patients had some response with intraocular pressures of 21 mmHg or less to a combination of antiglaucoma treatments.

  19. Dynamic properties of helium ions in the solar wind

    NASA Technical Reports Server (NTRS)

    Zurbuchen, Th.; Bochsler, P.; von Steiger, R.

    1995-01-01

    We characterize the dynamic properties of He ions of the solar wind. Because of the non-negligible abundance and the significant fraction of momentum flux inherent in helium ions, this species has an influence on the state of turbulence. Especially, we analyze the helium dynamic properties of different solar wind types. After a discussion of the influence of measurement errors on the statistical analysis of He bulk velocities, we investigate the structure function dependency on the solar wind state. We find a self-similar sealing in the range of minutes to days with characteristic structure function slopes deviating from the canonical Kolmogorov values. For comparison with previous studies, we also analyze H structure functions of the same time periods and discuss differences of coinciding He and H structure functions in the framework of the concept of intermittency.

  20. Observations of interstellar helium pickup ions in the inner heliosphere

    NASA Astrophysics Data System (ADS)

    Gershman, D. J.; Gloeckler, G.; Raines, J. M.; Fisk, L. A.; Solomon, S. C.; Stone, E. C.

    2011-12-01

    During the inner heliosphere transfer orbit of the MESSENGER spacecraft, the Fast Imaging Plasma Spectrometer (FIPS) measured the first pickup ion distributions at heliospheric distances of 0.3-0.75 AU. From several transits of MESSENGER through the interstellar helium gravitational focusing cone at 0.3 AU and 0.6 AU, we find an enhancement by a factor of 4 in measured pickup ion densities centered directly downwind from the direction of interstellar flow. These enhancements extend approximately 30 degrees around the cone center, consistent with corresponding observations made at 1 AU. For approximately time-stationary conditions from 2007 to 2009, we find a nearly 1/R dependence of pickup ion density in the inner heliosphere. We also present the first pitch-angle distributions of helium pickup ions in the inner heliosphere. Near the cone center at 0.3 AU, we observe a strong anti-sunward anisotropy with respect to the bulk solar wind flow, consistent with ions picked up in a nearly radial magnetic field and swept out into the heliosphere with inhibited pitch-angle scattering across 90 degrees. These data are compared with observations of He+ near 1 AU with the Solar Wind Ion Composition Spectrometer (SWICS) that is part of the ACE spacecraft. These measurements cover passes through the heliospheric focusing cone during the same time period. We compare FIPS and SWICS data with models of interstellar neutral density, ionization, and transport properties

  1. Effective doping of low energy ions into superfluid helium droplets

    PubMed Central

    Zhang, Jie; Chen, Lei; Freund, William M.; Kong, Wei

    2015-01-01

    We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 104 ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 105/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies. PMID:26298127

  2. Effective doping of low energy ions into superfluid helium droplets

    SciTech Connect

    Zhang, Jie; Chen, Lei; Freund, William M.; Kong, Wei

    2015-08-21

    We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10{sup 4} ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 10{sup 5}/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies.

  3. Effective doping of low energy ions into superfluid helium droplets.

    PubMed

    Zhang, Jie; Chen, Lei; Freund, William M; Kong, Wei

    2015-08-21

    We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10(4) ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 10(5)/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies.

  4. Transport coefficients of He(+) ions in helium.

    PubMed

    Viehland, Larry A; Johnsen, Rainer; Gray, Benjamin R; Wright, Timothy G

    2016-02-21

    This paper demonstrates that the transport coefficients of (4)He(+) in (4)He can be calculated over wide ranges of E/N, the ratio of the electrostatic field strength to the gas number density, with the same level of precision as can be obtained experimentally if sufficiently accurate potential energy curves are available for the X(2)Σu (+) and A(2)Σg (+) states and one takes into account resonant charge transfer. We start by computing new potential energy curves for these states and testing their accuracy by calculating spectroscopic values for the separate states. It is established that the potentials obtained by extrapolation of results from d-aug-cc-pVXZ (X = 6, 7) basis sets using the CASSCF+MRCISD approach are each in exceptionally close agreement with the best potentials available and with experiment. The potentials are then used in a new computer program to determine the semi-classical phase shifts and the transport cross sections, and from these the gaseous ion transport coefficients are determined. In addition, new experimental values are reported for the mobilities of (4)He(+) in (4)He at 298.7 K, as a function of E/N, where careful consideration is given to minimizing various sources of uncertainty. Comparison with previously measured values establishes that only one set of previous data is reliable. Finally, the experimental and theoretical ion transport coefficients are shown to be in very good to excellent agreement, once corrections are applied to account for quantum-mechanical effects. PMID:26896985

  5. Transport coefficients of He+ ions in helium

    NASA Astrophysics Data System (ADS)

    Viehland, Larry A.; Johnsen, Rainer; Gray, Benjamin R.; Wright, Timothy G.

    2016-02-01

    This paper demonstrates that the transport coefficients of 4He+ in 4He can be calculated over wide ranges of E/N, the ratio of the electrostatic field strength to the gas number density, with the same level of precision as can be obtained experimentally if sufficiently accurate potential energy curves are available for the X2Σu+ and A2Σg+ states and one takes into account resonant charge transfer. We start by computing new potential energy curves for these states and testing their accuracy by calculating spectroscopic values for the separate states. It is established that the potentials obtained by extrapolation of results from d-aug-cc-pVXZ (X = 6, 7) basis sets using the CASSCF+MRCISD approach are each in exceptionally close agreement with the best potentials available and with experiment. The potentials are then used in a new computer program to determine the semi-classical phase shifts and the transport cross sections, and from these the gaseous ion transport coefficients are determined. In addition, new experimental values are reported for the mobilities of 4He+ in 4He at 298.7 K, as a function of E/N, where careful consideration is given to minimizing various sources of uncertainty. Comparison with previously measured values establishes that only one set of previous data is reliable. Finally, the experimental and theoretical ion transport coefficients are shown to be in very good to excellent agreement, once corrections are applied to account for quantum-mechanical effects.

  6. Cryogenic helium as stopping medium for high-energy ions

    NASA Astrophysics Data System (ADS)

    Purushothaman, S.; Dendooven, P.; Moore, I.; Penttilä, H.; Ronkainen, J.; Saastamoinen, A.; Äystö, J.; Peräjärvi, K.; Takahashi, N.; Gloos, K.

    2008-10-01

    We have investigated the survival and transport efficiency of 219Rn ions emitted by a 223Ra source in high-density cryogenic helium gas, with ionisation of the gas induced by a proton beam. The combined efficiency of ion survival and transport by an applied electric field was measured as a function of ionisation rate density for electric fields up to 160 V/cm and for three temperature and density combinations: 77 K, 0.18 mg/cm3, 10 K, 0.18 mg/cm3 and 10 K, 0.54 mg/cm3. At low beam intensity or high electric field, an efficiency of 30 % is obtained, confirming earlier results. A sharp drop in efficiency is observed at a "threshold" ionisation rate density which increases with the square of the applied electric field. At 160 V/cm, the efficiency stays above 10% up to an ionisation rate density of 1012 ion-electron pairs/cm3/s. The observed behaviour is understood as the result of shielding of the applied field by the weak plasma created by the proton beam: it counteracts the effective transport of ions and electrons, leading to recombination between the two. We conclude that cryogenic helium gas at high-density and high electric field is a promising medium for the transformation of very high-energy ions into low-energy ones.

  7. Helium and heavy ion measurements with the CRRES satellite

    NASA Astrophysics Data System (ADS)

    Clayton, Edmund Gary

    The CRRES satellite was in service from July 1990 to October 1991, during a period of high solar modulation and solar activity. The ONR-604 experiment aboard CRRES measured helium with isotopic resolution in the energy range 38-110 MeV/nucleon, and heavy ions through iron at 200-500 MeV/nucleon. Although solar modulation was high throughout the CRRES mission, the mission included periods of solar quiescence as well as a number of large solar flares and associated solar energetic particle events. Measurements were made of helium and heavy ions during both the quiet times and the flare periods. A study was made to search for anomalous component helium in the Earth's magnetosphere using the magnetic field as a rigidity filter. This effort was inconclusive due to background in the outer electron radiation belt. During the solar quiet times, the helium spectrum above 60 MeV/nucleon is consistent with the galactic cosmic rays. Below that energy, a separate component appears early in the mission and rises in prominence over the course of the mission, dominating over the galactic cosmic rays below 60 MeV/nucleon. The distinctness of this component is seen both in the helium spectra and the 3He/4He ratio. An association of this component with interplanetary shocks driven by coronal mass ejections is suggested. During the March and June 1991 flare periods, helium spectral characteristics and isotopic ratios are measured. The results are compared to related diagnostic phenomena of gradual and impulsive solar energetic particle acceleration. The average 3He/4He ratio in both periods is enriched relative to the solar wind; 0.01 in June 1991 and 0.07 in March. The March period contains spikes in the isotopic ratio rising to 0.22. Signatures of known solar phenomena are compared to attempt to identify the predominant acceleration mechanism of each major flare. The development of the CRRES/SPACERAD Heavy Ion Model of the Environment (CHIME) is described and the results presented.

  8. Photoionization Energies and Oscillator Strengths of Helium and Helium-like Ions

    NASA Astrophysics Data System (ADS)

    Faye, N. A. B.; Ndao, A. S.; Konte, A.; Biaye, M.; Wague, A.

    2005-10-01

    We first studied the resonant photoionization of helium-like ions, such as C4+, N5+, and O6+, and determined the wave functions, the excitation energies, and the partial and total widths of the autoionizing states of these ions lying under the n = 3 thresholds of the residual ion. For more detailed analysis of the theory, and a better comprehension of the internal dynamics of atomic resonances and electronic phenomena of correlation, we extended these calculations to other helium-like ions, under higher thresholds (n = 4 and 5) of the hydrogen ions H-, and of Li+, C4+, N5+, and O6+. We were also interested in oscillator strengths. These parameters are important for interpreting the spectra and diagnosing astrophysical and laboratory plasmas, as well as for analyzing the spectra coming from space and determining the composition and relative abundance from the various elements of the stellar and interstellar environment. We sought a better comprehension of the coupling between autoionizing and continuum states and of the phenomena of electronic correlations. We used the method of diagonalization that has been used below the n = 2 threshold of the residual ion. The results are important for astrophysicists and physicists studying matter-radiation interaction and for the invention of new laser systems. We also measured laser-induced chlorophyll fluorescence (LICF) emission spectra of the leaves of some tropical plants using a compact fiber-optic fluorosensor with a continuous-wave violet diode laser as the exciting source and an integrated digital spectrometer to analyze the state of stress of the plants.

  9. Improving ion mobility measurement sensitivity by utilizing helium in an ion funnel trap.

    PubMed

    Ibrahim, Yehia M; Garimella, Sandilya V B; Tolmachev, Aleksey V; Baker, Erin S; Smith, Richard D

    2014-06-01

    Ion mobility instruments that utilize nitrogen as buffer gas are often preceded by an ion trap and accumulation region that also uses nitrogen, and for different inert gases, no significant effects upon performance are expected for ion mobility spectrometry (IMS) of larger ions. However, we have observed significantly improved performance for an ion funnel trap upon adding helium; the signal intensities for higher m/z species were improved by more than an order of magnitude compared to using pure nitrogen. The effect of helium upon IMS resolving power was also studied by introducing a He/N2 gas mixture into the drift cell, and in some cases, a slight improvement was observed compared to pure N2. The improvement in signal can be largely attributed to faster and more efficient ion ejection into the drift tube from the ion funnel trap.

  10. Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions

    National Institute of Standards and Technology Data Gateway

    SRD 124 Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions (Web, free access)   The databases ESTAR, PSTAR, and ASTAR calculate stopping-power and range tables for electrons, protons, or helium ions. Stopping-power and range tables can be calculated for electrons in any user-specified material and for protons and helium ions in 74 materials.

  11. Helium Tagging Infrared Photodissociation Spectroscopy of Reactive Ions.

    PubMed

    Roithová, Jana; Gray, Andrew; Andris, Erik; Jašík, Juraj; Gerlich, Dieter

    2016-02-16

    The interrogation of reaction intermediates is key for understanding chemical reactions; however their direct observation and study remains a considerable challenge. Mass spectrometry is one of the most sensitive analytical techniques, and its use to study reaction mixtures is now an established practice. However, the information that can be obtained is limited to elemental analysis and possibly to fragmentation behavior, which is often challenging to analyze. In order to extend the available experimental information, different types of spectroscopy in the infrared and visible region have been combined with mass spectrometry. Spectroscopy of mass selected ions usually utilizes the powerful sensitivity of mass spectrometers, and the absorption of photons is not detected as such but rather translated to mass changes. One approach to accomplish such spectroscopy involves loosely binding a tag to an ion that will be removed by absorption of one photon. We have constructed an ion trapping instrument capable of reaching temperatures that are sufficiently low to enable tagging by helium atoms in situ, thus permitting infrared photodissociation spectroscopy (IRPD) to be carried out. While tagging by larger rare gas atoms, such as neon or argon is also possible, these may cause significant structural changes to small and reactive species, making the use of helium highly beneficial. We discuss the "innocence" of helium as a tag in ion spectroscopy using several case studies. It is shown that helium tagging is effectively innocent when used with benzene dications, not interfering with their structure or IRPD spectrum. We have also provided a case study where we can see that despite its minimal size there are systems where He has a huge effect. A strong influence of the He tagging was shown in the IRPD spectra of HCCl(2+) where large spectral shifts were observed. While the presented systems are rather small, they involve the formation of mixtures of isomers. We have therefore

  12. Helium Tagging Infrared Photodissociation Spectroscopy of Reactive Ions.

    PubMed

    Roithová, Jana; Gray, Andrew; Andris, Erik; Jašík, Juraj; Gerlich, Dieter

    2016-02-16

    The interrogation of reaction intermediates is key for understanding chemical reactions; however their direct observation and study remains a considerable challenge. Mass spectrometry is one of the most sensitive analytical techniques, and its use to study reaction mixtures is now an established practice. However, the information that can be obtained is limited to elemental analysis and possibly to fragmentation behavior, which is often challenging to analyze. In order to extend the available experimental information, different types of spectroscopy in the infrared and visible region have been combined with mass spectrometry. Spectroscopy of mass selected ions usually utilizes the powerful sensitivity of mass spectrometers, and the absorption of photons is not detected as such but rather translated to mass changes. One approach to accomplish such spectroscopy involves loosely binding a tag to an ion that will be removed by absorption of one photon. We have constructed an ion trapping instrument capable of reaching temperatures that are sufficiently low to enable tagging by helium atoms in situ, thus permitting infrared photodissociation spectroscopy (IRPD) to be carried out. While tagging by larger rare gas atoms, such as neon or argon is also possible, these may cause significant structural changes to small and reactive species, making the use of helium highly beneficial. We discuss the "innocence" of helium as a tag in ion spectroscopy using several case studies. It is shown that helium tagging is effectively innocent when used with benzene dications, not interfering with their structure or IRPD spectrum. We have also provided a case study where we can see that despite its minimal size there are systems where He has a huge effect. A strong influence of the He tagging was shown in the IRPD spectra of HCCl(2+) where large spectral shifts were observed. While the presented systems are rather small, they involve the formation of mixtures of isomers. We have therefore

  13. A pencil beam algorithm for helium ion beam therapy

    SciTech Connect

    Fuchs, Hermann; Stroebele, Julia; Schreiner, Thomas; Hirtl, Albert; Georg, Dietmar

    2012-11-15

    Purpose: To develop a flexible pencil beam algorithm for helium ion beam therapy. Dose distributions were calculated using the newly developed pencil beam algorithm and validated using Monte Carlo (MC) methods. Methods: The algorithm was based on the established theory of fluence weighted elemental pencil beam (PB) kernels. Using a new real-time splitting approach, a minimization routine selects the optimal shape for each sub-beam. Dose depositions along the beam path were determined using a look-up table (LUT). Data for LUT generation were derived from MC simulations in water using GATE 6.1. For materials other than water, dose depositions were calculated by the algorithm using water-equivalent depth scaling. Lateral beam spreading caused by multiple scattering has been accounted for by implementing a non-local scattering formula developed by Gottschalk. A new nuclear correction was modelled using a Voigt function and implemented by a LUT approach. Validation simulations have been performed using a phantom filled with homogeneous materials or heterogeneous slabs of up to 3 cm. The beams were incident perpendicular to the phantoms surface with initial particle energies ranging from 50 to 250 MeV/A with a total number of 10{sup 7} ions per beam. For comparison a special evaluation software was developed calculating the gamma indices for dose distributions. Results: In homogeneous phantoms, maximum range deviations between PB and MC of less than 1.1% and differences in the width of the distal energy falloff of the Bragg-Peak from 80% to 20% of less than 0.1 mm were found. Heterogeneous phantoms using layered slabs satisfied a {gamma}-index criterion of 2%/2mm of the local value except for some single voxels. For more complex phantoms using laterally arranged bone-air slabs, the {gamma}-index criterion was exceeded in some areas giving a maximum {gamma}-index of 1.75 and 4.9% of the voxels showed {gamma}-index values larger than one. The calculation precision of the

  14. Whole-cell imaging at nanometer resolutions using fast and slow focused helium ions.

    PubMed

    Chen, Xiao; Udalagama, Chammika N B; Chen, Ce-Belle; Bettiol, Andrew A; Pickard, Daniel S; Venkatesan, T; Watt, Frank

    2011-10-01

    Observations of the interior structure of cells and subcellular organelles are important steps in unraveling organelle functions. Microscopy using helium ions can play a major role in both surface and subcellular imaging because it can provide subnanometer resolutions at the cell surface for slow helium ions, and fast helium ions can penetrate cells without a significant loss of resolution. Slow (e.g., 10-50 keV) helium ion beams can now be focused to subnanometer dimensions (∼0.25 nm), and keV helium ion microscopy can be used to image the surfaces of cells at high resolutions. Because of the ease of neutralizing the sample charge using a flood electron beam, surface charging effects are minimal and therefore cell surfaces can be imaged without the need for a conducting metallic coating. Fast (MeV) helium ions maintain a straight path as they pass through a cell. Along the ion trajectory, the helium ion undergoes multiple electron collisions, and for each collision a small amount of energy is lost to the scattered electron. By measuring the total energy loss of each MeV helium ion as it passes through the cell, we can construct an energy-loss image that is representative of the mass distribution of the cell. This work paves the way to use ions for whole-cell investigations at nanometer resolutions through structural, elemental (via nuclear elastic backscattering), and fluorescence (via ion induced fluorescence) imaging.

  15. Direct nano-patterning of graphene with helium ion beams

    SciTech Connect

    Naitou, Y.; Iijima, T.; Ogawa, S.

    2015-01-19

    Helium ion microscopy (HIM) was used for direct nano-patterning of single-layer graphene (SLG) on SiO{sub 2}/Si substrates. This technique involves irradiation of the sample with accelerated helium ions (He{sup +}). Doses of 2.0 × 10{sup 16 }He{sup + }cm{sup −2} from a 30 kV beam induced a metal-insulator transition in the SLG. The resolution of HIM patterning on SLG was investigated by fabricating nanoribbons and nanostructures. Analysis of scanning capacitance microscopy measurements revealed that the spatial resolution of HIM patterning depended on the dosage of He{sup +} in a non-monotonic fashion. Increasing the dose from 2.0 × 10{sup 16} to 5.0 × 10{sup 16 }He{sup + }cm{sup −2} improved the spatial resolution to several tens of nanometers. However, doses greater than 1.0 × 10{sup 17 }He{sup + }cm{sup −2} degraded the patterning characteristics. Direct patterning using HIM is a versatile approach to graphene fabrication and can be applied to graphene-based devices.

  16. Data-driven RBE parameterization for helium ion beams.

    PubMed

    Mairani, A; Magro, G; Dokic, I; Valle, S M; Tessonnier, T; Galm, R; Ciocca, M; Parodi, K; Ferrari, A; Jäkel, O; Haberer, T; Pedroni, P; Böhlen, T T

    2016-01-21

    Helium ion beams are expected to be available again in the near future for clinical use. A suitable formalism to obtain relative biological effectiveness (RBE) values for treatment planning (TP) studies is needed. In this work we developed a data-driven RBE parameterization based on published in vitro experimental values. The RBE parameterization has been developed within the framework of the linear-quadratic (LQ) model as a function of the helium linear energy transfer (LET), dose and the tissue specific parameter (α/β)ph of the LQ model for the reference radiation. Analytic expressions are provided, derived from the collected database, describing the RBEα = αHe/αph and Rβ = βHe/βph ratios as a function of LET. Calculated RBE values at 2 Gy photon dose and at 10% survival (RBE10) are compared with the experimental ones. Pearson's correlation coefficients were, respectively, 0.85 and 0.84 confirming the soundness of the introduced approach. Moreover, due to the lack of experimental data at low LET, clonogenic experiments have been performed irradiating A549 cell line with (α/β)ph = 5.4 Gy at the entrance of a 56.4 MeV u(-1)He beam at the Heidelberg Ion Beam Therapy Center. The proposed parameterization reproduces the measured cell survival within the experimental uncertainties. A RBE formula, which depends only on dose, LET and (α/β)ph as input parameters is proposed, allowing a straightforward implementation in a TP system.

  17. Precision, high dose radiotherapy: helium ion treatment of uveal melanoma

    SciTech Connect

    Saunders, W.M.; Char, D.H.; Quivey, J.M.; Castro, J.R.; Chen, G.T.Y.; Collier, J.M.; Cartigny, A.; Blakely, E.A.; Lyman, J.T.; Zink, S.R.

    1985-02-01

    The authors report on 75 patients with uveal melanoma who were treated by placing the Bragg peak of a helium ion beam over the tumor volume. The technique localizes the high dose region very tightly around the tumor volume. This allows critical structures, such as the optic disc and the macula, to be excluded from the high dose region as long as they are 3 to 4 mm away from the edge of the tumor. Careful attention to tumor localization, treatment planning, patient immobilization and treatment verification is required. With a mean follow-up of 22 months (3 to 60 months) the authors have had only five patients with a local recurrence, all of whom were salvaged with another treatment. Pretreatment visual acuity has generally been preserved as long as the tumor edge is at least 4 mm away from the macula and optic disc. The only serious complication to date has been an 18% incidence of neovascular glaucoma in the patients treated at our highest dose level. Clinical results and details of the technique are presented to illustrate potential clinical precision in administering high dose radiotherapy with charged particles such as helium ions or protons.

  18. Investigation of helium ion production in constricted direct current plasma ion source with layered-glows

    SciTech Connect

    Lee, Yuna; Chung, Kyoung-Jae; Park, Yeong-Shin; Hwang, Y. S.

    2014-02-15

    Generation of helium ions is experimentally investigated with a constricted direct current (DC) plasma ion source operated at layered-glow mode, in which electrons could be accelerated through multiple potential structures so as to generate helium ions including He{sup 2+} by successive ionization collisions in front of an extraction aperture. The helium discharge is sustained with the formation of a couple of stable layers and the plasma ball with high density is created near the extraction aperture at the operational pressure down to 0.6 Torr with concave cathodes. The ion beam current extracted with an extraction voltage of 5 kV is observed to be proportional to the discharge current and inversely proportional to the operating pressure, showing high current density of 130 mA/cm{sup 2} and power density of 0.52 mA/cm{sup 2}/W. He{sup 2+} ions, which were predicted to be able to exist due to multiple-layer potential structure, are not observed. Simple calculation on production of He{sup 2+} ions inside the plasma ball reveals that reduced operating pressure and increased cathode area will help to generate He{sup 2+} ions with the layered-glow DC discharge.

  19. Observation of a helium ion energy threshold for retention in tungsten exposed to hydrogen/helium mixture plasma

    NASA Astrophysics Data System (ADS)

    Thompson, M.; Deslandes, A.; Morgan, T. W.; Elliman, R. G.; De Temmerman, G.; Kluth, P.; Riley, D.; Corr, C. S.

    2016-10-01

    Helium retention is measured in tungsten samples exposed to mixed H/He plasma in the Magnum-PSI linear plasma device. It is observed that there is very little He retention below helium ion impact energies of 9.0+/- 1.4 eV, indicating the existence of a potential barrier which must be overcome for implantation to occur. The helium retention in samples exposed to plasma at temperatures  >1000 K is strongly correlated with nano-bubble formation measured using grazing incidence small-angle x-ray scattering. The diameters of nano-bubbles were not found to increase with increasing helium concentration, indicating that additional helium must be accommodated by increasing the bubble concentration or an increase in bubble pressure. For some samples pre-irradiation with heavy ions of 2.0 MeV energy is investigated to simulate the effects of neutron damage. It is observed that nano-bubble sizes are comparable between samples pre-irradiated with heavy-ions, and those without heavy-ion pre-irradiation.

  20. Effects of sequential tungsten and helium ion implantation on nano-indentation hardness of tungsten

    SciTech Connect

    Armstrong, D. E. J.; Edmondson, P. D.; Roberts, S. G.

    2013-06-24

    To simulate neutron and helium damage in a fusion reactor first wall sequential self-ion implantation up to 13 dpa followed by helium-ion implantation up to 3000 appm was performed to produce damaged layers of {approx}2 {mu}m depth in pure tungsten. The hardness of these layers was measured using nanoindentation and was studied using transmission electron microscopy. Substantial hardness increases were seen in helium implanted regions, with smaller hardness increases in regions which had already been self-ion implanted, thus, containing pre-existing dislocation loops. This suggests that, for the same helium content, helium trapped in distributed vacancies gives stronger hardening than helium trapped in vacancies condensed into dislocation loops.

  1. Theory of the Lamb shift in muonic helium ions

    SciTech Connect

    Krutov, A. A.; Martynenko, A. P. Martynenko, G. A.; Faustov, R. N.

    2015-01-15

    The Lamb shift (2P{sub 1/2}-2S{sub 1/2}) in muonic helium ions (μ{sub 2}{sup 3}){sup +}, (μ{sup 2/4}He){sup +} is calculated taking into account the contributions of the order of α{sup 3}, α{sup 4}, α{sup 5}, and α{sup 6}. Special attention is paid to corrections for the polarization of the vacuum, as well as the structure and recoil of the nucleus. Numerical values 1259.8583 meV ((μ{sub 2}{sup 3}He){sup +}) and 1379.1107 meV ((μ{sub 2}{sup 4}He){sup +}) obtained for the shifts can be considered reliable estimates when compared to the experimental data of the CREMA collaboration.

  2. Sympathetic ophthalmia complicating helium ion irradiation of a choroidal melanoma

    SciTech Connect

    Fries, P.D.; Char, D.H.; Crawford, J.B.; Waterhouse, W.

    1987-11-01

    Sympathetic ophthalmia was diagnosed 49 months after helium ion irradiation of a left choroidal melanoma. The patient maintained good vision until 18 months after therapy, when she developed neovascular glaucoma. This complication required multiple therapeutic procedures, including topical anti-inflammatory and antiglaucomatous drops, 360 degrees peripheral panretinal cryoblation, and a single 180 degrees application of inferior cyclocryotherapy over a 2 1/2-year period. Four weeks after the cyclocryotherapy, inflammation was noted in both eyes, and, one month later, enucleation of the left sympathogenic eye was performed. Serial histopathologic sections showed a full-thickness, fibrovascular, scleral scar and tantalum marker ring suture without uveal incarceration. Penetrating surgical trauma, a uveal melanoma, and multiple nonpenetrating treatments resulted in the development of sympathetic ophthalmia.

  3. Data-driven RBE parameterization for helium ion beams

    NASA Astrophysics Data System (ADS)

    Mairani, A.; Magro, G.; Dokic, I.; Valle, S. M.; Tessonnier, T.; Galm, R.; Ciocca, M.; Parodi, K.; Ferrari, A.; Jäkel, O.; Haberer, T.; Pedroni, P.; Böhlen, T. T.

    2016-01-01

    Helium ion beams are expected to be available again in the near future for clinical use. A suitable formalism to obtain relative biological effectiveness (RBE) values for treatment planning (TP) studies is needed. In this work we developed a data-driven RBE parameterization based on published in vitro experimental values. The RBE parameterization has been developed within the framework of the linear-quadratic (LQ) model as a function of the helium linear energy transfer (LET), dose and the tissue specific parameter {{(α /β )}\\text{ph}} of the LQ model for the reference radiation. Analytic expressions are provided, derived from the collected database, describing the \\text{RB}{{\\text{E}}α}={α\\text{He}}/{α\\text{ph}} and {{\\text{R}}β}={β\\text{He}}/{β\\text{ph}} ratios as a function of LET. Calculated RBE values at 2 Gy photon dose and at 10% survival (\\text{RB}{{\\text{E}}10} ) are compared with the experimental ones. Pearson’s correlation coefficients were, respectively, 0.85 and 0.84 confirming the soundness of the introduced approach. Moreover, due to the lack of experimental data at low LET, clonogenic experiments have been performed irradiating A549 cell line with {{(α /β )}\\text{ph}}=5.4 Gy at the entrance of a 56.4 MeV u-1He beam at the Heidelberg Ion Beam Therapy Center. The proposed parameterization reproduces the measured cell survival within the experimental uncertainties. A RBE formula, which depends only on dose, LET and {{(α /β )}\\text{ph}} as input parameters is proposed, allowing a straightforward implementation in a TP system.

  4. Energy-loss and straggling of hydrogen and helium ions in selenium

    NASA Astrophysics Data System (ADS)

    Conradie, J.; Lombaard, J.; Friedland, E.

    1983-01-01

    Using a transmission technique, the energy-loss and straggling of protons, deuterons and helium ions in Se were measured in the energy range between 0.3 and 2.5 MeV. The experimental stopping powers of the various ions are the same as the semiempirical values of Andersen and Ziegler, except in the vicinity of the stopping power maximum. The reduced straggling for the helium and hydrogen ions is energy independent above 0.25 MeV/amu with the helium values the same as predicted by Bohr but the hydrogen values are somewhat lower.

  5. Impact of helium implantation and ion-induced damage on reflectivity of molybdenum mirrors

    NASA Astrophysics Data System (ADS)

    Garcia-Carrasco, A.; Petersson, P.; Hallén, A.; Grzonka, J.; Gilbert, M. R.; Fortuna-Zalesna, E.; Rubel, M.

    2016-09-01

    Molybdenum mirrors were irradiated with Mo and He ions to simulate the effect of neutron irradiation on diagnostic first mirrors in next-generation fusion devices. Up to 30 dpa were produced under molybdenum irradiation leading to a slight decrease of reflectivity in the near infrared range. After 3 × 1017 cm-2 of helium irradiation, reflectivity decreased by up to 20%. Combined irradiation by helium and molybdenum led to similar effects on reflectivity as irradiation with helium alone. Ion beam analysis showed that only 7% of the implanted helium was retained in the first 40 nm layer of the mirror. The structure of the near-surface layer after irradiation was studied with scanning transmission electron microscopy and the extent and size distribution of helium bubbles was documented. The consequences of ion-induced damage on the performance of diagnostic components are discussed.

  6. Observation of electron spin resonance of negative ions in liquid helium

    NASA Technical Reports Server (NTRS)

    Reichert, J. F.; Dahm, A. J.

    1973-01-01

    Electron spin resonance signals of negative ions in liquid helium were observed. The line width and g-value were measured. Electrons injected into helium by field emission from ferromagnetic tips are shown to be polarized. A new technique for the measurement of electron spin polarization is presented.

  7. Arbitrary amplitude electrostatic wave propagation in a magnetized dense plasma containing helium ions and degenerate electrons

    NASA Astrophysics Data System (ADS)

    Mahmood, S.; Sadiq, Safeer; Haque, Q.; Ali, Munazza Z.

    2016-06-01

    The obliquely propagating arbitrary amplitude electrostatic wave is studied in a dense magnetized plasma having singly and doubly charged helium ions with nonrelativistic and ultrarelativistic degenerate electrons pressures. The Fermi temperature for ultrarelativistic degenerate electrons described by N. M. Vernet [(Cambridge University Press, Cambridge, 2007), p. 57] is used to define ion acoustic speed in ultra-dense plasmas. The pseudo-potential approach is used to solve the fully nonlinear set of dynamic equations for obliquely propagating electrostatic waves in a dense magnetized plasma containing helium ions. The upper and lower Mach number ranges for the existence of electrostatic solitons are found which depends on the obliqueness of the wave propagation with respect to applied magnetic field and charge number of the helium ions. It is found that only compressive (hump) soliton structures are formed in all the cases and only subsonic solitons are formed for a singly charged helium ions plasma case with nonrelativistic degenerate electrons. Both subsonic and supersonic soliton hump structures are formed for doubly charged helium ions with nonrelativistic degenerate electrons and ultrarelativistic degenerate electrons plasma case containing singly as well as doubly charged helium ions. The effect of propagation direction on the soliton amplitude and width of the electrostatic waves is also presented. The numerical plots are also shown for illustration using dense plasma parameters of a compact star (white dwarf) from literature.

  8. Fragmentation of HCN in optically selected mass spectrometry: Nonthermal ion cooling in helium nanodroplets

    SciTech Connect

    Lewis, William K.; Bemish, Raymond J.; Miller, Roger E.

    2005-10-08

    A technique that combines infrared laser spectroscopy and helium nanodroplet mass spectrometry, which we refer to as optically selected mass spectrometry, is used to study the efficiency of ion cooling in helium. Electron-impact ionization is used to form He{sup +} ions within the droplets, which go on to transfer their charge to the HCN dopant molecules. Depending upon the droplet size, the newly formed ion either fragments or is cooled by the helium before fragmentation can occur. Comparisons with gas-phase fragmentation data suggest that the cooling provided by the helium is highly nonthermal. An 'explosive' model is proposed for the cooling process, given that the initially hot ion is embedded in such a cold solvent.

  9. Helium Ion Microscopy Visualizes Lipid Nanodomains in Mammalian Cells.

    PubMed

    Schürmann, Matthias; Frese, Natalie; Beyer, André; Heimann, Peter; Widera, Darius; Mönkemöller, Viola; Huser, Thomas; Kaltschmidt, Barbara; Kaltschmidt, Christian; Gölzhäuser, Armin

    2015-11-18

    Cell membranes are composed of 2D bilayers of amphipathic lipids, which allow a lateral movement of the respective membrane components. These components are arranged in an inhomogeneous manner as transient micro- and nanodomains, which are believed to be crucially involved in the regulation of signal transduction pathways in mammalian cells. Because of their small size (diameter 10-200 nm), membrane nanodomains cannot be directly imaged using conventional light microscopy. Here, direct visualization of cell membrane nanodomains by helium ion microscopy (HIM) is presented. It is shown that HIM is capable to image biological specimens without any conductive coating and that HIM images clearly allow the identification of nanodomains in the ultrastructure of membranes with 1.5 nm resolution. The shape of these nanodomains is preserved by fixation of the surrounding unsaturated fatty acids while saturated fatty acids inside the nanodomains are selectively removed. Atomic force microscopy, fluorescence microscopy, 3D structured illumination microscopy, and direct stochastic optical reconstruction microscopy provide additional evidence that the structures in the HIM images of cell membranes originate from membrane nanodomains. The nanodomains observed by HIM have an average diameter of 20 nm and are densely arranged with a minimal nearest neighbor distance of ≈ 15 nm.

  10. Dopant profiling based on scanning electron and helium ion microscopy.

    PubMed

    Chee, Augustus K W; Boden, Stuart A

    2016-02-01

    In this paper, we evaluate and compare doping contrast generated inside the scanning electron microscope (SEM) and scanning helium ion microscope (SHIM). Specialised energy-filtering techniques are often required to produce strong doping contrast to map donor distributions using the secondary electron (SE) signal in the SEM. However, strong doping contrast can be obtained from n-type regions in the SHIM, even without energy-filtering. This SHIM technique is more sensitive than the SEM to donor density changes above its sensitivity threshold, i.e. of the order of 10(16) or 10(17)donorscm(-3) respectively on specimens with or without a p-n junction; its sensitivity limit is well above 2×10(17)acceptorscm(-3) on specimens with or without a p-n junction. Good correlation is found between the widths and slopes of experimentally measured doping contrast profiles of thin p-layers and the calculated widths and slopes of the potential energy distributions across these layers, at a depth of 1 to 3nm and 5 to 10nm below the surface in the SHIM and the SEM respectively. This is consistent with the mean escape depth of SEs in silicon being about 1.8nm and 7nm in the SHIM and SEM respectively, and we conclude that short escape depth, low energy SE signals are most suitable for donor profiling. PMID:26624515

  11. Helium Ion Microscopy Visualizes Lipid Nanodomains in Mammalian Cells.

    PubMed

    Schürmann, Matthias; Frese, Natalie; Beyer, André; Heimann, Peter; Widera, Darius; Mönkemöller, Viola; Huser, Thomas; Kaltschmidt, Barbara; Kaltschmidt, Christian; Gölzhäuser, Armin

    2015-11-18

    Cell membranes are composed of 2D bilayers of amphipathic lipids, which allow a lateral movement of the respective membrane components. These components are arranged in an inhomogeneous manner as transient micro- and nanodomains, which are believed to be crucially involved in the regulation of signal transduction pathways in mammalian cells. Because of their small size (diameter 10-200 nm), membrane nanodomains cannot be directly imaged using conventional light microscopy. Here, direct visualization of cell membrane nanodomains by helium ion microscopy (HIM) is presented. It is shown that HIM is capable to image biological specimens without any conductive coating and that HIM images clearly allow the identification of nanodomains in the ultrastructure of membranes with 1.5 nm resolution. The shape of these nanodomains is preserved by fixation of the surrounding unsaturated fatty acids while saturated fatty acids inside the nanodomains are selectively removed. Atomic force microscopy, fluorescence microscopy, 3D structured illumination microscopy, and direct stochastic optical reconstruction microscopy provide additional evidence that the structures in the HIM images of cell membranes originate from membrane nanodomains. The nanodomains observed by HIM have an average diameter of 20 nm and are densely arranged with a minimal nearest neighbor distance of ≈ 15 nm. PMID:26436577

  12. Dopant profiling based on scanning electron and helium ion microscopy.

    PubMed

    Chee, Augustus K W; Boden, Stuart A

    2016-02-01

    In this paper, we evaluate and compare doping contrast generated inside the scanning electron microscope (SEM) and scanning helium ion microscope (SHIM). Specialised energy-filtering techniques are often required to produce strong doping contrast to map donor distributions using the secondary electron (SE) signal in the SEM. However, strong doping contrast can be obtained from n-type regions in the SHIM, even without energy-filtering. This SHIM technique is more sensitive than the SEM to donor density changes above its sensitivity threshold, i.e. of the order of 10(16) or 10(17)donorscm(-3) respectively on specimens with or without a p-n junction; its sensitivity limit is well above 2×10(17)acceptorscm(-3) on specimens with or without a p-n junction. Good correlation is found between the widths and slopes of experimentally measured doping contrast profiles of thin p-layers and the calculated widths and slopes of the potential energy distributions across these layers, at a depth of 1 to 3nm and 5 to 10nm below the surface in the SHIM and the SEM respectively. This is consistent with the mean escape depth of SEs in silicon being about 1.8nm and 7nm in the SHIM and SEM respectively, and we conclude that short escape depth, low energy SE signals are most suitable for donor profiling.

  13. Positronium formation for positron scattering from helium ion

    NASA Astrophysics Data System (ADS)

    Zhi Zhang, Yong; Yu, Rong Mei; Xia Li, Shu; Song, Xiu Dan; Jiao, Li Guang

    2015-09-01

    Positronium (Ps) formation processes from helium ions by positron impact are studied using the two-channel two-center eikonal final state-continuum initial distorted wave method. The Ps(n = 1 and 2) and total Ps formation cross sections are calculated from the threshold to the high energy region, and the results are compared with other theoretical calculations available in the literature. It is found that the present results agree reasonably well with the close-coupling calculations, while other predictions, such as the Coulomb-Born approximation, the optical potential method, and the recent classical trajectory Monte Carlo method (Naginey 2014 Phys. Rev. A 89, 062704), are all much higher in the entire energy region. The maximum positions of the Ps(n) formation cross sections in our present work are in good agreement with the wave vector matching model of (Charlton 2014 J. Phys. B: At. Mol. Opt. Phys. 39, 4575). Finally, we discuss the scaling law of the Ps(n) formation cross sections with respect to the principal quantum number n of the Ps atom.

  14. Hydration of magnesia cubes: a helium ion microscopy study

    PubMed Central

    Schneider, Johannes; Bourret, Gilles R

    2016-01-01

    Summary Physisorbed water originating from exposure to the ambient can have a strong impact on the structure and chemistry of oxide nanomaterials. The effect can be particularly pronounced when these oxides are in physical contact with a solid substrate such as the ones used for immobilization to perform electron or ion microscopy imaging. We used helium ion microscopy (HIM) and investigated morphological changes of vapor-phase-grown MgO cubes after vacuum annealing and pressing into foils of soft and high purity indium. The indium foils were either used as obtained or, for reference, subjected to vacuum drying. After four days of storage in the vacuum chamber of the microscope and at a base pressure of p < 10−7 mbar, we observed on these cubic particles the attack of residual physisorbed water molecules from the indium substrate. As a result, thin magnesium hydroxide layers spontaneously grew, giving rise to characteristic volume expansion effects, which depended on the size of the particles. Rounding of the originally sharp cube edges leads to a significant loss of the morphological definition specific to the MgO cubes. Comparison of different regions within one sample before and after exposure to liquid water reveals different transformation processes, such as the formation of Mg(OH)2 shells that act as diffusion barriers for MgO dissolution or the evolution of brucite nanosheets organized in characteristic flower-like microstructures. The findings underline the significant metastability of nanomaterials under both ambient and high-vacuum conditions and show the dramatic effect of ubiquitous water films during storage and characterization of oxide nanomaterials. PMID:27335725

  15. Hydration of magnesia cubes: a helium ion microscopy study.

    PubMed

    Schwaiger, Ruth; Schneider, Johannes; Bourret, Gilles R; Diwald, Oliver

    2016-01-01

    Physisorbed water originating from exposure to the ambient can have a strong impact on the structure and chemistry of oxide nanomaterials. The effect can be particularly pronounced when these oxides are in physical contact with a solid substrate such as the ones used for immobilization to perform electron or ion microscopy imaging. We used helium ion microscopy (HIM) and investigated morphological changes of vapor-phase-grown MgO cubes after vacuum annealing and pressing into foils of soft and high purity indium. The indium foils were either used as obtained or, for reference, subjected to vacuum drying. After four days of storage in the vacuum chamber of the microscope and at a base pressure of p < 10(-7) mbar, we observed on these cubic particles the attack of residual physisorbed water molecules from the indium substrate. As a result, thin magnesium hydroxide layers spontaneously grew, giving rise to characteristic volume expansion effects, which depended on the size of the particles. Rounding of the originally sharp cube edges leads to a significant loss of the morphological definition specific to the MgO cubes. Comparison of different regions within one sample before and after exposure to liquid water reveals different transformation processes, such as the formation of Mg(OH)2 shells that act as diffusion barriers for MgO dissolution or the evolution of brucite nanosheets organized in characteristic flower-like microstructures. The findings underline the significant metastability of nanomaterials under both ambient and high-vacuum conditions and show the dramatic effect of ubiquitous water films during storage and characterization of oxide nanomaterials. PMID:27335725

  16. Diagnostics of a charge breeder electron cyclotron resonance ion source helium plasma with the injection of 23Na1+ ions

    NASA Astrophysics Data System (ADS)

    Tarvainen, O.; Koivisto, H.; Galatà, A.; Angot, J.; Lamy, T.; Thuillier, T.; Delahaye, P.; Maunoury, L.; Mascali, D.; Neri, L.

    2016-05-01

    This work describes the utilization of an injected 23Na1+ ion beam as a diagnostics of the helium plasma of a charge breeder electron cyclotron resonance ion source. The obtained data allows estimating the upper limit for the ion-ion collision mean-free path of the incident sodium ions, the lower limit of ion-ion collision frequencies for all charge states of the sodium ions and the lower limit of the helium plasma density. The ion-ion collision frequencies of high charge state ions are shown to be at least on the order of 1-10 MHz and the plasma density is estimated to be on the order of 1011 cm-3 or higher. The experimental results are compared to simulations of the 23Na1+ capture into the helium plasma. The results indicate that the lower breeding efficiency of light ions in comparison to heavier elements is probably due to different capture efficiencies in which the in-flight ionization of the incident 1 + ions plays a vital role.

  17. S-states of helium-like ions

    NASA Astrophysics Data System (ADS)

    Liverts, Evgeny Z.; Barnea, Nir

    2012-03-01

    A simple Mathematica (version 7) code for computing S-state energies and wave functions of two-electron (helium-like) ions is presented. The elegant technique derived from the classical papers of Pekeris is applied. The basis functions are composed of the Laguerre functions. The method is based on the perimetric coordinates and specific properties of the Laguerre polynomials. Direct solution of the generalized eigenvalues and eigenvectors problem is used, distinct from the Pekeris works. No special subroutines were used, only built-in objects supported by Mathematica. The accuracy of the results and computation times depend on the basis size. The ground state and the lowest triplet state energies can be computed with a precision of 12 and 14 significant figures, respectively. The accuracy of the higher excited states calculations is slightly worse. The resultant wave functions have a simple analytical form, that enables calculation of expectation values for arbitrary physical operators without any difficulties. Only three natural parameters are required in the input. The new version of Mathematica code takes into account the fact that the negative hydrogen ion has only one bound state. New version program summaryProgram title: TwoElAtomSL(SH) Catalogue identifier: AEHY_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHY_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 998 No. of bytes in distributed program, including test data, etc.: 286 543 Distribution format: tar.gz Programming language: Mathematica 7.0 and 8.0 Computer: Any PC with a Mathematica installation Operating system: Any which supports Mathematica; tested under Microsoft Windows XP and Linux SUSE 11.0 RAM:⩾10 bytes Classification: 2.1, 2.2, 2.7, 2.9 Catalogue identifier of previous

  18. A comparison of neon versus helium ion beam induced deposition via Monte Carlo simulations.

    PubMed

    Timilsina, Rajendra; Smith, Daryl A; Rack, Philip D

    2013-03-22

    The ion beam induced nanoscale synthesis of PtCx (where x ∼ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPt(IV)Me3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 μs, resulting in an equilibrium coverage of ∼4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied.

  19. Ion-molecule reactions and vibrational deactivation of H2/+/ ions in mixtures of hydrogen and helium

    NASA Technical Reports Server (NTRS)

    Theard, L. P.; Huntress, W. T., Jr.

    1974-01-01

    Use of ion cyclotron resonance methods to measure the thermal energy rate constants for a number of ion-molecule reactions involving hydrogen and hydrogen-helium mixtures. Assuming that the distribution of initial vibrational states in the H2(+) ion is a near-Franck-Condon distribution, the occurrence of collisional deactivation of vibrationally excited H2(+) ions by He atoms is identified, and an approximate rate constant for the deactivation process and its dependence on vibrational energy are given.

  20. The Effects of the Pauli Exclusion Principle in Determining the Ionization Energies of the Helium Atom and Helium-Like Ions

    ERIC Educational Resources Information Center

    Deeney, F. A.; O'Leary, J. P.

    2012-01-01

    For helium and helium-like ions, we have examined the differences between the values of the ionization energies as calculated from the Bohr theory and those measured in experiments. We find that these differences vary linearly with the atomic number of the system. Using this result, we show how the Bohr model for single-electron systems may be…

  1. 15 years experience with helium ion radiotherapy for uvealmelanoma

    SciTech Connect

    Castro, Joseph R.; D.H. Char, P.L. Petti; Daftarii, K.; Quivey,J.M.; Singh, R.P.; Blakeley, E.A.; Phillips, T.L.

    1997-06-01

    Purpose: To review the long-term experience of helium iontherapy as a therapeutic alternative to enucleation for uveal melanoma,particularly with respect to survival, local control, and morbidity.Methods and Materials: 347 patients with uveal melanoma were treated withheluim ion RT from 1978-1992. A nonrandomized dose-searching study wasundertaken, with doses progressively reduced from 80 GyE in fivefractionsto 48 GyE in four fractions, given in 3-15 days, mean of 7days. Results: Local control was achieved in 96 percent of patients, withno difference in the rate of local control being seen at 80, 70, 60, or50 GyE in five fractions. At the lowest dose level of 48 GyE in fourfractions, the local control rate fell to 87 percent. Fifteen of 347patients (4 percent) had local regrowth in the eye requiring enucleation(12 patients), laser (1 patient) or reirradiation (2 patients). The timeof appearance of local regrowth ranged from 4 months to 5 yearsposttreatment, with 85 percent occurring within 3 years. Of the 347patients, 208 are alive as of May 1, 1997. The median follow up of allpatients is 8.5 years, range 1-17 years. Kaplan-Maier (K-M) survival is80 percent at 5 years, 76 percent at 10 years, and 72 percent at 15 yearsposttreatment. Patients with tumors not involving the ciliary body have a15-year K-M survival of 80 percent. The results for patients whose tumorsinvolved the ciliary body are poor, with a 15-year K-M survival of 43percent. Seventy-five percent of patients with tumors at least 3.0 mmfrom the fovea and optic nerve, and initial ultrasound height less than6.0 mm, retained vision of 20/200 or better posttreatment. Patients withtumors larger than 6 mm in thickness, or with tumors lying close to theoptic nerve or fovea, have a reduced chance of retaining useful vision.The enucleation rate is 19 percent, 3 percent for local failure and 16percent because of complications of the helium RT, particularlyneovascular glaucoma, which occurred in 35 percent of

  2. Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions

    NASA Technical Reports Server (NTRS)

    Fahr, H. J.; Nass, H. U.; Rucinski, D.

    1984-01-01

    Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the Sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.

  3. Broadening of the interplanetary helium cone structure due to elastic collisions of LISM helium atoms with solar wind ions

    NASA Astrophysics Data System (ADS)

    Fahr, H. J.; Nass, H. U.; Rucinski, D.

    1984-11-01

    Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the Sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.

  4. Laser Spectroscopy of Radicals, Carbenes, and Ions in Superfluid Helium Droplets

    NASA Astrophysics Data System (ADS)

    Douberly, Gary E.

    2015-06-01

    The first beam of helium droplets was reported in the 1961 paper Strahlen aus kondensiertem Helium im Hochvakuum by Von E. W. Becker and co-workers. However, molecular spectroscopy of helium-solvated dopants wasn't realized until 30 years later in the laboratories of Scoles and Toennies. It has now been two decades since this early, seminal work on doped helium droplets, yet the field of helium droplet spectroscopy is still fresh with vast potential. Analogous in many ways to cryogenic matrix isolation spectroscopy, the helium droplet is an ideal environment to spectroscopically probe difficult to prepare molecular species, such as radicals, carbenes and ions. The quantum nature of helium at 0.35 K often results in molecular spectra that are sufficiently resolved to evoke an analysis of line shapes and fine-structure that is worthy of the International Symposium on Molecular Spectroscopy. The present talk will focus on our recent successful attempts to efficiently dope the title molecular species into helium droplets and probe their properties with infrared laser Stark and Zeeman spectroscopies. E. W. Becker, R. Klingelhöfer, P. Lohse, Z. Naturforsch. A 16A, 1259 (1961). S. Goyal, D. L. Schutt, G. Scoles, Phys. Rev. Lett. 69, 933 (1992). M. Hartmann, R. E. Miller, J. P. Toennies, A. F. Vilesov, Phys. Rev. Lett. 75, 1566, (1995).

  5. Low flux and low energy helium ion implantation into tungsten using a dedicated plasma source

    NASA Astrophysics Data System (ADS)

    Pentecoste, Lucile; Thomann, Anne-Lise; Melhem, Amer; Caillard, Amael; Cuynet, Stéphane; Lecas, Thomas; Brault, Pascal; Desgardin, Pierre; Barthe, Marie-France

    2016-09-01

    The aim of this work is to investigate the first stages of defect formation in tungsten (W) due to the accumulation of helium (He) atoms inside the crystal lattice. To reach the required implantation conditions, i.e. low He ion fluxes (1011-1014 ions.cm2.s-1) and kinetic energies below the W atom displacement threshold (about 500 eV for He+), an ICP source has been designed and connected to a diffusion chamber. Implantation conditions have been characterized by means of complementary diagnostics modified for measurements in this very low density helium plasma. It was shown that lowest ion fluxes could only be reached for the discharge working in capacitive mode either in α or γ regime. Special attention was paid to control the energy gained by the ions by acceleration through the sheath at the direct current biased substrate. At very low helium pressure, in α regime, a broad ion energy distribution function was evidenced, whereas a peak centered on the potential difference between the plasma and the biased substrate was found at higher pressures in the γ mode. Polycrystalline tungsten samples were exposed to the helium plasma in both regimes of the discharge and characterized by positron annihilation spectroscopy in order to detect the formed vacancy defects. It was found that W vacancies are able to be formed just by helium accumulation and that the same final implanted state is reached, whatever the operating mode of the capacitive discharge.

  6. Helium ion beam milling to create a nano-structured domain wall magnetoresistance spin valve.

    PubMed

    Wang, Yudong; Boden, S A; Bagnall, D M; Rutt, H N; de Groot, C H

    2012-10-01

    We have fabricated and measured single domain wall magnetoresistance devices with sub-20 nm gap widths using a novel combination of electron beam lithography and helium ion beam milling. The measurement wires and external profile of the spin valve are fabricated by electron beam lithography and lift-off. The critical bridge structure is created using helium ion beam milling, enabling the formation of a thinner gap (and so a narrower domain wall) than that which is possible with electron beam techniques alone. Four-point probe resistance measurements and scanning electron microscopy are used to characterize the milled structures and optimize the He ion dose. Successful operation of the device as a spin valve is demonstrated, with a 0.2% resistance change as the external magnetic field is cycled. The helium ion beam milling efficiency as extracted from electrical resistance measurements is 0.044 atoms/ion, about half the theoretical value. The gap in the device is limited to a maximum of 20 nm with this technique due to sub-surface swelling caused by injected ions which can induce catastrophic failure in the device. The fine patterning capabilities of the helium ion microscope milling technique indicate that sub-5 nm constriction widths could be possible. PMID:22972003

  7. Dark-Field Scanning Transmission Ion Microscopy via Direct Detection of Transmitted Helium Ions with a Multichannel Plate

    NASA Astrophysics Data System (ADS)

    Woehl, Taylor; White, Ryan; Keller, Robert

    A multichannel plate was used as an ion sensitive transmission detector in a commercial helium ion microscope for annular dark-field imaging of nanomaterials, i.e. scanning transmission ion microscopy. In contrast to previous transmission helium ion microscopy approaches that used secondary electron conversion holders, our new approach directly detects transmitted helium ions on an annular detector. Monte Carlo simulations are used to predict detector collection angles at which annular dark-field images with atomic number contrast are obtained. We demonstrate atomic number contrast imaging via scanning transmission ion imaging of silica-coated gold nanoparticles and magnetite nanoparticles. While the resolution of this transmission technique is limited by beam broadening in the substrate, we image magnetite nanoparticles with high contrast on a relatively thick silicon nitride substrate. We expect this new approach to annular dark-field scanning transmission ion microscopy will open avenues for more quantitative ion imaging techniques, such as direct mass-thickness determination, and advance fundamental understanding of underlying ion scattering mechanisms leading to image formation.

  8. Monte Carlo calculations of drift velocities and diffusion coefficients of Ar + ions in helium

    NASA Astrophysics Data System (ADS)

    Barata, J. A. S.; Conde, C. A. N.

    2007-09-01

    Results are presented for the calculated drift velocities and diffusion coefficients for Ar + ions in helium at atmospheric pressure, temperature T=300 K and for reduced electric fields E/ N from about 1 Td up to about 150 Td, using Monte Carlo techniques. The drift velocities range from 5.94×10 3 to 559.0×10 3 cm s -1 for the Ar + ions in the ground state 2P 3/2 and from 5.85×10 3 to 545.0×10 3 cm s -1 for the Ar + ions in the metastable excited state 2P 1/2. These values are in good agreement (within about 5%) with the few experimental values available. The mobilities and diffusion coefficients for atomic Ar + ions in helium gas show no significant dependence on the spin state of the ion.

  9. Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion source.

    PubMed

    Choi, Seyong; Lee, Byoung-Seob; Park, Jin Yong; Ok, Jung-Woo; Shin, Chang Seouk; Yoon, Jang-Hee; Won, Mi-Sook; Kim, Byoung-Chul

    2014-02-01

    Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

  10. Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion source

    NASA Astrophysics Data System (ADS)

    Choi, Seyong; Lee, Byoung-Seob; Park, Jin Yong; Ok, Jung-Woo; Shin, Chang Seouk; Yoon, Jang-Hee; Won, Mi-Sook; Kim, Byoung-Chul

    2014-02-01

    Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

  11. The interaction of a nanoscale coherent helium-ion probe with a crystal.

    PubMed

    D'Alfonso, A J; Forbes, B D; Allen, L J

    2013-11-01

    Thickness fringing was recently observed in helium ion microscopy (HIM) when imaging magnesium oxide cubes using a 40 keV convergent probe in scanning transmission mode. Thickness fringing is also observed in electron microscopy and is due to quantum mechanical, coherent, multiple elastic scattering attenuated by inelastic phonon excitation (thermal scattering). A quantum mechanical model for elastic scattering and phonon excitation correctly models the thickness fringes formed by the helium ions. However, unlike the electron case, the signal in the diffraction plane is due mainly to the channeling of ions which have first undergone inelastic thermal scattering in the first few atomic layers so that the origin of the thickness fringes is not due to coherent interference effects. This quantum mechanical model affords insight into the interaction of a nanoscale, focused coherent ion probe with the specimen and allows us to elucidate precisely what is needed to achieve atomic resolution HIM.

  12. Creation and physical aspects of luminescent patterns using helium ion microscopy

    SciTech Connect

    Veligura, Vasilisa; Hlawacek, Gregor; Gastel, Raoul van; Zandvliet, Harold J. W.; Poelsema, Bene; Jahn, Uwe

    2014-05-14

    The helium ion microscope provides a sub-nanometer size He{sup +} ion beam which can be employed for materials modification. We demonstrate how material properties can be tuned in a helium ion microscope with very high precision using, as an example, the modification of the luminescence properties of a sodium chloride crystal. Although the beam size is extremely small, the actually affected sample volume is much bigger due to collision cascades. We have directly measured the diameter of the interaction volume of the 35 keV He{sup +} beam with a sodium chloride crystal using ionoluminescence. The experimental results are compared to stopping and range of ions in matter simulations and calculations of the point spread function.

  13. Transport of Helium Pickup Ions within the Focusing Cone: Reconciling STEREO Observations with IBEX

    NASA Astrophysics Data System (ADS)

    Quinn, P. R.; Schwadron, N. A.; Möbius, E.

    2016-06-01

    Recent observations of the pickup helium focusing cone by STEREO/Plasma and Suprathermal Ion Composition indicate an inflow longitude of the interstellar wind that differs from the observations of IBEX by 1\\buildrel{\\circ}\\over{.} 8+/- 2\\buildrel{\\circ}\\over{.} 4. It has been under debate whether the transport of helium pickup ions with an anisotropic velocity distribution is the cause of this difference. If so, the roughly field-aligned pickup ion streaming relative to the solar wind should create a shift in the pickup ion density relative to the focusing cone. A large pickup ion streaming depends on the size of the mean free path. Therefore, the observed longitudinal shift in the pickup ion density relative to the neutral focusing cone may carry fundamental information about the mean free path experienced by pickup ions inside 1 au. We test this hypothesis using the Energetic Particle Radiation Environment Module (EPREM) model by simulating the transport of helium pickup ions within the focusing cone finding a mean free path of {λ }\\parallel =0.19+0.29(-0.19) au. We calculate the average azimuthal velocity of pickup ions and find that the anisotropic distribution reaches ˜8% of the solar wind speed. Lastly, we isolate transport effects within EPREM, finding that pitch-angle scattering, adiabatic focusing, perpendicular diffusion, and particle drift contribute to shifting the focusing cone 20.00%, 69.43%, 10.56%, and \\lt 0.01 % , respectively. Thus we show with the EPREM model that the transport of pickup ions does indeed shift the peak of the focusing cone relative to the progenitor neutral atoms and this shift provides fundamental information on the scattering of pickup ions inside 1 au.

  14. Zero Degree Target Electron Spectroscopy: Double Excitation-Autoionization of Helium in Fast Electron, Hydrogen Ion, HELIUM(+) Ion and HELIUM(+2) Ion Collisions

    NASA Astrophysics Data System (ADS)

    Wang, Houle

    The purpose of this work is to investigate few -body dynamical effects in fast ion-atom and electron-atom collisions using zero-degree high-resolution Auger electron spectroscopy. In this study we report the first zero degree high-resolution spectra and double differential cross sections (DDCS) measurement for double excitation-autoionization of He target atoms. We also measured direct ionization DDCS at zero degree observation angle. All of our cross sections are absolutely calibrated. The projectiles used in this work are energetic electrons in the energy range 150 to 1000eV, 100KeV to 1.5MeV protons, 400KeV to 1.5MeV He^+ and 400KeV to 1.6MeV He ^{2+}. The zero degree observation angle provide a unique opportunity to maximize interaction between the emitted electron, the ionized target atom and the charged projectile particle. Using an equal or better than 0.2% instrumental energy resolution allows us to study the autoionization line profiles. In particular the doubly excited autoionizing (2lnl') states of He have been observed as a function of the collision conditions such as impact velocity, projectile charge sign and type of projectile, specifically for dominating (2p^2)^1 Dto(1sepsilon d) and (2s2p)^1P ^circto(1sepsilon p) channels. The results of our measurement clearly indicate that the three-body Coulomb interaction in the final state (CIFS) not only affect autoionizing resonance energies and line widths but also strongly influences the interference of the transition amplitudes between competing processes such as direct ionization and autoionization. We found that the Fano or Shore parametrization generally fails for zero degree autoionization by positive ion impact at medium to high projectile energy. Therefore a new post collisional three-body CIFS model has been developed as a parametrization procedure. This model has been successfully applied to double excitation processes to study single differential cross sections of the (2p^2) ^1D and (2s2p)^1P

  15. Experiment and modeling of laser photodetachment of negative ions in helium oxygen barrier discharges

    NASA Astrophysics Data System (ADS)

    Tschiersch, Robert; Nemschokmichal, Sebastian; Meichsner, Jürgen

    2015-09-01

    Helium oxygen discharges operating at atmospheric pressure are of great interest for applications, such as surface treatment of biological samples. Helium as the buffer gas keeps the driving power low, and oxygen serves as the source of radicals. The large electronegativity of oxygen results in the formation of negative ions which in turn have a remarkable influence on the discharge development. To point out this role of negative ions, the change of the discharge behavior after the laser photodetachment of negative ions is measured in a helium oxygen barrier discharge. These measurements reveal a lower breakdown voltage when firing the laser during the pre-phase of the discharge. The reason is the additional pre-ionization by the detached electrons which was proved by an 1D numeric fluid modeling. The next step is the determination of absolute number densities of negative ions by a comparison of the experimental parameter variations with those from the modeling. Furthermore, the actual role of negative ions on the discharge behavior will be emphasized by the modeling.

  16. Study of the amorphization of surface silicon layers implanted by low-energy helium ions

    NASA Astrophysics Data System (ADS)

    Lomov, A. A.; Myakon'kikh, A. V.; Oreshko, A. P.; Shemukhin, A. A.

    2016-03-01

    The structural changes in surface layers of Si(001) substrates subjected to plasma-immersion implantation by (2-5)-keV helium ions to a dose of D = 6 × 1015-5 × 1017 cm-2 have been studied by highresolution X-ray diffraction, Rutherford backscattering, and spectral ellipsometry. It is found that the joint application of these methods makes it possible to determine the density depth distribution ρ( z) in an implanted layer, its phase state, and elemental composition. Treatment of silicon substrates in helium plasma to doses of 6 × 1016 cm-2 leads to the formation of a 20- to 30-nm-thick amorphized surface layer with a density close to the silicon density. An increase in the helium dose causes the formation of an internal porous layer.

  17. Charge stripping of U238 ion beam by helium gas stripper

    NASA Astrophysics Data System (ADS)

    Imao, H.; Okuno, H.; Kuboki, H.; Yokouchi, S.; Fukunishi, N.; Kamigaito, O.; Hasebe, H.; Watanabe, T.; Watanabe, Y.; Kase, M.; Yano, Y.

    2012-12-01

    Development of a nondestructive, efficient electric-charge-stripping method is a key requirement for next-generation high-intensity heavy-ion accelerators such as the RIKEN Radioactive-Isotope Beam Factory. A charge stripper employing a low-Z gas is an important candidate applicable to high-intensity uranium beams for replacing carbon-foil strippers. In this study, a high-beam-transmission charge-stripping system employing helium gas for U238 beams injected at 10.8MeV/u was developed and demonstrated for the first time. The charge-state evolution measured using helium in a thickness range of 0.24-1.83mg/cm2 is compared with theoretical predictions. Energy attenuation and energy spread due to the helium stripper are also investigated.

  18. Temperature dependent mobility measurements of alkali earth ions in superfluid helium

    NASA Astrophysics Data System (ADS)

    Putlitz, Gisbert Zu; Baumann, I.; Foerste, M.; Jungmann, K.; Riediger, O.; Tabbert, B.; Wiebe, J.; Zühlke, C.

    1998-05-01

    Mobility measurements of impurity ions in superfluid helium are reported. Alkali earth ions were produced with a laser sputtering technique and were drawn inside the liquid by an electric field. The experiments were carried out in the temperature region from 1.27 up to 1.66 K. The temperature dependence of the mobility of Be^+-ions (measured here for the first time) differs from that of the other alkali earth ions Mg^+, Ca^+, Sr^+ and Ba^+, but behaves similar to that of He^+ (M. Foerste, H. Günther, O. Riediger, J. Wiebe, G. zu Putlitz, Z. Phys. B) 104, 317 (1997). Theories of Atkins (A. Atkins, Phys. Rev.) 116, 1339 (1959) and Cole (M.W. Cole, R.A. Bachmann Phys. Rev. B) 15, 1388 (1977) predict a different defect structure for He^+ and the alkali earth ions: the helium ion is assumed to form a snowball like structure whereas for the alkali earth ions a bubble structure is assumed. If the temperature dependence is a characteristic feature for the different structures, then it seems likely that the Be^+ ion builds a snowball like structure.

  19. Dark-Field Scanning Transmission Ion Microscopy via Detection of Forward-Scattered Helium Ions with a Microchannel Plate.

    PubMed

    Woehl, Taylor J; White, Ryan M; Keller, Robert R

    2016-06-01

    A microchannel plate was used as an ion sensitive detector in a commercial helium ion microscope (HIM) for dark-field transmission imaging of nanomaterials, i.e. scanning transmission ion microscopy (STIM). In contrast to previous transmission HIM approaches that used secondary electron conversion holders, our new approach detects forward-scattered helium ions on a dedicated annular shaped ion sensitive detector. Minimum collection angles between 125 mrad and 325 mrad were obtained by varying the distance of the sample from the microchannel plate detector during imaging. Monte Carlo simulations were used to predict detector angular ranges at which dark-field images with atomic number contrast could be obtained. We demonstrate atomic number contrast imaging via scanning transmission ion imaging of silica-coated gold nanoparticles and magnetite nanoparticles. Although the resolution of STIM is known to be degraded by beam broadening in the substrate, we imaged magnetite nanoparticles with high contrast on a relatively thick silicon nitride substrate. We expect this new approach to annular dark-field STIM will open avenues for more quantitative ion imaging techniques and advance fundamental understanding of underlying ion scattering mechanisms leading to image formation.

  20. Dark-Field Scanning Transmission Ion Microscopy via Detection of Forward-Scattered Helium Ions with a Microchannel Plate.

    PubMed

    Woehl, Taylor J; White, Ryan M; Keller, Robert R

    2016-06-01

    A microchannel plate was used as an ion sensitive detector in a commercial helium ion microscope (HIM) for dark-field transmission imaging of nanomaterials, i.e. scanning transmission ion microscopy (STIM). In contrast to previous transmission HIM approaches that used secondary electron conversion holders, our new approach detects forward-scattered helium ions on a dedicated annular shaped ion sensitive detector. Minimum collection angles between 125 mrad and 325 mrad were obtained by varying the distance of the sample from the microchannel plate detector during imaging. Monte Carlo simulations were used to predict detector angular ranges at which dark-field images with atomic number contrast could be obtained. We demonstrate atomic number contrast imaging via scanning transmission ion imaging of silica-coated gold nanoparticles and magnetite nanoparticles. Although the resolution of STIM is known to be degraded by beam broadening in the substrate, we imaged magnetite nanoparticles with high contrast on a relatively thick silicon nitride substrate. We expect this new approach to annular dark-field STIM will open avenues for more quantitative ion imaging techniques and advance fundamental understanding of underlying ion scattering mechanisms leading to image formation. PMID:27153003

  1. Reflection properties of hydrogen ions at helium irradiated tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Doi, K.; Tawada, Y.; Lee, H. T.; Kato, S.; Tanaka, N.; Sasao, M.; Kisaki, M.; Nishiura, M.; Matsumoto, Y.; Kenmotsu, T.; Wada, M.; Ueda, Y.; Yamaoka, H.

    2016-02-01

    Nanostructured W surfaces prepared by He bombardment exhibit characteristic angular distributions of hydrogen ion reflection upon injection of 1 keV H+ beam. A magnetic momentum analyzer that can move in the vacuum chamber has measured the angular dependence of the intensity and the energy of reflected ions. Broader angular distributions were observed for He-irradiated tungsten samples compared with that of the intrinsic polycrystalline W. Both intensity and energy of reflected ions decreased in the following order: the polycrystalline W, the He-bubble containing W, and the fuzz W. Classical trajectory Monte Carlo simulations based on Atomic Collision in Amorphous Target code suggests that lower atom density near the surface can make the reflection coefficients lower due to increasing number of collisions.

  2. Narrow conducting channels defined by helium ion beam damage

    SciTech Connect

    Cheeks, T.L.; Roukes, M.L.; Scherer, A.; Craighead, H.G.

    1988-11-14

    We have developed a new technique for patterning narrow conducting channels in GaAs-AlGaAs two-dimensional electron gas (2DEG) materials. A low-energy He ion beam successfully patterned narrow wires with little or no etching of the thin GaAs cap. The damage propagation of the He ion even at low energies was sufficient to decrease the mobility of the 2DEG located deep within the structure. The damage can be removed by a low-temperature anneal but remains stable at room temperature. Conducting channels as narrow as 300 nm have been fabricated and measured using low-temperature magnetoresistance.

  3. HELIUM ION ANISOTROPIES IN COROTATING INTERACTION REGIONS AT 1 AU

    SciTech Connect

    Ebert, R. W.; Desai, M. I.; Dayeh, M. A.; Mason, G. M.

    2012-08-01

    We investigated the first-order flow anisotropies in the solar wind frame of {approx}0.06-0.95 MeV nucleon{sup -1} He ions during three corotating interaction region (CIR)-associated particle intensity enhancements observed at 1 AU by Wind, examining CIRs with (1) a reverse shock, (2) a well-formed compression region, and (3) a weak compression region. We identified anti-sunward flows in the compression region downstream of the CIR trailing edge in the events with a reverse shock and well-formed compression that transitioned to sunward flows across and upstream of this boundary. These observations suggest that the trailing edge is organizing the He ion flows and is a local source for the particles in these events, this source being inside 1 AU prior to the trailing edge arrival and beyond 1 AU after its passage. The event with the weak compression region had predominantly sunward flows throughout, indicating that the source of the He ions was beyond 1 AU. These observations provide compelling evidence that He ions at 1 AU can be accelerated to suprathermal energies at the CIR trailing edge in events where the compression region is well formed.

  4. Study of Exotic Ions in Superfluid Helium-4 Using a Carbon Nanotube Source

    NASA Astrophysics Data System (ADS)

    Wei, W.; Xie, Z.-L.; Yang, Y.; Seidel, G. M.; Maris, H. J.

    2014-12-01

    We have extended our measurements of the properties of exotic negatively-charged ions in superfluid helium-4. We measured the ion mobility using the time-of-of-flight method at temperatures in the range between 1.03 and 1.16 K. Ions were generated by an electrical discharge produced by applying a voltage to sharp tips in the helium vapor above the liquid surface. Previous studies by Ihas and Sanders, Eden and McClintock, and by our group used tungsten tips and were able to detect at least twelve exotic ions in addition to the normal electron bubble. In the present work we have experimented with tips each consisting of a stainless steel wire coated with carbon nanotubes. We have found that with these tips the strength of the exotic ion signal is substantially increased making it possible to detect several ions which previously could not be seen. The present data combined with the results of the previous studies indicate that there are at least eighteen exotic ions with different mobility.

  5. Macroscopic quasi-linear theory and particle-in-cell simulation of helium ion anisotropy instabilities

    NASA Astrophysics Data System (ADS)

    Yoon, Peter H.; Seough, Jungjoon; Hwang, Junga; Nariyuki, Yasuhiro

    2015-08-01

    The protons and helium ions in the solar wind are observed to possess anisotropic temperature profiles. The anisotropy appears to be limited by various marginal instability conditions. One of the efficient methods to investigate the global dynamics and distribution of various temperature anisotropies in the large-scale solar wind models may be that based upon the macroscopic quasi-linear approach. The present paper investigates the proton and helium ion anisotropy instabilities on the basis of the quasi-linear theory versus particle-in-cell simulation. It is found that the overall dynamical development of the particle temperatures is quite accurately reproduced by the macroscopic quasi-linear scheme. The wave energy development in time, however, shows somewhat less restrictive comparisons, indicating that while the quasi-linear method is acceptable for the particle dynamics, the wave analysis probably requires higher-order physics, such as wave-wave coupling or nonlinear wave-particle interaction.

  6. Stereotactic helium-ion radiosurgery for the treatment of intracranial arteriovenous malformations

    SciTech Connect

    Fabrikant, J.I.; Levy, R.P.; Frankel, K.A.; Phillips, M.H.; Lyman, J.T.; Chuang, F.Y.S.; Steinberg, G.K.; Marks, M.P.

    1989-12-01

    One of the more challenging problems of vascular neurosurgery is the management of surgically-inaccessible arteriovenous malformations (AVMs) of the brain. At Lawrence Berkeley Laboratory, we have developed the method of stereotactic heavy-charged-particle (helium-ion) Bragg peak radiosurgery for treatment of inoperable intracranial AVMs in over 300 patients since 1980 (Fabrikant et al. 1989, Fabrikant et al. 1985, Levy et al. 1989). This report describes patient selection, treatment method, clinical and neuroradiologic results and complications encountered. 4 refs.

  7. A Measurement of the Adiabatic Cooling Index for Interstellar Helium Pickup Ions in the Inner Heliosphere

    NASA Astrophysics Data System (ADS)

    Saul, Lukas; Wurz, Peter; Kallenbach, Reinald

    2009-09-01

    Interstellar neutral gas enters the inner heliosphere where it is ionized and becomes the pickup ion population of the solar wind. It is often assumed that this population will subsequently cool adiabatically, like an expanding ideal gas due, to the divergent flow of the solar wind. Here, we report the first independent measure of the effective adiabatic cooling index in the inner heliosphere from SOHO CELIAS measurements of singly charged helium taken during times of perpendicular interplanetary magnetic field. We use a simple adiabatic transport model of interstellar pickup helium ions, valid for the upwind region of the inner heliosphere. The time averaged velocity spectrum of helium pickup ions measured by CELIAS/CTOF is fit to this model with a single free parameter which indicates an effective cooling rate with a power-law index of γ = 1.35 ± 0.2. While this average is consistent with the "ideal-gas" assumption of γ = 1.5, the analysis indicates that such an assumption will not apply in general, and that due to observational constraints further measurements are necessary to constrain the cooling process. Implications are discussed for understanding the transport processes in the inner heliosphere and improving this measurement technique.

  8. A MEASUREMENT OF THE ADIABATIC COOLING INDEX FOR INTERSTELLAR HELIUM PICKUP IONS IN THE INNER HELIOSPHERE

    SciTech Connect

    Saul, Lukas; Wurz, Peter; Kallenbach, Reinald

    2009-09-20

    Interstellar neutral gas enters the inner heliosphere where it is ionized and becomes the pickup ion population of the solar wind. It is often assumed that this population will subsequently cool adiabatically, like an expanding ideal gas due, to the divergent flow of the solar wind. Here, we report the first independent measure of the effective adiabatic cooling index in the inner heliosphere from SOHO CELIAS measurements of singly charged helium taken during times of perpendicular interplanetary magnetic field. We use a simple adiabatic transport model of interstellar pickup helium ions, valid for the upwind region of the inner heliosphere. The time averaged velocity spectrum of helium pickup ions measured by CELIAS/CTOF is fit to this model with a single free parameter which indicates an effective cooling rate with a power-law index of gamma = 1.35 +- 0.2. While this average is consistent with the 'ideal-gas' assumption of gamma = 1.5, the analysis indicates that such an assumption will not apply in general, and that due to observational constraints further measurements are necessary to constrain the cooling process. Implications are discussed for understanding the transport processes in the inner heliosphere and improving this measurement technique.

  9. Cavity morphology in a Ni based superalloy under heavy ion irradiation with hot pre-injected helium. II

    SciTech Connect

    Zhang, He; Yao, Zhongwen Daymond, Mark R.; Kirk, Marquis A.

    2014-03-14

    In the current investigation, TEM in-situ heavy ion (1 MeV Kr{sup 2+}) irradiation with helium pre-injected at elevated temperature (400 °C) was conducted to simulate in-reactor neutron irradiation induced damage in CANDU spacer material Inconel X-750, in an effort to understand the effects of helium on irradiation induced cavity microstructures. Three different quantities of helium, 400 appm, 1000 appm, and 5000 appm, were pre-injected directly into TEM foils at 400 °C. The samples containing helium were then irradiated in-situ with 1 MeV Kr{sup 2+} at 400 °C to a final dose of 5.4 dpa (displacement per atom). Cavities were formed from the helium injection solely and the cavity density and size increased with increasing helium dosage. In contrast to previous heavy ion irradiations with cold pre-injected helium, heterogeneous nucleation of cavities was observed. During the ensuing heavy ion irradiation, dynamical observation showed noticeable size increase in cavities which nucleated close to the grain boundaries. A “bubble-void” transformation was observed after Kr{sup 2+} irradiation to high dose (5.4 dpa) in samples containing 1000 appm and 5000 appm helium. Cavity distribution was found to be consistent with in-reactor neutron irradiation induced cavity microstructures. This implies that the distribution of helium is greatly dependent on the injection temperature, and helium pre-injection at high temperature is preferred for simulating the migration of the transmutation produced helium.

  10. Precise milling of nano-gap chains in graphene with a focused helium ion beam

    NASA Astrophysics Data System (ADS)

    Zhou, Yangbo; Maguire, Pierce; Jadwiszczak, Jakub; Muruganathan, Manoharan; Mizuta, Hiroshi; Zhang, Hongzhou

    2016-08-01

    A focused helium ion beam was used to introduce nano-sized gap chains in graphene. The effect of beam scanning strategies in the fabrication of the nano-gap chains was investigated. The tuning of graphene conductivity has been achieved by modulating the magnitude and uniformity of the ion dose and hence the morphology of the nano-gap chains. A model based on the site-specific and dose-dependent conductivity was built to understand the tuning of the conductivity, taking into account the nanoscale non-uniformity of irradiation.

  11. Synthesis of nanowires via helium and neon focused ion beam induced deposition with the gas field ion microscope.

    PubMed

    Wu, H M; Stern, L A; Chen, J H; Huth, M; Schwalb, C H; Winhold, M; Porrati, F; Gonzalez, C M; Timilsina, R; Rack, P D

    2013-05-01

    The ion beam induced nanoscale synthesis of platinum nanowires using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPt(IV)Me3) precursor is investigated using helium and neon ion beams in the gas field ion microscope. The He(+) beam induced deposition resembles material deposited by electron beam induced deposition with very small platinum nanocrystallites suspended in a carbonaceous matrix. The He(+) deposited material composition was estimated to be 16% Pt in a matrix of amorphous carbon with a large room-temperature resistivity (∼3.5 × 10(4)-2.2 × 10(5) μΩ cm) and temperature-dependent transport behavior consistent with a granular material in the weak intergrain tunnel coupling regime. The Ne(+) deposited material has comparable composition (17%), however a much lower room-temperature resistivity (∼600-3.0 × 10(3) μΩ cm) and temperature-dependent electrical behavior representative of strong intergrain coupling. The Ne(+) deposited nanostructure has larger platinum nanoparticles and is rationalized via Monte Carlo ion-solid simulations which show that the neon energy density deposited during growth is much larger due to the smaller ion range and is dominated by nuclear stopping relative to helium which has a larger range and is dominated by electronic stopping.

  12. Oxide dispersion strengthened steel irradiation with helium ions

    NASA Astrophysics Data System (ADS)

    Pouchon, M. A.; Chen, J.; Döbeli, M.; Hoffelner, W.

    2006-06-01

    Oxide dispersion strengthened (ODS) ferritic steels are investigated as possible structural material for the future generation of high temperature gas cooled nuclear reactors. ODS-steels are considered to replace other high temperature materials for tubing or structural parts. The oxide particles serve for interfacial pinning of moving dislocations. Therefore, the creep resistance is improved. In case of the usage of these materials in reactors, the behavior under irradiation must be further clarified. In this paper the effects induced by 4He2+ implantation into a ferritic ODS steel are investigated. The fluence ranges from 1016 to 1017 cm-2 and the energy from 1 to 2 MeV. The induced swelling is investigated for implantations at room temperature and 470 K. It is derived from the irradiation induced surface displacement, which is measured with an atomic force microscope (AFM). With a displacement damage of 0.6 dpa, a volume increase of 0.65% is observed at room temperature and 0.33% at 470 K. A cross-sectional cut is performed by focused ion beam and investigated by transmission electron microcopy (TEM). The defect density observed on the TEM micrographs agrees well with the computational simulation (TRIM) of the damage profile.

  13. Energy-loss and straggling of hydrogen and helium ions in silver

    NASA Astrophysics Data System (ADS)

    Lombaard, J.; Conradie, J.; Friedland, E.

    1983-10-01

    Energy-loss and straggling of protons, deuterons and 4He ions in silver were measured in the energy range between 0.14 MeV and 2.6 MeV. For energies between 0.25 and 0.60 MeV/amu the stopping powers of the hydrogen ions in silver are up to 10% lower than the semi-empirical values of Andersen and Ziegler. Better agreement is obtained with the shell-correction fit for energies above 0.6 MeV/amu. In the case of the helium ions the measured values are between 8% to 13% lower than the semi-empirical values of Ziegler. The reduced straggling for the 4He and hydrogen ions is energy independent above 0.3 MeV/amu with the He values the same as predicted by the Bohr estimate but the hydrogen values are about 15% lower.

  14. Crystal orientation effects on helium ion depth distributions and adatom formation processes in plasma-facing tungsten

    SciTech Connect

    Hammond, Karl D.; Wirth, Brian D.

    2014-10-14

    We present atomistic simulations that show the effect of surface orientation on helium depth distributions and surface feature formation as a result of low-energy helium plasma exposure. We find a pronounced effect of surface orientation on the initial depth of implanted helium ions, as well as a difference in reflection and helium retention across different surface orientations. Our results indicate that single helium interstitials are sufficient to induce the formation of adatom/substitutional helium pairs under certain highly corrugated tungsten surfaces, such as (1 1 1)-orientations, leading to the formation of a relatively concentrated layer of immobile helium immediately below the surface. The energies involved for helium-induced adatom formation on (1 1 1) and (2 1 1) surfaces are exoergic for even a single adatom very close to the surface, while (0 0 1) and (0 1 1) surfaces require two or even three helium atoms in a cluster before a substitutional helium cluster and adatom will form with reasonable probability. This phenomenon results in much higher initial helium retention during helium plasma exposure to (1 1 1) and (2 1 1) tungsten surfaces than is observed for (0 0 1) or (0 1 1) surfaces and is much higher than can be attributed to differences in the initial depth distributions alone. The layer thus formed may serve as nucleation sites for further bubble formation and growth or as a source of material embrittlement or fatigue, which may have implications for the formation of tungsten “fuzz” in plasma-facing divertors for magnetic-confinement nuclear fusion reactors and/or the lifetime of such divertors.

  15. Hyperfine structure measurement of 87Rb atoms injected into superfluid helium as highly energetic ion beam

    NASA Astrophysics Data System (ADS)

    Imamura, Kei; Furukawa, Takeshi; Yang, Xiaofei; Fujita, Tomomi; Wakui, Takashi; Mitsuya, Yousuke; Hayasaka, Miki; Ichikawa, Yuichi; Hatakeyama, Atsushi; Kobayashi, Tohru; Odashima, Hitoshi; Ueno, Hideki; Matsuo, Yukari; Orochi Collaboration

    2014-09-01

    We have developed a new nuclear laser spectroscopy technique that is called OROCHI (Optical RI-atoms Observation in Condensed Helium as Ioncatcher). In OROCHI, highly energetic ion beam is injected into superfluid helium (He II) and is trapped as atoms. Hyperfine structure (HFS) and Zeeman splitting of trapped atoms is measured using laser-microwave (MW)/radiofrequency (RF) double resonance method. We deduce nuclear moments and spin values from the measured splittings, respectively So far, we measured Zeeman splitting of 84-87Rb atoms To evaluate the validity of the OROCHI method, it is necessary to investigate the following two points not only for Zeeman but also for HFS splitings. (i) What is the accuracy in frequency in our measurement? (ii) How high beam intensity is necessary to observe resonance spectra? For this purpose we conducted online experiment using 87Rb beam and measured the HFS splitting of injected 87Rb atoms in He II.

  16. Postmortem examination of 22 pancreatic carcinoma patients treated with helium ion irradiation

    SciTech Connect

    Woodruff, K.H.; Castro, J.R.; Quivey, J.M.; Saunders, W.M.; Chen, G.T.; Lyman, J.T.; Pitluck, S.; Tobias, C.A.; Walton, R.E.; Peters, T.C.

    1984-02-01

    Postmortem findings are available in this report in 22 patients with pancreatic carcinoma treated with helium ions at Lawrence Berkeley Laboratory; California. This represents the largest group evaluated histologically in the literature and is the first report evaluating effects of particle radiation in pancreatic tissue. Patient survival after therapy averaged 9 months. Most died of infection and/or pulmonary emboli. Local control was achieved in 27%. The pancreatic tumors had histologically more severe radiation changes than nontumor bearing pancreas. Irradiated bone marrow was severely hypocellular, and irradiated skin was atrophic. Five patients had radiation injury in the gastrointestinal tract. The spinal cord, liver, and kidneys showed no damage. This study demonstrates the safety of helium particle irradiation with present therapeutic planning. Injury to tumor was seen without excessive damage to adjacent tissues.

  17. Focused helium-ion beam irradiation effects on electrical properties of multi-layer WSe2

    NASA Astrophysics Data System (ADS)

    Pudasaini, Pushpa Raj; Stanford, Michael; Cross, Nick; Duscher, Gerd; Mandrus, David; Rack, Philip

    Atomically thin transition metal dichalcogenides (TMDs) are currently receiving great attention due to their excellent opto-electronic properties. Tuning optical and electrical properties of mono and few layers TMDs, such as Tungsten diselenide (WSe2), by controlling the defects, is an intriguing opportunity to fabricate the next generation opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on structural, optical and electrical properties of few layer WSe2, via high resolution scanning transmission electron microscopy, Raman spectroscopy and electrical measurements. By controlling the ion irradiation dose, we selectively introduced precise defects in few layer WSe2 thereby locally tuning the electrically resistivity of the material. Hole transport in the few layer WSe2 is severely affected compared to electron transport for the same dose of helium ion beam irradiation studied. Furthermore, by selectively exposing the ion beams, we demonstrate the lateral p-n junction in few layer WSe2 flakes, which constitute an important advance towards two dimensional opto-electronic devices. Materials Science and Technology Division, ORNL, Oak Ridge, TN 37831, USA.

  18. Surface Modifications Induced by High Fluxes of Low Energy Helium Ions

    PubMed Central

    Tanyeli, İrem; Marot, Laurent; Mathys, Daniel; van de Sanden, Mauritius C. M.; De Temmerman, Gregory

    2015-01-01

    Several metal surfaces, such as titanium, aluminum and copper, were exposed to high fluxes (in the range of 1023 m−2s−1) of low energy (<100 eV) Helium (He) ions. The surfaces were analyzed by scanning electron microscopy and to get a better understanding on morphology changes both top view and cross sectional images were taken. Different surface modifications, such as voids and nano pillars, are observed on these metals. The differences and similarities in the development of surface morphologies are discussed in terms of the material properties and compared with the results of similar experimental studies. The results show that He ions induced void growth and physical sputtering play a significant role in surface modification using high fluxes of low energy He ions. PMID:25919912

  19. Energy levels and transition rates for helium-like ions with Z = 10-36

    NASA Astrophysics Data System (ADS)

    Si, R.; Guo, X. L.; Wang, K.; Li, S.; Yan, J.; Chen, C. Y.; Brage, T.; Zou, Y. M.

    2016-08-01

    Aims: Helium-like ions provide an important X-ray spectral diagnostics in astrophysical and high-temperature fusion plasmas. An interpretation of the observed spectra provides information on temperature, density, and chemical compositions of the plasma. Such an analysis requires information for a wide range of atomic parameters, including energy levels and transition rates. Our aim is to provide a set of accurate energy levels and transition rates for helium-like ions with Z = 10-36. Methods: The second-order many-body perturbation theory (MBPT) was adopted in this paper. To support our MBPT results, we performed an independent calculation using the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Results: We provide accurate energies for the lowest singly excited 70 levels among 1snl(n ≤ 6,l ≤ (n-1)) configurations and the lowest doubly excited 250 levels arising from the K-vacancy 2ln'l'(n' ≤ 6,l' ≤ (n'-1)) configurations of helium-like ions with Z = 10-36. Wavelengths, transition rates, oscillator strengths, and line strengths are calculated for the E1, M1, E2, and M2 transitions among these levels. The radiative lifetimes are reported for all the calculated levels. Conclusions: Our MBPT results for singly excited n ≤ 2 levels show excellent agreement with other elaborate calculations, while those for singly excited n ≥ 3 and doubly excited levels show significant improvements over previous theoretical results. Our results will be very helpful for astrophysical line identification and plasma diagnostics. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A141

  20. High aspect ratio AFM Probe processing by helium-ion-beam induced deposition.

    PubMed

    Onishi, Keiko; Guo, Hongxuan; Nagano, Syoko; Fujita, Daisuke

    2014-11-01

    A Scanning Helium Ion Microscope (SHIM) is a high resolution surface observation instrument similar to a Scanning Electron Microscope (SEM) since both instruments employ finely focused particle beams of ions or electrons [1]. The apparent difference is that SHIMs can be used not only for a sub-nanometer scale resolution microscopic research, but also for the applications of very fine fabrication and direct lithography of surfaces at the nanoscale dimensions. On the other hand, atomic force microscope (AFM) is another type of high resolution microscopy which can measure a three-dimensional surface morphology by tracing a fine probe with a sharp tip apex on a specimen's surface.In order to measure highly uneven and concavo-convex surfaces by AFM, the probe of a high aspect ratio with a sharp tip is much more necessary than the probe of a general quadrangular pyramid shape. In this paper we report the manufacture of the probe tip of the high aspect ratio by ion-beam induced gas deposition using a nanoscale helium ion beam of SHIM.Gas of platinum organic compound was injected into the sample surface neighborhood in the vacuum chamber of SHIM. The decomposition of the gas and the precipitation of the involved metal brought up a platinum nano-object in a pillar shape on the normal commercial AFM probe tip. A SHIM system (Carl Zeiss, Orion Plus) equipped with the gas injection system (OmniProbe, OmniGIS) was used for the research. While the vacuum being kept to work, we injected platinum organic compound ((CH3)3(CH3C5H4)Pt) into the sample neighborhood and irradiated the helium ion beam with the shape of a point on the apex of the AFM probe tip. It is found that we can control the length of the Pt nano-pillar by irradiation time of the helium ion beam. The AFM probe which brought up a Pt nano-pillar is shown in Figure 1. It is revealed that a high-aspect-ratio Pt nano-pillar of ∼40nm diameter and up to ∼2000 nm length can be grown. In addition, for possible heating

  1. Negative ion productions in high velocity collision between small carbon clusters and Helium atom target

    NASA Astrophysics Data System (ADS)

    M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

    2012-11-01

    We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

  2. Fabrication of carbon nanotube nanogap electrodes by helium ion sputtering for molecular contacts

    SciTech Connect

    Thiele, Cornelius; Vieker, Henning; Beyer, André; Gölzhäuser, Armin; Flavel, Benjamin S.; Hennrich, Frank; Muñoz Torres, David; Eaton, Thomas R.; Mayor, Marcel; Kappes, Manfred M.; Löhneysen, Hilbert v.; and others

    2014-03-10

    Carbon nanotube nanogaps have been used to contact individual organic molecules. However, the reliable fabrication of a truly nanometer-sized gap remains a challenge. We use helium ion beam lithography to sputter nanogaps of only (2.8 ± 0.6) nm size into single metallic carbon nanotubes embedded in a device geometry. The high reproducibility of the gap size formation provides a reliable nanogap electrode testbed for contacting small organic molecules. To demonstrate the functionality of these nanogap electrodes, we integrate oligo(phenylene ethynylene) molecular rods, and measure resistance before and after gap formation and with and without contacted molecules.

  3. Spectroscopic study of energetic helium-ion irradiation effects on nuclear graphite tiles

    NASA Astrophysics Data System (ADS)

    Kim, Do Wan; Lee, K. W.; Choi, D. M.; Noh, S. J.; Kim, H. S.; Lee, Cheol Eui

    2016-02-01

    Helium ion-irradiation effects on the nuclear graphite tiles were studied in order to understand the structural modifications and damages that can be produced by fusion reaction in tokamaks. The surface morphological changes due to increasing dose of the irradiation were examined by the field-effect scanning electron microscopy, and X-ray photoelectron spectroscopy elucidated the changes in the shallow surface bonding configurations caused by the energetic irradiation. Raman spectroscopy revealed the structural defects and diamond-like carbon sites that increased with increasing irradiation dose, and the average inter-defect distance was found from the Raman peak intensities as a function of the irradiation dose.

  4. Direct-write three-dimensional nanofabrication of nanopyramids and nanocones on Si by nanotumefaction using a helium ion microscope

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Heinig, N. F.; Bazargan, S.; Abd-Ellah, M.; Moghimi, N.; Leung, K. T.

    2015-06-01

    The recently commercialized helium ion microscope (HIM) has already demonstrated its outstanding imaging capabilities in terms of resolution, surface sensitivity, depth of field and ease of charge compensation. Here, we show its exceptional patterning capabilities by fabricating dense lines and three-dimensional (3D) nanostructures on a Si substrate. Small focusing spot size and confined ion-Si interaction volume of a high-energy helium ion beam account for the high resolution in HIM patterning. We demonstrate that a set of resolvable parallel lines with a half pitch as small as 3.5 nm can be achieved. During helium ion bombardment of the Si surface, implantation outperforms milling due to the small mass of the helium ions, which produces tumefaction instead of depression in the Si surface. The Si surface tumefaction is the result of different kinetic processes including diffusion, coalescence and nanobubble formation of the implanted ions, and is found to be very stable structurally at room temperature. Under appropriate conditions, a linear dependence of the surface swollen height on the ion doses can be observed. This relation has enabled us to fabricate nanopyramids and nanocones, thus demonstrating that HIM patterning provides a new ‘bottom-up’ approach to fabricate 3D nanostructures. This surface tumefaction method is direct, both positioning and height accurate, and free of resist, etch, mode and precursor, and it promises new applications in nanoimprint mold fabrication and photomask clear defect reparation.

  5. Investigation of hydrogen and helium pumping by sputter ion pumps for Jupiter and outer planets mass spectrometer

    NASA Technical Reports Server (NTRS)

    Scott, B. W.

    1977-01-01

    The phenomena of ion pumping is reviewed with emphasis on the pumping mechanism for hydrogen and helium. The experimental tests measure the performance of a small, flight proven ion pump which has a nominal four liter/second pumping speed for air. The speed of this pump for hydrogen and helium, and for hydrogen/helium mixes, is presented with particular detail regarding the time dependence. Pump test results are related to anticipated performance of the mass spectrometer by the pumping speeds for the gases to the partial pressure in the ion source. From this analysis, the pump specifications are quantified in terms of mission goals and in terms of observed pumping speeds for the various gases, load levels, and time periods.

  6. Water equivalent thickness values of materials used in beams of protons, helium, carbon and iron ions.

    PubMed

    Zhang, Rui; Taddei, Phillip J; Fitzek, Markus M; Newhauser, Wayne D

    2010-05-01

    Heavy charged particle beam radiotherapy for cancer is of increasing interest because it delivers a highly conformal radiation dose to the target volume. Accurate knowledge of the range of a heavy charged particle beam after it penetrates a patient's body or other materials in the beam line is very important and is usually stated in terms of the water equivalent thickness (WET). However, methods of calculating WET for heavy charged particle beams are lacking. Our objective was to test several simple analytical formulas previously developed for proton beams for their ability to calculate WET values for materials exposed to beams of protons, helium, carbon and iron ions. Experimentally measured heavy charged particle beam ranges and WET values from an iterative numerical method were compared with the WET values calculated by the analytical formulas. In most cases, the deviations were within 1 mm. We conclude that the analytical formulas originally developed for proton beams can also be used to calculate WET values for helium, carbon and iron ion beams with good accuracy.

  7. Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision.

    PubMed

    Hlawacek, Gregor; Jankowski, Maciej; Wormeester, Herbert; van Gastel, Raoul; Zandvliet, Harold J W; Poelsema, Bene

    2016-03-01

    Helium Ion Microscopy is known for its surface sensitivity and high lateral resolution. Here, we present results of a Helium Ion Microscopy based investigation of a surface confined alloy of Ag on Pt(111). Based on a change of the work function of 25meV across the atomically flat terraces we can distinguish Pt rich from Pt poor areas and visualize the single atomic layer high steps between the terraces. Furthermore, dechanneling contrast has been utilized to measure the periodicity of the hcp/fcc pattern formed in the 2-3 layers thick Ag/Pt alloy film. A periodicity of 6.65nm along the ⟨112⟩ surface direction has been measured. In terms of crystallography a hcp domain is obtained through a lateral displacement of a part of the outermost layer by 1/√3 of a nearest neighbor spacing along ⟨112⟩. This periodicity is measured with atomic precision: coincidence between the Ag and the Pt lattices is observed for 23 Ag atoms on 24 Pt atoms. The findings are perfectly in line with results obtained with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy. PMID:26720438

  8. Nanoscale helium ion microscopic analysis of collagen fibrillar changes following femtosecond laser dissection of human cornea.

    PubMed

    Riau, Andri K; Poh, Rebekah; Pickard, Daniel S; Park, Chris H J; Chaurasia, Shyam S; Mehta, Jodhbir S

    2014-08-01

    Over the last decade, femtosecond lasers have emerged as an important tool to perform accurate and fine dissections with minimal collateral damage in biological tissue. The most common surgical procedure in medicine utilizing femtosecond laser is LASIK. During the femtosecond laser dissection process, the corneal collagen fibers inevitably undergo biomechanical and thermal changes on a sub-micro- or even a nanoscale level, which can potentially lead to post-surgical complications. In this study, we utilized helium ion microscopy, complemented with transmission electron microscopy to examine the femtosecond laser-induced collagen fibrillar damage in ex vivo human corneas. We found that the biomechanical damage induced by laser etching, generation of tissue bridges, and expansion of cavitation bubble and its subsequent collapse, created distortion to the surrounding collagen lamellae. Femtosecond laser-induced thermal damage was characterized by collapsed collagen lamellae, loss of collagen banding, collagen coiling, and presence of spherical debris. Our findings have shown the ability of helium ion microscopy to provide high resolution images with unprecedented detail of nanoscale fibrillar morphological changes in order to assess a tissue damage, which could not be resolved by conventional scanning electron microscopy previously. This imaging technology has also given us a better understanding of the tissue-laser interactions in a nano-structural manner and their possible effects on post-operative wound recovery. PMID:25016655

  9. Pumping of helium and hydrogen by sputter-ion pumps. II. Hydrogen pumping

    SciTech Connect

    Welch, K.M.; Pate, D.J.; Todd, R.J. )

    1994-05-01

    The pumping of helium by various forms of sputter-ion pumps (i.e., SIPs) is given in part I [K. M. Welch, D. J. Pate, and R. J. Todd, J. Vac. Sci. Technol. A [bold 11], 1607 (1993)]. The pumping of hydrogen in diode and triode SIPs is herein discussed. The type of cathode material used in these pumps is shown to have a significant impact on the effectiveness with which hydrogen is pumped. Examples of this include data for pumps with aluminum, titanium, and titanium-alloy cathodes. Diode pumps with aluminum cathodes are shown to be no more effective in the pumping of hydrogen than in the pumping of helium. The use of titanium anodes and titanium [ital shielding] of a pump body is also shown to impact measurably the speed of a pump at very low pressures. This stems from the fact that hydrogen is [times]10[sup 6] more soluble in titanium than in stainless steel. Hydrogen becomes resident in the anodes because of fast neutral burial. Ions and fast neutrals of hydrogen are also buried in the walls of pump bodies. Outgassing of this hydrogen from the anodes and pump bodies results in a gradual increase in pump base pressure and consequential decrease in hydrogen pump speed at very low base pressures.

  10. Ion formation upon electron collisions with valine embedded in helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Weinberger, Nikolaus; Ralser, Stefan; Renzler, Michael; Harnisch, Martina; Kaiser, Alexander; Denifl, Stefan; Böhme, Diethard K.; Scheier, Paul

    2016-04-01

    We report here experimental results for the electron ionization of large superfluid helium nanodroplets with sizes of about 105 atoms that are doped with valine and clusters of valine. Spectra of both cations and anions were monitored with high-resolution time-of-flight mass spectrometry (mass resolution >4000). Clear series of peaks with valine cluster sizes up to at least 40 and spaced by the mass of a valine molecule are visible in both the cation and anion spectra. Ion efficiency curves are presented for selected cations and anions at electron energies up to about 40 eV and these provide insight into the mode of ion formation. The measured onset of 24.59 eV for cations is indicative of valine ionization by He+ whereas broad resonances at 2, 10 and 22 eV (and beyond) in the formation of anions speak to the occurrence of various modes of dissociative electron attachment by collisions with electrons or He*- and the influence of droplet size on the relative importance of these processes. Comparisons are also made with gas phase results and these provide insight into a matrix effect within the superfluid helium nanodroplet. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

  11. ERDA with an external helium ion micro-beam: Advantages and potential applications

    NASA Astrophysics Data System (ADS)

    Calligaro, T.; Castaing, J.; Dran, J.-C.; Moignard, B.; Pivin, J.-C.; Prasad, G. V. R.; Salomon, J.; Walter, P.

    2001-07-01

    Preliminary ERDA experiments at atmospheric pressure have been performed with our external microprobe set-up currently used for the analysis of museum objects by PIXE, RBS and NRA. The objective was to check the feasibility of hydrogen (and deuterium) profiling with an external beam of 3-MeV helium ions. The standard scattering geometry (incident beam at 15° with respect to sample surface and emerging protons or deuterons at 15° in the forward direction) was kept, but the thin foil absorber was replaced by helium gas filling the space between the beam spot and the detector over a distance of about 84 mm. Several standards prepared by ion implantation, with well known H or D depth profiles, were first analysed, which indicated that the analytical capability was as good as under vacuum. A striking feature is the much lower surface peak than under vacuum, a fact that enhances the sensitivity for H analysis near the surface. The same type of measurement was then performed on different materials to show the usefulness of the technique. As a first example, we have checked that the incorporation of H or D into sapphire crystals during mechanical polishing is below the detection limit. Another example is the measurement of the H content in emeralds which can be used as an additional compositional criterion for determining the provenance of emeralds set in museum jewels. The advantages and limitations of our set-up are discussed and several possible applications in the field of cultural heritage are described.

  12. Water equivalent thickness values of materials used in beams of protons, helium, carbon and iron ions.

    PubMed

    Zhang, Rui; Taddei, Phillip J; Fitzek, Markus M; Newhauser, Wayne D

    2010-05-01

    Heavy charged particle beam radiotherapy for cancer is of increasing interest because it delivers a highly conformal radiation dose to the target volume. Accurate knowledge of the range of a heavy charged particle beam after it penetrates a patient's body or other materials in the beam line is very important and is usually stated in terms of the water equivalent thickness (WET). However, methods of calculating WET for heavy charged particle beams are lacking. Our objective was to test several simple analytical formulas previously developed for proton beams for their ability to calculate WET values for materials exposed to beams of protons, helium, carbon and iron ions. Experimentally measured heavy charged particle beam ranges and WET values from an iterative numerical method were compared with the WET values calculated by the analytical formulas. In most cases, the deviations were within 1 mm. We conclude that the analytical formulas originally developed for proton beams can also be used to calculate WET values for helium, carbon and iron ion beams with good accuracy. PMID:20371908

  13. Ultrastructural analysis of wild type and mutant Drosophila melanogaster using helium ion microscopy.

    PubMed

    Boseman, Adam; Nowlin, Kyle; Ashraf, Sarmadia; Yang, Jijin; Lajeunesse, Dennis

    2013-08-01

    Insects have evolved numerous adaptations to survive a variety of environmental conditions. Given that the primary interface between insects and the environment is mediated through their skin or cuticle, many of these adaptations are found in extraordinary cuticle diversity both in morphology and structure. Not all of these adaptions manifest themselves in changes in the chemical composition of the cuticle but rather as elaborations of the surface structures of the cuticle. Typically the examination of these micro- and nanoscale structures has been performed using scanning electron microscopy (SEM). Typically, in order to decrease surface charging and increase resolution, an obscuring conductive layer is applied to the sample surface, but this layer limits the ability to identify nanoscale surface structures. In this paper we use a new technology, helium ion microscopy (HIM) to examine surface structures on the cuticle of wild type and mutant Drosophila. Helium ion microscopy permits high resolution imaging of biological samples without the need for coating. We compare HIM to traditional SEM and demonstrate certain advantages of this type of microscopy, with our focus being high resolution characterization of nanostructures on the cuticle of Drosophila melanogaster and potentially other biological specimens.

  14. Nanoscale helium ion microscopic analysis of collagen fibrillar changes following femtosecond laser dissection of human cornea.

    PubMed

    Riau, Andri K; Poh, Rebekah; Pickard, Daniel S; Park, Chris H J; Chaurasia, Shyam S; Mehta, Jodhbir S

    2014-08-01

    Over the last decade, femtosecond lasers have emerged as an important tool to perform accurate and fine dissections with minimal collateral damage in biological tissue. The most common surgical procedure in medicine utilizing femtosecond laser is LASIK. During the femtosecond laser dissection process, the corneal collagen fibers inevitably undergo biomechanical and thermal changes on a sub-micro- or even a nanoscale level, which can potentially lead to post-surgical complications. In this study, we utilized helium ion microscopy, complemented with transmission electron microscopy to examine the femtosecond laser-induced collagen fibrillar damage in ex vivo human corneas. We found that the biomechanical damage induced by laser etching, generation of tissue bridges, and expansion of cavitation bubble and its subsequent collapse, created distortion to the surrounding collagen lamellae. Femtosecond laser-induced thermal damage was characterized by collapsed collagen lamellae, loss of collagen banding, collagen coiling, and presence of spherical debris. Our findings have shown the ability of helium ion microscopy to provide high resolution images with unprecedented detail of nanoscale fibrillar morphological changes in order to assess a tissue damage, which could not be resolved by conventional scanning electron microscopy previously. This imaging technology has also given us a better understanding of the tissue-laser interactions in a nano-structural manner and their possible effects on post-operative wound recovery.

  15. New views of the Toxoplasma gondii parasitophorous vacuole as revealed by Helium Ion Microscopy (HIM).

    PubMed

    de Souza, Wanderley; Attias, Marcia

    2015-07-01

    The Helium Ion Microscope (HIM) is a new technology that uses a highly focused helium ion beam to scan and interact with the sample, which is not coated. The images have resolution and depth of field superior to field emission scanning electron microscopes. In this paper, we used HIM to study LLC-MK2 cells infected with Toxoplasma gondii. These samples were chemically fixed and, after critical point drying, were scraped with adhesive tape to expose the inner structure of the cell and parasitophorous vacuoles. We confirmed some of the previous findings made by field emission-scanning electron microscopy and showed that the surface of the parasite is rich in structures suggestive of secretion, that the nanotubules of the intravacuolar network (IVN) are not always straight, and that bifurcations are less frequent than previously thought. Fusion of the tubules with the parasite membrane or the parasitophorous vacuole membrane (PVM) was also infrequent. Tiny adhesive links were observed for the first time connecting the IVN tubules. The PVM showed openings of various sizes that even allowed the observation of endoplasmic reticulum membranes in the cytoplasm of the host cell. These findings are discussed in relation to current knowledge on the cell biology of T. gondii. PMID:26004092

  16. New views of the Toxoplasma gondii parasitophorous vacuole as revealed by Helium Ion Microscopy (HIM).

    PubMed

    de Souza, Wanderley; Attias, Marcia

    2015-07-01

    The Helium Ion Microscope (HIM) is a new technology that uses a highly focused helium ion beam to scan and interact with the sample, which is not coated. The images have resolution and depth of field superior to field emission scanning electron microscopes. In this paper, we used HIM to study LLC-MK2 cells infected with Toxoplasma gondii. These samples were chemically fixed and, after critical point drying, were scraped with adhesive tape to expose the inner structure of the cell and parasitophorous vacuoles. We confirmed some of the previous findings made by field emission-scanning electron microscopy and showed that the surface of the parasite is rich in structures suggestive of secretion, that the nanotubules of the intravacuolar network (IVN) are not always straight, and that bifurcations are less frequent than previously thought. Fusion of the tubules with the parasite membrane or the parasitophorous vacuole membrane (PVM) was also infrequent. Tiny adhesive links were observed for the first time connecting the IVN tubules. The PVM showed openings of various sizes that even allowed the observation of endoplasmic reticulum membranes in the cytoplasm of the host cell. These findings are discussed in relation to current knowledge on the cell biology of T. gondii.

  17. X-ray line ratios from helium-like ions - Updated theory and SMM flare observations

    NASA Technical Reports Server (NTRS)

    Wolfson, C. J.; Leibacher, J. W.; Doyle, J. G.; Phillips, K. J. H.

    1983-01-01

    The potential which the conduction of measurements of the three principal lines emitted from helium-like ions has for the determination of plasma electron density was initially pointed out by Gabriel and Jordan (1969). The diagnostic technique is based on the fact that the ratio, R, of the intensity of a forbidden line to the intensity of an intercombination line decreases as electron density increases due to collisional excitation of levels. In the present investigation a further refinement of this procedure is provided by specifically calculating the effects of cascades from levels with principal quantum numbers up to n=6. Two improved spectrometers recently placed in operation include the SOLEX instrument on the satellite P78-1 and the X-ray Polychromator (XRP) instrument on the NASA Solar Maximum Mission satellite. Measurements obtained with one of the spectrometers making up the XRP are presented, taking into account the emission from Ne IX ions.

  18. Membrane Thickness Dependence of Nanopore Formation with a Focused Helium Ion Beam

    PubMed Central

    Sawafta, Furat; Carlsen, Autumn T.; Hall, Adam R.

    2014-01-01

    Solid-state nanopores are emerging as a valuable tool for the detection and characterization of individual biomolecules. Central to their success is the realization of fabrication strategies that are both rapid and flexible in their ability to achieve diverse device dimensions. In this paper, we demonstrate the membrane thickness dependence of solid-state nanopore formation with a focused helium ion beam. We vary membrane thickness in situ and show that the rate of pore expansion follows a reproducible trend under all investigated membrane conditions. We show that this trend shifts to lower ion dose for thin membranes in a manner that can be described quantitatively, allowing devices of arbitrary dimension to be realized. Finally, we demonstrate that thin, small-diameter nanopores formed with our approach can be utilized for high signal-to-noise ratio resistive pulse sensing of DNA. PMID:24806739

  19. Helium-ion damage and nanowire fabrication in GaAs/AlGaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Knoedler, C. M.

    1990-08-01

    Nanometer scale features (75-1000 nm) were defined on GaAs/AlGaAs heterostructure surfaces by electron beam patterning. The use of low-voltage, helium-ion damage laterally confined the two dimensional electron gas to these patterned areas. Electrical characterization of the conducting channels as well as the ion-damaged material outside the patterned areas included measurements of the Hall mobility, the carrier concentration and the sheet resistance at various temperatures. The major problem encountered with the nanowires was an increase in the wire sheet resistance over the as-grown value at 4.2 K. Process-related factors contributed to this increase, but the most probable cause is boundary scattering at the lateral edges of the nanowires.

  20. Membrane thickness dependence of nanopore formation with a focused helium ion beam.

    PubMed

    Sawafta, Furat; Carlsen, Autumn T; Hall, Adam R

    2014-05-06

    Solid-state nanopores are emerging as a valuable tool for the detection and characterization of individual biomolecules. Central to their success is the realization of fabrication strategies that are both rapid and flexible in their ability to achieve diverse device dimensions. In this paper, we demonstrate the membrane thickness dependence of solid-state nanopore formation with a focused helium ion beam. We vary membrane thickness in situ and show that the rate of pore expansion follows a reproducible trend under all investigated membrane conditions. We show that this trend shifts to lower ion dose for thin membranes in a manner that can be described quantitatively, allowing devices of arbitrary dimension to be realized. Finally, we demonstrate that thin, small-diameter nanopores formed with our approach can be utilized for high signal-to-noise ratio resistive pulse sensing of DNA.

  1. Blistering and cracking of LiTaO3 single crystal under helium ion implantation

    NASA Astrophysics Data System (ADS)

    Ma, Changdong; Lu, Fei; Ma, Yujie

    2015-03-01

    Blistering and cracking in LiTaO3 surface are investigated after 200-keV helium ion implantation and subsequent post-implantation annealing. Rutherford backscattering/channeling is used to examine the lattice damage caused by ion implantation. Blistering is observed through optical microscopy in a dynamic heating process. Atomic force microscopy and scanning electron microscopy measurements are used to detect the LiTaO3 surface morphology. Experimental results show that blistering and flaking are dependent on implantation fluence, beam current, and also annealing temperature. We speculate that the surface cracking of He+-implanted LiTaO3 results from the implantation-induced stress and compression.

  2. Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Green, S.

    1984-01-01

    The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

  3. Interstellar helium pickup ion flux variations observed with SOHO/CELIAS

    NASA Astrophysics Data System (ADS)

    Saul, Lukas A.

    Interstellar pickup ions are formed when neutral atoms freely enter the heliosphere and are subsequently ionized. Once these particles are charged they become a component of the interplanetary plasma and are transported outward with the solar wind (SW). Measurements of these particles give information about the local interstellar gas in which our sun resides. However, fluxes of pickup ions in the solar wind are observed to vary substantially in both magnitude and energy spectrum. Hypothesized is that the main causes of these variations are transport phenomenon in the solar wind, determined by the solar wind and the interplanetary magnetic field. If so, solar wind conditions can be used to predict pickup ion fluxes, and pickup ion fluxes can be used to indicate solar wind transport conditions. To prove the feasibility of this hypothesis, in situ measurements of helium pickup ions from the CTOF instrument on the SOHO spacecraft are used to characterize transport parameters. Results are presented which show the effect of solar wind structures on pickup ions. Compression regions are shown to strongly affect measured fluxes of pickup ions. Observations show that compression regions can also cause an adiabatic heating or a shift in the pickup ion velocity distribution. Also investigated is the effect of interplanetary magnetic field fluctuations and waves on pickup ions. These fluctuations can scatter pickup ions, in both pitch angle and energy. Comparison with WIND/MFI magnetic field measurements show that the pitch angle scattering rate is correlated with the wave-power hemispheric model for the pickup ion distribution is used to determine pitch angle diffusion coefficients from observed spectra. We find that the observed scattering rate differs from the predictions of simple diffusion models, especially in low wave-powers. Energy diffusion or particle acceleration is also observed in the pickup ion velocity distribution, most notably in the passage of solar wind

  4. Influence of the ionization-energy losses of high-energy bismuth ions on the development of helium blisters in silicon

    SciTech Connect

    Reutov, V. F. Dmitriev, S. N.; Sohatsky, A. S.; Zaluzhnyi, A. G.

    2015-10-15

    Understanding the behavior of helium in solids under conditions of intense ionizing radiation is of particular interest in solving many problems of nuclear, fusion, and space materials science and also in microelectronics. The observed effect of suppressing the formation of helium blisters on the surface of helium ion-doped silicon as a result of irradiation with high-energy bismuth ions is reported in this publication. It is suggested that a possible decrease in the concentration of helium atoms in silicon is due to their radiationinduced desorption from the area of doping in terms of the high-impact ionization of bismuth ions.

  5. Dynamical response of helium bubble motion to irradiation with high-energy self-ions in aluminum at high temperature.

    SciTech Connect

    Ono, K.; Miyamoto, M.; Arakawa, K.; Birtcher, R. C.; Materials Science Division; Shimane Univ.; Osaka Univ.

    2009-02-21

    Brownian-type motion of helium bubbles in aluminum and its dynamical response to irradiation with 100-keV Al{sup +} ions at high temperatures has been studied using in situ irradiation and transmission electron microscopy. It is found that, for most bubbles, the Brownian-type motion is retarded under irradiation, while the mobility returns when the irradiation is stopped. In contrast, under irradiation, a small number of bubbles display exceptionally rapid motion associated with the change in bubble size. These effects are discussed in terms of the dynamical interaction of helium bubbles with cascade damage formed by the high-energy self-ion irradiation.

  6. A Experimental Study of Ion Dynamic Effects on Helium Line Profiles.

    NASA Astrophysics Data System (ADS)

    Pease, Dennis Carl

    Time-resolved spectral line profiles for several neutral helium lines were determined in the afterglow of a linear z-discharge. The plasma temperature ((TURNEQ)10,000(DEGREES)K) was derived from both absolute and relative line intensities and was nearly constant during the afterglow. A monotonically decreasing electron density (5 x 10('14) > N(,e) > 4 x 10('13) cm('-3)) was measured using H(,(beta)) profile fitting and laser interferometry. Additional diagnostics indicated that the afterglow plasma was homogeneous and reproducible, and thereby confirmed its usefulness for detailed spectroscopic investigations. Detailed profiles were obtained for five neutral helium lines with nearby forbidden (i.e. (DELTA)l (NOT=) (+OR-)1) components: 2('3)P-4('3)D,('3)F ((lamda) 4471(ANGSTROM)); 2('3)P-5('3)D,('3)F,('3)G ((lamda) 4026(ANGSTROM)); 2('3)P -6('3)D,('3)F,('3)G,('3)H ((lamda) 3819(ANGSTROM)); 2('1)P -4('1)D,('1)F ((lamda) 4921(ANGSTROM)); and 2('1)P-5('1)D,('1)F,('1)G ((lamda) 4388(ANGSTROM)). Comparison of these profiles was made to published theoretical Stark broadening calculations which assumed either static ions or dynamic ions. Substantial discrepancies were found when comparing static ion calculations to the experimental profiles. The observed differences, a forbidden line which was too broad and a filled-in dip between the allowed and forbidden lines, agreed qualitatively with the results of published experimental data at higher densities. Excellent agreement was found between experimental profiles and those Stark broadening calculations which included the effects of ion dynamics. The high instrumental resolution used ((delta)(lamda)(,FWHM)(TURNEQ) .08(ANGSTROM)), the low electron densities, and the good plasma reproducibility enabled a number of subtle contributors to the line profile structure to be discerned including: hydrogen molecular lines, which had integrated intensities < 10('-4) that of the principal helium lines; intercombination lines, which were

  7. Electron emission in collisions of fast highly charged bare ions with helium atoms

    NASA Astrophysics Data System (ADS)

    Mondal, Abhoy; Mandal, Chittranjan; Purkait, Malay

    2016-01-01

    We have studied the electron emission from ground state helium atom in collision with fast bare heavy ions at intermediate and high incident energies. In the present study, we have applied the present three-body formalism of the three Coulomb wave (3C-3B) model and the previously adopted four-body formalism of the three Coulomb wave (3C-4B). To represent the active electron in the helium atom in the 3C-3B model, the initial bound state wavefunction is chosen to be hydrogenic with an effective nuclear charge. The wavefunction for the ejected electron in the exit channel has been approximated to be a Coulomb continuum wavefunction with same effective nuclear charge. Effectively the continuum-continuum correlation effect has been considered in the present investigation. Here we have calculated the energy and angular distribution of double differential cross sections (DDCS) at low and high energy electron emission from helium atom. The large forward-backward asymmetry is observed in the angular distribution which is explained in terms of the two-center effect (TCE). Our theoretical results are compared with available experimental results as well as other theoretical calculations based on the plain wave Born approximation (PWBA), continuum-distorted wave (CDW) approximation, continuum-distorted wave eikonal-initial state (CDW-EIS) approximation, and the corresponding values obtained from the 3C-4B model [S. Jana, R. Samanta, M. Purkait, Phys. Scr. 88, 055301 (2013)] respectively. It is observed that the four-body version of the present investigation produces results which are in better agreement with experimental observations for all cases.

  8. Helium Gas Regulation System for the Light-Ion Guide Gas Cell

    NASA Astrophysics Data System (ADS)

    Frazier, Bryan; Clark, Henry; Chen, Lixin

    2013-10-01

    This is a proof-of-concept project to show that it is possible to construct a cost-effective helium gas regulation system for TAMU Cyclotron Institute's light-ion guide gas cell, using store ordered components. By purchasing the individual necessary parts, we designed and constructed a system that was less expensive than purchasing a pre-constructed system from a manufacturer, and could easily be scaled larger or smaller to accommodate any number of gas bottles. Utilizing LabVIEW software, I was able to write a program that allows the system to be controlled remotely, and an automation program that causes the system to change immediately between bottles, whenever one is almost empty, allowing the system to supply a constant flow of helium gas for several days. Although both the construction and the programming of the system can be seen as rough and unrefined, due to the time-restraints placed on me, the project adequately proves that the concept is valid and entirely possible, as the system is fully functional and able to fulfill its intended purpose. Funded by DOE and NSF-REU Program.

  9. Nanoforging Single Layer MoSe2 Through Defect Engineering with Focused Helium Ion Beams

    DOE PAGES

    Iberi, Vighter; Liang, Liangbo; Ievlev, Anton V.; Stanford, Michael G.; Lin, Ming-Wei; Li, Xufan; Mahjouri-Samani, Masoud; Jesse, Stephen; Sumpter, Bobby G.; Kalinin, Sergei V.; et al

    2016-08-02

    Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe2 locally, and decipher associated mechanisms at atomic level. We demonstrate He+ beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and thereby increases the Young s modulus of elasticity. Furthermore, we observe formore » the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at room temperature. In conclusion, the approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region.« less

  10. Ab initio simulation of helium-ion microscopy images: the case of suspended graphene.

    PubMed

    Zhang, Hong; Miyamoto, Yoshiyuki; Rubio, Angel

    2012-12-28

    Helium ion microscopy (HIM), which was released in 2006 by Ward et al., provides nondestructive imaging of nanoscale objects with higher contrast than scanning electron microscopy. HIM measurement of suspended graphene under typical conditions is simulated by first-principles time-dependent density functional theory and the 30 keV He+ collision is found to induce the emission of electrons dependent on the impact point. This finding suggests the possibility of obtaining a highly accurate image of the honeycomb pattern of suspended graphene by HIM. Comparison with a simulation of He0 under the same kinetic energy shows that electron emission is governed by the impact ionization instead of Auger process initiated by neutralization of He+.

  11. Nanoforging Single Layer MoSe2 Through Defect Engineering with Focused Helium Ion Beams.

    PubMed

    Iberi, Vighter; Liang, Liangbo; Ievlev, Anton V; Stanford, Michael G; Lin, Ming-Wei; Li, Xufan; Mahjouri-Samani, Masoud; Jesse, Stephen; Sumpter, Bobby G; Kalinin, Sergei V; Joy, David C; Xiao, Kai; Belianinov, Alex; Ovchinnikova, Olga S

    2016-08-02

    Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction the of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe2 locally, and decipher associated mechanisms at the atomic level. We demonstrate He(+) beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and increases the Young's modulus of elasticity. Furthermore, we observe for the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at the room temperature. The approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region.

  12. Five-year follow-up of helium ion therapy for uveal melanoma

    SciTech Connect

    Char, D.H.; Castro, J.R.; Kroll, S.M.; Irvine, A.R.; Quivey, J.M.; Stone, R.D. )

    1990-02-01

    One hundred sixty-four patients with uveal melanoma were treated with helium ion irradiation prior to May 1984, and the data were analyzed in June 1989. Most uveal melanomas were large, with a mean tumor thickness of 6.5 mm; approximately 60% of the patients had tumors that extended anterior to the equator. A complete follow-up was obtained for all patients. One hundred twelve patients were alive at the time of this report; 18% of the patients developed clinical and laboratory evidence of metastases and eventually died of widespread tumor. Eighty-four percent of eyes were retained. Data were analyzed with a number of parametric and nonparametric techniques. Larger tumors and those located in close proximity to the optic nerve and fovea had a higher incidence of most complications, especially visual loss.

  13. Helium Ion Microscopy (HIM) for the imaging of biological samples at sub-nanometer resolution

    PubMed Central

    Joens, Matthew S.; Huynh, Chuong; Kasuboski, James M.; Ferranti, David; Sigal, Yury J.; Zeitvogel, Fabian; Obst, Martin; Burkhardt, Claus J.; Curran, Kevin P.; Chalasani, Sreekanth H.; Stern, Lewis A.; Goetze, Bernhard; Fitzpatrick, James A. J.

    2013-01-01

    Scanning Electron Microscopy (SEM) has long been the standard in imaging the sub-micrometer surface ultrastructure of both hard and soft materials. In the case of biological samples, it has provided great insights into their physical architecture. However, three of the fundamental challenges in the SEM imaging of soft materials are that of limited imaging resolution at high magnification, charging caused by the insulating properties of most biological samples and the loss of subtle surface features by heavy metal coating. These challenges have recently been overcome with the development of the Helium Ion Microscope (HIM), which boasts advances in charge reduction, minimized sample damage, high surface contrast without the need for metal coating, increased depth of field, and 5 angstrom imaging resolution. We demonstrate the advantages of HIM for imaging biological surfaces as well as compare and contrast the effects of sample preparation techniques and their consequences on sub-nanometer ultrastructure. PMID:24343236

  14. Nanoforging Single Layer MoSe2 Through Defect Engineering with Focused Helium Ion Beams.

    PubMed

    Iberi, Vighter; Liang, Liangbo; Ievlev, Anton V; Stanford, Michael G; Lin, Ming-Wei; Li, Xufan; Mahjouri-Samani, Masoud; Jesse, Stephen; Sumpter, Bobby G; Kalinin, Sergei V; Joy, David C; Xiao, Kai; Belianinov, Alex; Ovchinnikova, Olga S

    2016-01-01

    Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction the of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe2 locally, and decipher associated mechanisms at the atomic level. We demonstrate He(+) beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and increases the Young's modulus of elasticity. Furthermore, we observe for the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at the room temperature. The approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region. PMID:27480346

  15. Helium Ion Microscopy (HIM) for the imaging of biological samples at sub-nanometer resolution.

    PubMed

    Joens, Matthew S; Huynh, Chuong; Kasuboski, James M; Ferranti, David; Sigal, Yury J; Zeitvogel, Fabian; Obst, Martin; Burkhardt, Claus J; Curran, Kevin P; Chalasani, Sreekanth H; Stern, Lewis A; Goetze, Bernhard; Fitzpatrick, James A J

    2013-12-17

    Scanning Electron Microscopy (SEM) has long been the standard in imaging the sub-micrometer surface ultrastructure of both hard and soft materials. In the case of biological samples, it has provided great insights into their physical architecture. However, three of the fundamental challenges in the SEM imaging of soft materials are that of limited imaging resolution at high magnification, charging caused by the insulating properties of most biological samples and the loss of subtle surface features by heavy metal coating. These challenges have recently been overcome with the development of the Helium Ion Microscope (HIM), which boasts advances in charge reduction, minimized sample damage, high surface contrast without the need for metal coating, increased depth of field, and 5 angstrom imaging resolution. We demonstrate the advantages of HIM for imaging biological surfaces as well as compare and contrast the effects of sample preparation techniques and their consequences on sub-nanometer ultrastructure.

  16. Nanoforging Single Layer MoSe2 Through Defect Engineering with Focused Helium Ion Beams

    PubMed Central

    Iberi, Vighter; Liang, Liangbo; Ievlev, Anton V.; Stanford, Michael G.; Lin, Ming-Wei; Li, Xufan; Mahjouri-Samani, Masoud; Jesse, Stephen; Sumpter, Bobby G.; Kalinin, Sergei V.; Joy, David C.; Xiao, Kai; Belianinov, Alex; Ovchinnikova, Olga S.

    2016-01-01

    Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction the of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe2 locally, and decipher associated mechanisms at the atomic level. We demonstrate He+ beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and increases the Young’s modulus of elasticity. Furthermore, we observe for the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at the room temperature. The approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region. PMID:27480346

  17. Nanoforging Single Layer MoSe2 Through Defect Engineering with Focused Helium Ion Beams

    NASA Astrophysics Data System (ADS)

    Iberi, Vighter; Liang, Liangbo; Ievlev, Anton V.; Stanford, Michael G.; Lin, Ming-Wei; Li, Xufan; Mahjouri-Samani, Masoud; Jesse, Stephen; Sumpter, Bobby G.; Kalinin, Sergei V.; Joy, David C.; Xiao, Kai; Belianinov, Alex; Ovchinnikova, Olga S.

    2016-08-01

    Development of devices and structures based on the layered 2D materials critically hinges on the capability to induce, control, and tailor the electronic, transport, and optoelectronic properties via defect engineering, much like doping strategies have enabled semiconductor electronics and forging enabled introduction the of iron age. Here, we demonstrate the use of a scanning helium ion microscope (HIM) for tailoring the functionality of single layer MoSe2 locally, and decipher associated mechanisms at the atomic level. We demonstrate He+ beam bombardment that locally creates vacancies, shifts the Fermi energy landscape and increases the Young’s modulus of elasticity. Furthermore, we observe for the first time, an increase in the B-exciton photoluminescence signal from the nanoforged regions at the room temperature. The approach for precise defect engineering demonstrated here opens opportunities for creating functional 2D optoelectronic devices with a wide range of customizable properties that include operating in the visible region.

  18. Maskless Lithography and in situ Visualization of Conductivity of Graphene using Helium Ion Microscopy

    SciTech Connect

    Iberi, Vighter O.; Vlassiouk, Ivan V.; Zhang, X. -G.; Matola, Brad R.; Linn, Allison R.; Joy, David Charles; Adam Justin Rondinone

    2015-07-07

    The remarkable mechanical and electronic properties of graphene make it an ideal candidate for next generation nanoelectronics. With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to patterning the graphene into devices. In the case of graphene supported on a substrate, traditional nanofabrication techniques such as e-beam lithography (EBL) are often used in fabricating graphene nanoribbons but the multi-step processes they require can result in contamination of the graphene with resists and solvents. In this letter, we report the utility of scanning helium ion lithography for fabricating functional graphene nanoconductors that are supported directly on a silicon dioxide layer, and we measure the minimum feature size achievable due to limitations imposed by thermal fluctuations and ion scattering during the milling process. Further we demonstrate that ion beams, due to their positive charging nature, may be used to observe and test the conductivity of graphene-based nanoelectronic devices in situ.

  19. Maskless Lithography and in situ Visualization of Conductivity of Graphene using Helium Ion Microscopy

    PubMed Central

    Iberi, Vighter; Vlassiouk, Ivan; Zhang, X.-G.; Matola, Brad; Linn, Allison; Joy, David C.; Rondinone, Adam J.

    2015-01-01

    The remarkable mechanical and electronic properties of graphene make it an ideal candidate for next generation nanoelectronics. With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to patterning the graphene into devices. In the case of graphene supported on a substrate, traditional nanofabrication techniques such as e-beam lithography (EBL) are often used in fabricating graphene nanoribbons but the multi-step processes they require can result in contamination of the graphene with resists and solvents. In this letter, we report the utility of scanning helium ion lithography for fabricating functional graphene nanoconductors that are supported directly on a silicon dioxide layer, and we measure the minimum feature size achievable due to limitations imposed by thermal fluctuations and ion scattering during the milling process. Further we demonstrate that ion beams, due to their positive charging nature, may be used to observe and test the conductivity of graphene-based nanoelectronic devices in situ. PMID:26150202

  20. The influence of negative ions in helium-oxygen barrier discharges: I. Laser photodetachment experiment

    NASA Astrophysics Data System (ADS)

    Tschiersch, R.; Nemschokmichal, S.; Meichsner, J.

    2016-04-01

    This work is the experimental part of a comprehensive study that aims to understand the influence of negative ions on the development of atmospheric pressure barrier discharges in electronegative systems. The investigations will be complemented by a 1D numerical fluid simulation. Laser photodetachment experiments were performed in a glow-like barrier discharge operated in helium with admixtures of oxygen up to 1 vol.% at a gas pressure of 500 mbar. The discharge gap between the glass-coated electrodes was 3 mm. The discharge properties were characterized by electrical measurements and optical emission spectroscopy. Laser photodetachment of {{\\text{O}}-} , {\\text{O}}2- , and {\\text{O}}3- was studied using the fundamental and second harmonic wavelength of a Nd-YAG laser. The laser photodetachment of negative ions influences the breakdown characteristics when the laser is fired during the prephase of the discharge only. The breakdown voltage is reduced, which indicates an enhanced pre-ionization initiated by the detached electrons. Systematic variations in the laser pulse in time, the axial laser beam position, the laser pulse energy, and the laser wavelength provided detailed knowledge on this process. The investigation underlines the importance of the discharge prephase in general and aims to differentiate between the negative ion species {{\\text{O}}-} , {\\text{O}}2- , and {\\text{O}}3- .

  1. Calculated distributions of hydrogen and helium ions in the low-latitude ionosphere.

    NASA Technical Reports Server (NTRS)

    Moffett, R. J.; Hanson, W. B.

    1973-01-01

    The simultaneous time-dependent continuity equations for O(+), H(+) and He(+) in the low latitude F-region are solved. Account is taken of E x B drift, a meridional neutral wind, and ion-ion and ion-neutral drag. The calculated profiles of O(+) and H(+) concentrations at 1630 LT are in fair agreement with the observations of Hanson et al. The He(+) field-aligned velocity is almost matched to the O(+) field-aligned velocity and, above the chemical equilibrium region and around the He(+) peak, the He(+) concentration is determined largely by production and transport. There is disagreement between the theoretical vertical He(+) profile and the profile observed by Hanson et al. Satisfactory agreement is obtained with Taylor's satellite results at fixed height for O(+) and H(+). It is found that the He(+) concentration is greater in the winter hemisphere than in the summer hemisphere, even if the neutral helium distribution is symmetrical about the Equator. The He(+) results are consistent with Taylor's results.

  2. Biologically optimized helium ion plans: calculation approach and its in vitro validation

    NASA Astrophysics Data System (ADS)

    Mairani, A.; Dokic, I.; Magro, G.; Tessonnier, T.; Kamp, F.; Carlson, D. J.; Ciocca, M.; Cerutti, F.; Sala, P. R.; Ferrari, A.; Böhlen, T. T.; Jäkel, O.; Parodi, K.; Debus, J.; Abdollahi, A.; Haberer, T.

    2016-06-01

    Treatment planning studies on the biological effect of raster-scanned helium ion beams should be performed, together with their experimental verification, before their clinical application at the Heidelberg Ion Beam Therapy Center (HIT). For this purpose, we introduce a novel calculation approach based on integrating data-driven biological models in our Monte Carlo treatment planning (MCTP) tool. Dealing with a mixed radiation field, the biological effect of the primary 4He ion beams, of the secondary 3He and 4He (Z  =  2) fragments and of the produced protons, deuterons and tritons (Z  =  1) has to be taken into account. A spread-out Bragg peak (SOBP) in water, representative of a clinically-relevant scenario, has been biologically optimized with the MCTP and then delivered at HIT. Predictions of cell survival and RBE for a tumor cell line, characterized by {{(α /β )}\\text{ph}}=5.4 Gy, have been successfully compared against measured clonogenic survival data. The mean absolute survival variation ({μΔ \\text{S}} ) between model predictions and experimental data was 5.3%  ±  0.9%. A sensitivity study, i.e. quantifying the variation of the estimations for the studied plan as a function of the applied phenomenological modelling approach, has been performed. The feasibility of a simpler biological modelling based on dose-averaged LET (linear energy transfer) has been tested. Moreover, comparisons with biophysical models such as the local effect model (LEM) and the repair-misrepair-fixation (RMF) model were performed. {μΔ \\text{S}} values for the LEM and the RMF model were, respectively, 4.5%  ±  0.8% and 5.8%  ±  1.1%. The satisfactorily agreement found in this work for the studied SOBP, representative of clinically-relevant scenario, suggests that the introduced approach could be applied for an accurate estimation of the biological effect for helium ion radiotherapy.

  3. Maskless Lithography and in situ Visualization of Conductivity of Graphene using Helium Ion Microscopy

    DOE PAGES

    Iberi, Vighter O.; Vlassiouk, Ivan V.; Zhang, X. -G.; Matola, Brad R.; Linn, Allison R.; Joy, David Charles; Adam Justin Rondinone

    2015-07-07

    The remarkable mechanical and electronic properties of graphene make it an ideal candidate for next generation nanoelectronics. With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to patterning the graphene into devices. In the case of graphene supported on a substrate, traditional nanofabrication techniques such as e-beam lithography (EBL) are often used in fabricating graphene nanoribbons but the multi-step processes they require can result in contamination of the graphene with resists and solvents. In this letter, we report the utility of scanning helium ionmore » lithography for fabricating functional graphene nanoconductors that are supported directly on a silicon dioxide layer, and we measure the minimum feature size achievable due to limitations imposed by thermal fluctuations and ion scattering during the milling process. Further we demonstrate that ion beams, due to their positive charging nature, may be used to observe and test the conductivity of graphene-based nanoelectronic devices in situ.« less

  4. Helium effects on mechanical properties and microstructure of high fluence ion-irradiated RAFM steel

    NASA Astrophysics Data System (ADS)

    Ogiwara, H.; Kohyama, A.; Tanigawa, H.; Sakasegawa, H.

    2007-08-01

    Reduced-activation ferritic/martensitic steels, RAFS, are leading candidates for the blanket and first wall of fusion reactors, and effects of displacement damage and helium production on mechanical properties and microstructures are important to these applications. Because it is the most effective way to obtain systematic and accurate information about microstructural response under fusion environment, single-(Fe 3+) and dual-(Fe 3+ + He +) irradiations were performed followed by TEM observation and nano-indentation hardness measurement. Dual-ion irradiation at 420 °C induced finer defect clusters compared to single-ion irradiation. These fine defect clusters caused large differences in the hardness increase between these irradiations. TEM analysis clarified that radiation induced precipitates were MX precipitates (M: Ta, W). Small defects invisible to TEM possibly caused the large increase in hardness, in addition to the hardness increment produced by radiation induced MX. In this work, radiation hardening and microstructural evolution accompanied by the synergistic effects to high fluences are discussed.

  5. A miniaturised electron ionisation time-of-flight mass spectrometer that uses a unique helium ion removal pulsing technique specifically for gas analysis.

    PubMed

    Qing, Jiang; Huang, Zhengxu; Zhang, Yan; Zhu, Hui; Tan, Guobin; Gao, Wei; Yang, Peng-yuan

    2013-06-21

    A miniaturised reflectron time-of-flight mass spectrometer combined with an electron ionisation ion source has been developed for the analysis of gases. An entirely new helium ion removal pulsing technique in this mass spectrometer is used to achieve an improved performance for the first time. The helium carrier gas, which enters into the source along with the gaseous sample, is simultaneously ionised and then orthogonally introduced into the time-of-fight mass analyser. Once the relatively light helium ions in the ion packet become extremely close to the reflectron plate (B-plate for short in this article), a modulated pulse is instantaneously applied on the B-plate and a negative reflectron voltage is set to the B-plate and lasts for a very short period, during which all the helium ions are directly bumped into the B-plate and subsequently removed. The helium ion removal pulsing technique can efficiently avoid saturation of the micro-channel plate caused by too many helium ions. A compact and durable instrument is designed, which has a mass resolving resolution greater than 400 FWHM for online gas analysis. The technology may also be further developed to remove other ions for TOF mass spectrometry.

  6. Retardation (Casimir) energy shifts for Rydberg helium-like low-Z ions: An exploratory study

    NASA Astrophysics Data System (ADS)

    Babb, James F.; Habs, Dietrich; Spruch, Larry; Wolf, Andreas

    1992-09-01

    The development of storage rings and electromagnetic traps for heavy charged particles is opening up new regimes of atomic physics, including, in particular, spectroscopic studies of Rydberg helium-like ions — with nuclear charge Z, one electron in the 1 s state, and one electron in a near-hydrogenic state of high n and l < n, with n and l the principal and orbital quantum numbers, respectively. We consider the possibility of detecting energy shifts due to retardation, Δ E ret ( n, l), Casimir-like effects. These are quantum electrodynamic (QED) retardation effects associated with the finite speed of light. (As opposed to basically kinematic and dynamic QED effects for small quantum numbers n and l, the appropriate expansion parameter for n and l large for retardation QED corrections is not Z( e 2/ħ c) but [( Z - 1)/ n 2 Z 2](ħ c/e 2).) We wish to provide some orientation to those planning experiments in the area, with regard to the choices of n, l, and Z most likely to be able to generate a high-precision confirmation of a retarded interaction. To do so, we provide extensive tables of estimates, for 1 s, nl states, of Δ E ret( n, l), of radiative widths, and of E, the spin-independent (“electric” fine structure) energy in the absence of retardation shifts, for (nuclear spin zero) ions with Z=2, 6, 8, 16 and 20. These ions might be experimentally accessible in storage rings, and the Z's are low enough that virtual pair production effects may not yet be significant. There is also a brief survey of possible experimental techniques.

  7. Heavy-ion irradiation defect accumulation in ZrN characterized by TEM, GIXRD, nanoindentation, and helium desorption

    NASA Astrophysics Data System (ADS)

    Egeland, G. W.; Valdez, J. A.; Maloy, S. A.; McClellan, K. J.; Sickafus, K. E.; Bond, G. M.

    2013-04-01

    A study on zirconium nitride was performed to assess the effect of radiation damage by heavy ions at cryogenic and elevated temperatures. Cross-sectional transmission electron microscopy, grazing incidence X-ray diffraction, nanoindentation, and helium desorption studies were used to assess the damage and its effects. Xenon and krypton were used as heavy ions at 300 keV to displacement damage as high as 200 dpa. Implants were cryogenic, 350 °C, 580 °C, and 800 °C. Amorphization was not observed at low temperatures nor was bubble formation observed at elevated temperatures, however, defect migration was observed at elevated temperatures. Nanoindenter results showed the onset of defect saturation. Helium release studies were performed to show the effect of increasing damage by Xe to 40 dpa.

  8. Improved adhesion for SiO/sub 2/ particles in silica substrates using helium-ion irradiation

    SciTech Connect

    Musket, R.G.; Thomas, I.M.

    1988-03-01

    We have examined the effects of irradiation with 200-keV helium ions on the adhesion and optical transmission properties of 220 nm thick antireflective, optical coatings that consisted of layers of spherical, 20 nm diameter silica particles. In the as-deposited state these sol-gel coatings have very low adhesion to the fused silica subtrates. Results for adhesion and optical transmission have been obtained for doses of 10/sup 13/-10/sup 17/ Hecm/sup 2/. Significant improvement in adhesion was found for doses exceeding about 2 /times/ 10/sup 14/ Hecm/sup 2/. Optical transmission measurements for wavelengths of 200-1200 nm showed increasing absorption with dose. We have evidence that the helium ions decompose various contaminants in the coating into two types of degradation products. One is volatile and the other remains in the coating as optically absorbing species. UVoxidative-gas treatment effectively removes the absorbing species.

  9. Electromagnetic Ion Cyclotron Waves in the Helium Branch Induced by Multiple Electromagnetic Ion Cyclotron Triggered Emissions

    NASA Astrophysics Data System (ADS)

    Shoji, M.; Omura, Y.; Grison, B.; Pickett, J. S.; Dandouras, I. S.; Engebretson, M. J.

    2011-12-01

    Electromagnetic ion cyclotron (EMIC) triggered emissions with rising tones between the H+ and He+ cyclotron frequencies were found in the inner magnetosphere by the recent Cluster observations. Another type of EMIC wave with a constant frequency is occasionally observed below the He+ cyclotron frequency after the multiple EMIC triggered emissions. We performed a self-consistent hybrid simulation with a one-dimensional cylindrical magnetic flux model approximating the dipole magnetic field of the Earth's inner magnetosphere. In the presence of energetic protons with a sufficient density and temperature anisotropy, multiple EMIC triggered emissions are reproduced due to the nonlinear wave growth mechanism of rising-tone chorus emissions, and a constant frequency wave in the He+ EMIC branch is subsequently generated. Through interaction with the multiple EMIC rising-tone emissions, the velocity distribution function of the energetic protons is strongly modified. Because of the pitch angle scattering of the protons, the gradient of the distribution in velocity phase space is enhanced along the diffusion curve of the He+ branch wave, resulting in the linear growth of the EMIC wave in the He+ branch.

  10. Cavity morphology in a Ni based superalloy under heavy ion irradiation with cold pre-injected helium. I

    SciTech Connect

    Zhang, He; Yao, Zhongwen Daymond, Mark R.; Kirk, Marquis A.

    2014-03-14

    In order to understand radiation damage in the nickel based superalloy Inconel X-750 in thermal reactors, where (n, α) transmutation reaction also occurred in addition to fast neutron induced atomic displacement, heavy ion (1 MeV Kr{sup 2+}) irradiation with pre-injected helium was performed under in-situ observations of an intermediate voltage electron microscope at Argonne National Laboratory. By comparing to our previous studies using 1 MeV Kr{sup 2+} irradiation solely, the pre-injected helium was found to be essential in cavity nucleation. Cavities started to be visible after Kr{sup 2+} irradiation to 2.7 dpa at ≥200 °C in samples containing 200 appm, 1000 appm, and 5000 appm helium, respectively, but not at lower temperatures. The cavity growth was observed during the continuous irradiation. Cavity formation appeared along with a reduced number density of stacking fault tetrahedra, vacancy type defects. With higher pre-injected helium amount, a higher density of smaller cavities was observed. This is considered to be the result of local trapping effect of helium which disperses vacancies. The average cavity size increases with increasing irradiation temperatures; the density reduced; and the distribution of cavities became heterogeneous at elevated temperatures. In contrast to previous characterization of in-reactor neutron irradiated Inconel X-750, no obvious cavity sink to grain boundaries and phase boundaries was found even at high doses and elevated temperatures. MC-type carbides were observed as strong sources for agglomeration of cavities due to their enhanced trapping strength of helium and vacancies.

  11. Measurements of the intercombination and forbidden lines from helium-like ions in Tokamaks and Electron Beam Ion Traps

    SciTech Connect

    Bitter, M; Hill, K W; von Goeler, S; Stodiek, W; Beiersdorfer, P; Rice, J E; Ince-Cushman, A

    2007-08-22

    The paper reviews the results from tokamak experiments for the line ratios x/w, y/w, and z/w from helium-like ions with Z in the range from 14 to 28. With exception of the DITE experiments, where these line ratios were found to be in agreement with theoretical predictions, all other tokamak experiments yielded values that were significantly larger than predicted. The reasons for these discrepancies are not yet understood. It is possible that radial profile effects were not properly taken into account in the majority of the tokamak experiments. The paper also gives a short historical review of the X-ray diagnostic developments and also presents very recent data from a new type of X-ray imaging crystal spectrometer, which records spatially resolved spectra with a spatial resolution of about 1 cm in the plasma. These new data can be Abel inverted, so that it will be possible to determine line ratios at each radial position in the plasma. Effects of radial profiles, which may have affected the chord-integrated measurements of the past, will thus be eliminated in the future.

  12. Towards secondary ion mass spectrometry on the helium ion microscope: An experimental and simulation based feasibility study with He{sup +} and Ne{sup +} bombardment

    SciTech Connect

    Wirtz, T.; Vanhove, N.; Pillatsch, L.; Dowsett, D.; Sijbrandij, S.; Notte, J.

    2012-07-23

    The combination of the high-brightness He{sup +}/Ne{sup +} atomic level ion source with secondary ion mass spectrometry detection capabilities opens up the prospect of obtaining chemical information with high lateral resolution and high sensitivity on the Zeiss ORION helium ion microscope. The analytical performance in terms of sputtering yield, useful yield, and detection limit is studied and subsequently optimized by oxygen and cesium flooding. Detection limits down to 10{sup -6} and 10{sup -5} can be obtained for silicon using Ne{sup +} and He{sup +}, respectively. A simulation based study reveals furthermore that a lateral resolution <10 nm can be obtained.

  13. High-resolution helium ion microscopy of epididymal epithelial cells and their interaction with spermatozoa

    PubMed Central

    Păunescu, Teodor G.; Shum, Winnie W.C.; Huynh, Chuong; Lechner, Lorenz; Goetze, Bernhard; Brown, Dennis; Breton, Sylvie

    2014-01-01

    We examined the rat and mouse epididymis using helium ion microscopy (HIM), a novel imaging technology that uses a scanning beam of He+ ions to produce nanometer resolution images of uncoated biological samples. Various tissue fixation, sectioning and dehydration methods were evaluated for their ability to preserve tissue architecture. The cauda epididymidis was luminally perfused in vivo to remove most spermatozoa and the apical surface of the epithelial lining was exposed. Fixed epididymis samples were then subjected to critical point drying (CPD) and HIM. Apical stereocilia in principal cells and smaller apical membrane extensions in clear cells were clearly distinguishable in both rat and mouse epididymis using this technology. After perfusion with an activating solution containing CPT-cAMP, a permeant analog of cAMP, clear cells exhibited an increase in the number and size of membrane ruffles or microplicae. In contrast, principal cells did not exhibit detectable structural modifications. High-resolution HIM imaging clearly showed the ultrastructure of residual sperm cells, including the presence of concentric rings on the midpiece, and of cytoplasmic droplets in some spermatozoa. Close epithelium–sperm interactions were also detected. We found a number of sperm cells whose heads were anchored within the epididymal epithelium. In certain cases, the surface of the sperm cytoplasmic droplet was covered with vesicle-like structures whose size is consistent with that of epididymosomes. In conclusion, we describe here the first application of HIM technology to the study of the structure and morphology of the rodent epididymis. HIM technology represents a major imaging breakthrough that can be successfully applied to study the epididymis and spermatozoa, with the goal of advancing our understanding of their structure and function. PMID:25015675

  14. Angular anisotropy parameters and recoil-ion momentum distribution in two-photon double ionization of helium

    SciTech Connect

    Kheifets, A. S.; Ivanov, I. A.; Bray, Igor

    2007-08-15

    We present convergent-close-coupling (CCC) calculations of the angular anisotropy parameters {beta}{sub 2},{beta}{sub 4} and the recoil ion momentum distribution d{sigma}/dp in two-photon double ionization (TPDI) of helium. In a stark contrast to single-photon double ionization (SPDI), where the {beta}{sub 2} parameter varies widely changing the angular distribution from isotropic to nearly dipole for slow and fast photoelectrons, respectively, the {beta} parameters for TPDI show very little change. The angular distribution of the recoil ion is fairly isotropic in TPDI as opposed to a strong alignment with the polarization of light in SPDI.

  15. TH-A-19A-05: Modeling Physics Properties and Biologic Effects Induced by Proton and Helium Ions

    SciTech Connect

    Taleei, R; Titt, U; Peeler, C; Guan, F; Mirkovic, D; Grosshans, D; Mohan, R

    2014-06-15

    Purpose: Currently, proton and carbon ions are used for cancer treatment. More recently, other light ions including helium ions have shown interesting physical and biological properties. The purpose of this work is to study the biological and physical properties of helium ions (He-3) in comparison to protons. Methods: Monte Carlo simulations with FLUKA, GEANT4 and MCNPX were used to calculate proton and He-3 dose distributions in water phantoms. The energy spectra of proton and He-3 beams were calculated with high resolution for use in biological models. The repair-misrepairfixation (RMF) model was subsequently used to calculate the RBE. Results: The proton Bragg curve calculations show good agreement between the three general purpose Monte Carlo codes. In contrast, the He-3 Bragg curve calculations show disagreement (for the magnitude of the Bragg peak) between FLUKA and the other two Monte Carlo codes. The differences in the magnitude of the Bragg peak are mainly due to the discrepancy in the secondary fragmentation cross sections used by the codes. The RBE for V79 cell lines is about 0.96 and 0.98 at the entrance of proton and He-3 ions depth dose respectively. The RBE increases to 1.06 and 1.59 at the Bragg peak of proton and He-3 ions. The results demonstrated that LET, microdosimetric parameters (such as dose-mean lineal energy) and RBE are nearly constant along the plateau region of Bragg curve, while all parameters increase within the Bragg peak and at the distal edge for both proton and He-3 ions. Conclusion: The Monte Carlo codes should revise the fragmentation cross sections to more accurately simulate the physical properties of He-3 ions. The increase in RBE for He-3 ions is higher than for proton beams at the Bragg peak.

  16. Excitation and Ionization-Excitation of Helium in Fast Ion-Atom Collisions.

    NASA Astrophysics Data System (ADS)

    Fuelling, Stephan R. K.

    1991-02-01

    The purpose of this work is to investigate several aspects of many-body effects in fast ion-atom collisions using the target gas helium where the projectile velocities are above the Bohr velocity. The method of high resolution extreme ultraviolet (EUV) spectroscopy has been applied in order to measure absolute state selective cross sections of emitted light from excited HeI and HeII target states. We have performed a relative intensity calibration of our 1.5 m spectrometer by comparing 1MeV C^+ + Ne spectra with those examined from a wavelength-calibrated 2.2 m grazing incidence monochromator installed at the Dynamitron Tandem Laboratory at the University of Bochum, Germany. The absolute calibration of our instrument has been accomplished with a single measurement of the Ly_alpha transition of He^+ from 200 eV e-He collisions, where the absolute cross section is known. A comparison between the two-electron processes of ionization-excitation and the one-electron process of excitation of helium following e^-, H^+ and C^{6+ } impact is made for projectile Bohr velocities (v_0) ranging between 1.5 and 9.6. Therefore, the Lyman series of He^+(np) ^2P to (1s) ^2S for n = 2 to 5 and the Rydberg series of He (1snp) ^1P to (1s^2) ^1 S for n = 2 to 5 have been measured. We have been the first to report such extensive absolute state selective cross section measurements. The absolute EUV emission cross sections for ionization-excitation show a significant difference in magnitude for projectiles e^ -, H^+ and C^ {6+} when compared at equal velocities. These differences are possibly due to interference effects between different collision processes. These differences can also be considered as interference between first and second order Born expansions terms. The cross section for electron impact at projectile velocities between 1.5 and 8 v _0 exceeds that for protons by a factor of up to about 3. The H^+ and C ^{6+} cross sections scale approximately as Z_sp{p}{3}. Finally, cross

  17. Helium ion microscopy of enamel crystallites and extracellular tooth enamel matrix

    PubMed Central

    Bidlack, Felicitas B.; Huynh, Chuong; Marshman, Jeffrey; Goetze, Bernhard

    2014-01-01

    An unresolved problem in tooth enamel studies has been to analyze simultaneously and with sufficient spatial resolution both mineral and organic phases in their three dimensional (3D) organization in a given specimen. This study aims to address this need using high-resolution imaging to analyze the 3D structural organization of the enamel matrix, especially amelogenin, in relation to forming enamel crystals. Chemically fixed hemi-mandibles from wild type mice were embedded in LR White acrylic resin, polished and briefly etched to expose the organic matrix in developing tooth enamel. Full-length amelogenin was labeled with specific antibodies and 10 nm immuno-gold. This allowed us to use and compare two different high-resolution imaging techniques for the analysis of uncoated samples. Helium ion microscopy (HIM) was applied to study the spatial organization of organic and mineral structures, while field emission scanning electron microscopy (FE-SEM) in various modes, including backscattered electron detection, allowed us to discern the gold-labeled proteins. Wild type enamel in late secretory to early maturation stage reveals adjacent to ameloblasts a lengthwise parallel alignment of the enamel matrix proteins, including full-length amelogenin proteins, which then transitions into a more heterogeneous appearance with increasing distance from the mineralization front. The matrix adjacent to crystal bundles forms a smooth and lacey sheath, whereas between enamel prisms it is organized into spherical components that are interspersed with rod-shaped protein. These findings highlight first, that the heterogeneous organization of the enamel matrix can be visualized in mineralized en bloc samples. Second, our results illustrate that the combination of these techniques is a powerful approach to elucidate the 3D structural organization of organic matrix molecules in mineralizing tissue in nanometer resolution. PMID:25346697

  18. Radiative properties of molecular nitrogen ions produced by helium Penning ionization and argon effects

    NASA Technical Reports Server (NTRS)

    Miller, George, III; Song, Kyo-Dong

    1994-01-01

    The development of hypersonic aerospace vehicles requires a better understanding on the thermal and chemical nonequilibrium kinetics of participating species in shock layers. The computational fluid dynamic (CFD) codes developed for such flowfields overestimate the radiation in the spectral region of 300 - 600 nm. A speculation for this overestimation is that inclusion of Ar, CO2, and H2O at the upper atmosphere flight region makes a significant impact on radiative kinetics of molecular nitrogen ions. To define the effects of minority species on the radiative kinetics of N2(+), an experimental setup was made by using the helium Penning ionization. The vibrational and rotational temperature were measured by mapping the vibrational and rotational distributions of N2(+) emission with high spectroscopic resolution and absolute intensity measurements. Measured vibrational temperatures were in the range from 18,000 to 36,000 K, and rotational temperatures were in the range from 300 to 370 K. The irradiance of 391.44 nm line and rotational and vibrational temperatures were analyzed to define argon and CO2 effects on the N2(+) emission. When Ar or CO2 is injected with N2, the rotational temperature did not change. The irradiances were reduced by 34 percent and 78 percent for the 50 percent of mixture of Ar and CO2, respectively. The vibrational temperatures were increased by 24.1 percent and 82.9 percent for the 50 percent of mixture of Ar and CO2, respectively. It appears that there are no significant effects from small concentrations of Ar and CO2 at the upper atmosphere flight region.

  19. Fabrication of porous TiO2 nanorod array photoelectrodes with enhanced photoelectrochemical water splitting by helium ion implantation.

    PubMed

    Liu, Yichao; Shen, Shaohua; Ren, Feng; Chen, Jianan; Fu, Yanming; Zheng, Xudong; Cai, Guangxu; Xing, Zhuo; Wu, Hengyi; Jiang, Changzhong

    2016-05-19

    Porous photoelectrodes show high efficiency in hydrogen production by water splitting. However, fabrication of porous nanorods is usually difficult. Here, we report a simple approach to fabricate a kind of novel porous rutile titanium dioxide nanorod array by an advanced ion implantation method using multiple-energy helium ion implantation and subsequent annealing. The porous nanostructure enhances the photoelectrochemical performance of the titanium dioxide nanorod array photoelectrodes under Uv-visible light illumination, where the highest photocurrent density was relatively about 10 times higher than that of the pristine titanium dioxide nanorod array. The formation of nanocavities mainly contributes to the enhancement of the photocurrent density by trapping holes inside to separate the charge carriers. The study demonstrates that ion implantation could be an effective approach to develop novel porous nanostructural photoelectrodes for the application of hydrogen production.

  20. Effects of composition and helium injection on dislocation loop development in pure FeNiCr alloys under Ni ion irradiation

    NASA Astrophysics Data System (ADS)

    Kimoto, Takayoshi

    1993-08-01

    Pure Fe35Ni7Cr, Fe45Ni7Cr, Fe40Ni13Cr and Fe45Ni15Cr alloys were irradiated by 4MeV Ni 2+ ions at 948 K to doses of about 0.05, 0.3 and 1.0 dpa without helium injection or with simultaneous helium injection. With increasing Ni content and decreasing Cr content, the diameter of radiation-induced dislocation loops increased, and the dose at which the dislocation loops disappeared to develop into dislocation networks decreased. The diameter of dislocation loops induced by Ni 2+ ions irradiation with simultaneous helium injection was larger than that without helium injection for the Fe35Ni7Cr and Fe45Ni7Cr alloys.

  1. Development and testing of a pulsed helium ion source for probing materials and warm dense matter studies.

    PubMed

    Ji, Q; Seidl, P A; Waldron, W L; Takakuwa, J H; Friedman, A; Grote, D P; Persaud, A; Barnard, J J; Schenkel, T

    2016-02-01

    The neutralized drift compression experiment was designed and commissioned as a pulsed, linear induction accelerator to drive thin targets to warm dense matter (WDM) states with peak temperatures of ∼1 eV using intense, short pulses (∼1 ns) of 1.2 MeV lithium ions. At that kinetic energy, heating a thin target foil near the Bragg peak energy using He(+) ions leads to more uniform energy deposition of the target material than Li(+) ions. Experiments show that a higher current density of helium ions can be delivered from a plasma source compared to Li(+) ions from a hot plate type ion source. He(+) beam pulses as high as 200 mA at the peak and 4 μs long were measured from a multi-aperture 7-cm-diameter emission area. Within ±5% variation, the uniform beam area is approximately 6 cm across. The accelerated and compressed pulsed ion beams can be used for materials studies and isochoric heating of target materials for high energy density physics experiments and WDM studies. PMID:26932070

  2. Development and testing of a pulsed helium ion source for probing materials and warm dense matter studies

    NASA Astrophysics Data System (ADS)

    Ji, Q.; Seidl, P. A.; Waldron, W. L.; Takakuwa, J. H.; Friedman, A.; Grote, D. P.; Persaud, A.; Barnard, J. J.; Schenkel, T.

    2016-02-01

    The neutralized drift compression experiment was designed and commissioned as a pulsed, linear induction accelerator to drive thin targets to warm dense matter (WDM) states with peak temperatures of ˜1 eV using intense, short pulses (˜1 ns) of 1.2 MeV lithium ions. At that kinetic energy, heating a thin target foil near the Bragg peak energy using He+ ions leads to more uniform energy deposition of the target material than Li+ ions. Experiments show that a higher current density of helium ions can be delivered from a plasma source compared to Li+ ions from a hot plate type ion source. He+ beam pulses as high as 200 mA at the peak and 4 μs long were measured from a multi-aperture 7-cm-diameter emission area. Within ±5% variation, the uniform beam area is approximately 6 cm across. The accelerated and compressed pulsed ion beams can be used for materials studies and isochoric heating of target materials for high energy density physics experiments and WDM studies.

  3. Helium-3 transport experiments in the scrape-off layer with the Alcator C-Mod omegatron ion mass spectrometer

    SciTech Connect

    Nachtrieb, R.; LaBombard, B.

    2000-11-01

    {sup 3}He gas was puffed from the wall into Ohmic low confinement-mode discharges of the Alcator C-Mod [I. H. Hutchinson , Phys. Plasmas 1, 1551 (1994)] tokamak and the charged states were measured near the wall with the omegatron ion mass spectrometer. Analysis of the data shows that the concentrations of singly- and doubly-ionized helium near the wall are approximately equal. The electron temperature and density at the omegatron are too low to account for ionization of helium in the local flux tube, therefore the helium is ionized in a hotter region of the edge plasma and is transported to the omegatron. A simple one-dimensional radial transport model reproduces the observed values of charge state flux and density, but only if rapid cross-field transport is included, increasing with distance from the separatrix. A constant cross-field diffusion coefficient of order 2m{sup 2}/s and an outward convection velocity profile increasing to of order 100 m/s in the far scrape-off layer is implied.

  4. VizieR Online Data Catalog: Helium-like ions with Z=10-36 transition rates (Si+, 2016)

    NASA Astrophysics Data System (ADS)

    Si, R.; Guo, X. L.; Wang, K.; Li, S.; Yan, J.; Chen, C. Y.; Brage, T.; Zou, Y. M.

    2016-08-01

    We provide accurate energies for the lowest singly excited 70 levels among 1snl(n<=6,l<=(n-1)) configurations and the lowest doubly excited 250 levels arising from the K-vacancy 2ln'l(n'<=6,l<=(n'-1)) configurations of helium-like ions with Z=10-36. Wavelengths, transition rates, oscillator strengths, and line strengths are calculated for the E1, M1, E2, and M2 transitions among these levels. The radiative lifetimes are reported for all the calculated levels. (4 data files).

  5. State-Selective and Total Single-Capture Cross Sections for Fast Collisions of Multiply Charged Ions with Helium Atoms

    NASA Astrophysics Data System (ADS)

    Mančev, Ivan; Milojević, Nenad; Belkić, Dževad

    2013-11-01

    The four-body boundary corrected first Born approximation (CB1-4B) is used to calculate the single electron capture cross sections for collisions between fully stripped ions (He2+, Be4+, B5+ and C6+) and helium target at intermediate and high impact energies. The main goal of this study is to assess the usefulness of the CB1-4B method at intermediate and high impact energies for these collisions. Detailed comparisons with the measurements are carried out and the obtained theoretical cross sections are in reasonable agreement with the available experimental data.

  6. Can particle beam therapy be improved using helium ions? - a planning study focusing on pediatric patients.

    PubMed

    Knäusl, Barbara; Fuchs, Hermann; Dieckmann, Karin; Georg, Dietmar

    2016-06-01

    Aim To explore the potential of scanned helium ion beam therapy ((4)He) compared to proton therapy in a comparative planning study focusing on pediatric patients. This was motivated by the superior biological and physical characteristics of (4)He. Material and methods For eleven neuroblastoma (NB), nine Hodgkin lymphoma (HL), five Wilms tumor (WT), five ependymoma (EP) and four Ewing sarcoma (EW) patients, treatment plans were created for protons and (4)He. Dose prescription to the planning target volume (PTV) was 21 Gy [relative biological effectiveness (RBE)] (NB), 19.8 Gy (RBE) (HL), 25.2 Gy (RBE) for the WT boost volume and 54 Gy (RBE) for EP and EW patients. A pencil beam algorithm for protons (constant RBE = 1.1) and (4)He was implemented in the treatment planning system Hyperion. For (4)He the relative biological effectiveness (RBE) was calculated with a 'zonal' model based on different linear energy transfer regions. Results Target constraints were fulfilled for all indications. For NB patients differences for kidneys and liver were observed for all dose-volume areas, except the high-dose volume. The body volume receiving up to 12.6 Gy (RBE) was reduced by up to 10% with (4)He. For WT patients the mean and high-dose volume for the liver was improved when using (4)He. For EP normal tissue dose was reduced using (4)He with 12.7% of the voxels receiving higher doses using protons. For HL and EW sarcoma patients the combination of large PTV volumes with the position of the organs at risk (OARs) obliterated the differences between the two particle species, while patients with the heart close to the PTV could benefit from (4)He. Conclusion Treatment plan quality improved with (4)He compared to proton plans, but advantages in OAR sparing were depending on indication and tumor geometries. These first results of scanned (4)He therapy motivate comprehensive research on (4)He, including acquisition of experimental data to improve modeling of (4)He. PMID

  7. Mobilities of ground-state and metastable O/+/, O2/+/, O/2+/, and O2/2+/ ions in helium and neon

    NASA Astrophysics Data System (ADS)

    Johnsen, R.; Biondi, M. A.; Hayashi, M.

    1982-09-01

    The ionic mobilities of O(+), O2(+), O(2+), and O2(2+) in helium and neon have been measured using a selected-ion drift apparatus (SIDA). It is found that the mobilities of both O(+) and O2(+) ions in the metastable states (2D or 4Pi u) are measurably smaller than those of the same ions carried out by using known, state-selective ion-molecule reactions. A similar mobility differentiation of ground-state and metastable ions was not observed for the O(2+) and O2(2+) ions.

  8. A calculation for radial expectation values of helium like actinide ions (Z=89-93)

    NASA Astrophysics Data System (ADS)

    Ürer, G.; Arslan, M.; Balkaya, E.; Keçeli, A.

    2016-03-01

    Radial expectation values, , for helium like actinides (ZAc=89, ZTh=90, ZPa=91, ZU=92, and ZNp=93) are reported using the Multiconfiguration Hartree-Fock (MCHF) within the framework Breit-Pauli corrections. Atomic data as energy levels, wavelengths, weighted oscillator strengths, and transition probabilities for allowed and forbidden transitions need these calculations. The obtained results are compared available works.

  9. Gas bubbles evolution peculiarities in ferritic-martensitic and austenitic steels and alloys under helium-ion irradiation

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Kalashnikov, A. N.; Kalin, B. A.; Binyukova, S. Yu

    2003-12-01

    Transmission electron microscopy has been used to investigate the gas bubble evolution in model alloys of the Fe-C system, ferritic-martensitic steels of 13Cr type, nickel and austenitic steels under 40-keV helium-ion irradiation up to a fluence of 5 × 10 20 m -2 at the temperature of 920 K. It was shown that helium-ion irradiation at high temperature resulted in formation of bubbles with a greater size and a smaller density in Fe and ferritic-martensitic steels than those in nickel and austenitic steels. Large gaseous bubbles in ferritic component are uniformly distributed in grains body in Fe-C alloys as well as in ferritic-martensitic steels. The bubbles with a higher density and a smaller size than those in ferritic component are formed in martensitic grains of steels and Fe-C alloys with a high carbon content ( NC>0.01 wt%), which leads to a small level of swelling of martensite in comparison with that of ferrite. In addition, the bubbles in martensitic grains have a tendency to ordered distribution.

  10. Helium ion microscopy based wall thickness and surface roughness analysis of polymer foams obtained from high internal phase emulsion.

    PubMed

    Rodenburg, C; Viswanathan, P; Jepson, M A E; Liu, X; Battaglia, G

    2014-04-01

    Due to their wide range of applications, porous polymers obtained from high internal phase emulsions have been widely studied using scanning electron microscopy. However, due to their lack of electrical conductivity, quantitative information of wall thicknesses and surface roughness, which are of particular interest to tissue engineering, has not been obtained. Here, Helium Ion Microscopy is used to examine uncoated polymer foams and some very strong but unexpected contrast is observed, the origin of which is established here. Based on this analysis, a method for the measurement of wall thickness variations and wall roughness measurements has been developed, based on the modeling of Helium ion transmission. The results presented here indicate that within the walls of the void structure there exist small features with height variations of ~30 nm and wall thickness variations from ~100 nm to larger 340 nm in regions surrounding interconnecting windows within the structure. The suggested imaging method is applicable to other porous carbon based structures with wall thicknesses in the range of 40-340 nm.

  11. Effective particle energies for stopping power calculation in radiotherapy treatment planning with protons and helium, carbon, and oxygen ions

    NASA Astrophysics Data System (ADS)

    Inaniwa, T.; Kanematsu, N.

    2016-10-01

    The stopping power ratio (SPR) of body tissues relative to water depends on the particle energy. For simplicity, however, most analytical dose planning systems do not account for SPR variation with particle energy along the beam’s path, but rather assume a constant energy for SPR estimation. The range error due to this simplification could be indispensable depending on the particle species and the assumed energy. This error can be minimized by assuming a suitable energy referred to as an ‘effective energy’ in SPR estimation. To date, however, the effective energy has never been investigated for realistic patient geometries. We investigated the effective energies for proton, helium-, carbon-, and oxygen-ion radiotherapy using volumetric models of the reference male and female phantoms provided by the International Commission on Radiological Protection (ICRP). The range errors were estimated by comparing the particle ranges calculated when particle energy variations were and were not considered. The effective energies per nucleon for protons and helium, carbon, and oxygen ions were 70 MeV, 70 MeV, 131 MeV, and 156 MeV, respectively. Using the determined effective energies, the range errors were reduced to  ⩽0.3 mm for respective particle species. For SPR estimation of multiple particle species, an effective energy of 100 MeV is recommended, with which the range error is  ⩽0.5 mm for all particle species.

  12. Determination of the light ion abundances in the strong-helium star HR 3089

    NASA Technical Reports Server (NTRS)

    Lester, J. B.

    1975-01-01

    Using line blanketed model stellar atmospheres and a spectrum synthesis approach, a differential abundance study of the ultraviolet spectrum of HR 3089 relative to the normal star lambda Sco was performed. Both stars were found to have the same abundances of carbon and silicon, but the helium and nitrogen are significantly enhanced in HR 3089. The atmospheric parameters and the distribution of abundances found for HR 3089 agree well with the results of Osmer and Peterson on sharp-lined helium-rich stars. The rotational velocity of 160 km/sec found for HR 3089 places a constraint on the role of diffusion in producing the abundance anomalies. Examination of the resonance lines of C II, N II, Si III and Si IV shows no evidence for mass loss in either star.

  13. Application of relativistic coupled cluster linear response theory to helium-like ions embedded in plasma environment

    NASA Astrophysics Data System (ADS)

    Das, Madhulita; Chaudhuri, Rajat K.; Chattopadhyay, Sudip; Sinha Mahapatra, Uttam; Mukherjee, P. K.

    2011-08-01

    Ionization potential and low lying 1S0\\longrightarrow1P1 excitation energies (EE) of highly stripped He-like ions C4 +, Al11 +, and Ar16 + embedded in plasma environment are calculated for the first time using the state-of-the-art coupled cluster (CC)-based linear response theory (LRT) with the four-component relativistic spinors and compared with available experimental data from laser plasma experiments. Debye's screening model is used to estimate the effect of plasma on the ions within the relativistic and non-relativistic framework. The transition energies computed at the CCLRT level using the Debye model agree well with experiment and with other available theoretical data. To our knowledge, no prior CCLRT calculations within the Dirac-Fock framework are available for these systems. Our calculated transition energies for helium-like ions are in accord with experiment; we trust that our predicted EE might be acceptably good for the systems considered. Our preliminary result indicates that CCLRT with the four-component relativistic spinors appears to be a valuable tool for studying the atomic systems where accurate treatments of correlation effects play a crucial role in shaping the spectral lines of ions subjected to plasma environment.

  14. Bubbles formation in helium ion irradiated Cu/W multilayer nanocomposites: Effects on structure and mechanical properties

    NASA Astrophysics Data System (ADS)

    Callisti, M.; Karlik, M.; Polcar, T.

    2016-05-01

    This study investigates the effects of He bubbles on structural and mechanical properties of sputter-deposited Cu/W multilayers. A multilayer with a periodicity of 10 nm was deposited and subjected to helium ion irradiation with two different fluences. He bubbles formed mostly in Cu layers and their distribution was affected by He concentration and radiation damage. According to SRIM calculations, in low He concentration regions bubbles formed mostly along interfaces, while more homogeneously distributed bubbles were found in Cu layers and along columnar grain boundaries in higher He concentration regions. We suggest that the capability of interfaces to annihilate point defects is weakened by the He bubbles shielding effect. Nanoindentation tests revealed a hardness decrease amounting to ∼0.5 and ∼1 GPa for low and high fluences, respectively. The observed softening effect is attributed to He storage-induced changes in residual stresses and columnar grain boundary/interfacial sliding facilitated by He bubbles.

  15. Double ionization of helium by highly-charged-ion impact analyzed within the frozen-correlation approximation

    SciTech Connect

    Ciappina, M. F.; Kirchner, T.; Schulz, M.

    2011-09-15

    We apply the frozen-correlation approximation (FCA) to analyze double ionization of helium by energetic highly charged ions. In this model the double ionization amplitude is represented in terms of single ionization amplitudes, which we evaluate within the continuum distorted wave-eikonal initial state (CDW-EIS) approach. Correlation effects are incorporated in the initial and final states, but are neglected during the time the collision process takes place. We implement the FCA using the Monte Carlo event generator technique, which allows us to generate theoretical event files and to compare theory and experiment using the same analysis tools. The comparison with previous theoretical results and with experimental data demonstrates, on the one hand, the validity of our earlier simple models to account for higher-order mechanisms, and, on the other hand, the robustness of the FCA.

  16. Modification of the crystal structure of gadolinium gallium garnet by helium ion irradiation

    SciTech Connect

    Ostafiychuk, B. K.; Yaremiy, I. P. Yaremiy, S. I.; Fedoriv, V. D.; Tomyn, U. O.; Umantsiv, M. M.; Fodchuk, I. M.; Kladko, V. P.

    2013-12-15

    The structure of gadolinium gallium garnet (GGG) single crystals before and after implantation by He{sup +} ions has been investigated using high-resolution X-ray diffraction methods and the generalized dynamic theory of X-ray scattering. The main types of growth defects in GGG single crystals and radiation-induced defects in the ion-implanted layer have been determined. It is established that the concentration of dislocation loops in the GGG surface layer modified by ion implantation increases and their radius decreases with an increase in the implantation dose.

  17. Modification of the crystal structure of gadolinium gallium garnet by helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Ostafiychuk, B. K.; Yaremiy, I. P.; Yaremiy, S. I.; Fedoriv, V. D.; Tomyn, U. O.; Umantsiv, M. M.; Fodchuk, I. M.; Kladko, V. P.

    2013-12-01

    The structure of gadolinium gallium garnet (GGG) single crystals before and after implantation by He+ ions has been investigated using high-resolution X-ray diffraction methods and the generalized dynamic theory of X-ray scattering. The main types of growth defects in GGG single crystals and radiation-induced defects in the ion-implanted layer have been determined. It is established that the concentration of dislocation loops in the GGG surface layer modified by ion implantation increases and their radius decreases with an increase in the implantation dose.

  18. Contraints on the Velocity and Spatial Distribution of Helium-like Ions in the Wind of SMC X-1 from Observations with XMM/RGS

    NASA Astrophysics Data System (ADS)

    Wojdowski, P. S.; Liedahl, D. A.; Kallman, T. R.

    2004-08-01

    We present here X-ray spectra of the HMXB SMC X-1 obtained in an observation with the XMM-Newton observatory beginning before eclipse and ending near the end of eclipse. With the Reflection Grating Spectrometers (RGS), we resolve the emission line triplets of nitrogen, oxygen, neon, and magnesium but detect flux only from the intercombination lines of those triplets. From the fluxes of the lines of these triplets, we derive constraints on the distribution of helium-like ions in coordinate and velocity space. Among other results, we find upper limits of order 1 km s-1 for the product of the velocity dispersion of the ions and the solid angle divided by 4π subtended at the neutron star by the helium-like ions.

  19. Gettering of transition metals by cavities in silicon formed by helium ion implantation

    SciTech Connect

    Petersen, G.A.; Myers, S.M.; Follstaedt, D.M.

    1996-09-01

    We have recently completed studies which quantitatively characterize the ability of nanometer-size cavities formed by He ion implantation to getter detrimental metal impurities in Si. Cavity microstructures formed in Si by ion implantation of He and subsequent annealing have been found to capture metal impurities by two mechanisms: (1) chemisorption on internal walls at low concentrations and (2) silicide precipitation at concentrations exceeding the solid solubility. Experiments utilizing ion-beam analysis, cross-sectional transmission electron microscopy, and secondary ion mass spectrometry were performed to quantitatively characterize the gettering effects and to determine the free energies associated with the chemisorbed metal atoms as a function of temperature. Mathematical models utilizing these results have been developed to predict gettering behavior.

  20. VizieR Online Data Catalog: Line ratios for helium-like ions (Porquet+, 2001)

    NASA Astrophysics Data System (ADS)

    Porquet, D.; Mewe, R.; Dubau, J.; Raassen, A. J. J.; Kaastra, J. S.

    2001-09-01

    The tables include data concerning six He-like ions: wavelengths, transition probabilities, wavelengths at which the radiation temperatures should be determined. Line ratios (G and R, see definition in table 1 below) for six He-like ions from Tables 3 to 69 for various parameters: density (ne), temperature (Te), dilution factor (W), radiation temperature (Trad), and spectral resolution. Atomic data (appendix A) concerning the unresolved satellite lines are displayed (from Tables A1 to A6). (4 data files).

  1. Two-wavelength Raman study of poly(ethylene terephthalate) surfaces modified by helium plasma-based ion implantation

    NASA Astrophysics Data System (ADS)

    Veres, M.; Tóth, A.; Mohai, M.; Bertóti, I.; Szépvölgyi, J.; Tóth, S.; Himics, L.; Koós, M.

    2012-12-01

    The surface of poly(ethylene terephthalate) (PET) was modified by helium plasma-based ion implantation (He PBII). The untreated and surface modified samples were characterised with optical absorption spectroscopy and two-wavelength micro-Raman spectroscopy excited with 488 nm and 785 nm light sources, allowing to examine the chemical bonding configuration of the surface layers on different depths and by selective enhancement of vibrations of different structural units. Upon treatment, simultaneously with the development of the broad D and G bands, a gradual decrease of the peaks corresponding to the Cdbnd C stretching and Cdbnd O stretching modes were observed with both excitations. Downshifting and broadening were detected for the Cdbnd C peak with both excitations and also for the Cdbnd O peak with the 488 nm excitation due to formation of condensed aromatic rings. Oppositely, upshifting was found with 785 nm excitation for the Cdbnd O peak and especially for its broad shoulder newly developed at the high wavenumber side. The latter feature was assigned to Cdbnd O groups attached to polymer chains without conjugation and the bands behaviour was interpreted by breaking of the Cdbnd C bonds of the polymer, leading to the formation of a crosslinked, disordered and stressed structure with still intact Cdbnd O groups, due to the increased nuclear damage at the end of the ion track.

  2. Structural response of transient heat loading on a molybdenum surface exposed to low-energy helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Sinclair, G.; Tripathi, J. K.; Diwakar, P. K.; Hassanein, A.

    2016-03-01

    The advancement of fusion reactor engineering is currently inhibited by the lack of knowledge surrounding the stability of plasma facing components (PFCs) in a tokamak environment. During normal operation, events of high heat loading occur periodically where large amounts of energy are imparted onto the PFC surface. Concurrently, irradiation by low-energy helium ions present in the fusion plasma can result in the synthesis of a fibre form nanostructure on the PFC surface, called ‘fuzz’. In order to understand how this heterogeneous structure evolves and deforms in response to transient heat loading, a pulsed Nd:YAG millisecond laser is used to simulate these events on a fuzz form molybdenum (Mo) surface. Performance was analysed by three metrics: nanostructure evolution, particle emission, and improvement in optical properties. Experiments performed at the upper end of the expected range for type-I edge-localized modes (ELMs) found that the helium-induced nanostructure completely disappears after 200 pulses of the laser at 1.5 MJ m-2. In situ mass loss measurements found that the amount of particles leaving the surface increases as energy density increases and the rate of emission increases with pulse count. Finally, optical properties assisted in providing a qualitative indication of fuzz density on the Mo surface; after 400 pulses at 1.5 MJ m-2, the optical reflectivity of the damaged surface is ~90% of that of a mirror polished Mo sample. These findings provide different results than previous studies done with tungsten (W), and further help illustrate the complicated nature of how transient events of high heat loading in a tokamak environment might impact the performance and lifetime of PFCs in ITER and future DEMO devices (Ueda et al 2014 Fusion Eng. Des. 89 901-6).

  3. Resource Letter SH-1: Superfluid Helium.

    ERIC Educational Resources Information Center

    Hallock, Robert B.

    1982-01-01

    Provides an annotated list of books, textbooks, and films on superfluid helium. Also lists research reports/reviews arranged by category, including among others, early history, microscopic understanding, ions in helium, helium in rotation, vortices and quantization, helium films and constricted geometrics, persistence flow, and superfluid helium…

  4. Stochastic acceleration and charge change of helium ions in the solar flare plasma.

    NASA Astrophysics Data System (ADS)

    Kartavykh, Yu. Yu.; Ostryakov, V. M.; Stepanov, I. Yu.; Yoshimori, M.

    1998-10-01

    In order to explain the energy spectra and abundances of the He+ and He++ solar flare ions measured in some works, the authors calculated the behavior of these ions in solar plasma, taking into account both their stochastic acceleration by Alfvén waves and the possibility of charge exchange with the surrounding plasma. The results agree with the experiments if the plasma in the regions where acceleration takes place has a concentration and temperature on the order of N = 2×107 cm-3 and T = 6.31×104K, respectively. Recent observations of solar flares onboard the Yohkoh satellite have demonstrated that it is apparently impractical to expect the existence of such rarefied and low-temperature plasma in the flare loops. The calculations indicate that the high abundance of He+ is most likely due to its nonsolar origin. Some possibilities of enrichment of energetic particle fluxes by He+ ions are briefly discussed.

  5. Theoretical state-selective and total cross sections for electron capture from helium atoms by fully stripped ions

    NASA Astrophysics Data System (ADS)

    Mančev, I.; Milojević, N.; Belkić, Dž.

    2015-03-01

    The four-body boundary-corrected first Born (CB1-4B) approximation is used to compute cross sections for single electron capture from helium targets by fully stripped ions. The projectile ions are H+, He2+, Li3+, Be4+, B5+, C6+, N7+, O8+, and F9+. An extensive list of theoretical state-to-state cross sections in these collisions at energies ranging from 20 to 10 000 keV/amu is given. This list includes the state-selective cross sections Qnlm for each individual triple of the usual quantum numbers { n , l , m } of the final hydrogen-like states alongside Qnl and Qn for the pertinent sub-shells and shells where the respective summations over m and { l , m } have been carried out. The maximal value of the principal quantum number n was chosen to vary from 4 (H+) to 10 (F9+) so as to satisfy the condition n ≥ZP, where ZP is the nuclear charge of the projectile. Usually, the largest cross sections stem from those values of n that match the projectile charge (n =ZP) . The total cross sections for capture summed over all the quantum numbers { n , l , m } are also tabulated. The overall goal of this study is to fill in lacunae in the existing databases of charge exchange cross sections that are needed in several inter-disciplinary fields. For example, in particle transport physics, which is of utmost importance in such emerging branches as hadron therapy, these cross sections constitute a part of the multifaceted input data for stochastic simulations of energy losses of multiply charged ions in matter, including tissue. Other significant uses of the present data are anticipated in charge exchange diagnostics within thermonuclear research project as well as in applications covering the relevant parts of plasma physics and astrophysics.

  6. Differential Ion Mobility Separations in up to 100% Helium Using Microchips

    SciTech Connect

    Shvartsburg, Alexandre A.; Ibrahim, Yehia M.; Smith, Richard D.

    2014-01-09

    The performance of differential IMS (FAIMS) analyzers is much enhanced by gases comprising He, especially He/N2 buffers. However, electrical breakdown has limited the He fraction in those mixtures to ~50 - 75%, depending on the field strength. By Paschen law, the threshold field for breakdown increases at shorter distances. This allows FAIMS using chips with microscopic channels to utilize much stronger field intensities (E) than “full-size” analyzers with wider gaps. Here we show that those chips can employ higher He fractions up to 100%. Use of He-rich gases improves the resolution and resolution/sensitivity balance substantially, although less than for full-size analyzers. The optimum He fraction is ~80%, in line with first-principles theory. Hence one can now measure the dependences of ion mobility on E in pure He, where ion-molecule cross section calculations are much more tractable than in other gases that form deeper and more complex interaction potentials. This capability may facilitate quantitative modeling of high-field ion mobility behavior and thus FAIMS separation properties, which would enable a priori extraction of structural information about the ions from FAIMS data.

  7. Toward plasmonics with nanometer precision: nonlinear optics of helium-ion milled gold nanoantennas.

    PubMed

    Kollmann, Heiko; Piao, Xianji; Esmann, Martin; Becker, Simon F; Hou, Dongchao; Huynh, Chuong; Kautschor, Lars-Oliver; Bösker, Guido; Vieker, Henning; Beyer, André; Gölzhäuser, Armin; Park, Namkyoo; Vogelgesang, Ralf; Silies, Martin; Lienau, Christoph

    2014-08-13

    Plasmonic nanoantennas are versatile tools for coherently controlling and directing light on the nanoscale. For these antennas, current fabrication techniques such as electron beam lithography (EBL) or focused ion beam (FIB) milling with Ga(+)-ions routinely achieve feature sizes in the 10 nm range. However, they suffer increasingly from inherent limitations when a precision of single nanometers down to atomic length scales is required, where exciting quantum mechanical effects are expected to affect the nanoantenna optics. Here, we demonstrate that a combined approach of Ga(+)-FIB and milling-based He(+)-ion lithography (HIL) for the fabrication of nanoantennas offers to readily overcome some of these limitations. Gold bowtie antennas with 6 nm gap size were fabricated with single-nanometer accuracy and high reproducibility. Using third harmonic (TH) spectroscopy, we find a substantial enhancement of the nonlinear emission intensity of single HIL-antennas compared to those produced by state-of-the-art gallium-based milling. Moreover, HIL-antennas show a vastly improved polarization contrast. This superior nonlinear performance of HIL-derived plasmonic structures is an excellent testimonial to the application of He(+)-ion beam milling for ultrahigh precision nanofabrication, which in turn can be viewed as a stepping stone to mastering quantum optical investigations in the near-field.

  8. Lithography exposure characteristics of poly(methyl methacrylate) (PMMA) for carbon, helium and hydrogen ions

    NASA Astrophysics Data System (ADS)

    Puttaraksa, Nitipon; Norarat, Rattanaporn; Laitinen, Mikko; Sajavaara, Timo; Singkarat, Somsorn; Whitlow, Harry J.

    2012-02-01

    Poly(methyl methacrylate) is a common polymer used as a lithographic resist for all forms of particle (photon, ion and electron) beam writing. Faithful lithographic reproduction requires that the exposure dose, Θ, lies in the window Θ0⩽Θ<Θ, where Θ0 and Θ represent the clearing and cross-linking onset doses, respectively. In this work we have used the programmable proximity aperture ion beam lithography systems in Chiang Mai and Jyväskylä to determine the exposure characteristics in terms of fluence for 2 MeV protons, 3 MeV 4He and 6 MeV 12C ions, respectively. After exposure the samples were developed in 7:3 by volume propan-2-ol:de-ionised water mixture. At low fluences, where the fluence is below the clearing fluence, the exposed regions were characterised by rough regions, particularly for He with holes around the ion tracks. As the fluence (dose) increases so that the dose exceeds the clearing dose, the PMMA is uniformly removed with sharp vertical walls. When Θ exceeds the cross-linking onset fluence, the bottom of the exposed regions show undissolved PMMA.

  9. Differential ion mobility separations in up to 100% helium using microchips.

    PubMed

    Shvartsburg, Alexandre A; Ibrahim, Yehia M; Smith, Richard D

    2014-03-01

    The performance of differential IMS (FAIMS) analyzers is much enhanced by gases comprising He, especially He/N2 mixtures. However, electrical breakdown has limited the He fraction to ~50%-75%, depending on the field strength. By the Paschen law, the threshold field for breakdown increases at shorter distances. This allows FAIMS using chips with microscopic channels to utilize much stronger field intensities (E) than "full-size" analyzers with wider gaps. Here we show that those chips can employ higher He fractions up to 100%. Use of He-rich gases improves the resolution and resolution/sensitivity balance substantially, although less than for full-size analyzers. The optimum He fraction is ~80%, in line with first-principles theory. Hence, one can now measure the dependences of ion mobility on E in pure He, where ion-molecule cross section calculations are much more tractable than in other gases that form deeper and more complex interaction potentials. This capability may facilitate quantitative modeling of high-field ion mobility behavior and, thus, FAIMS separation properties, which would enable a priori extraction of structural information about the ions.

  10. A liquid-helium-free superconducting coil system forming a flat minimum-magnetic-field distribution of an electron cyclotron resonance ion source

    SciTech Connect

    Yoshida, Ken-ichi Nara, Takayuki; Saitoh, Yuichi; Yokota, Watalu

    2014-02-15

    A flat distribution of the minimum magnetic field (flat-B{sub min}) of an electron cyclotron resonance ion source (ECRIS) is expected to perform better in highly charged ion production than classical B{sub min}. To form a flat-B{sub min} structure with a liquid helium-free superconducting device, a coil system of seven coils with four current leads has been designed. The lead number was reduced by connecting the plural coils in series to maintain the flat-B{sub min} structure even when the coil currents are changed for adjustment. This coil system can be operated with a helium-free cryostat, since the estimation of heat from the leads to the coils is nearly equivalent to the existing superconducting ECRIS of a similar type.

  11. Proton or helium ion beam written channel waveguides in Nd:YAG ceramics

    NASA Astrophysics Data System (ADS)

    Yao, Yicun; Zhang, Chao; Vanga, Sudheer Kumar; Bettiol, A. A.; Chen, Feng

    2013-10-01

    We report on the fabrication of channel waveguides in Nd:YAG ceramics, using either focused proton beam writing (PBW) or He beam writing (HeBW) techniques. Energies of ions used in the writing process were at 1 MeV and 2 MeV, respectively, with different writing fluence. High quality channel waveguides were produced in both H+ and He+ implanted regions. Characteristics of the waveguides were explored, and refractive index distribution of the waveguide was reconstructed.

  12. Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

    NASA Astrophysics Data System (ADS)

    Fan, Hongyu; Yang, Qi; Li, Xin; Ni, Weiyuan; Niu, Jinhai; Liu, Dongping

    2015-04-01

    Polycrystalline tungsten (W) and molybdenum (Mo) materials both non-annealed and annealed at temperatures of 800-1750°C have been irradiated with low-energy (220 eV), high-flux (∼1021 ions/m2 ·s) He+ at an irradiation temperature of 600°C and at a dose of 1.0×1025 ions/m2. This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials. A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He+ dose of 1.0×1025 ions/m2. Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W. Compared to W, Mo suffered much less surface damage after being irradiated at various He+ doses. supported by the National Magnetic Confinement Fusion Program of China (No. 2011GB108011), National Natural Science Foundation of China (No. 11405023) and the Scientific Research Fund of Liaoning Provincial Education Department (No. L2014539) and the Fundamental Research Funds for the Central Universities of China (No. DC201502080410)

  13. Precision, high dose radiotherapy. II. Helium ion treatment of tumors adjacent to critical central nervous system structures

    SciTech Connect

    Saunders, W.M.; Chen, G.T.Y.; Austin-Seymour, M.; Castro, J.R.; Collier, J.M.; Gauger, G.; Gutin, P.; Phillips, T.L.; Pitluck, S.; Walton, R.E.

    1985-07-01

    In this paper, the authors present a technique for treating relatively small, low grade tumors located very close to critical, radiation sensitive central nervous system structures such as the spinal cord and the brain stem. A beam of helium ions is used to irradiate the tumor. The nearby normal tissues are protected by exploiting the superb dose localization properties of this beam, particularly its well defined and controllable range in tissue, the increased dose deposited near the end of this range (i.e., the Bragg peak), the sharp decrease in dose beyond the Bragg peak, and the sharp penumbra of the beam. To illustrate the technique, the authors present a group of 19 patients treated for chordomas, meningiomas and low grade chondrosarcomas in the base of the skull or spinal column. They have been able to deliver high, uniform doses to the target volumes, while keeping the doses to the nearby critical tissues below the threshold for radiation damage. Follow-up on this group of patients is short, averaging 22 months (2 to 75 months). Currently, 15 patients have local control of their tumor. Two major complications, a spinal cord transsection and optic tract damage, are discussed in detail. Their treatment policies have been modified to minimize the risk of these complications in the future, and they are continuing to use this method to treat such patients.

  14. Active voltage contrast imaging of cross-sectional surface of multilayer ceramic capacitor using helium ion microscopy

    NASA Astrophysics Data System (ADS)

    Sakai, C.; Ishida, N.; Masuda, H.; Nagano, S.; Kitahara, M.; Ogata, Y.; Fujita, D.

    2016-08-01

    We studied active voltage contrast (AVC) imaging using helium ion microscopy (HIM). We observed secondary electron (SE) images of the cross-sectional surface of multilayer ceramic capacitors (MLCCs) with and without a voltage applied to the internal electrodes. When no voltage was applied, we obtained an image reflecting the material contrast between the Ni internal electrode region and the BaTiO3 dielectric region of the cross-sectional surface of the MLCC. When a voltage was applied, the electrical potential difference between the grounded and the positively biased internal electrodes affected the contrast (voltage contrast). Moreover, attenuation of the SE intensity from the grounded to the positively biased internal electrodes was observed in the dielectric region. Kelvin probe force microscopy (KPFM) measurements of the contact potential difference (CPD) were performed on the same sample. By using the AVC image from the HIM observation and the CPD image from the KPFM measurement, we could quantitatively evaluate the electrical potential. We think that the results of this study will lead to an expansion in the number of applications of HIM.

  15. [Cytological and cytogenetic damages of spermatogonial cells in mice in the acute and late periods after irradiation by protons, helium ions, and gamma-rays].

    PubMed

    Fedorenko, B S; Vaglenov, A; Abrosimova, A N

    2010-01-01

    Experiments with small test animals have been carried out to study the survival rate of spermatogenic cells in the acute period after exposure to protons with the energy 9 GeV, helium ions with the energy 4 GeV/nucleon, and 60Co gamma radiation in doses of 0.5-7.5 Gy and the reciprocal translocation frequency in spermatocytes under meiosis at the diakinesis-metaphase-1 stage six months after the exposure of the animals to protons with the energy 50 MeV and 9 GeV, helium ions with the energy 4 GeV/nucleon, and 60Co gamma-radiation in doses of 0.5-4.0 Gy. It is shown that the dependence of the effect on the dose is linear or near to linear for all kinds of radiation used. Relative biological effectiveness coefficients of the accelerated nuclei obtained by correlating equally effective doses of the standard and investigated radiations turned out to be higher in survival rate of type B spermatogonium and amounted to 2.0 and 1.3 for 9 GeV protons and helium ions respectively. At the same time, the use of the nonparametric method to determine the RBE coefficients in the course of finding out the reciprocal translocation frequency in spermatocytes points to an increase in the RBE coefficients of charged particles from 1.0 to 2.0.

  16. Young-type interference in collisions between hydrogen molecular ions and helium.

    PubMed

    Schmidt, L Ph H; Schössler, S; Afaneh, F; Schöffler, M; Stiebing, K E; Schmidt-Böcking, H; Dörner, R

    2008-10-24

    The dissociative electron transfer from He into 10 keV H2+ was measured in a kinematically complete experiment by using the cold target recoil ion momentum spectroscopy imaging technique in combination with a highly resolving molecular fragment imaging technique. The electron transfer into the dissociative b(3)Sigma+_(u) state of H2 could be selected by kinematic conditions. We find a striking double slit interference pattern in the transverse momentum transfer which we can modify by selecting different internuclear distances. Compared to an optical double slit, interference minima and maxima are interchanged. The latter is the result of a phase shift in the electronic part of the wave function.

  17. Depopulation of metastable helium by radiative association with hydrogen and lithium ions

    SciTech Connect

    Augustovičová, L.; Soldán, P.; Kraemer, W. P.

    2014-02-10

    Depopulation of metastable He(2{sup 3}S) by radiative association with hydrogen and lithium ions is investigated using a fully quantal approach. Rate coefficients for spontaneous and stimulated radiative association of the HeH{sup +}, HeD{sup +}, and LiHe{sup +} molecular ions on the spin-triplet manifold are presented as functions of temperature considering the association to rotational-vibrational states of the lowest triplet electronic states a {sup 3}Σ{sup +} and b {sup 3}Σ{sup +} from the continuum states of the b {sup 3}Σ{sup +} electronic state. Evaluation of the rate coefficients is based on highly accurate quantum calculations, taking into account all possible state-to-state transitions at thermal energies (for spontaneous association) or at higher background energies (stimulated association). As expected, calculations show that the rate coefficients for radiative association to the a state are several orders of magnitude larger than the one for the b state formation. A noticeable effect by blackbody background radiation on the radiative association is only obtained for the b → b process. Aspects of the formation and abundance of the metastable HeH{sup +}(a {sup 3}Σ{sup +}) in astrophysical environments are briefly discussed.

  18. Quantal and Semiclassical Methods of Slow Ion - Scattering with Applications to NEON(4+) + Helium.

    NASA Astrophysics Data System (ADS)

    Tan, Jiang

    1987-12-01

    The dynamics of low-energy ion-atom collisions is investigated at a two-state level of approximation. We have proposed a new semiclassical method based upon the two-level theory in spinor representation. The new approach presents a more transparent picture of the present ion -atom scattering for the charge-transfer process. The new results for the transition probability of the system Ne ^{4+} +He compare very well with existing full quantum mechanical methods. Particularly, we give a new view of the S-matrix as a rotation operator which serves to rotate the scattering state. Finally, the single charge-transfer differential cross-sections (sigma(theta)) are calculated at laboratory impact energies from 220 eV to 500 eV for the same system (Ne^{4+} + He) and are compared with the recent experimental data of Tunnell et al. Our calculations explain the experimental data both in quality and quantity. The model scattering potential is used in the sigma(theta) calculation and its construction is discussed.

  19. Double ionization of helium by bare ions: Theoretical study of the fully differential cross sections

    NASA Astrophysics Data System (ADS)

    López, S. D.; Garibotti, C. R.; Otranto, S.

    2011-06-01

    This work presents a theoretical study of fully differential cross sections (FDCSs) for the double ionization of an He target by ion impact within a distorted wave model. The initial atomic system is described by two approximated wave functions of different accuracy proposed by Bonham and Kohl. For the final channel several models are considered based upon improvements and simplifications of the well-known three-body Coulomb (3C) model. The influence of the receding projectile on the resulting fragments is also studied by implementing a model with effective charges that depend on the momenta of the four particles. The FDCSs resulting for different electron energy sharing are discussed. The sensitivity of the FDCSs to the projectile charge sign and magnitude is explored over the energy range 700 keV/amu through 6 MeV/amu.

  20. Radiation chemical behavior of aqueous butanal oxime solutions irradiated with helium ion beams

    NASA Astrophysics Data System (ADS)

    Costagliola, A.; Venault, L.; Deroche, A.; Garaix, G.; Vermeulen, J.; Omnee, R.; Duval, F.; Blain, G.; Vandenborre, J.; Fattahi-Vanani, M.; Vigier, N.

    2016-02-01

    Samples of butanal oxime in aqueous solution have been irradiated with the helion (4He2+) beam of the ARRONAX (Nantes) and the CEMHTI (Orléans) cyclotrons. The consumption yield of butanal oxime has been measured by gas-chromatography coupled with mass spectrometry. Yields of gaseous products (mainly H2) have also been measured by micro-gas-chromatography. Butanal oxime can react with H• radicals by abstraction mechanism to enhance H2 production. Yields of liquid phase products (hydrogen peroxide and nitrite ion) have been measured by colorimetric methods. Butanal oxime acts as a scavenger of OH• radical to inhibit the production of H2O2. The observation of the radiolytic products allows then to discuss a degradation mechanism of butanal oxime in aqueous solutions.

  1. Thermal stability of nanostructured TiZrSiN thin films subjected to helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Uglov, V. V.; Abadias, G.; Zlotski, S. V.; Saladukhin, I. A.; Skuratov, V. A.; Leshkevich, S. S.; Petrovich, S.

    2015-07-01

    The phase stability, upon vacuum annealing up to 1000 °C, of nanostructured (Ti,Zr)1-xSixN thin films is investigated by X-ray diffraction analysis as a function of Si content (0.13 ⩽ x ⩽ 0.25) and prior irradiation with He ions (40 kV). The quaternary TiZrSiN thin films were deposited by reactive magnetron sputtering from elemental targets at the substrate temperature of 600 °C. It was found that the increase in Si content, x, results in the transformation of structure from nanocrystalline (x = 0.13, grain size of 11 nm) to nanocomposite state (0.19 < x ⩽ 0.25, grain size of 5 nm). The phase composition of the films changes from single-phase, cubic c-(Ti,Zr)N columns with (1 1 1) preferred orientation to dual-phase system consisting of c-(Ti,Zr)N crystallites and amorphous SiNy. Irradiation with He ions at the doses of 2 × 1016 and 5 × 1016 cm-2 does change the phase composition of the films. It is found that the onset temperature for phase decomposition decreases from 1000 °C to 800 °C with increasing Si content for unirradiated films. The formation of a secondary ZrN phase is observed concomitantly with increased broadening of the (2 0 0) c-(Ti,Zr)N diffraction peak. For irradiated films, the subsequent annealing at 1000 °C leads to decomposition of the c-(Ti,Zr)N solid solution into TiN- and ZrN-rich phases as well as crystallization of hexagonal Si3N4 phase.

  2. Stress relaxation in unirradiated and in helium ion bombarded glass plates: Dimensional stability

    SciTech Connect

    Primak, W.

    1984-02-15

    The deformation of thin glass plates during bombardment with 140-keV He/sup +/ ions was measured with an external capacitor. The contour of the plates was determined interferometrically before irradiation, after irradiation, and after aging for several years. These results showed that the calibration of the capacitor equipment by dead-weight loading a silica plate was faulty. The deflection of a vitreous silica free cantilever on dead-weight loading was measured interferometrically, and the results showed that deformation occurred within the clamp. It was confirmed that placing a ground shield about the electrode of the capacitor increases the calculated deflections. Data for the permanent deformation of a stressed plate of vitreous silica are analyzed, and it is concluded that stress relaxation by a bulk viscoelastic deformation cannot be detected by a change in plate contour because the maximum precision for such a determination could not detect apparent viscosities greater than approx.10/sup 29/ P. The stress relaxation of the irradiated vitreous silica plates was about 10% in three years corresponding to an apparent post-irradiation viscosity of approx.10/sup 20/ P. The stress relaxations observed for the other glasses, Pyrex, BK7, and LF2 were much greater, and it is uncertain to what extent they were a viscoelastic effect or an annealing effect. The behavior of a sample of a facsimile radioactive waste storage glass, 76--68 indicated it was not a uniform product; the contour became irregular; hence, these techniques were not appropriate for it.

  3. Observational study of the cooling behavior of interstellar helium pickup ions in the inner heliosphere

    NASA Astrophysics Data System (ADS)

    Chen, Jun Hong; Möbius, Eberhard; Gloeckler, George; Bochsler, Peter; Bzowski, Maciej; Isenberg, Philip A.; Sokół, Justyna M.

    2013-07-01

    velocity distribution of interstellar pickup ions (PUIs) has typically been described as evolving through fast pitch angle scattering followed by adiabatic cooling while being transported radially outward with the solar wind. In combination, the ionization rate, which controls the radial profile of the interstellar neutrals, and the cooling process determine the slope of the observed PUI distributions. Thus far, a cooling index of 3/2 for the PUI velocity distributions has been used in almost all studies. This value is based on the implicit assumptions of immediate PUI isotropization due to pitch angle scattering and solar wind expansion with the square of the distance from the Sun. Here we determine the observed cooling index in a comparison of He+ PUI distributions taken for 1 month in the upwind direction with ACE SWICS from 1999 through 2010 over the past solar cycle with such an isotropic PUI model, treating the cooling index as a free parameter. The ionization rate is obtained simultaneously from independent observations. To separate effects of slow pitch angle scattering of PUIs, the comparison is repeated for times restricted to perpendicular interplanetary magnetic field (IMF). When averaged over the entire data set, the cooling index is very close to 3/2. However, it varies substantially from 1.1 to 1.9 between samples, shows a distinct variation with solar activity, and has a significant correlation with sunspot number when data are restricted to nearly perpendicular IMF (θBvSW>60°) excluding the slow pitch angle scattering in the radial IMF direction. The potential influence of slow pitch angle scattering, solar wind structures, and electron ionization on the cooling index and its variations is discussed.

  4. Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe2: enabling nanoscale direct write homo-junctions

    NASA Astrophysics Data System (ADS)

    Stanford, Michael G.; Pudasaini, Pushpa Raj; Belianinov, Alex; Cross, Nicholas; Noh, Joo Hyon; Koehler, Michael R.; Mandrus, David G.; Duscher, Gerd; Rondinone, Adam J.; Ivanov, Ilia N.; Ward, T. Zac; Rack, Philip D.

    2016-06-01

    Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe2 thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe2 is degraded more severely relative to electron transport after helium ion irradiation. Furthermore, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.

  5. The influence of negative ions in helium-oxygen barrier discharges: II. 1D fluid simulation and adaption to the experiment

    NASA Astrophysics Data System (ADS)

    Nemschokmichal, Sebastian; Tschiersch, Robert; Meichsner, Jürgen

    2016-10-01

    A 1D fluid simulation was developed to investigate the influence of negative ions in a helium-oxygen barrier discharge between two glass plates at a distance of 3~\\text{mm} . The paper describes setting up the simulation for a pressure of 500~\\text{mbar} and an admixture of 400~\\text{ppm} oxygen to helium. In order to enable the comparison with laser photodetachment experiments, the simulation is adapted to the experimentally observed discharge current and gap voltage by varying gas temperature, flux of thermally desorpted electrons and secondary electron emission coefficients. The discharge is characterized by evaluation of the most important elementary collision processes as well as the kinetics of the charged species. Besides, the influence of long-living species on the discharge behavior is taken into account by long-time simulations. The negative ions are characterized by their spatio-temporal distribution in the gap and their production and loss processes. The comparison between simulations without and with consideration of negative ions reveals the importance of negative ions on the discharge development.

  6. Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe2: Enabling nanoscale direct write homo-junctions

    DOE PAGES

    Stanford, Michael; Noh, Joo Hyon; Koehler, Michael R.; Mandrus, David G.; Duscher, Gerd; Rondinone, Adam Justin; Ivanov, Ilia N.; Ward, Thomas Zac; Rack, Philip D.; Pudasaini, Pushpa Raj; et al

    2016-06-06

    Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe2 thereby locally tuningmore » the resistivity and transport properties of the material. Hole transport in the few layer WSe2 is degraded more severely relative to electron transport after helium ion irradiation. Moreover, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.« less

  7. Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe2: enabling nanoscale direct write homo-junctions.

    PubMed

    Stanford, Michael G; Pudasaini, Pushpa Raj; Belianinov, Alex; Cross, Nicholas; Noh, Joo Hyon; Koehler, Michael R; Mandrus, David G; Duscher, Gerd; Rondinone, Adam J; Ivanov, Ilia N; Ward, T Zac; Rack, Philip D

    2016-06-06

    Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe2 thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe2 is degraded more severely relative to electron transport after helium ion irradiation. Furthermore, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices.

  8. Focused helium-ion beam irradiation effects on electrical transport properties of few-layer WSe2: enabling nanoscale direct write homo-junctions

    PubMed Central

    Stanford, Michael G.; Pudasaini, Pushpa Raj; Belianinov, Alex; Cross, Nicholas; Noh, Joo Hyon; Koehler, Michael R.; Mandrus, David G.; Duscher, Gerd; Rondinone, Adam J.; Ivanov, Ilia N.; Ward, T. Zac; Rack, Philip D.

    2016-01-01

    Atomically thin transition metal dichalcogenides (TMDs) are currently receiving significant attention due to their promising opto-electronic properties. Tuning optical and electrical properties of mono and few-layer TMDs, such as tungsten diselenide (WSe2), by controlling the defects, is an intriguing opportunity to synthesize next generation two dimensional material opto-electronic devices. Here, we report the effects of focused helium ion beam irradiation on the structural, optical and electrical properties of few-layer WSe2, via high resolution scanning transmission electron microscopy, Raman spectroscopy, and electrical transport measurements. By controlling the ion irradiation dose, we selectively introduce precise defects in few-layer WSe2 thereby locally tuning the resistivity and transport properties of the material. Hole transport in the few layer WSe2 is degraded more severely relative to electron transport after helium ion irradiation. Furthermore, by selectively exposing material with the ion beam, we demonstrate a simple yet highly tunable method to create lateral homo-junctions in few layer WSe2 flakes, which constitutes an important advance towards two dimensional opto-electronic devices. PMID:27263472

  9. Spatial distribution and yield of DNA double-strand breaks induced by 3-7 MeV helium ions in human fibroblasts

    NASA Technical Reports Server (NTRS)

    Rydberg, Bjorn; Heilbronn, Lawrence; Holley, William R.; Lobrich, Markus; Zeitlin, Cary; Chatterjee, Aloke; Cooper, Priscilla K.

    2002-01-01

    Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulate alpha-particle radiation from radon daughters. The experimental setup and calibration procedure allowed determination of the helium-ion energy distribution and dose in the nuclei of irradiated cells. Using this system, the induction of DNA double-strand breaks and their spatial distributions along DNA were studied in irradiated human fibroblasts. It was found that the apparent number of double-strand breaks as measured by a standard pulsed-field gel assay (FAR assay) decreased with increasing LET in the range 67-120 keV/microm (corresponding to the energy of 7-3 MeV). On the other hand, the generation of small and intermediate-size DNA fragments (0.1-100 kbp) increased with LET, indicating an increased intratrack long-range clustering of breaks. The fragment size distribution was measured in several size classes down to the smallest class of 0.1-2 kbp. When the clustering was taken into account, the actual number of DNA double-strand breaks (separated by at least 0.1 kbp) could be calculated and was found to be in the range 0.010-0.012 breaks/Mbp Gy(-1). This is two- to threefold higher than the apparent yield obtained by the FAR assay. The measured yield of double-strand breaks as a function of LET is compared with theoretical Monte Carlo calculations that simulate the track structure of energy depositions from helium ions as they interact with the 30-nm chromatin fiber. When the calculation is performed to include fragments larger than 0.1 kbp (to correspond to the experimental measurements), there is good agreement between experiment and theory.

  10. HELIOS: A helium line-ratio spectral-monitoring diagnostic used to generate high resolution profiles near the ion cyclotron resonant heating antenna on TEXTOR

    SciTech Connect

    Unterberg, E. A.; Fehling, D. H.; Klepper, C. C.; Hillis, D. L.; Schmitz, O.; Stoschus, H.; Munoz-Burgos, J. M.; Van Wassenhove, G.

    2012-10-15

    Radial profiles of electron temperature and density are measured at high spatial ({approx}1 mm) and temporal ( Greater-Than-Or-Slanted-Equal-To 10 {mu}s) resolution using a thermal supersonic helium jet. A highly accurate detection system is applied to well-developed collisional-radiative model codes to produce the profiles. Agreement between this measurement and an edge Thomson scattering measurement is found to be within the error bars ( Less-Than-Or-Equivalent-To 20%). The diagnostic is being used to give profiles near the ion cyclotron resonant heating antenna on TEXTOR to better understand RF coupling to the core.

  11. HELIOS: a helium line-ratio spectral-monitoring diagnostic used to generate high resolution profiles near the ion cyclotron resonant heating antenna on TEXTOR.

    PubMed

    Unterberg, E A; Schmitz, O; Fehling, D H; Stoschus, H; Klepper, C C; Muñoz-Burgos, J M; Van Wassenhove, G; Hillis, D L

    2012-10-01

    Radial profiles of electron temperature and density are measured at high spatial (∼1 mm) and temporal (≥10 μs) resolution using a thermal supersonic helium jet. A highly accurate detection system is applied to well-developed collisional-radiative model codes to produce the profiles. Agreement between this measurement and an edge Thomson scattering measurement is found to be within the error bars (≲20%). The diagnostic is being used to give profiles near the ion cyclotron resonant heating antenna on TEXTOR to better understand RF coupling to the core.

  12. Constraints on the Velocity and Spatial Distribution of Helium-like Ions in the Wind of SMC X-1 from Observations with the XMM-Newton Reflection Grating Spectrometer

    NASA Astrophysics Data System (ADS)

    Wojdowski, Patrick S.; Liedahl, Duane A.; Kallman, Timothy R.

    2008-02-01

    We present here X-ray spectra of the HMXB SMC X-1 obtained in an observation with the XMM-Newton observatory beginning before eclipse and ending near the end of eclipse. With RGS on board XMM-Newton, we observe emission lines from hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon. Although the resolution of the RGS is sufficient to resolve the helium-like n = 2→ 1 emission into three line components, only one of these components, the intercombination line, is detected in our data. The lack of flux in the forbidden lines of the helium-like triplets is explained by pumping by ultraviolet photons from the B0 star, and, from this, we set an upper limit on the distance of the emitting ions from the star. The lack of observable flux in the resonance lines of the helium-like triplets indicates a lack of enhancement due to resonance line scattering, and, from this, we derive a new observational constraint on the distribution of the wind in SMC X-1 in velocity and coordinate space. We find that the solid angle subtended by the volume containing the helium-like ions at the neutron star multiplied by the velocity dispersion of the helium-like ions must be less than 4π sr km s-1. This constraint will be satisfied if the helium-like ions are located primarily in clumps distributed throughout the wind or in a thin layer along the surface of the B0 star.

  13. Effects of indirect actions and oxygen on relative biological effectiveness: estimate of DSB induction and conversion induced by gamma rays and helium ions.

    PubMed

    Tsai, Ju-Ying; Chen, Fang-Hsin; Hsieh, Tsung-Yu; Hsiao, Ya-Yun

    2015-07-01

    Clustered DNA damage other than double-strand breaks (DSBs) can be detrimental to cells and can lead to mutagenesis or cell death. In addition to DSBs induced by ionizing radiation, misrepair of non-DSB clustered damage contributes extra DSBs converted from DNA misrepair via pathways for base excision repair and nucleotide excision repair. This study aimed to quantify the relative biological effectiveness (RBE) when DSB induction and conversion from non-DSB clustered damage misrepair were used as biological endpoints. The results showed that both linear energy transfer (LET) and indirect action had a strong impact on the yields for DSB induction and conversion. RBE values for DSB induction and maximum DSB conversion of helium ions (LET = 120 keV/μm) to (60)Co gamma rays were 3.0 and 3.2, respectively. These RBE values increased to 5.8 and 5.6 in the absence of interference of indirect action initiated by addition of 2-M dimethylsulfoxide. DSB conversion was ∼1-4% of the total non-DSB damage due to gamma rays, which was lower than the 10% estimate by experimental measurement. Five to twenty percent of total non-DSB damage due to helium ions was converted into DSBs. Hence, it may be possible to increase the yields of DSBs in cancerous cells through DNA repair pathways, ultimately enhancing cell killing.

  14. Measurement of radial profiles of density ratio of helium to hydrogen ion using charge exchange spectroscopy with two-wavelength spectrometer.

    PubMed

    Ida, K; Yoshinuma, M; Wieland, B; Goto, M; Nakamura, Y; Kobayashi, M; Murakami, I; Moon, C

    2015-12-01

    Radial profiles of density ratio of helium to hydrogen ions are measured using the charge exchange spectroscopy technique with the two-wavelength spectrometer system in the large helical device. The two-wavelength spectrometer system consists of a dichroic mirror box, a spectrometer with two grating and two camera lenses, and one CCD detector. The dichroic mirror box is used to divide the light of one fiber from the plasma to two fibers, one for HeII (λ = 468.6 nm) and the other for H(α) (λ = 656.3 nm), that are connected to the entrance slit of the spectrometer to eliminate the interference between the HeII and the H(α) spectra on the CCD. This system provides a simultaneous measurement of helium and hydrogen ion density ratio at 8 exact same locations (8 spatial channels) with a time resolution of >40 ms in the wide range of the density ratio of 0.05-5.

  15. Resonant-transfer-and-excitation for highly charged ions (16 less than or equal to Z less than or equal to 23) in collisions with helium

    SciTech Connect

    Tanis, J.A.; Bernstein, E.M.; Oglesby, C.S.; Graham, W.G.; Clark, M.; McFarland, R.H.; Morgan, T.J.; Stockli, M.P.; Berkner, K.H.; Johnson, B.M.

    1984-01-01

    Significant new evidence is presented for resonant-transfer-and-excitation (RTE) in ion-atom collisions. This process occurs when a target electron is captured simultaneously with the excitation of the projectile followed by deexcitation via photon emission. RTE, which is analogous to dielectronic recombination (DR), proceeds via the inverse of an Auger transition, and is expected to be resonant for projectile velocities corresponding to the energy of the ejected electron in the Auger process. RTE was investigated by measuring cross sections for projectile K x-ray emission coincident with single electron capture for 15 to 200 MeV /sub 16/S/sup 13 +/, 100 to 360 MeV /sub 20/Ca/sup 16 +/ /sup 17 +/ /sup 18 +/ and 180 to 460 MeV /sub 23/V/sup 19 +/ /sup 20 +/ /sup 21 +/ ions colliding with helium. Strong resonant behavior, in agreement with theoretical calculations of RTE, was observed in the coincidence cross sections.

  16. The effect of carbon impurities on molybdenum surface morphology evolution under high-flux low-energy helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Tripathi, J. K.; Novakowski, T. J.; Gonderman, S.; Bharadwaj, N.; Hassanein, A.

    2016-09-01

    We report on the role of carbon (C) impurities, in molybdenum (Mo) fuzz evolutions on Mo surface during 100 eV He+ ion irradiations. In this study we considered 0.01, 0.05, and 0.5% C+ ion impurities in He+ ion irradiations. For introducing such tiny C+ ion impurities, gas mixtures of He and CH4 have been chosen in following ratios; 99.95: 0.05, 99.75: 0.25, and 97.5: 2.5. Apart from these three cases, two additional cases, 100% He+ ion (for Mo fuzz growth due to only He+ ions) and 100% H+ ion (for confirming the significance of tiny 0.04-2.0% H+ ions in terms of Mo fuzz evolutions on Mo surface, if any), have also been considered. Ion energy (100 eV), ion fluence (2.6 × 1024 ions m-2), and target temperature (923 K) were kept constant for each experiment and their selections were based on our previous studies [1,2]. Our study shows homogeneously populated and highly dense Mo fuzz evolutions on entire Mo surface for 100% He+ ion irradiation case. Enhancement of C+ ion impurities in He+ ions causes a sequential reduction in Mo fuzz evolutions, leading to almost complete prevention of Mo fuzz evolutions for 0.5% C+ ion impurity concentrations. Additionally, no fuzz formation for 100% H+ ion irradiation at all, were seen (apart from some tiny nano-structuring, in very limited regions). This indicates that there is no significant role of H+ ions in Mo fuzz evolutions (at least for such tiny amount, 0.04-2.0% H+ ions). The study is significant to understand the behavior of potential high-Z plasma facing components (PFCs), in the, presence of tiny amount of C impurities, for nuclear fusion relevant applications.

  17. Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light-emitting diodes

    PubMed Central

    2011-01-01

    Light-emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid catalytic growth method were irradiated with 2-MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of approximately 2 × 1013 ions/cm2 and approximately 4 × 1013 ions/cm2. Scanning electron microscopy images showed that the morphology of the irradiated samples is not changed. The as-grown and He+-irradiated LEDs showed rectifying behavior with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 and 0.082 eV in the near-band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near-band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centered at 398 nm nearly disappeared after irradiations. The color-rendering properties show a small decrease in the color-rendering indices of 3% after 2 MeV He+ ions irradiation. PMID:22152066

  18. Effect of pre-implanted helium on void swelling evolution in self-ion irradiated HT9

    NASA Astrophysics Data System (ADS)

    Getto, E.; Jiao, Z.; Monterrosa, A. M.; Sun, K.; Was, G. S.

    2015-07-01

    Void evolution in Fe++-irradiated ferritic-martensitic alloy HT9 was characterized in the temperature range of 400-480 °C between doses of 25 and 375 displacements per atom (dpa) with pre-implanted helium levels of 0-100 appm. A systematic study using depth profiling in cross-section samples was conducted to determine a valid region of analysis between 300 and 700 nm from the surface, which excluded effects due to the injected interstitial and the surface. Pre-implanted helium was found to promote void swelling at low doses by shortening the nucleation regime and to retard void growth at doses in the transient regime by enhancement of nucleation of small voids. Swelling was found to peak at a temperature of 460 °C. The primary effect of temperature was on the nucleation regime; nucleation regime was the shortest at 460 °C compared to that at 440 and 480 °C. The growth rate of voids was temperature-invariant. Steady state swelling was reached at 460 °C between 188 and 375 dpa at a rate of 0.02%/dpa.

  19. SU-E-T-539: Maximum Energy of Helium and Carbon Ions Clinically Needed for Spine, Lung, Prostate and Pancreas Cancer

    SciTech Connect

    Pompos, A; Choy, H; Jia, X; Jiang, S; Timmerman, R

    2015-06-15

    Purpose: Maximum available kinetic energy of accelerated heavy ions is a critical parameter to consider during the establishment of a heavy ion therapy center. It dictates the maximum range in tissue and determines the size and cost of ion gantry. We have started planning our heavy ion therapy center and we report on the needed ion range. Methods: We analyzed 50 of random SBRT-spine, SBRT- lung, prostate and pancreatic cancer patients from our photon clinic. In the isocentric axial CT cut we recorded the maximum water equivalent depth (WED4Field) of PTV’s most distal edge in four cardinal directions and also in a beam direction that required the largest penetration, WEDGantry. These depths were then used to calculate the percentage of our patients we would be able to treat as a function of available maximum carbon and helium beam energy. Based on the Anterior-Posterior WED for lung patients and the maximum available ion energy we estimated the largest possible non-coplanar beam entry angle φ (deviation from vertical) in the isocentric vertical sagittal plane. Results: We found that if 430MeV/u C-12, equivalently 220MeV/u He-4, beams are available, more than 96% (98%) of all patients can be treated without any gantry restrictions (in cardinals angles only) respectively. If the energy is reduced to 400MeV/u C-12, equivalently 205MeV/u He-4, the above fractions reduce to 80% (87%) for prostate and 88% (97%) for other sites. This 7% energy decrease translates to almost 5% gantry size and cost decrease for both ions. These energy limits in combination with the WED in the AP direction for lung patients resulted in average non-coplanar angles of φ430MeV/u = 68°±8° and φ400MeV/u = 65°±10° if nozzle clearance permits them. Conclusion: We found that the two worldwide most common maximum carbon beam energies will treat above 80% of all our patients.

  20. Measurements of energetic helium-3 minority distributions during ion cyclotron radio-frequency heating in the Princeton Large Torus

    SciTech Connect

    Hammett, G.W.; Kaita, R.; Wilson, J.R.

    1988-03-01

    Ion cyclotron radio-frequency heating experiments were performed with a /sup 3/He minority ion species in a /sup 4/He majority plasma in the Princeton Large Torus. The energetic /sup 3/He ion ''tail'' was measured directly with a charge exchange neutral analyzer for the first time. Comparisons with bounce-averaged quasi-linear calculations suggest a modestly peaked radi-frequency power deposition profile. The double charge exchange process /sup 3/He/sup + +/ )plus) /sup 4/He/sup 0/ )plus) /sup 3/He/sup 0/ )plus) /sup 4/He/sup + +/ demonstrated in these measurements may be useful as part of an alpha particle diagnostic in a fusion reactor experiment. 18 refs., 4 figs.

  1. Variation in RBE for Survival of V79-4 Cells as a Function of Alpha-Particle (Helium Ion) Energy.

    PubMed

    Tracy, Bliss L; Stevens, David L; Goodhead, Dudley T; Hill, Mark A

    2015-07-01

    High linear energy transfer (LET) α particles are important with respect to the carcinogenic risk associated with human exposure to ionizing radiation, most notably to radon and its progeny. Additionally, the potential use of alpha-particle-emitting radionuclides in radiotherapy is increasingly being explored. Within the body the emitted alpha particles slow down, traversing a number of cells with a range of energies and therefore with varying efficiencies at inducing biological response. The LET of the particle typically rises from between ~70-90 keV μm(-1) at the start of the track (depending on initial energy) to a peak of ~237 keV μm(-1) towards the end of the track, before falling again at the very end of its range. To investigate the variation in biological response with incident energy, a plutonium-238 alpha-particle irradiator was calibrated to enable studies with incident energies ranging from 4.0 MeV down to 1.1 MeV. The variation in clonogenic survival of V79-4 cells was determined as a function of incident energy, along with the relative variation in the initial yields of DNA double-strand breaks (DSB) measured using the FAR assay. The clonogenic survival data also extends previously published data obtained at the Medical Research Council (MRC), Harwell using the same cells irradiated with helium ions, with energies ranging from 34.9 MeV to 5.85 MeV. These studies were performed in conjunction with cell morphology measurements on live cells enabling the determination of absorbed dose and calculation of the average LET in the cell. The results show an increase in relative biological effectiveness (RBE) for cell inactivation with decreasing helium ion energy (increasing LET), reaching a maximum for incident energies of ~3.2 MeV and corresponding average LET of 131 keV μm(-1), above which the RBE is observed to fall at lower energies (higher LETs). The effectiveness of single alpha-particle traversals (relevant to low-dose exposure) at inducing cell

  2. Helium ion microscopy and ultra-high-resolution scanning electron microscopy analysis of membrane-extracted cells reveals novel characteristics of the cytoskeleton of Giardia intestinalis.

    PubMed

    Gadelha, Ana Paula Rocha; Benchimol, Marlene; de Souza, Wanderley

    2015-06-01

    Giardia intestinalis presents a complex microtubular cytoskeleton formed by specialized structures, such as the adhesive disk, four pairs of flagella, the funis and the median body. The ultrastructural organization of the Giardia cytoskeleton has been analyzed using different microscopic techniques, including high-resolution scanning electron microscopy. Recent advances in scanning microscopy technology have opened a new venue for the characterization of cellular structures and include scanning probe microscopy techniques such as ultra-high-resolution scanning electron microscopy (UHRSEM) and helium ion microscopy (HIM). Here, we studied the organization of the cytoskeleton of G. intestinalis trophozoites using UHRSEM and HIM in membrane-extracted cells. The results revealed a number of new cytoskeletal elements associated with the lateral crest and the dorsal surface of the parasite. The fine structure of the banded collar was also observed. The marginal plates were seen linked to a network of filaments, which were continuous with filaments parallel to the main cell axis. Cytoplasmic filaments that supported the internal structures were seen by the first time. Using anti-actin antibody, we observed a labeling in these filamentous structures. Taken together, these data revealed new surface characteristics of the cytoskeleton of G. intestinalis and may contribute to an improved understanding of the structural organization of trophozoites. PMID:25956335

  3. Fractional Diffusion, Low Exponent Lévy Stable Laws, and ‘Slow Motion’ Denoising of Helium Ion Microscope Nanoscale Imagery

    PubMed Central

    Carasso, Alfred S.; Vladár, András E.

    2012-01-01

    Helium ion microscopes (HIM) are capable of acquiring images with better than 1 nm resolution, and HIM images are particularly rich in morphological surface details. However, such images are generally quite noisy. A major challenge is to denoise these images while preserving delicate surface information. This paper presents a powerful slow motion denoising technique, based on solving linear fractional diffusion equations forward in time. The method is easily implemented computationally, using fast Fourier transform (FFT) algorithms. When applied to actual HIM images, the method is found to reproduce the essential surface morphology of the sample with high fidelity. In contrast, such highly sophisticated methodologies as Curvelet Transform denoising, and Total Variation denoising using split Bregman iterations, are found to eliminate vital fine scale information, along with the noise. Image Lipschitz exponents are a useful image metrology tool for quantifying the fine structure content in an image. In this paper, this tool is applied to rank order the above three distinct denoising approaches, in terms of their texture preserving properties. In several denoising experiments on actual HIM images, it was found that fractional diffusion smoothing performed noticeably better than split Bregman TV, which in turn, performed slightly better than Curvelet denoising. PMID:26900518

  4. Helium ion microscopy and ultra-high-resolution scanning electron microscopy analysis of membrane-extracted cells reveals novel characteristics of the cytoskeleton of Giardia intestinalis.

    PubMed

    Gadelha, Ana Paula Rocha; Benchimol, Marlene; de Souza, Wanderley

    2015-06-01

    Giardia intestinalis presents a complex microtubular cytoskeleton formed by specialized structures, such as the adhesive disk, four pairs of flagella, the funis and the median body. The ultrastructural organization of the Giardia cytoskeleton has been analyzed using different microscopic techniques, including high-resolution scanning electron microscopy. Recent advances in scanning microscopy technology have opened a new venue for the characterization of cellular structures and include scanning probe microscopy techniques such as ultra-high-resolution scanning electron microscopy (UHRSEM) and helium ion microscopy (HIM). Here, we studied the organization of the cytoskeleton of G. intestinalis trophozoites using UHRSEM and HIM in membrane-extracted cells. The results revealed a number of new cytoskeletal elements associated with the lateral crest and the dorsal surface of the parasite. The fine structure of the banded collar was also observed. The marginal plates were seen linked to a network of filaments, which were continuous with filaments parallel to the main cell axis. Cytoplasmic filaments that supported the internal structures were seen by the first time. Using anti-actin antibody, we observed a labeling in these filamentous structures. Taken together, these data revealed new surface characteristics of the cytoskeleton of G. intestinalis and may contribute to an improved understanding of the structural organization of trophozoites.

  5. Proton, Helium and Minor Ion Interactions with Circularly Polarized Alfven and Ion-cyclotron waves in the Expanding Solar Wind: Hybrid Simulations

    NASA Astrophysics Data System (ADS)

    Velli, M.; Liewer, P. C.; Goldstein, B. E.

    2000-05-01

    We present simulations of parallel propagating Alfvén waves in the accelerating solar wind and their interactions with protons, alpha particles, and minor ions using an expanding box hybrid code (Liewer et al., 1999). In this model, the average solar wind flow speed is a given external function, and the simulation domain follows a plasma parcel as it expands both in the radial and transverse directions accordingly: the decrease of Alfvén speed and density with distance from the Sun are taken into account self-consistently. It is therefore possible to carry out a detailed study of frequency drifting and the coming into resonance with the waves at different radial locations of particles with differing charge to mass ratios. Simulations of monochromatic waves as well as waves with well-developed spectra are presented for plasmas with one, two and three ion species. We observe preferential heating and acceleration of protons and minor ions. Under some conditions, we obtain the scaling observed in coronal hole solar wind: the heavy ion temperature is proportional to its mass (Liewer et al., 2000). A comparison with predictions from models based on such quasi-linear or linear analyses will also be presented. P. C. Liewer, M. Velli and B. E. Goldstein, in Solar Wind Nine, S. Habbal, R. Esser, J. V. Hollweg, P. A. Isenberg, eds., (AIP Conference Proceedings 471, 1999) 449. P. C. Liewer, M. Velli, and B. E. Goldstein, in Proc. ACE 2000 Conference (2000) to be published.

  6. Electron Capture Accompanied by Helium Ion Excitation in C^5+ + He Collisions at keV Energies.

    NASA Astrophysics Data System (ADS)

    Phaneuf, R. A.; Golovkina, V.; Kantsyrev, V.; Shlyaptseva, A.; Bruch, R.

    1997-04-01

    Cross sections for emission of He^+(2p-1s) radiation produced in single-electron-capture collisions of C^5+ ions with He atoms have been determined at energies in the range 4-8 keV/amu. High-resolution EUV collision spectroscopy measurements were facilitated by a glass-capillary-converter array, which increased the efficiency of the photon collection system by an order of magnitude. Cross sections for C^5+ + He collisions were determined by normalization to absolute measurements of Hoekstra et al.(R. Hoekstra, J.P.M. Beijers, F.J. de Heer and R. Morgenstern, Z. Phys. D. 25), 209 (1993). for He^+(2p-1s) emission in C^4+ + He collisions, and exceed the latter by 2-3 times in this energy range.

  7. Photodetachment of negative helium ions below and above the 1s ionization threshold: A complex scaled configuration-interaction approach

    SciTech Connect

    Sanz-Vicario, Jose Luis; Lindroth, Eva; Brandefelt, Nicklas

    2002-11-01

    The photodetachment of the metastable He{sup -} 1s2s2p {sup 4}P{sup o} state has been calculated in two photon energy regions of interest: the first, named here as energy region I, below the double photoionization threshold He{sup +}(n=1), involving outer-shell ionization and doubly excited states of He{sup -}, and the second, named here as region II, above the He{sup -} 1s ionization threshold and below the He{sup +}(n=2) threshold, involving K-shell detachment and triply excited states of a He{sup -} ''hollow ion.'' We have implemented an ab initio three-electron configuration-interaction method in the LS-coupling scheme combined with complex scaling to obtain resonance positions and widths and the photodetachment cross sections. We have revisited region I, although widely studied before, as a test of our method. Notwithstanding some small discrepancies, our complex scaling results compare well with the previously published results and also add new understanding to some features in the cross section. Our emphasis is given to K-shell photodetachment in photon energy region II, where comparison is made with two other recent theoretical calculations that use completely different methods, and that were in dispute. We also compare with a very recent experiment for the He{sup -} K-shell photodetachment, which displays three major features; a broad nonresonant hump after the He 2s2p {sup 3}P{sup o} threshold and two other peaks. A complex scaling analysis of prominent structures in the photodetachment spectra in region II, previously claimed to be nonresonant structures, leads to a different conclusion; i.e., they are all true triply excited-state resonances, and two of them correspond to the peaks observed experimentally.

  8. Use of double and triple-ion irradiation to study the influence of high levels of helium and hydrogen on void swelling of 8-12% Cr ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Kupriiyanova, Y. E.; Bryk, V. V.; Borodin, O. V.; Kalchenko, A. S.; Voyevodin, V. N.; Tolstolutskaya, G. D.; Garner, F. A.

    2016-01-01

    In accelerator-driven spallation (ADS) devices, some of the structural materials will be exposed to intense fluxes of very high energy protons and neutrons, producing not only displacement damage, but very high levels of helium and hydrogen. Unlike fission flux-spectra where most helium and hydrogen are generated by transmutation in nickel and only secondarily in iron or chromium, gas production in ADS flux-spectra are rather insensitive to alloy composition, such that Fe-Cr base ferritic alloys also generate very large gas levels. While ferritic alloys are known to swell less than austenitic alloys in fission spectra, there is a concern that high gas levels in fusion and especially ADS facilities may strongly accelerate void swelling in ferritic alloys. In this study of void swelling in response to helium and hydrogen generation, irradiation was conducted on three ferritic-martensitic steels using the Electrostatic Accelerator with External Injector (ESUVI) facility that can easily produce any combination of helium to dpa and/or hydrogen to dpa ratios. Irradiation was conducted under single, dual and triple beam modes using 1.8 MeV Cr+3, 40 keV He+, and 20 keV H+. In the first part of this study we investigated the response of dual-phase EP-450 to variations in He/dpa and H/dpa ratio, focusing first on dual ion studies and then triple ion studies, showing that there is a diminishing influence on swelling with increasing total gas content. In the second part we investigated the relative response of three alloys spanning a range of starting microstructure and composition. In addition to observing various synergisms between He and H, the most important conclusion was that the tempered martensite phase, known to lag behind the ferrite phase in swelling in the absence of gases, loses much of its resistance to void nucleation when irradiated at large gas/dpa levels.

  9. Observations of solar-wind helium

    NASA Technical Reports Server (NTRS)

    Neugebauer, M.

    1981-01-01

    It is pointed out that the concentration of helium in the solar wind relative to hydrogen fluctuates wildly. Under certain circumstances, the helium to hydrogen abundance ratio is strongly enhanced over probable solar values; at other times, the amount of helium in the solar wind is immeasurably small. In spite of the fact that helium is heavier than hydrogen, solar-wind helium often leaves the solar gravitational field with a higher velocity than does the hydrogen. It is thought that the mechanisms responsible for helium behavior may contain clues to unanswered questions concerning the acceleration and energy exchange processes of the entire solar wind. A brief review is given of the principal features and theories of the solar wind as a whole. In addition, measurement techniques are discussed. Emphasis throughout is on the experimental data concerning the dynamics of solar-wind helium. On the basis of coronal temperatures, it is shown that helium in the solar wind is almost always doubly ionized. It is also shown that the average abundance of helium ions in the solar wind is usually in the range of 3 to 6% by number.

  10. Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

    SciTech Connect

    Martin, Guillaume; Desgardin, Pierre; Sauvage, Thierry; Barthe, Marie-France; Garcia, Philippe; Carlot, Gaelle

    2007-07-01

    This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO{sub 2} sintered samples presenting different microstructures were implanted with {sup 3}He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the {sup 3}He(d,{alpha}){sup 1}H reaction. {sup 3}He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

  11. Initial yields of DNA double-strand breaks and DNA Fragmentation patterns depend on linear energy transfer in tobacco BY-2 protoplasts irradiated with helium, carbon and neon ions.

    PubMed

    Yokota, Yuichiro; Yamada, Shinya; Hase, Yoshihiro; Shikazono, Naoya; Narumi, Issay; Tanaka, Atsushi; Inoue, Masayoshi

    2007-01-01

    The ability of ion beams to kill or mutate plant cells is known to depend on the linear energy transfer (LET) of the ions, although the mechanism of damage is poorly understood. In this study, DNA double-strand breaks (DSBs) were quantified by a DNA fragment-size analysis in tobacco protoplasts irradiated with high-LET ions. Tobacco BY-2 protoplasts, as a model of single plant cells, were irradiated with helium, carbon and neon ions having different LETs and with gamma rays. After irradiation, DNA fragments were separated into sizes between 1600 and 6.6 kbp by pulsed-field gel electrophoresis. Information on DNA fragmentation was obtained by staining the gels with SYBR Green I. Initial DSB yields were found to depend on LET, and the highest relative biological effectiveness (about 1.6) was obtained at 124 and 241 keV/microm carbon ions. High-LET carbon and neon ions induced short DNA fragments more efficiently than gamma rays. These results partially explain the large biological effects caused by high-LET ions in plants.

  12. Equation of state of metallic helium

    SciTech Connect

    Shvets, V. T.

    2013-01-15

    The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.

  13. Helium anion formation inside helium droplets

    NASA Astrophysics Data System (ADS)

    Maalouf, Elias Jabbour Al; Reitshammer, Julia; Ribar, Anita; Scheier, Paul; Denifl, Stephan

    2016-07-01

    The formation of He∗- is examined with improved electron energy resolution of about 100 meV utilizing a hemispherical electron monochromator. The work presented provides a precise determination of the three previously determined resonance peak positions that significantly contribute to the formation of He∗- inside helium nanodroplets in the energy range from 20 eV to 29.5 eV. In addition, a new feature is identified located at 27.69 ± 0.18 eV that we assign to the presence of O2 as a dopant inside the droplet. With increasing droplet size a small blue shift of the resonance positions is observed. Also for the relatively low electron currents used in the present study (i.e., 15-70 nA) a quadratic dependence of the He∗- ion yield on the electron current is observed. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

  14. Geomagnetically trapped energetic helium nuclei

    SciTech Connect

    Chen, J.; Gregory Guzik, T.; Wefel, J.P.; Roger Pyle, K.; Cooper, J.F.

    1996-07-01

    Geomagnetically trapped helium nuclei, at high energy ({approximately}40{endash}100 MeV/nucleon), have been measured by the ONR-604 instrument during the 1990/1991 CRRES mission. The ONR-604 instrument resolved the isotopes of helium with a mass resolution of 0.1 amu. The energetic helium observed at {ital L}{lt}2.3 have a pitch angle distribution peaking perpendicular to the local magnetic field, which is characteristic of a trapped population. Both the trapped {sup 3}He and {sup 4}He show two peaks at {ital L}=1.2 and 1.9. Each isotope{close_quote}s flux, in each peak, can be characterized by a power law energy spectrum. The energy spectrum of the {sup 3}He is different from that of {sup 4}He, indicating that the {sup 3}He/{sup 4}He ratio is energy dependent. Over the energy range of 51{endash}86 MeV/nucleon, the {sup 3}He/{sup 4}He ratio is 8.7{plus_minus}3.1 at {ital L}=1.1{endash}1.5 and is 2.4{plus_minus}0.6 at {ital L}=1.5{endash}2.3. The trapped helium counting rates decrease gradually with time during the CRRES mission, when the anomalous component is excluded from the inner heliosphere, indicating that these high energy ions were not injected by flares during this time period. The decrease in intensity is attributed mainly to the events around {ital L}=1.9. The helium around {ital L}=1.2, dominated by {sup 3}He, does not show a significant temporal evolution, which implies a long-term energetic trapped {sup 3}He population. Two possible origins of the geomagnetically trapped helium isotopes are the interactions of energetic protons with the upper atmosphere and/or the inward diffusion and acceleration of helium ions due to electric-field fluctuations. {copyright} {ital 1996 American Institute of Physics.}

  15. Helium-Recycling Plant

    NASA Technical Reports Server (NTRS)

    Cook, Joseph

    1996-01-01

    Proposed system recovers and stores helium gas for reuse. Maintains helium at 99.99-percent purity, preventing water vapor from atmosphere or lubricating oil from pumps from contaminating gas. System takes in gas at nearly constant low back pressure near atmospheric pressure; introduces little or no back pressure into source of helium. Concept also extended to recycling of other gases.

  16. Helium technology issues

    NASA Technical Reports Server (NTRS)

    Kittel, Peter

    1987-01-01

    A number of future space missions require liquid helium for cooling scientific payloads. These missions will require the long term storage and resupply of liquid helium at temperatures of 1.4 - 2.1 Kelvin. In addition, some of the proposed instruments will require refrigeration to temperatures as low as 50 mK. A variety of liquid helium based refrigerator systems could provide this subkelvin cooling. The status of helium storage and refrigeration technologies and of several alternative technologies is presented here along with areas where further research and development are needed. (Helium resupply technologies are the topic of another presentation at this symposium). The technologies covered include passive and dynamic liquid helium storage, alternatives to liquid helium storage, He -3 refrigerators, He -3/He -4 dilution refrigerators, and alternative sub-kelvin coolers.

  17. Nonrelativistic contributions of order {alpha}{sup 5}m{sub {mu}c}{sup 2} to the Lamb shift in muonic hydrogen and deuterium, and in the muonic helium ion

    SciTech Connect

    Karshenboim, S. G.; Ivanov, V. G.; Korzinin, E. Yu.; Shelyuto, V. A.

    2010-06-15

    Contributions to the energy levels in light muonic atoms and, in particular, to the Lamb shift fall into a few well-distinguished classes. The related diagrams are calculated using different approaches. In particular, there is a specific type of nonrelativistic (NR) contribution. Here, we consider such corrections to the Lamb shift of order {alpha}{sup 5}m{sub {mu}.} These contributions are due to free vacuum-polarization loops as well as to various effects of light-by-light scattering. The closed loop in the related diagrams is an electronic one, which allows an NR consideration of the muon. Both types of contributions have been known for some time, however, the results obtained to date are only partial results. We complete a calculation of the {alpha}{sup 5}m{sub {mu}}contributions for muonic hydrogen. The results are also adjusted for muonic deuterium atom and helium ion.

  18. Space and time resolved spectroscopy of laser-produced plasmas: A study of density-sensitive x-ray transitions in helium-like and neon-like ions

    SciTech Connect

    Young, Bruce Kai Fong

    1988-09-01

    The determination of level populations and detailed population mechanisms in dense plasmas has become an increasingly important problem in atomic physics. In this work, the density variation of line intensities and level populations in aluminum K-shell and molybdenum and silver L-shell emission spectra have been measured from high-powered, laser-produced plasmas. For each case, the density dependence of the observed line emission is due to the effect of high frequency electron-ion collisions on metastable levels. The density dependent line intensities vary greatly in laser-produced plasmas and can be used to extract detailed information concerning the population kinetics and level populations of the ions. The laser-plasmas had to be fully characterized in order to clearly compare the observed density dependence with atomic theory predictions. This has been achieved through the combined use of new diagnostic instruments and microdot targets which provided simultaneously space, time, and spectrally resolved data. The plasma temperatures were determined from the slope of the hydrogen-like recombination continuum. The time resolved electron density profiles were measured using multiple frame holographic interferometry. Thus, the density dependence of K-shell spectral lines could be clearly examined, independent of assumptions concerning the dynamics of the plasma. In aluminum, the electron density dependence of various helium-like line intensity ratios were measured. Standard collisional radiative equilibrium models fail to account for the observed density dependence measured for the ''He/sub ..cap alpha..//IC'' ratio. Instead, a quasi-steady state atomic model based on a purely recombining plasma is shown to accurately predict the measured density dependence. This same recombining plasma calculation successfully models the density dependence of the high-n ''He/sub ..gamma..//He/sub ..beta../'' and ''He/sub delta//He/sub ..beta../'' helium-like resonance line intensity

  19. The adsorption of helium atoms on coronene cations

    NASA Astrophysics Data System (ADS)

    Kurzthaler, Thomas; Rasul, Bilal; Kuhn, Martin; Lindinger, Albrecht; Scheier, Paul; Ellis, Andrew M.

    2016-08-01

    We report the first experimental study of the attachment of multiple foreign atoms to a cationic polycyclic aromatic hydrocarbon (PAH). The chosen PAH was coronene, C24H12, which was added to liquid helium nanodroplets and then subjected to electron bombardment. Using mass spectrometry, coronene cations decorated with helium atoms were clearly seen and the spectrum shows peaks with anomalously high intensities ("magic number" peaks), which represent ion-helium complexes with added stability. The data suggest the formation of a rigid helium layer consisting of 38 helium atoms that completely cover both faces of the coronene ion. Additional magic numbers can be seen for the further addition of 3 and 6 helium atoms, which are thought to attach to the edge of the coronene. The observation of magic numbers for the addition of 38 and 44 helium atoms is in good agreement with a recent path integral Monte Carlo prediction for helium atoms on neutral coronene. An understanding of how atoms and molecules attach to PAH ions is important for a number of reasons including the potential role such complexes might play in the chemistry of the interstellar medium.

  20. Formation process of dislocation loops in iron under irradiations with low-energy helium, hydrogen ions or high-energy electrons

    NASA Astrophysics Data System (ADS)

    Arakawa, K.; Mori, H.; Ono, K.

    2002-12-01

    Formation processes of interstitial-type dislocation loops (I loops) in high-purity Fe under irradiations with 5 keV H + ions or 1000 keV electrons are examined by in situ transmission electron microscopy at temperatures below room temperature, and the results are compared with that obtained under He + ion irradiation. For the electron irradiation, conventional model of I-loop nucleation based on the assumption that di-interstitial atoms are stable nuclei of I loops is questioned. The volume density of I loops by H + ion irradiation is one-order of magnitude higher than that by electron irradiation, and several times lower than that by He + ion irradiation. The temperature dependence of the volume density of I loops by H + ion irradiation supports the idea that such enhancement of I-loop formation is due to trapping of self-interstitial atoms by gas atom-vacancy complexes.

  1. Formation of Positively Charged Liquid Helium Clusters in Supercritical Helium and their Solidification upon Compression.

    PubMed

    Tarchouna, Hejer Gharbi; Bonifaci, Nelly; Aitken, Frédéric; Mendoza Luna, Luis Guillermo; von Haeften, Klaus

    2015-08-01

    Positively charged ions were produced in supercritical helium at temperatures from 6 to 10 K and up to 2 MPa using a corona discharge. Their mobility was measured via current-voltage curves, and the hydrodynamic radius was derived using Stokes law. An initial increase and subsequent decrease of hydrodynamic radius was observed and interpreted in terms of growth, compression and solidification of ion clusters. The mobility was modeled using a van der Waals-type thermodynamic state equation for the ion-in-helium mixed system and a temperature-dependent Millikan-Cunningham factor, describing experimental data both in the Knudsen and the Stokes flow region. Regions of maximum hydrodynamic radius and large compressibility were interpreted as boiling points. These points were modeled over a large range of pressures and found to match the Frenkel line of pure helium up to 0.7 MPa, reflecting similarity of density fluctuations in pure supercritical helium and gas-liquid phase transitions of ionic helium clusters. PMID:26267199

  2. Formation of Positively Charged Liquid Helium Clusters in Supercritical Helium and their Solidification upon Compression.

    PubMed

    Tarchouna, Hejer Gharbi; Bonifaci, Nelly; Aitken, Frédéric; Mendoza Luna, Luis Guillermo; von Haeften, Klaus

    2015-08-01

    Positively charged ions were produced in supercritical helium at temperatures from 6 to 10 K and up to 2 MPa using a corona discharge. Their mobility was measured via current-voltage curves, and the hydrodynamic radius was derived using Stokes law. An initial increase and subsequent decrease of hydrodynamic radius was observed and interpreted in terms of growth, compression and solidification of ion clusters. The mobility was modeled using a van der Waals-type thermodynamic state equation for the ion-in-helium mixed system and a temperature-dependent Millikan-Cunningham factor, describing experimental data both in the Knudsen and the Stokes flow region. Regions of maximum hydrodynamic radius and large compressibility were interpreted as boiling points. These points were modeled over a large range of pressures and found to match the Frenkel line of pure helium up to 0.7 MPa, reflecting similarity of density fluctuations in pure supercritical helium and gas-liquid phase transitions of ionic helium clusters.

  3. Frequency of collisions between ion and neutral particles from the cloning characteristics of filamentary currents in an atmospheric pressure helium plasma jet

    NASA Astrophysics Data System (ADS)

    Qi, Bing; Zhang, Mengdie; Pan, Lizhu; Zhou, Qiujiao; Huang, Jianjun; Liu, Ying

    2015-02-01

    In this paper, a cold He atmospheric pressure plasma jet that is generated using a dielectric barrier discharge configuration device is presented. This device is equipped with double-grounded ring electrodes that are driven by a sinusoidal excitation voltage. The properties of the cloning of filamentous current are studied. The frequency of the collisions between the ion and the neutral particles is calculated by measuring the current phase difference between the filamentous current and its corresponding clone. The frequency of the collisions between the ion and the neutral particles is of the order of 108 Hz.

  4. Effects of helium injection mode on void formation in Fe-Ni-Cr alloys

    NASA Astrophysics Data System (ADS)

    Kimoto, T.; Lee, E. H.; Mansur, L. K.

    1988-09-01

    The effect of the helium injection mode on void formation during ion irradiation of the pure solution-annealing alloys Fe-15Ni-7Cr, Fe-35Ni-7Cr, Fe-45Ni-7Cr, Fe-10Ni-13Cr, Fe-40Ni-13Cr, Fe-45Ni-15Cr was examined. Ion irradiation was carried out with 4 MeV Ni ions at 948 K to doses of 30 to 100 dpa with: (1) no helium injection, (2) simultaneous helium injection and (3) helium preinjection and aging. Swelling variation with helium injection differed among the 7Cr alloys and 13-15Cr alloys. Only the simultaneous helium injection mode produced a bimodal cavity size distribution in the high Ni alloys. The critical radius, as estimated from the cavity size distributions appears to have increased with increasing dose, but no clear variation of the critical radius with composition was observed. Helium preinjection and one-hour aging at 948 K formed helium bubbles along the residual dislocations, while subsequent Ni irradiation caused void formation along the dislocation lines. The calculated helium concentration deduced from observable helium bubbles was low compared with the injected helium concentration in the alloys containing higher Ni and lower Cr.

  5. Core helium flash

    SciTech Connect

    Cole, P.W.; Deupree, R.G.

    1980-01-01

    The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required. The core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely.

  6. The Descending Helium Balloon

    ERIC Educational Resources Information Center

    Helseth, Lars Egil

    2014-01-01

    I describe a simple and fascinating experiment wherein helium leaks out of a rubber balloon, thereby causing it to descend. An estimate of the volumetric leakage rate is made by measuring its rate of descent.

  7. Helium atoms and molecules in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Mori, K.

    Recent theoretical studies have shown that the neutron star surface may be composed of helium or heavier elements as hydrogen may be quickly depleted by diffuse nuclear burning Chang Bildsten However while Hydrogen atmospheres have been studied in great details atomic data for helium is available only for He ion Pavlov Bezchastnov 2005 We performed Hartree-Fock type calculation for Helium atom and molecules and computed their binding ionization and dissociation energies in strong magnetic fields B sim10 12 -- 10 15 G We will present ionization balance of Helium atmospheres at typical magnetic field strengths and temperatures to radio-quiet neutron stars and AXPs We will also discuss several implications of helium atmosphere to X-ray data of isolated neutron stars focusing on the detected spectral features

  8. Helium cooling systems for large superconducting physics detector magnets

    NASA Astrophysics Data System (ADS)

    Green, M. A.

    The large superconducting detector magnets used for high energy physics experiments are virtually all indirectly cooled. In general, these detector magnets are not cryogenically stabilized. Therefore, there are a number of choices for cooling large indirectly cooled detector magnets. These choices include; 1) forced two-phase helium cooling driven by the helium refrigerator J-T circuit, 2) forced two-phase helium cooling driven by a helium pump, and 3) a peculation gravity feed cooling system which uses liquid helium from a large storage dewar. The choices for the cooling of a large detector magnet are illustrated by applying these concepts to a 4.2 meter diameter 0.5 tesla thin superconducting solenoid for an experiment at the Relativistic Heavy Ion Collider (RHIC).

  9. Advances in Helium Cryogenics

    NASA Astrophysics Data System (ADS)

    Sciver, S. W. Van

    This review provides a survey of major advances that have occurred in recent years in the area of helium cryogenics. Helium-temperature cryogenics is the enabling technology for a substantial and growing number of low-temperature systems from superconducting magnets to space-based experimental facilities. In recent years there have been many advances in the technology of low-temperature helium, driven mostly by new applications. However, to keep the review from being too broad, this presentation focuses mainly on three of the most significant advances. These are: (1) the development of large-scale recuperative refrigeration systems mainly for superconducting magnet applications in accelerators and other research facilities; (2) the use of stored superfluid helium (He II) as a coolant for spacebased astrophysics experiments; and (3) the application of regenerative cryocoolers operating at liquid helium temperatures primarily for cooling superconducting devices. In each case, the reader should observe that critical technologies were developed to facilitate these applications. In addition to these three primary advances, other significant helium cryogenic technologies are briefly reviewed at the end of this chapter, along with some vision for future developments in these areas.

  10. Competitive Deprotonation and Superoxide [O2 -•] Radical-Anion Adduct Formation Reactions of Carboxamides under Negative-Ion Atmospheric-Pressure Helium-Plasma Ionization (HePI) Conditions

    NASA Astrophysics Data System (ADS)

    Hassan, Isra; Pinto, Spencer; Weisbecker, Carl; Attygalle, Athula B.

    2016-03-01

    Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O•) preferentially form superoxide radical-anion (O2 -•) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2 -•) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2 -• adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O•) to generate the superoxide radical-anion ( m/z 32) or the deprotonated amide [ m/z (M - H)-], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions.

  11. Competitive Deprotonation and Superoxide [O₂⁻•)] Radical-Anion Adduct Formation Reactions of Carboxamides under Negative-Ion Atmospheric-Pressure Helium-Plasma Ionization (HePI) Conditions.

    PubMed

    Hassan, Isra; Pinto, Spencer; Weisbecker, Carl; Attygalle, Athula B

    2016-03-01

    Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O(•)) preferentially form superoxide radical-anion (O2(-•)) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2(-•)) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2(-•) adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O(•)) to generate the superoxide radical-anion (m/z 32) or the deprotonated amide [m/z (M - H)(-)], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions. PMID:26545766

  12. Argon clusters embedded in helium nanodroplets.

    PubMed

    da Silva, Filipe Ferreira; Bartl, Peter; Denifl, Stephan; Echt, Olof; Märk, Tilmann D; Scheier, Paul

    2009-11-14

    Electron impact ionization of argon clusters embedded in helium droplets is investigated. Superior mass resolution makes it possible to distinguish between nominally isobaric cluster ions. An abundance maximum for ArHe(12)(+) is unambiguously confirmed; the spectra also prove the formation of Ar(2)He(n)(+) complexes that had been claimed to fragment into pure Ar(2)(+). Distributions of larger argon cluster ions containing up to 60 atoms closely resemble distributions observed upon electron impact or photoionization of bare argon clusters; caging and evaporative cooling provided by the helium matrix do not suffice to quench fragmentation of the nascent argon cluster ions. Intriguing abundance anomalies are observed in distributions of argon cluster ions that contain water, nitrogen or oxygen impurities. The strong abundance of Ar(55)H(2)O(+), Ar(54)O(2)(+) and Ar(54)N(2)(+) contrasts with the virtual absence of slightly larger cluster ions containing the corresponding impurities. The features are probably related to enhanced cluster ion stability upon closure of the second icosahedral shell but the difference in magic numbers (54 versus 55) and the well-known reactivity of charged argon-nitrogen complexes suggest structural differences. PMID:19851558

  13. Helium-refrigeration system

    SciTech Connect

    Specht, J.R.; Millar, B.; Sutherland, A.

    1995-08-01

    The design, procurement, and preliminary construction was completed for adding two more wet expansion engines to two helium refrigerators. These will be added in mid-year FY 1995. In addition a variable speed drive will be added to an existing helium compressor. This is part of an energy conservation upgrade project to reduce operating costs from the use of electricity and liquid nitrogen. This project involves the replacement of Joule-Thompson valves in the refrigerators with expansion engines resulting in system efficiency improvements of about 30% and improved system reliability.

  14. Is solid helium a supersolid?

    SciTech Connect

    Hallock, Robert

    2015-05-15

    Recent experiments suggest that helium-4 atoms can flow through an experimental cell filled with solid helium. But that incompletely understood flow is quite different from the reported superfluid-like motion that so excited physicists a decade ago.

  15. Cavitation in flowing superfluid helium

    NASA Technical Reports Server (NTRS)

    Daney, D. E.

    1988-01-01

    Flowing superfluid helium cavitates much more readily than normal liquid helium, and there is a marked difference in the cavitation behavior of the two fluids as the lambda point is traversed. Examples of cavitation in a turbine meter and centrifugal pump are given, together with measurements of the cavitation strength of flowing superfluid helium. The unusual cavitation behavior of superfluid helium is attributed to its immense thermal conductivity .

  16. Energetic helium particles trapped in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Chen, Jiasheng; Guzik, T. Gregory; Sang, Yeming; Wefel, John P.; Cooper, John F.

    1994-01-01

    High energy (approximately 40-100 MeV/nucleon) geomagnetically trapped helium nuclei have been measured, for the first time, by the ONR-604 instrument during the 1990/1991 Combined Release and Radiation Effects Satellite (CRRES) mission. The helium events observed at L less than 2.3 have a pitch angle distribution peaking perpendicular to the local magnetic field and are contained in peaks located at L = 1.2 and 1.9. The events in each peak can be characterized by power law energy spectra with indices of 10.0 +/- 0.7 for L = 1.9-2.3 and 6.8 +/- 1.0 for L = 1.15-1.3, before the large storm of 24 March 1991. CRRES was active during solar maximum when the anomalous component is excluded from the inner heliosphere, making it unlikely that the observed events derived from the anomalous component. The trapped helium counting rates decrease gradually with time indicating that these high energy ions were not injected by flares during the 1990/91 mission. Flare injection prior to mid-1990 may account for the highest energy particles, while solar wind injection during magnetic storms and subsequent acceleration could account for the helium at lower energies.

  17. NUCLEAR CONDENSATE AND HELIUM WHITE DWARFS

    SciTech Connect

    Bedaque, Paulo F.; Berkowitz, Evan; Cherman, Aleksey E-mail: evanb@umd.edu

    2012-04-10

    We consider a high-density region of the helium phase diagram, where the nuclei form a Bose-Einstein condensate rather than a classical plasma or a crystal. Helium in this phase may be present in helium-core white dwarfs. We show that in this regime there is a new gapless quasiparticle not previously noticed, arising when the constraints imposed by gauge symmetry are taken into account. The contribution of this quasiparticle to the specific heat of a white dwarf core turns out to be comparable in a range of temperatures to the contribution from the particle-hole excitations of the degenerate electrons. The specific heat in the condensed phase is two orders of magnitude smaller than in the uncondensed plasma phase, which is the ground state at higher temperatures, and four orders of magnitude smaller than the specific heat that an ion lattice would provide, if formed. Since the specific heat of the core is an important input for setting the rate of cooling of a white dwarf star, it may turn out that such a change in the thermal properties of the cores of helium white dwarfs has observable implications.

  18. Helium transport in the core and stochastic edge layer in LHD

    NASA Astrophysics Data System (ADS)

    Ida, K.; Yoshinuma, M.; Goto, M.; Schmitz, O.; Dai, S.; Bader, A.; Kobayashi, M.; Kawamura, G.; Moon, C.; Nakamura, Y.; The LHD Experiment Group

    2016-07-01

    Radial profiles of the density ratio of helium to hydrogen ions are measured using charge exchange spectroscopy with a two-wavelength spectrometer in the large helical device. Helium transport at the last closed flux surface (LCFS) and stochastic magnetic field layer outside the LCFS as well as in the core plasma is studied for a wide range of helium fractions, i.e. from hydrogen-dominated plasmas up to helium-dominated plasmas. The helium density profile becomes more peaked and inward convection velocity increases in the hydrogen-dominant plasma, while it becomes flat or hollow and the convection velocity is in the outward direction in the helium-dominant plasmas. The density gradient of helium at the LCFS is twice that of hydrogen and becomes steeper as the hydrogen becomes more dominant.

  19. Indirect detection of the Martian helium corona

    NASA Astrophysics Data System (ADS)

    Barabash, S.; Norberg, O.

    1994-07-01

    The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M/q = 4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He(+) from ionisation within the Martian helium corona. The particles had typical energies of either more than 10 keV or about 500 eV. The former correspond to ion pickup in the solar wind and the latter might be ions extracted from the upper ionosphere by an electric field. The observed density of pickup He(+) ions was 0.02-0.1/cc and the He(+) density in the plasmasheet was of 0.2-0.7/cc. According to a recent model of the Martian neutral atmosphere (Moroz et al, 1991) the He(+) density could reach 0.2/cc at the Phobos orbit. Such values give mass densities comparable to those of the solar wind. Thus, helium may play a role in the solar wind mass loading process near Mars.

  20. LETTER: H-mode threshold and confinement in helium and deuterium in ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Ryter, F.; Pütterich, T.; Reich, M.; Scarabosio, A.; Wolfrum, E.; Fischer, R.; Gemisic Adamov, M.; Hicks, N.; Kurzan, B.; Maggi, C.; Neu, R.; Rohde, V.; Tardini, G.; ASDEX Upgrade TEAM

    2009-06-01

    In 2008, experiments have been carried out in ASDEX Upgrade to compare H-mode power threshold and confinement time in helium and deuterium. A scan in magnetic field and a wide density variation indicate that the threshold power in the two gases is very similar. The density dependence of the threshold exhibits a clear minimum. Confinement in helium is about 30% lower than in deuterium, mainly due to the reduction in the ion density caused by Z = 2 in helium.

  1. A self-circulation helium liquefaction system with five 4 K G-M cryocoolers

    NASA Astrophysics Data System (ADS)

    Xu, Dong; Gong, Linghui; Li, Laifeng; Xu, Xiangdong; Xie, Zuqi; Zhao, Hongwei; Guo, Xiaohong

    2011-06-01

    A self-circulation helium liquefaction system (SCHLS) with five 4 K G-M cryocoolers is developed to supply liquid helium (LHe) for SECRAL (a superconducting ECR ion source used in Lanzhou city, China). LHe is vaporized in SECRAL and warmed up to room temperature. SCHLS will re-liquefy the helium gas at a rate of 83.2 L/day under normal atmosphere pressure. With SCHLS, SECRAL system can run online without any interruption of refilling LHe.

  2. Helium solubility in SON68 nuclear waste glass

    SciTech Connect

    Fares, Toby; Peuget, Sylvain; Bouty, Olivier; Broudic, Veronique; Maugeri, Emilio; Bes, Rene; Jegou, Christophe; Chamssedine, Fadel; Sauvage, Thierry; Deschanels, Xavier

    2012-12-15

    Helium behavior in a sodium borosilicate glass (SON68) dedicated to the immobilization of high-level nuclear waste is examined. Two experimental approaches on nonradioactive glass specimens are implemented: pressurized helium infusion experiments and {sup 3}He ion implantation experiments. The temperature variation of helium solubility in SON68 glass was determined and analyzed with the harmonic oscillator model to determine values of the energy of interaction E(0) at the host sites (about -4000 J/mol), the vibration frequency (about 1.7 x 10{sup 11} s{sup -1}), and the density of solubility sites (2.2 x 10{sup 21} sites cm{sup -3}). The implantation experiments show that a non diffusive transport phenomenon (i.e., athermal diffusion) is involved in the material when the helium concentration exceeds 2.3 x 10{sup 21} He cm{sup -3}, and thus probably as soon as it exceeds the density of solubility sites accessible to helium in the glass. We propose that this transport mechanism could be associated with the relaxation of the stress gradient induced by the implanted helium profile, which is favored by the glass damage. Microstructural characterization by TEM and ESEM of glass specimens implanted with high helium concentrations showed a homogeneous microstructure free of bubbles, pores, or cracking at a scale of 10 nm. (authors)

  3. Calculations of cosmic-ray helium transport in shielding materials

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.

    1993-01-01

    The transport of galactic cosmic-ray helium nuclei and their secondaries through bulk shielding is considered using the straight-ahead approximation to the Boltzmann equation. A data base for nuclear interaction cross sections and secondary particle energy spectra for high-energy light-ion breakup is presented. The importance of the light ions H-2, H-3, and He-3 for cosmic-ray risk estimation is discussed, and the estimates of the fractional contribution to the neutron flux from helium interactions compared with other particle interactions are presented using a 1977 solar minimum cosmic-ray spectrum.

  4. Helium bubble evolution in a Zr–Sn–Nb–Fe–Cr alloy during post-annealing: An in-situ investigation

    SciTech Connect

    Shen, H.H.; Peng, S.M.; Chen, B.; Naab, F.N.; Sun, G.A.; Zhou, W.; Xiang, X.; Sun, K.; Zu, X.T.

    2015-09-15

    The formation of helium bubbles is considered to be detrimental to the mechanical performance of the nuclear materials. The growth behaviors of helium bubbles in a helium ion implanted Zr–Sn–Nb–Fe–Cr alloy with respect to the helium fluence and subsequently annealing procedure were investigated by in-situ transmission electron microscopy. In the as-implanted sample, the measured size distributions of the helium bubbles are consistent with the simulated helium concentrations. Moreover, the mean size of the helium bubbles increases with the increase of the irradiation temperatures and the helium fluence. The in-situ heating study performed in a transmission electron microscope indicates that the mean size of the helium bubbles increase slowly below 923 K and dramatically above 923 K. The coarsening mechanism of the helium bubbles in the alloy is suggested based on the study. - Highlights: • Helium bubble growth in zirconium with annealing was in-situ investigated in TEM. • The mean helium bubble size increase with helium fluence and annealing temperature. • Helium bubble size distribution is same as that of helium concentration by SRIM. • Mean bubble size increases slowly and quickly with temperature below and above 923 K. • The growth mechanism of the helium bubbles in Zr alloy has been discussed.

  5. Electronic structure and enthalpy of hydrogen and helium mixtures

    NASA Astrophysics Data System (ADS)

    Ross, M.; Klepeis, J. E.; Schafer, K. J.; Barbee, T. W., III

    1992-11-01

    The first local density approximation (LDA) calculations of the electronic structure, equation of state, and enthalpy of mixing were carried out for a number of different compositions of hydrogen and helium in bcc and fcc lattices. These are fully quantum mechanical, self-consistent calculations utilizing state-of-the-art methods of electron band theory, which make no assumptions regarding pressure ionization. The major approximation in the LDA method is that the exchange and correlation energy is given by a free electron functional in terms of the local electron density. The majority of previous mixture calculations start with the assumption that both hydrogen and helium are pressure-ionized so that the electronic structure is approximately that of free or weakly screened electrons in the presence of positive ions. Stevenson used a hard-sphere mixture model for the ions with an ion-ion pseudopotential to account for electron screening and predicted that a mixture containing 7% helium by number, the composition believed to be present in Jupiter and Saturn, would phase separate at a temperature of about 7000 K at 8 Mbar. Subsequent calculations carried out for the fully ionized mixture and for a mixture of screened ions (linear response theory) have all arrived at predictions similar to those of Stevenson. MacFarlane and Hubbard performed Thomas-Fermi-Dirac calculations for mixing enthalpies of hydrogen and helium in bcc and fcc lattices and predicted that phase separation would not occur at any temperature.

  6. Applications of Groundwater Helium

    USGS Publications Warehouse

    Kulongoski, Justin T.; Hilton, David R.

    2011-01-01

    Helium abundance and isotope variations have widespread application in groundwater-related studies. This stems from the inert nature of this noble gas and the fact that its two isotopes ? helium-3 and helium-4 ? have distinct origins and vary widely in different terrestrial reservoirs. These attributes allow He concentrations and 3He/4He isotope ratios to be used to recognize and quantify the influence of a number of potential contributors to the total He budget of a groundwater sample. These are atmospheric components, such as air-equilibrated and air-entrained He, as well as terrigenic components, including in situ (aquifer) He, deep crustal and/or mantle He and tritiogenic 3He. Each of these components can be exploited to reveal information on a number of topics, from groundwater chronology, through degassing of the Earth?s crust to the role of faults in the transfer of mantle-derived volatiles to the surface. In this review, we present a guide to how groundwater He is collected from aquifer systems and quantitatively measured in the laboratory. We then illustrate the approach of resolving the measured He characteristics into its component structures using assumptions of endmember compositions. This is followed by a discussion of the application of groundwater He to the types of topics mentioned above using case studies from aquifers in California and Australia. Finally, we present possible future research directions involving dissolved He in groundwater.

  7. Education in Helium Refrigeration

    SciTech Connect

    Gistau Baguer, G. M.

    2004-06-23

    On the one hand, at the end of the time I was active in helium refrigeration, I noticed that cryogenics was stepping into places where it was not yet used. For example, a conventional accelerator, operating at room temperature, was to be upgraded to reach higher particle energy. On the other hand, I was a little bit worried to let what I had so passionately learned during these years to be lost. Retirement made time available, and I came gradually to the idea to teach about what was my basic job. I thought also about other kinds of people who could be interested in such lessons: operators of refrigerators or liquefiers who, often by lack of time, did not get a proper introduction to their job when they started, young engineers who begin to work in cryogenics... and so on.Consequently, I have assembled a series of lessons about helium refrigeration. As the audiences have different levels of knowledge in the field of cryogenics, I looked for a way of teaching that is acceptable for all of them. The course is split into theory of heat exchangers, refrigeration cycles, technology and operation of main components, process control, and helium purity.

  8. Multiple ionization of argon by helium ions

    NASA Astrophysics Data System (ADS)

    Montanari, C. C.; Miraglia, J. E.

    2016-09-01

    We apply the continuum distorted-wave eikonal initial state and the independent electron model to describe the multiple ionization of Ar by He2+ and He+ in the energy range 0.1-10 Mev amu-1. Auger-like post collisional processes are included, which enhance the high energy multiple ionization cross sections via ionization of the inner shells. All Ar electrons (K, L and M-shells) have been included in these calculations. The results agree well with the experimental data at high energies, where the post-collisional ionization is the main contribution. At intermediate impact energies the description is also good though it tends to overestimate the triple and quadruple ionization data at intermediate energies. We analyze this by comparing the present results for He+2 in Ar, with previous ones for He+2 in Ne and Kr. It was found that the theoretical description improves from Ne to Ar and Kr, with the latter being nicely described even at intermediate energies. The present formalism is also tested for Ar inner shell and total ionization cross sections. In all the cases the results above 0.1 MeV amu-1 are quite reasonable, as compared with the experimental data available and with the ECPSSR values.

  9. Multiple ionization of argon by helium ions

    NASA Astrophysics Data System (ADS)

    Montanari, C. C.; Miraglia, J. E.

    2016-09-01

    We apply the continuum distorted-wave eikonal initial state and the independent electron model to describe the multiple ionization of Ar by He2+ and He+ in the energy range 0.1–10 Mev amu–1. Auger-like post collisional processes are included, which enhance the high energy multiple ionization cross sections via ionization of the inner shells. All Ar electrons (K, L and M-shells) have been included in these calculations. The results agree well with the experimental data at high energies, where the post-collisional ionization is the main contribution. At intermediate impact energies the description is also good though it tends to overestimate the triple and quadruple ionization data at intermediate energies. We analyze this by comparing the present results for He+2 in Ar, with previous ones for He+2 in Ne and Kr. It was found that the theoretical description improves from Ne to Ar and Kr, with the latter being nicely described even at intermediate energies. The present formalism is also tested for Ar inner shell and total ionization cross sections. In all the cases the results above 0.1 MeV amu–1 are quite reasonable, as compared with the experimental data available and with the ECPSSR values.

  10. Measurements of the nonthermal helium escape from Mars

    NASA Astrophysics Data System (ADS)

    Barabash, S.; Kallio, E.; Lundin, R.; Koskinen, H.

    1995-11-01

    The automatic space plasma experiment with a rotating analyzer (ASPERA) onboard the Phobos 2 spacecraft has recently revealed the presence of planetary He+ ions at Mars (Barabash and Norberg, 1994). In the present work the analysis is continued in order to estimate the total outflow of the He+ ions which are swept away by the solar wind. For the Phobos epoch the total He+ outflow rate was found to be (1.2+/-0.6)×1024 ions/s. The escape occurs mainly near the Martian magnetopause. Considering extreme errors in the measurements, the maximum helium outflow could range up to 2.4×1024 s-1. From a scaling of the helium profile suggested by Moroz et al. (1990) to obtain the measured loss rate, one can deduce the helium abundance in the Martian upper atmosphere. It turns out that helium is a dominant gas in the Martian exosphere at altitudes between 500 and 1250 km. However, recently reported observations of the weak EUV emissions (108 photons) from the Martian He I suggest an abundance that is 18.5 times lower (Krasnopolsky et al., 1994). Possible reasons for this disagreement are discussed. The helium production rate near Mars can, in turn, be roughly estimated from the production rate for the Earth by using a scaling argument, since the only source of helium in the atmospheres of the terrestrial planets is radioactive decay of certain isotopes of uranium and thorium. Present estimates suggest a degassing rate of 8×1022 atoms/s only (Krasnopolsky et al., 1993). However, under steady state conditions one would expect the production and loss rates to be equal. The discrepancy leads us to the conclusion that either the helium degassing rate should be corrected (or the amount of uranium is higher on Mars than anticipated) or helium may also be delivered on Mars by other sources, for example, as solar wind α particles. The observed high total outflow of ions which are 4 times heavier than protons may result in an effective mass loading. Thus helium may play an important

  11. Helium cryopumping for fusion applications

    SciTech Connect

    Sedgley, D.W.; Batzer, T.H.; Call, W.R.

    1988-05-01

    Large quantities of helium and hydrogen isotopes will be exhausted continuously from fusion power reactors. This paper summarizes two development programs undertaken to address vacuum pumping for this application: (i) A continuous duty cryopump for pumping helium and/or hydrogen species using charcoal sorbent and (ii) a cryopump configuration with an alternative shielding arrangement using charcoal sorbent or argon spray. A test program evaluated automatic pumping of helium, helium pumping by charcoal cryosorption and with argon spray, and cryosorption of helium/hydrogen mixtures. The continuous duty cryopump pumped helium continuously and conveniently. Helium pumping speed was 7.7 l/s/cm/sup 2/ of charcoal, compared to 5.8 l/s/cm/sup 2/ for the alternative pump. Helium speed using argon spray was 18% of that obtained by charcoal cryosorption in the same (W-panel) pump. During continuous duty cryopump mixture tests with helium and hydrogen copumped on charcoal, gas was released sporadically. Testing was insufficient to explain this unacceptable event.

  12. Helium jet dispersion to atmosphere

    NASA Technical Reports Server (NTRS)

    Khan, Hasna J.

    1986-01-01

    On the event of loss of vacuum guard of superinsulated helium dewar, high rate of heat transfer into the tank occurs. The rapid boiling of liquid helium causes the burst disk to rupture at four atmospheres and consequently the helium passes to the atmosphere through vent lines. The gaseous helium forms a vertical buoyant jet as it exits the vent line into a stagnant environment. Characterization of the gaseous jet is achieved by detailed analysis of the axial and radial dependence of the flow parameters.

  13. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Helium and Helium Usage Data. 52.208-8 Section 52.208-8 Federal Acquisition Regulations System FEDERAL... Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in 8.505, insert the following clause: Required Sources for Helium and Helium Usage Data (APR 2002) (a)...

  14. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Helium and Helium Usage Data. 52.208-8 Section 52.208-8 Federal Acquisition Regulations System FEDERAL... Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in 8.505, insert the following clause: Required Sources for Helium and Helium Usage Data (APR 2002) (a)...

  15. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Helium and Helium Usage Data. 52.208-8 Section 52.208-8 Federal Acquisition Regulations System FEDERAL... Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in 8.505, insert the following clause: Required Sources for Helium and Helium Usage Data (APR 2014) (a)...

  16. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Helium and Helium Usage Data. 52.208-8 Section 52.208-8 Federal Acquisition Regulations System FEDERAL... Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in 8.505, insert the following clause: Required Sources for Helium and Helium Usage Data (APR 2002) (a)...

  17. 48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Helium and Helium Usage Data. 52.208-8 Section 52.208-8 Federal Acquisition Regulations System FEDERAL... Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in 8.505, insert the following clause: Required Sources for Helium and Helium Usage Data (APR 2002) (a)...

  18. Stability of the Helium-Antiproton System

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J.

    2006-01-01

    In the course of their Born-Oppenheimer calculations of this system Todd and Armour noted that the lowest-lying state closely resembles the hydrogen negative ion, since the antiproton lies very close to the helium nucleus and shields one unit of nuclear charge. In the present paper this observation will be taken seriously to produce a variationally correct estimate of the total energy of this system, along with a similar estimate of the energy of the once-ionized system. The nonadiabatic effect of exactly treating the reduced masses improves the results.

  19. Liquid Helium Acoustic Microscope.

    NASA Astrophysics Data System (ADS)

    Steer, Andrew Paul

    Available from UMI in association with The British Library. In an acoustic microscope, images are generated by monitoring the intensity of the ultrasonic reflection, or echo, from the surface of a sample. In order to achieve this a pulse of acoustic energy is produced by the excitation of a thin film transducer. The pulse thus generated propagates through a crystal and is incident upon the acoustic lens surface, which is the boundary between the crystal and an acoustic coupling liquid. The acoustic lens is a converging element, and brings the ultrasonic beam to a focus within the liquid. A sample, placed at the focus, can act as a reflector, and the returned pulse then contains information regarding the acoustic reflectivity of this specimen. Acoustic pulses are repeatedly launched and detected while the acoustic lens is scanned over the surface of the sample. In this manner an acoustic image is constructed. Acoustic losses in room temperature liquid coupling media represent a considerable source of difficulty in the recovery of acoustic echo signals. At the frequencies of operation required in a microscope which is capable of high resolution, the ultrasonic attenuation is not only large but increases with the square of frequency. In superfluid liquid helium at temperatures below 0.1 K, however, the ultrasonic attenuation becomes negligible. Furthermore, the low sound velocity in liquid helium results in an increase in resolution, since the acoustic wavelength is proportional to velocity. A liquid helium acoustic microscope has been designed and constructed. Details of the various possible detection methods are given, and comparisons are made between them. Measurements of the performance of the system that was adopted are reported. The development of a cooled preamplifier is also described. The variation of reflected signal with object distance has been measured and compared with theoretical predictions. This variation is important in the analysis of acoustic

  20. Electron-impact ionization mass-spectrometry of molecules and clusters in a pulsed helium droplet source

    NASA Astrophysics Data System (ADS)

    Yang, Shengfu; Brereton, Scott; Ellis, Andrew M.

    2006-03-01

    A pulsed helium droplet source has been developed and characterized. The nozzle geometry was found to be critical in allowing controlled tuning of helium nanodroplet size by variation of the stagnation pressure and temperature. The average droplet size scales according to a simple p,T scaling law, placing pulsed helium nanodroplet sources on a par with cw sources for the first time. Using this pulsed source, the ability of helium nanodroplets to impede ion fragmentation in electron impact mass spectrometry has been explored. A number of haloalkanes and C1--C6 alcohols were selected as the target species. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others. Parent ion intensities are also enhanced by the helium for alcohols, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. The results obtained are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels.

  1. Helium dilution refrigeration system

    DOEpatents

    Roach, Patrick R.; Gray, Kenneth E.

    1988-01-01

    A helium dilution refrigeration system operable over a limited time period, and recyclable for a next period of operation. The refrigeration system is compact with a self-contained pumping system and heaters for operation of the system. A mixing chamber contains .sup.3 He and .sup.4 He liquids which are precooled by a coupled container containing .sup.3 He liquid, enabling the phase separation of a .sup.3 He rich liquid phase from a dilute .sup.3 He-.sup.4 He liquid phase which leads to the final stage of a dilution cooling process for obtaining low temperatures. The mixing chamber and a still are coupled by a fluid line and are maintained at substantially the same level with the still cross sectional area being smaller than that of the mixing chamber. This configuration provides maximum cooling power and efficiency by the cooling period ending when the .sup.3 He liquid is depleted from the mixing chamber with the mixing chamber nearly empty of liquid helium, thus avoiding unnecessary and inefficient cooling of a large amount of the dilute .sup.3 He-.sup.4 He liquid phase.

  2. Helium dilution refrigeration system

    DOEpatents

    Roach, P.R.; Gray, K.E.

    1988-09-13

    A helium dilution refrigeration system operable over a limited time period, and recyclable for a next period of operation is disclosed. The refrigeration system is compact with a self-contained pumping system and heaters for operation of the system. A mixing chamber contains [sup 3]He and [sup 4]He liquids which are precooled by a coupled container containing [sup 3]He liquid, enabling the phase separation of a [sup 3]He rich liquid phase from a dilute [sup 3]He-[sup 4]He liquid phase which leads to the final stage of a dilution cooling process for obtaining low temperatures. The mixing chamber and a still are coupled by a fluid line and are maintained at substantially the same level with the still cross sectional area being smaller than that of the mixing chamber. This configuration provides maximum cooling power and efficiency by the cooling period ending when the [sup 3]He liquid is depleted from the mixing chamber with the mixing chamber nearly empty of liquid helium, thus avoiding unnecessary and inefficient cooling of a large amount of the dilute [sup 3]He-[sup 4]He liquid phase. 2 figs.

  3. IBA studies of helium mobility in nuclear materials revisited

    NASA Astrophysics Data System (ADS)

    Trocellier, P.; Agarwal, S.; Miro, S.; Vaubaillon, S.; Leprêtre, F.; Serruys, Y.

    2015-12-01

    The aim of this paper is to point out and to discuss some features extracted from the study of helium migration in nuclear materials performed during the last fifteen years using ion beam analysis (IBA) measurements. The first part of this paper is devoted to a brief description of the two main IBA methods used, i.e. deuteron induced nuclear reaction for 3He depth profiling and high-energy heavy-ion induced elastic recoil detection analysis for 4He measurement. In the second part, we provide an overview of the different studies carried out on model nuclear waste matrices and model nuclear reactor structure materials in order to illustrate and discuss specific results in terms of key influence parameters in relation with thermal or radiation activated migration of helium. Finally, we show that among the key parameters we have investigated as able to influence the height of the helium migration barrier, the following can be considered as pertinent: the experimental conditions used to introduce helium (implanted ion energy and implantation fluence), the grain size of the matrix, the lattice cell volume, the Young's modulus, the ionicity degree of the chemical bond between the transition metal atom M and the non-metal atom X, and the width of the band gap.

  4. Doubly charged CO2 clusters formed by ionization of doped helium nanodroplets☆

    PubMed Central

    Daxner, Matthias; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2014-01-01

    Helium nanodroplets are doped with carbon dioxide and ionized by electrons. Doubly charged cluster ions are, for the first time, identified based on their characteristic patterns of isotopologues. Thanks to the high mass resolution, large dynamic range, and a novel method to eliminate contributions from singly charged ions from the mass spectra, we are able to observe doubly charged cluster ions that are smaller than the ones reported in the past. The likely mechanism by which doubly charged ions are formed in doped helium droplets is discussed. PMID:25844051

  5. Precision spectroscopy of Helium

    SciTech Connect

    Cancio, P.; Giusfredi, G.; Mazzotti, D.; De Natale, P.; De Mauro, C.; Krachmalnicoff, V.; Inguscio, M.

    2005-05-05

    Accurate Quantum-Electrodynamics (QED) tests of the simplest bound three body atomic system are performed by precise laser spectroscopic measurements in atomic Helium. In this paper, we present a review of measurements between triplet states at 1083 nm (23S-23P) and at 389 nm (23S-33P). In 4He, such data have been used to measure the fine structure of the triplet P levels and, then, to determine the fine structure constant when compared with equally accurate theoretical calculations. Moreover, the absolute frequencies of the optical transitions have been used for Lamb-shift determinations of the levels involved with unprecedented accuracy. Finally, determination of the He isotopes nuclear structure and, in particular, a measurement of the nuclear charge radius, are performed by using hyperfine structure and isotope-shift measurements.

  6. Superfluid Helium Heat Pipe

    NASA Astrophysics Data System (ADS)

    Gully, P.

    This paper reports on the development and the thermal tests of three superfluid helium heat pipes. Two of them are designed to provide a large transport capacity (4 mW at 1.7 K). They feature a copper braid located inside a 6 mm outer diameter stainless tube fitted with copper ends for mechanical anchoring. The other heat pipe has no copper braid and is designed to get much smaller heat transport capacity (0.5 mW) and to explore lower temperature (0.7 - 1 K). The copper braid and the tube wall is the support of the Rollin superfluid helium film in which the heat is transferred. The low filling pressure makes the technology very simple with the possibility to easily bend the tube. We present the design and discuss the thermal performance of the heat pipes tested in the 0.7 to 2.0 K temperature range. The long heat pipe (1.2 m with copper braid) and the short one (0.25 m with copper braid) have similar thermal performance in the range 0.7 - 2.0 K. At 1.7 K the long heat pipe, 120 g in weight, reaches a heat transfer capacity of 6.2 mW and a thermal conductance of 600 mW/K for 4 mW transferred power. Due to the pressure drop of the vapor flow and Kapitza thermal resistance, the conductance of the third heat pipe dramatically decreases when the temperature decreases. A 3.8 mW/K is obtained at 0.7 K for 0.5 mW transferred power.

  7. PROPERTIES OF THE DIFFUSE NEUTRAL HELIUM IN THE INNER HELIOSPHERE

    SciTech Connect

    Moise, E.; Raymond, J.; Kuhn, J. R.

    2010-10-20

    Sensitive SOLARC imaging spectropolarimetric observations from Haleakala reveal a diffuse coronal surface brightness in the He I 1083 nm line. A series of observations suggests that this signal originates from an 'inner source' of neutral helium atoms in the solar corona. Here, we explore the possibility that this cold coronal component originates from helium ions that are neutralized by the near-Sun dust and subsequently excited to the metastable 1s2s {sup 3} S state, which then scatters photons from the solar disk. This picture suggests a deficit of coronal dust inside about 2-4 R{sub sun} in order to account for both the flat radial brightness distribution and the small velocity line width of the observations. We find a strong correlation between the polarized He brightness and coronal white light brightness that supports the argument that electronic collisional excitation of the metastable helium triplet level is responsible for our polarization signal.

  8. Detached divertor operation in DIII-D helium plasmas

    SciTech Connect

    Hill, D. N., LLNL

    1998-05-01

    This paper presents results from operating helium plasmas in DIII-D in which helium gas puffing is used to reduce the peak divertor heat flux by factors of four or more. The threshold density for achieving these conditions is nearly the same as for deuterium plasmas, which is surprising given the fact that lack of chemical sputtering reduces the carbon concentration in the plasma by more than a factor of five. Spectroscopic analysis shows that helium becomes the primary radiation in these plasmas, which is possible because, unlike carbon, it is the primary species present. These plasmas differ from the usual partially detached divertor (PDD) plasmas in that there is no concomitant reduction in target plate ion flux with target plate heat flux in the scrape off later outside the separatrix.

  9. Resistor monitors transfer of liquid helium

    NASA Technical Reports Server (NTRS)

    Hesketh, W. D.

    1966-01-01

    Large resistance change of a carbon resistor at the liquid helium temperature distinguishes between the transfer of liquid helium and gaseous helium into a closed Dewar. The resistor should be physically as small as possible to reduce the heat load to the helium.

  10. Modeling the chemical kinetics of high-pressure glow discharges in mixtures of helium with real air

    SciTech Connect

    Stalder, K.R.; Vidmar, R.J.; Nersisyan, G.; Graham, W.G.

    2006-05-01

    Atmospheric and near-atmospheric pressure glow discharges generated in both pure helium and helium-air mixtures have been studied using a plasma chemistry code originally developed for simulations of electron-beam-produced air plasmas. Comparisons are made with experimental data obtained from high-pressure glow discharges in helium-air mixtures developed by applying sinusoidal voltage wave forms between two parallel planar metallic electrodes covered by glass plates, with frequencies ranging from 10 to 50 kHz and electric field strengths up to 5 kV/cm. The code simulates the plasma chemistry following periodic pulsations of ionization in prescribed E/N environments. Many of the rate constants depend on gas temperature, electron temperature, and E/N. In helium plasmas with small amounts ({approx}850 ppm) of air added, rapid conversion of atomic helium ions to molecular helium ions dominate the positive ion kinetics and these species are strongly modulated while the radical species are not. The charged and neutral species concentrations at atmospheric pressure with air impurity levels up to 10 000 ppm are predicted. The negative ion densities are very small but increase as the air impurity level is raised, which indicates that in helium-based systems operated in open air the concentration of negative ions would be significant. If water vapor at typical humidity levels is present as one of the impurities, hydrated cluster ions eventually comprise a significant fraction of the charged species.

  11. Low temperature uses of helium

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1970-01-01

    Helium is used for purging and pressurizing cryogenic rocket propellants, welding, atmosphere control, leak detection, and refrigeration. It provides the lowest possible liquid-bath temperature and produces superconductivity in certain materials. Its superfluid effects are used in superconducting magnets.

  12. Radiation source for helium magnetometers

    NASA Technical Reports Server (NTRS)

    Slocum, Robert E. (Inventor)

    1991-01-01

    A radiation source (12) for optical magnetometers (10) which use helium isotopes as the resonance element (30) includes an electronically pumped semiconductor laser (12) which produces a single narrow line of radiation which is frequency stabilized to the center frequency of the helium resonance line to be optically pumped. The frequency stabilization is accomplished using electronic feedback (34, 40, 42, 44) to control a current sources (20) thus eliminating the need for mechanical frequency tuning.

  13. Effect of kinetic energy on the doping efficiency of cesium cations into superfluid helium droplets

    SciTech Connect

    Chen, Lei; Zhang, Jie; Freund, William M.; Kong, Wei

    2015-07-28

    We present an experimental investigation of the effect of kinetic energy on the ion doping efficiency of superfluid helium droplets using cesium cations from a thermionic emission source. The kinetic energy of Cs{sup +} is controlled by the bias voltage of a collection grid collinearly arranged with the droplet beam. Efficient doping from ions with kinetic energies from 20 eV up to 480 V has been observed in different sized helium droplets. The relative ion doping efficiency is determined by both the kinetic energy of the ions and the average size of the droplet beam. At a fixed source temperature, the number of doped droplets increases with increasing grid voltage, while the relative ion doping efficiency decreases. This result implies that not all ions are captured upon encountering with a sufficiently large droplet, a deviation from the near unity doping efficiency for closed shell neutral molecules. We propose that this drop in ion doping efficiency with kinetic energy is related to the limited deceleration rate inside a helium droplet. When the source temperature changes from 14 K to 17 K, the relative ion doping efficiency decreases rapidly, perhaps due to the lack of viable sized droplets. The size distribution of the Cs{sup +}-doped droplet beam can be measured by deflection and by energy filtering. The observed doped droplet size is about 5 × 10{sup 6} helium atoms when the source temperature is between 14 K and 17 K.

  14. Effect of kinetic energy on the doping efficiency of cesium cations into superfluid helium droplets.

    PubMed

    Chen, Lei; Zhang, Jie; Freund, William M; Kong, Wei

    2015-07-28

    We present an experimental investigation of the effect of kinetic energy on the ion doping efficiency of superfluid helium droplets using cesium cations from a thermionic emission source. The kinetic energy of Cs(+) is controlled by the bias voltage of a collection grid collinearly arranged with the droplet beam. Efficient doping from ions with kinetic energies from 20 eV up to 480 V has been observed in different sized helium droplets. The relative ion doping efficiency is determined by both the kinetic energy of the ions and the average size of the droplet beam. At a fixed source temperature, the number of doped droplets increases with increasing grid voltage, while the relative ion doping efficiency decreases. This result implies that not all ions are captured upon encountering with a sufficiently large droplet, a deviation from the near unity doping efficiency for closed shell neutral molecules. We propose that this drop in ion doping efficiency with kinetic energy is related to the limited deceleration rate inside a helium droplet. When the source temperature changes from 14 K to 17 K, the relative ion doping efficiency decreases rapidly, perhaps due to the lack of viable sized droplets. The size distribution of the Cs(+)-doped droplet beam can be measured by deflection and by energy filtering. The observed doped droplet size is about 5 × 10(6) helium atoms when the source temperature is between 14 K and 17 K.

  15. Effect of kinetic energy on the doping efficiency of cesium cations into superfluid helium droplets

    PubMed Central

    Chen, Lei; Zhang, Jie; Freund, William M.; Kong, Wei

    2015-01-01

    We present an experimental investigation of the effect of kinetic energy on the ion doping efficiency of superfluid helium droplets using cesium cations from a thermionic emission source. The kinetic energy of Cs+ is controlled by the bias voltage of a collection grid collinearly arranged with the droplet beam. Efficient doping from ions with kinetic energies from 20 eV up to 480 V has been observed in different sized helium droplets. The relative ion doping efficiency is determined by both the kinetic energy of the ions and the average size of the droplet beam. At a fixed source temperature, the number of doped droplets increases with increasing grid voltage, while the relative ion doping efficiency decreases. This result implies that not all ions are captured upon encountering with a sufficiently large droplet, a deviation from the near unity doping efficiency for closed shell neutral molecules. We propose that this drop in ion doping efficiency with kinetic energy is related to the limited deceleration rate inside a helium droplet. When the source temperature changes from 14 K to 17 K, the relative ion doping efficiency decreases rapidly, perhaps due to the lack of viable sized droplets. The size distribution of the Cs+-doped droplet beam can be measured by deflection and by energy filtering. The observed doped droplet size is about 5 × 106 helium atoms when the source temperature is between 14 K and 17 K. PMID:26233132

  16. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2011-12-01

    Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm

  17. Genetic changes in Mammalian cells transformed by helium cells

    SciTech Connect

    Durante, M.; Grossi, G. . Dipt. di Scienze Fisiche); Yang, T.C.; Roots, R. )

    1990-11-01

    Midterm Syrian Hamster embryo (SHE) cells were employed to study high LET-radiation induced tumorigenesis. Normal SHE cells (secondary passage) were irradiated with accelerated helium ions at an incident energy of 22 MeV/u (9--10 keV/{mu}m). Transformed clones were isolated after growth in soft agar of cells obtained from the foci of the initial monolayer plated postirradiation. To study the progression process of malignant transformation, the transformed clones were followed by monolayer subculturing for prolonged periods of time. Subsequently, neoplasia tests in nude mice were done. In this work, however, we have focused on karyotypic changes in the banding patterns of the chromosomes during the early part of the progressive process of cell transformation for helium ion-induced transformed cells. 26 refs., 5 figs., 2 tabs.

  18. Convergent close-coupling calculations of helium single ionization by antiproton impact

    SciTech Connect

    Abdurakhmanov, I. B.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T.

    2011-12-15

    We apply the fully quantum-mechanical convergent close-coupling method to the calculation of antiproton scattering on the ground state of helium. The helium target is treated as a three-body Coulomb system using frozen-core and multiconfiguration approximations. The electron-electron correlation of the target is fully treated in both cases. Though both calculations yield generally good agreement with experiment for the total ionization cross sections, the multiconfiguration results are substantially higher at the lower energies than the frozen-core ones. Calculated longitudinal ejected electron and recoil-ion momentum distributions for the single ionization of helium are in good agreement with the experiment.

  19. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  20. COSMIC-RAY HELIUM HARDENING

    SciTech Connect

    Ohira, Yutaka; Ioka, Kunihito

    2011-03-01

    Recent observations by the CREAM and ATIC-2 experiments suggest that (1) the spectrum of cosmic-ray (CR) helium is harder than that of CR protons below the knee energy, 10{sup 15}eV, and (2) all CR spectra become hard at {approx}>10{sup 11}eV nucleon{sup -1}. We propose a new idea, that higher energy CRs are generated in a more helium-rich region, to explain the hardening without introducing different sources for CR helium. The helium-to-proton ratio at {approx}100 TeV exceeds the Big Bang abundance Y = 0.25 by several times, and the different spectrum is not reproduced within the diffusive shock acceleration theory. We argue that CRs are produced in a chemically enriched region, such as a superbubble, and the outward-decreasing abundance naturally leads to the hard spectrum of CR helium if CRs escape from the supernova remnant shock in an energy-dependent way. We provide a simple analytical spectrum that also fits well the hardening due to the decreasing Mach number in the hot superbubble with {approx}10{sup 6} K. Our model predicts hard and concave spectra for heavier CR elements.

  1. Charge transfer dissociation (CTD) mass spectrometry of peptide cations using kiloelectronvolt helium cations.

    PubMed

    Hoffmann, William D; Jackson, Glen P

    2014-11-01

    A kiloelectronvolt beam of helium ions is used to ionize and fragment precursor peptide ions starting in the 1+ charge state. The electron affinity of helium cations (24.6 eV) exceeds the ionization potential of protonated peptides and can therefore be used to abstract an electron from--or charge exchange with--the isolated precursor ions. Kiloelectronvolt energies are used, (1) to overcome the Coulombic repulsion barrier between the cationic reactants, (2) to overcome ion-defocussing effects in the ion trap, and (3) to provide additional activation energy. Charge transfer dissociation (CTD) of the [M+H](+) precursor of Substance P gives product ions such as [M+H](2+•) and a dominant series of a ions in both the 1+ and 2+ charge states. These observations, along with the less-abundant a + 1 ions, are consistent with ultraviolet photodissociation (UVPD) results of others and indicate that C-C(α) cleavages are possible through charge exchange with helium ions. Although the efficiencies and timescale of CTD are not yet suitable for on-line chromatography, this new approach to ion activation provides an additional potential tool for the interrogation of gas phase ions.

  2. Compact hydrogen/helium isotope mass spectrometer

    DOEpatents

    Funsten, Herbert O.; McComas, David J.; Scime, Earl E.

    1996-01-01

    The compact hydrogen and helium isotope mass spectrometer of the present invention combines low mass-resolution ion mass spectrometry and beam-foil interaction technology to unambiguously detect and quantify deuterium (D), tritium (T), hydrogen molecule (H.sub.2, HD, D.sub.2, HT, DT, and T.sub.2), .sup.3 He, and .sup.4 He concentrations and concentration variations. The spectrometer provides real-time, high sensitivity, and high accuracy measurements. Currently, no fieldable D or molecular speciation detectors exist. Furthermore, the present spectrometer has a significant advantage over traditional T detectors: no confusion of the measurements by other beta-emitters, and complete separation of atomic and molecular species of equivalent atomic mass (e.g., HD and .sup.3 He).

  3. Single ionization of helium by electron impact

    SciTech Connect

    Bray, I.; Fursa, D. V.; Kadyrov, A. S.; Stelbovics, A. T.

    2010-06-15

    We suggest that the problem of single ionization of helium by electron impact, leaving the ion in the ground state, has been solved theoretically for the full range of kinematics and collision geometries of practical interest. Following the emphasis on the study of out-of-plane geometries where the cross sections are very small [Schulz et al., Nature 422, 48 (2003)], we find that the convergent close-coupling calculations, in either a frozen- or a multicore treatment of the target, are in excellent agreement with the available measurements. Curiously, some systematic discrepancies are identified for some in-plane cases where the cross sections are an order of magnitude larger. Further measurements are required to resolve these discrepancies. If subsequent measurements confirm the present calculations, then we would have a strong case that the problem has been solved.

  4. Formation of Au and tetrapyridyl porphyrin complexes in superfluid helium.

    PubMed

    Feng, Cheng; Latimer, Elspeth; Spence, Daniel; Al Hindawi, Aula M A A; Bullen, Shem; Boatwright, Adrian; Ellis, Andrew M; Yang, Shengfu

    2015-07-14

    Binary clusters containing a large organic molecule and metal atoms have been formed by the co-addition of 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) molecules and gold atoms to superfluid helium nanodroplets, and the resulting complexes were then investigated by electron impact mass spectrometry. In addition to the parent ion H2TPyP yields fragments mainly from pyrrole, pyridine and methylpyridine ions because of the stability of their ring structures. When Au is co-added to the droplets the mass spectra are dominated by H2TPyP fragment ions with one or more Au atoms attached. We also show that by switching the order in which Au and H2TPyP are added to the helium droplets, different types of H2TPyP-Au complexes are clearly evident from the mass spectra. This study suggests a new route for the control over the growth of metal-organic compounds inside superfluid helium nanodroplets.

  5. STIRAP on helium: Excitation to Rydberg states

    NASA Astrophysics Data System (ADS)

    Yuan, Deqian

    Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S→33P→nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of ~ 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable ~790 nm IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S → 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections.

  6. Mass Spectrometric Investigation of Anions Formed upon Free Electron Attachment to Nucleobase Molecules and Clusters Embedded in Superfluid Helium Droplets

    SciTech Connect

    Denifl, Stephan; Zappa, Fabio; Maehr, Ingo; Lecointre, Julien; Probst, Michael; Maerk, Tilmann D.; Scheier, Paul

    2006-07-28

    Here we report the first mass spectrometric study of negative ions formed via free electron attachment (EA) to nucleobases (NBs) embedded in helium clusters. Pure and mixed clusters of adenine and thymine have been formed by pickup of isolated NB molecules by cold helium droplets. In contrast to EA of isolated molecules in the gas phase we observe a long-lived parent anion NB{sup -} and, in addition, parent cluster ions NB{sub n}{sup -} up to size n=6. Moreover, we show that a low energy electron penetrating into a doped helium droplet causes efficient damage of the embedded nucleobases via resonant, site selective, dissociative electron attachment.

  7. Counting Electrons on Liquid Helium

    NASA Astrophysics Data System (ADS)

    Glasson, Phillip

    2004-03-01

    Electrons on liquid helium, localised in an array of quantum dots, have been proposed as condensed matter qubits [M.I.Dykman et al. Phys.Rev. B 67, 155402 (2003)]. The ground and first excited Rydberg states in the vertical potential well on the helium surface would represent |0> and |1>. This requires (a) novel electronic devices on helium using microstructured substrates, (b) excitation of Rydberg states using millimetric microwaves and (c) detection of individual electrons and their quantum states. Progress in meeting these challenges will be presented. An AC-coupled Field Effect Transistor (FET) has been made on GaAs, using free electrons on suspended liquid helium microchannels, 16 micron wide and 1.6 microns deep [P.Glasson et al, Phys.Rev.Lett. 87 176802 (2001)]. The microwave absorption to the first excited Rydberg state near 200 GHz has been measured below 1 K [E.Collin et al. Phys.Rev.Lett. 89, 245301 (2002)], where the temperature-dependent contribution to the linewidth is small. High values of the ratio of the Rabi frequency to the linewidth are obtained. Electrons are trapped on a 5 micron diameter pool of superfluid helium, above a single-electron-transistor (SET) as a detector. The pool is charged from a surface electron reservoir and we count the electrons into and out of the trap. Individual electrons can be stored, detected and counted: the next stage is quantum state detection. The prospects for qubits and quantum information processing with electrons on helium will be assessed.

  8. Pulsed helium ionization detection system

    DOEpatents

    Ramsey, Roswitha S.; Todd, Richard A.

    1987-01-01

    A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

  9. Pulsed helium ionization detection system

    DOEpatents

    Ramsey, R.S.; Todd, R.A.

    1985-04-09

    A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

  10. Helium release during shale deformation: Experimental validation

    NASA Astrophysics Data System (ADS)

    Bauer, Stephen J.; Gardner, W. Payton; Heath, Jason E.

    2016-07-01

    This work describes initial experimental results of helium tracer release monitoring during deformation of shale. Naturally occurring radiogenic 4He is present in high concentration in most shales. During rock deformation, accumulated helium could be released as fractures are created and new transport pathways are created. We present the results of an experimental study in which confined reservoir shale samples, cored parallel and perpendicular to bedding, which were initially saturated with helium to simulate reservoir conditions, are subjected to triaxial compressive deformation. During the deformation experiment, differential stress, axial, and radial strains are systematically tracked. Release of helium is dynamically measured using a helium mass spectrometer leak detector. Helium released during deformation is observable at the laboratory scale and the release is tightly coupled to the shale deformation. These first measurements of dynamic helium release from rocks undergoing deformation show that helium provides information on the evolution of microstructure as a function of changes in stress and strain.

  11. Peculiarities of helium porosity formation in the surface layer of the structural materials used for the first wall of fusion reactor

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Stal'tsov, M. S.; Kalin, B. A.; Bogachev, I. A.; Guseva, L. Yu.

    2016-03-01

    Transmission electron microscopy is used to study the formation of helium porosity in the nearsurface layer of ferritic-martensitic steels and vanadium irradiated by 40-keV He+ ions at a temperature of 923 K up to fluence of 5 × 1020 He+/m2 and, then, by 7.5-MeV Ni2+ ions at 923 K up to dose of 100 dpa. Large gas bubbles are found to form in the zone with the maximum concentration of radiation vacancies during He+ ion irradiation. Moreover, small bubbles form in some grains at the depths that are larger than the He+ ion range in the irradiated material. Sequential irradiation by He+ and Ni2+ ions leads to the nucleation of helium bubbles at still larger depths due to helium atom transport via recoil and/or ion mixing. The precipitation hardening of the steels by Y2O3 oxide nanoparticles is found to suppress helium swelling substantially.

  12. Automatic Refilling System For Liquid Helium

    NASA Technical Reports Server (NTRS)

    Serlemitsos, Aristides; Sansebastian, Mark; Geagen, Jay; Warner, Brent

    1990-01-01

    Cryogenic experiments left unattended for days. System automatically replenishes liquid helium in cryogenic experimental apparatus as liquid evaporates. Automatic filling system transfers liquid helium from storage vessel to experimental apparatus under computer control. Gaseous helium from cylinder supplies pumping pressure. Circuit senses level of liquid helium by sensing voltage across measuring resistors in series with silicon resistance thermometers (SRT's). Low voltage indicates SRT covered, while high voltage indicates uncovered.

  13. 21 CFR 582.1355 - Helium.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Helium. 582.1355 Section 582.1355 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS, FEEDS... Helium. (a) Product. Helium. (b) Conditions of use. This substance is generally recognized as safe...

  14. 43 CFR 3100.1 - Helium.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Helium. 3100.1 Section 3100.1 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE... Helium. The ownership of and the right to extract helium from all gas produced from lands leased...

  15. 43 CFR 3100.1 - Helium.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Helium. 3100.1 Section 3100.1 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE... Helium. The ownership of and the right to extract helium from all gas produced from lands leased...

  16. 21 CFR 582.1355 - Helium.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Helium. 582.1355 Section 582.1355 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS, FEEDS... Helium. (a) Product. Helium. (b) Conditions of use. This substance is generally recognized as safe...

  17. 21 CFR 582.1355 - Helium.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Helium. 582.1355 Section 582.1355 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS, FEEDS... Helium. (a) Product. Helium. (b) Conditions of use. This substance is generally recognized as safe...

  18. 30 CFR 556.11 - Helium.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 2 2012-07-01 2012-07-01 false Helium. 556.11 Section 556.11 Mineral Resources... § 556.11 Helium. (a) Each lease issued or continued under these regulations shall be subject to a... helium from all gas produced from the leased area. (b) In case the United States elects to take...

  19. 30 CFR 556.11 - Helium.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 2 2014-07-01 2014-07-01 false Helium. 556.11 Section 556.11 Mineral Resources... § 556.11 Helium. (a) Each lease issued or continued under these regulations shall be subject to a... helium from all gas produced from the leased area. (b) In case the United States elects to take...

  20. 43 CFR 3100.1 - Helium.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Helium. 3100.1 Section 3100.1 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE... Helium. The ownership of and the right to extract helium from all gas produced from lands leased...

  1. 30 CFR 556.11 - Helium.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 2 2013-07-01 2013-07-01 false Helium. 556.11 Section 556.11 Mineral Resources... § 556.11 Helium. (a) Each lease issued or continued under these regulations shall be subject to a... helium from all gas produced from the leased area. (b) In case the United States elects to take...

  2. Multipurpose top for liquid helium Dewar

    NASA Technical Reports Server (NTRS)

    Murphy, R. S.; Anderholm, J. R.

    1972-01-01

    Multipurpose top was fabricated for liquid helium Dewar flask which guards against flash vaporization of liquid helium and allows boiling temperature of liquid helium to be lowered by reduction of ambient pressure in Dewar flask. Device is rugged and simple, and does not require frequent calibrations or adjustments.

  3. Applying the helium ionization detector in chromatography

    NASA Technical Reports Server (NTRS)

    Gibson, E. K.; Andrawes, F. F.; Brazell, R. S.

    1981-01-01

    High noise levels and oversensitivity of helium detector make flame-ionization and thermal-conductivity detectors more suitable for chromotography. Deficiencies are eliminated by modifying helium device to operate in saturation rather than multiplication mode. Result is low background current, low noise, high stability, and high sensitivity. Detector analyzes halocarbons, hydrocarbons, hydrogen cyanide, ammonia, and inorganics without requiring expensive research-grade helium.

  4. 21 CFR 582.1355 - Helium.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Helium. 582.1355 Section 582.1355 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS, FEEDS... Helium. (a) Product. Helium. (b) Conditions of use. This substance is generally recognized as safe...

  5. 21 CFR 582.1355 - Helium.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Helium. 582.1355 Section 582.1355 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS, FEEDS... Helium. (a) Product. Helium. (b) Conditions of use. This substance is generally recognized as safe...

  6. 43 CFR 3100.1 - Helium.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Helium. 3100.1 Section 3100.1 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE... Helium. The ownership of and the right to extract helium from all gas produced from lands leased...

  7. Effect of Helium ion irradiation on the structure, the phase stability, and the microhardness of TiN, TiAlN, and TiAlYN nanostructured coatings

    NASA Astrophysics Data System (ADS)

    Komarov, F. F.; Konstantinov, S. V.; Strel'nitskij, V. E.; Pilko, V. V.

    2016-05-01

    The radiation resistance of nanostructured TiN, TiAlN, and TiAlYN coatings is studied after 500-keV He+ ion irradiation in the fluence range 5 × 1016-3 × 1017 ions/cm2. The radiation-induced changes in the phase composition, the structure, the lattice parameters, the morphology, and the mechanical properties of coatings are investigated. Blistering is found to be absent, and the radiation fluence is shown to affect the strength properties of the thin coatings nonlinearly. A significant decrease in the grain sizes is detected upon ion irradiation, which causes an increase in the microhardness and the radiation resistance of the coatings. The TiN, TiAlN, and TiAlYN coatings are found to be radiation-resistant coatings, which do not undergo serious degradation during high-fluence ion irradiation.

  8. Vortex Rings in Superfluid Helium

    NASA Astrophysics Data System (ADS)

    Alamri, Sultan Z.; Barenghi, Carlo F.

    2008-11-01

    We present results of numerical simulations of large-scale vortex rings in superfluid helium. These large-scale vortex rings consists of many discrete (quantized) vortex filaments which interact with each other moving according to the Biot-Savart law. Lifetime, structural stability and speed of large-scale vortex rings will be discussed and compared to experimental results.

  9. Why Helium Ends in "-Ium"

    ERIC Educational Resources Information Center

    Jensen, William B.; Holme, Thomas; Cooper, Melanie; White, Carol

    2004-01-01

    Edward Frankland and Norman Lockyer researched upon a gaseous spectra in relation to the physical constitution of the sun and named it as "helium" (from Greek "helios" meaning "sun"). Since Lockyer apparently never formally proposed the name in print, it is not known why he chose to use a metallic end "ium".

  10. Helium diffusion in the sun

    NASA Technical Reports Server (NTRS)

    Bahcall, J. N.; Pinsonneault, M. H.

    1992-01-01

    We calculate improved standard solar models using the new Livermore (OPAL) opacity tables, an accurate (exportable) nuclear energy generation routine which takes account of recent measurements and analyses, and the recent Anders-Grevesse determination of heavy element abundances. We also evaluate directly the effect of the diffusion of helium with respect to hydrogen on the calculated neutrino fluxes, on the primordial solar helium abundance, and on the depth of the convective zone. Helium diffusion increases the predicted event rates by about 0.8 SNU, or 11 percent of the total rate, in the chlorine solar neutrino experiment, by about 3.5 SNU, or 3 percent, in the gallium solar neutrino experiments, and by about 12 percent in the Kamiokande and SNO solar neutrino experiments. The best standard solar model including helium diffusion and the most accurate nuclear parameters, element abundances, and radiative opacity predicts a value of 8.0 SNU +/- 3.0 SNU for the C1-37 experiment and 132 +21/-17 SNU for the Ga - 71 experiment, where the uncertainties include 3 sigma errors for all measured input parameters.

  11. Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

    PubMed Central

    He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M.; Kong, Wei

    2015-01-01

    We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He2+ and He4+, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl4 doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)nC+, (He)nCl+, and (He)nCCl+. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets. PMID:26329210

  12. Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams.

    PubMed

    He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M; Kong, Wei

    2015-08-01

    We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He2(+) and He4(+), which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl4 doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)(n)C(+), (He)(n)Cl(+), and (He)(n)CCl(+). Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.

  13. Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

    NASA Astrophysics Data System (ADS)

    He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M.; Kong, Wei

    2015-08-01

    We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He2+ and He4+, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl4 doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)nC+, (He)nCl+, and (He)nCCl+. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.

  14. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    NASA Astrophysics Data System (ADS)

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-01

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope 4He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O2. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  15. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    SciTech Connect

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-27

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope {sup 4}He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O{sub 2}. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  16. Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

    SciTech Connect

    He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M.; Kong, Wei

    2015-08-15

    We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He{sub 2}{sup +} and He{sub 4}{sup +}, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl{sub 4} doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He){sub n}C{sup +}, (He){sub n}Cl{sup +}, and (He){sub n}CCl{sup +}. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.

  17. High-temperature helium-loop facility

    SciTech Connect

    Tokarz, R.D.

    1981-09-01

    The high-temperature helium loop is a facility for materials testing in ultrapure helium gas at high temperatures. The closed loop system is capable of recirculating high-purity helium or helium with controlled impurities. The gas loop maximum operating conditions are as follows: 300 psi pressure, 500 lb/h flow rate, and 2100/sup 0/F temperature. The two test sections can accept samples up to 3.5 in. diameter and 5 ft long. The gas loop is fully instrumented to continuously monitor all parameters of loop operation as well as helium impurities. The loop is fully automated to operate continuously and requires only a daily servicing by a qualified operator to replenish recorder charts and helium makeup gas. Because of its versatility and high degree of parameter control, the helium loop is applicable to many types of materials research. This report describes the test apparatus, operating parameters, peripheral systems, and instrumentation system.

  18. Approximating the Helium Wavefunction in Positronium-Helium Scattering

    NASA Technical Reports Server (NTRS)

    DiRienzi, Joseph; Drachman, Richard J.

    2003-01-01

    In the Kohn variational treatment of the positronium- hydrogen scattering problem the scattering wave function is approximated by an expansion in some appropriate basis set, but the target and projectile wave functions are known exactly. In the positronium-helium case, however, a difficulty immediately arises in that the wave function of the helium target atom is not known exactly, and there are several ways to deal with the associated eigenvalue in formulating the variational scattering equations to be solved. In this work we will use the Kohn variational principle in the static exchange approximation to d e t e e the zero-energy scattering length for the Ps-He system, using a suite of approximate target functions. The results we obtain will be compared with each other and with corresponding values found by other approximation techniques.

  19. The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows

    NASA Technical Reports Server (NTRS)

    Hoppe, J. C.; Honaker, W. C.

    1979-01-01

    Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.

  20. Helium-Implantation-Induced Damage in NHS Steel Investigated by Slow-Positron Annihilation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Yuan-Fei; Shen, Tie-Long; Gao, Xing; Gao, Ning; Yao, Cun-Feng; Sun, Jian-Rong; Wei, Kong-Fang; Li, Bing-Sheng; Zhang, Peng; Cao, Xing-Zhong; Zhu, Ya-Bin; Pang, Li-Long; Cui, Ming-Huan; Chang, Hai-Long; Wang, Ji; Zhu, Hui-Ping; Wang, Dong; Song, Peng; Sheng, Yan-Bin; Zhang, Hong-Peng; Hu, Bi-Tao; Wang, Zhi-Guang

    2014-03-01

    Evolutions of defects and helium contained defects produced by atomic displacement and helium deposition with helium implantation at different temperatures in novel high silicon (NHS) steel are investigated by a slow positron beam. Differences of the defect information among samples implanted by helium to a fluence of 1 × 1017 ions/cm2 at room temperature, 300°C, 450°C and 750°C are discussed. It is found that the mobility of vacancies and vacancy clusters, a recombination of vacancy-type defects and the formation of the He-V complex lead to the occurrence of these differences. At high temperature irradiations, a change of the diffusion mechanism of He atoms/He bubbles might be one of the reasons for the change of the S-parameter.

  1. Phase separation of metallic hydrogen-helium alloys

    NASA Technical Reports Server (NTRS)

    Straus, D. M.; Ashcroft, N. W.; Beck, H.

    1976-01-01

    Calculations are presented for the thermodynamic functions and phase separation boundaries of solid metallic hydrogen helium alloys at temperatures between 0 K and 19,000 K and at pressures between 15 and 90 megabars. Expressions for the band structure energy of a randomly disordered alloy (including third order in the electron ion interaction) are derived and evaluated. Short and long range order are included by the quasi-chemical method, and lattice dynamics in the virtual crystal harmonic approximation. We conclude that at temperatures below 4,000 K there is complete phase separation of hydrogen helium alloys, and that a miscibility gap remains at the highest temperatures and pressures considered. The relevance of these results to models of the deep interior of Jupiter is briefly discussed.

  2. Helium-like magnesium embedded in strongly coupled plasma

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Sukhamoy

    2016-05-01

    In recent days, with the advent of the x-ray free electron laser (FEL) with Linac coherent light source (LCLS) and the Orion laser, experimental studies on atomic systems within strongly coupled plasma environment with remarkable improvement in accuracy as compared to earlier experiments have become possible. In these kinds of experiments, hydrogen-like and helium-like spectral lines are used for determination of plasma parameters such as temperature, density. Accurate theoretical calculations are, therefore, necessary for such kind of studies within a dense plasma environment. In this work, ab initio calculations are carried out in the framework of the Rayleigh-Ritz variation principle to estimate the ground state energy of helium-like magnesium within strongly coupled plasma environment. Explicitly correlated wave functions in Hylleraas coordinates have been used to incorporate the effect of electron correlation. The ion-sphere model potential that confines the central positive ion in a finite domain filled with plasma electrons has been adopted to mimic the strongly coupled plasma environment. Thermodynamic pressure 'felt' by the ion in the ground states due to the confinement inside the ion spheres is also estimated.

  3. Helium Retention and Desorption Behaviour of Reduced Activation Ferritic/Martenstic Steel

    NASA Astrophysics Data System (ADS)

    Wang, Pinghuai; Nobuta, Yuji; Hino, Tomoaki; Yamauchi, Yuji; Chen, Jiming; Xu, Zengyu; Li, Xiongwei; Liu, Shi

    2009-04-01

    The reduced activation ferritic/martenstic steel CLF-1 prepared by the Southwestern Institute of Physics in China was irradiated by helium ions with an energy of 5 keV at room temperature using an electron cyclotron resonance (ECR) ion irradiation apparatus. After the irradiation, the helium retention and desorption were investigated using a technique of thermal desorption spectroscopy (TDS). The experiment was conducted with both the normal and welded samples. Blisters were observed after the helium ion irradiation, and the surface density of blisters in the welded samples was lower than that in the non-welded samples. Three desorption peaks were observed in both the non-welded and welded samples. These desorption peaks corresponded to those of blister ruptures and the helium release from the inner bubbles and the defects. The amount of helium retained in the welded samples was approximately the same as that in the non-welded samples, which was much less than other reduced activation materials, such as vanadium alloy and SiC/SiC composites.

  4. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  5. Confined helium on Lagrange meshes.

    PubMed

    Baye, D; Dohet-Eraly, J

    2015-12-21

    The Lagrange-mesh method has the simplicity of a calculation on a mesh and can have the accuracy of a variational method. It is applied to the study of a confined helium atom. Two types of confinement are considered. Soft confinements by potentials are studied in perimetric coordinates. Hard confinement in impenetrable spherical cavities is studied in a system of rescaled perimetric coordinates varying in [0,1] intervals. Energies and mean values of the distances between electrons and between an electron and the helium nucleus are calculated. A high accuracy of 11 to 15 significant figures is obtained with small computing times. Pressures acting on the confined atom are also computed. For sphere radii smaller than 1, their relative accuracies are better than 10(-10). For larger radii up to 10, they progressively decrease to 10(-3), still improving the best literature results.

  6. Superfluid helium leak sealant study

    NASA Technical Reports Server (NTRS)

    Vorreiter, J. W.

    1981-01-01

    Twenty-one leak specimens were fabricated in the ends of stainless steel and aluminum tubes. Eighteen of these tubes were coated with a copolymer material to seal the leak. The other three specimens were left uncoated and served as control specimens. All 21 tubes were cold shocked in liquid helium 50 times and then the leak rate was measured while the tubes were submerged in superfluid helium at 1.7 K. During the cold shocks two of the coated specimens were mechanically damaged and eliminated from the test program. Of the remaining 16 coated specimens one suffered a total coating failure and resulting high leak rate. Another three of the coated specimens suffered partial coating failures. The leak rates of the uncoated specimens were also measured and reported. The significance of various leak rates is discussed in view of the infrared astronomical satellite (IRAS) Dewar performance.

  7. Rapidly pulsed helium droplet source

    SciTech Connect

    Pentlehner, Dominik; Riechers, Ricarda; Dick, Bernhard; Slenczka, Alkwin; Even, Uzi; Lavie, Nachum; Brown, Raviv; Luria, Kfir

    2009-04-15

    A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules. The average size of this part can be varied between 10{sup 4} and 10{sup 6} helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.

  8. Superfluid Helium Tanker (SFHT) study

    NASA Technical Reports Server (NTRS)

    Eberhardt, Ralph N.; Dominick, Sam M.; Anderson, John E.; Gille, John P.; Martin, Tim A.; Marino, John S.; Paynter, Howard L.; Traill, R. Eric; Herzl, Alfred; Gotlib, Sam

    1988-01-01

    Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997.

  9. Cryopumping of hydrogen and helium

    SciTech Connect

    Halama, H.J.; Hseuh, H.C.; Chou, T.S.

    1981-01-01

    Results obtained in numerous tests on small (approx. 1000 l/S) and large (approx. 10/sup 5/ l/S) cryopumps cooled to 4.2/sup 0/K by LHe or between 10 to 20/sup 0/K by closed-cycle helium refrigerator are summarized. Then, measurements of the compound cryopump, designed to work on Tokamaks to handle the exhaust gases from the Torus are presented.

  10. Helium in interplanetary dust particles

    NASA Technical Reports Server (NTRS)

    Nier, A. O.; Schlutter, D. J.

    1993-01-01

    Helium and neon were extracted from fragments of individual stratosphere-collected interplanetary dust particles (IDP's) by subjecting them to increasing temperature by applying short-duration pulses of power in increasing amounts to the ovens containing the fragments. The experiment was designed to see whether differences in release temperatures could be observed which might provide clues as to the asteroidal or cometary origin of the particles. Variations were observed which show promise for elucidating the problem.

  11. The Chemical Evolution of Helium

    NASA Astrophysics Data System (ADS)

    Balser, Dana S.

    2006-12-01

    We report on measurements of the 4He abundance toward the outer Galaxy H II region S206 with the NRAO Green Bank Telescope. Observations of hydrogen and helium radio recombination lines between 8 and 10 GHz were made toward the peak radio continuum position in S206. We derive 4He/H=0.08459+/-0.00088 (random)+/-0.0010 (known systematic), 20% lower than optical recombination line results. It is difficult to reconcile the large discrepancy between the optical and radio values even when accounting for temperature, density, and ionization structure or for optical extinction by dust. Using only M17 and S206 we determine ΔY/ΔZ=1.41+/-0.62 in the Galaxy, consistent with standard chemical evolution models. High helium abundances in the old stellar population of elliptical galaxies can help explain the increase in UV emission with shorter wavelength between 2000 and 1200 Å, called the ``UV upturn'' or UVX. Our lower values of ΔY/ΔZ are consistent with a normal helium abundance at higher metallicity and suggest that other factors, such as a variable red giant branch mass loss with metallicity, may be important. When combined with 4He abundances in metal-poor galaxy H II regions, Magellanic Cloud H II regions, and M17 that have been determined from optical recombination lines, including the effects of temperature fluctuations, our radio 4He/H abundance ratio for S206 is consistent with a helium evolution of ΔY/ΔZ=1.6. A linear extrapolation to zero metallicity predicts a 4He/H primordial abundance ratio about 5% lower than that given by the Wilkinson Microwave Anisotropy Probe and standard big bang nucleosynthesis. The measured 4He abundances may be systematically underestimated by a few percent if clumping exists in these H II regions.

  12. Detecting scintillations in liquid helium

    NASA Astrophysics Data System (ADS)

    Huffman, P. R.; McKinsey, D. N.

    2013-09-01

    We review our work in developing a tetraphenyl butadiene (TPB)-based detection system for a measurement of the neutron lifetime using magnetically confined ultracold neutrons (UCN). As part of the development of the detection system for this experiment, we studied the scintillation properties of liquid helium itself, characterized the fluorescent efficiencies of different fluors, and built and tested three detector geometries. We provide an overview of the results from these studies as well as references for additional information.

  13. Vorticity matching in superfluid helium

    NASA Astrophysics Data System (ADS)

    Samuels, David C.

    1991-12-01

    Recent experiments have rekindled interest in high Reynolds number flows using superfluid helium. In a continuing series of experiments, the flow of helium II through various devices (smooth pipes, corrugated pipes, valves, venturies, turbine flowmeters, and coanda flowmeters for example) was investigated. In all cases, the measured values (typically, mass flow rates and pressure drops) were found to be well described by classical relations for high Reynolds flows. This is unexpected since helium II consists of two interpenetrating fluids; one fluid with nonzero viscosity (the normal fluid) and one with zero viscosity (the superfluid). Only the normal fluid component should directly obey classical relations. Since the experiments listed above only measure the external behavior of the flow (i.e., pressure drops over devices), there is a great deal of room for interpretation of their results. One possible interpretation is that in turbulent flows the normal fluid and the superfluid velocity fields are somehow 'locked' together, presumably by the mutual friction force between the superfluid vortex filaments and the normal fluid. We refer to this locking together of the two fluids as 'vorticity matching.'

  14. Particle detection using superfluid helium

    SciTech Connect

    Bandler, S.R.; Lanou, R.E.; Maris, H.J.; More, T.; Porter, F.S.; Seidel, G.M.; Torii, R.

    1991-01-01

    We have observed 5 MeV {alpha} particles stopped in volumes-up to two liters of liquid helium at 70 mK. A fraction of the kinetic energy of an {alpha} particle is converted to elementary excitations (rotons and phonons), which progagate ballistically in isotopically pure {sup 4}He below 0.1 K. Most of these excitations have sufficient energy to evaporate helium atoms on hitting a free surface. The evaporated helium atoms can be detected calorimetrically when adsorbed on a thin silicon wafer ({approximately}1.7 g, 35 cm{sup 2}) suspended above the liquid. Temperature changes of the silicon are measured with a NTD germanium bolometer. For the geometry studied the observed temperature change of the silicon resulting from an {alpha} event in the liquid is approximately 5% of the temperature rise from an {alpha} hitting the silicon directly. The implications of these measurements will be discussed as they relate to the possible construction of a large scale detector of solar neutrinos.

  15. Particle detection using superfluid helium

    SciTech Connect

    Bandler, S.R.; Lanou, R.E.; Maris, H.J.; More, T.; Porter, F.S.; Seidel, G.M.; Torii, R.

    1991-12-31

    We have observed 5 MeV {alpha} particles stopped in volumes-up to two liters of liquid helium at 70 mK. A fraction of the kinetic energy of an {alpha} particle is converted to elementary excitations (rotons and phonons), which progagate ballistically in isotopically pure {sup 4}He below 0.1 K. Most of these excitations have sufficient energy to evaporate helium atoms on hitting a free surface. The evaporated helium atoms can be detected calorimetrically when adsorbed on a thin silicon wafer ({approximately}1.7 g, 35 cm{sup 2}) suspended above the liquid. Temperature changes of the silicon are measured with a NTD germanium bolometer. For the geometry studied the observed temperature change of the silicon resulting from an {alpha} event in the liquid is approximately 5% of the temperature rise from an {alpha} hitting the silicon directly. The implications of these measurements will be discussed as they relate to the possible construction of a large scale detector of solar neutrinos.

  16. Variation in Atmospheric Helium Isotopes

    NASA Astrophysics Data System (ADS)

    Mabry, J. C.; Marty, B.; Burnard, P.; Blard, P.

    2010-12-01

    Anthropogenic activity such as oil and gas exploitation releases crustal helium, which has excess 4He compared to atmospheric helium. This may give rise to both spatial and temporal variations in the atmospheric 3He/4He. Helium is present in trace quantities in the air (5 ppm) and has a very low ratio (3He/4Heair = 1.38 x 10-6), consequently high precision measurements of atmospheric He presents a significant analytical challenge. Recent work by Sano et al. [1] has endeavored to experimentally quantify these potential variations in the atmospheric 3He/4He by measuring the helium isotopes from air samples collected around the globe and from samples of ancient trapped atmosphere. Their results indicate an increase in the atmospheric 3He/4He from northern to southern latitudes of the order 2 - 4 ‰, which they attribute to greater use of fossil fuels in the northern hemisphere. However, since most of their data points overlap at the 2-3 ‰ (2σ) level, additional measurements (with increased precision if possible) are needed. We have constructed an automated extraction line dedicated to measuring He in samples of air which can rapidly switch between measuring aliquots of sample with standards. It additionally features an adjustable bellows on the sample aliquot volume that enables us to adjust the size of a sample aliquot to precisely match the standard, eliminating biases arising from nonlinear pressure effects in the mass spectrometer. The measurements are made using a Helix SFT multi-collector mass spectrometer. At present, repeat measurements of 3He/4He from our standard (purified air) have a reproducibility of 2‰ (2σ), while measurements of local (Nancy, France) air samples have a reproducibility of 3He/4He of 3‰ (2σ), which are at a similar level to the uncertainties reported by Sano. Modifications are underway to improve 3He measurements which are the principal source of error. We have collected atmospheric samples from around the globe over a wide

  17. Investigations of levitated helium drops

    NASA Astrophysics Data System (ADS)

    Whitaker, Dwight Lawrence

    1999-11-01

    We report on the development of two systems capable of levitating drops of liquid helium. Helium drops of ˜20 mum have been levitated with the radiation pressure from two counter-propagating Nd:YAG laser beams. Drops are produced with a submerged piezoelectric transducer, and could be held for up to three minutes in our optical trap. Calculations show that Brillouin and Raman scattering of the laser light in the liquid helium produces a negligible rate of evaporation of the drop. Evaporation caused by the enhanced vapor pressure of the curved drop surfaces appears to be a significant effect limiting the drop lifetimes. Helium drops as large as 2 cm in diameter have been suspended in the earth's gravitational field with a magnetic field. A commercial superconducting solenoid provides the necessary field, field-gradient product required to levitate the drops. Drops are cooled to 0.5 K with a helium-3 refrigerator, and can be held in the trap indefinitely. We have found that when two or more drops are levitated in the same magnetic trap, the drops often remain in a state of apparent contact without coalescing. This effect is a result of the evaporation of liquid from between the two drops, and is found to occur only for normal fluid drops. We can induce shape oscillations in charged, levitated drops with an applied ac electric field. We have measured the resonance frequencies and damping rates for the l = 2 mode of oscillation as function of temperature. We have also developed a theory to describe the small amplitude shape oscillations of a He II drop surrounded by its saturated vapor. In our theory, we have considered two sets of boundary conditions---one where the drop does not evaporate and another in which the liquid and vapor are in thermodynamic equilibrium. We have found that both solutions give a frequency that agrees well with experiment, but that the data for the damping rate agree better with the solution without evaporation.

  18. Critical Landau velocity in helium nanodroplets.

    PubMed

    Brauer, Nils B; Smolarek, Szymon; Loginov, Evgeniy; Mateo, David; Hernando, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren J; Drabbels, Marcel

    2013-10-11

    The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecules embedded in helium nanodroplets of various sizes are accelerated out of the droplets by means of optical excitation, and the speed distributions of the ejected particles are determined. The measurements reveal the existence of a critical velocity in these systems, even for nanodroplets consisting of only a thousand helium atoms. Accompanying theoretical simulations based on a time-dependent density functional description of the helium confirm and further elucidate this experimental finding.

  19. On charged impurity structures in liquid helium

    NASA Astrophysics Data System (ADS)

    Pelmenev, A. A.; Krushinskaya, I. N.; Bykhalo, I. B.; Boltnev, R. E.

    2016-03-01

    The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warm-up of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium.

  20. 43 CFR 16.2 - Applications for helium disposition agreements.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 1 2014-10-01 2014-10-01 false Applications for helium disposition... HELIUM § 16.2 Applications for helium disposition agreements. The application for a helium disposition... Secretary to determine that the proposal will conserve helium that will otherwise be wasted, drained,...

  1. 43 CFR 16.2 - Applications for helium disposition agreements.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 1 2012-10-01 2011-10-01 true Applications for helium disposition... HELIUM § 16.2 Applications for helium disposition agreements. The application for a helium disposition... Secretary to determine that the proposal will conserve helium that will otherwise be wasted, drained,...

  2. 43 CFR 16.2 - Applications for helium disposition agreements.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 1 2013-10-01 2013-10-01 false Applications for helium disposition... HELIUM § 16.2 Applications for helium disposition agreements. The application for a helium disposition... Secretary to determine that the proposal will conserve helium that will otherwise be wasted, drained,...

  3. 43 CFR 16.2 - Applications for helium disposition agreements.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Applications for helium disposition... HELIUM § 16.2 Applications for helium disposition agreements. The application for a helium disposition... Secretary to determine that the proposal will conserve helium that will otherwise be wasted, drained,...

  4. 43 CFR 16.2 - Applications for helium disposition agreements.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 1 2011-10-01 2011-10-01 false Applications for helium disposition... HELIUM § 16.2 Applications for helium disposition agreements. The application for a helium disposition... Secretary to determine that the proposal will conserve helium that will otherwise be wasted, drained,...

  5. Energy, helium, and the future: II

    SciTech Connect

    Krupka, M.C.; Hammel, E.F.

    1980-01-01

    The importance of helium as a critical resource material has been recognized specifically by the scientific community and more generally by the 1960 Congressional mandate to institute a long-range conservation program. A major study mandated by the Energy Reorganization Act of 1974 resulted in the publication in 1975 of the document, The Energy-Related Applications of Helium, ERDA-13. This document contained a comprehensive review and analysis relating to helium resources and present and future supply/demand relationships with particular emphasis upon those helium-dependent energy-related technologies projected to be implemented in the post-2000 year time period, e.g., fusion. An updated overview of the helium situation as it exists today is presented. Since publication of ERDA-13, important changes in the data base underlying that document have occurred. The data have since been reexamined, revised, and new information included. Potential supplies of helium from both conventional and unconventional natural gas resources, projected supply/demand relationships to the year 2030 based upon a given power-generation scenario, projected helium demand for specific energy-related technologies, and the supply options (national and international) available to meet that demand are discussed. An updated review will be given of the energy requirements for the extraction of helium from natural gas as they relate to the concentration of helium. A discussion is given concerning the technical and economic feasibility of several methods available both now and conceptually possible, to extract helium from helium-lean natural gas, the atmosphere, and outer space. Finally, a brief review is given of the 1980 Congressional activities with respect to the introduction and possible passage of new helium conservation legislation.

  6. Helium isotopic abundance variation in nature

    SciTech Connect

    Holden, N.E.

    1993-08-01

    The isotopic abundance of helium in nature has been reviewed. This atomic weight value is based on the value of helium in the atmosphere, which is invariant around the world and up to a distance of 100,000 feet. Helium does vary in natural gas, volcanic rocks and gases, ocean floor sediments, waters of various types and in radioactive minerals and ores due to {alpha} particle decay of radioactive nuclides.

  7. Radioactive transitions in the helium isoelectronic sequence

    NASA Technical Reports Server (NTRS)

    Dalgarno, A.

    1971-01-01

    The principles of the atomic spectrum theory are used to quantitatively analyze radiation transitions in two-electron helium-like atomic systems. Quantum theoretical methods, describing absorption and emission of a single photon in a radiative transition between two stationary states of an atomic system, reproduced the energy level diagram for the low lying states of helium. Reliable values are obtained from accurate variationally determined two-electron nonrelativistic wave functions for radiative transition probabilities of 2 3p states in the helium isoelectric sequence, and for the 2 1s and 2 3s1 states of the helium sequence.

  8. Helium transport studies on DIII-D

    SciTech Connect

    Finkenthal, D.F.; Hillis, D.L.; Wade, M.R.; Hogan, J.T.; Klepper, C.C.; Mioduszewski, P.K.; West, W.P.; Burrell, K.H.; Seraydarian, R.P.; Groebner, R.J.; Gohil, P.

    1992-05-01

    The measurement of Helium density profiles in tokamak plasmas is necessary for helium transport studies. These studies are important in predicting the helium ash transport properties for ITER and win have important implications for the design. Poor helium transport in reactors could lead to a buildup of fusion ash, causing fuel dilution and increased radiation that will result in degraded fusion power and possibly quench ignition altogether. Present estimates indicate that He concentrations in the core must be kept below 10% in order to maintain continuous reactor operation. Helium transport studies have begun on the DM-D tokamak using charge exchange recombination (CER) spectroscopy for helium density measurements. Helium transport behavior has been observed by injecting helium gas puffs into DM-D plasmas and measuring the He density profile evolution. The profiles are used to calculate the relevant helium transport properties. This paper covers the results obtained from puffing He gas into L-mode plasmas of various electron densities. The results obtained in DIII-D L-mode plasmas are similar to measurements made at TEXTOR and JT-60.

  9. Helium-3 emission related to volcanic activity

    SciTech Connect

    Sano, Y.; Nakamura, Y.; Wakita, H.; Urabe, A.; Tominaga, T.

    1984-04-13

    The helium-3/helium-4 ratio in bubbling gases from ten hot springs located around Mount Ontake, an active volcano in central Japan, ranges from 1.71 R/sub atm/ (1.71 times the atmospheric ratio of 1.40 x 10/sup -6/) to 6.15 R/sub atm/. The value of the ratio decreases with distance from the central cone of the volcano. Such a tendency may be a characteristic of helium-3 emission in volcanic areas and suggests more primitive helium-3 is carried with fluid flowing through a conduit during volcanic activity. 6 references, 1 figure, 1 table.

  10. Helium, Iron and Electron Particle Transport and Energy Transport Studies on the TFTR Tokamak

    DOE R&D Accomplishments Database

    Synakowski, E. J.; Efthimion, P. C.; Rewoldt, G.; Stratton, B. C.; Tang, W. M.; Grek, B.; Hill, K. W.; Hulse, R. A.; Johnson, D .W.; Mansfield, D. K.; McCune, D.; Mikkelsen, D. R.; Park, H. K.; Ramsey, A. T.; Redi, M. H.; Scott, S. D.; Taylor, G.; Timberlake, J.; Zarnstorff, M. C. (Princeton Univ., NJ (United States). Plasma Physics Lab.); Kissick, M. W. (Wisconsin Univ., Madison, WI (United States))

    1993-03-01

    Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.

  11. Optical and mechanical properties of electron bubbles in superfluid helium-4

    SciTech Connect

    Xie, Z.; Wei, W.; Yang, Y.; Maris, H. J.

    2014-12-15

    A series of experiments has revealed the existence of a large number (about 18) of different types of negative ions in superfluid helium-4. Despite much effort, the physical nature of these “exotic ions” has still not been determined. We discuss possible experiments which may be able to help determine the structure of these objects.

  12. Helium, iron and electron particle transport and energy transport studies on the TFTR tokamak

    SciTech Connect

    Synakowski, E.J.; Efthimion, P.C.; Rewoldt, G.; Stratton, B.C.; Tang, W.M.; Grek, B.; Hill, K.W.; Hulse, R.A.; Johnson, D.W.; Mansfield, D.K.; McCune, D.; Mikkelsen, D.R.; Park, H.K.; Ramsey, A.T.; Redi, M.H.; Scott, S.D.; Taylor, G.; Timberlake, J.; Zarnstorff, M.C.; Kissick, M.W.

    1993-03-01

    Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.

  13. 43 CFR 3195.35 - What happens if I have an outstanding obligation to purchase refined helium under a Helium...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... obligation to purchase refined helium under a Helium Distribution Contract? 3195.35 Section 3195.35 Public... OF THE INTERIOR MINERALS MANAGEMENT (3000) HELIUM CONTRACTS Federal Helium Supplier Requirements § 3195.35 What happens if I have an outstanding obligation to purchase refined helium under a...

  14. 43 CFR 3195.35 - What happens if I have an outstanding obligation to purchase refined helium under a Helium...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... obligation to purchase refined helium under a Helium Distribution Contract? 3195.35 Section 3195.35 Public... OF THE INTERIOR MINERALS MANAGEMENT (3000) HELIUM CONTRACTS Federal Helium Supplier Requirements § 3195.35 What happens if I have an outstanding obligation to purchase refined helium under a...

  15. 43 CFR 3195.35 - What happens if I have an outstanding obligation to purchase refined helium under a Helium...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... obligation to purchase refined helium under a Helium Distribution Contract? 3195.35 Section 3195.35 Public... OF THE INTERIOR MINERALS MANAGEMENT (3000) HELIUM CONTRACTS Federal Helium Supplier Requirements § 3195.35 What happens if I have an outstanding obligation to purchase refined helium under a...

  16. 43 CFR 3195.35 - What happens if I have an outstanding obligation to purchase refined helium under a Helium...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... obligation to purchase refined helium under a Helium Distribution Contract? 3195.35 Section 3195.35 Public... OF THE INTERIOR MINERALS MANAGEMENT (3000) HELIUM CONTRACTS Federal Helium Supplier Requirements § 3195.35 What happens if I have an outstanding obligation to purchase refined helium under a...

  17. 43 CFR 3195.20 - Who must purchase major helium requirements from Federal helium suppliers?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Who must purchase major helium requirements from Federal helium suppliers? 3195.20 Section 3195.20 Public Lands: Interior Regulations Relating... (3000) HELIUM CONTRACTS Federal Agency Requirements § 3195.20 Who must purchase major...

  18. 43 CFR 3195.20 - Who must purchase major helium requirements from Federal helium suppliers?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Who must purchase major helium requirements from Federal helium suppliers? 3195.20 Section 3195.20 Public Lands: Interior Regulations Relating... (3000) HELIUM CONTRACTS Federal Agency Requirements § 3195.20 Who must purchase major...

  19. 43 CFR 3195.20 - Who must purchase major helium requirements from Federal helium suppliers?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Who must purchase major helium requirements from Federal helium suppliers? 3195.20 Section 3195.20 Public Lands: Interior Regulations Relating... (3000) HELIUM CONTRACTS Federal Agency Requirements § 3195.20 Who must purchase major...

  20. 43 CFR 3195.20 - Who must purchase major helium requirements from Federal helium suppliers?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Who must purchase major helium requirements from Federal helium suppliers? 3195.20 Section 3195.20 Public Lands: Interior Regulations Relating... (3000) HELIUM CONTRACTS Federal Agency Requirements § 3195.20 Who must purchase major...

  1. Mass separation of deuterium and helium with conventional quadrupole mass spectrometer by using varied ionization energy

    NASA Astrophysics Data System (ADS)

    Yu, Yaowei; Hu, Jiansheng; Wan, Zhao; Wu, Jinhua; Wang, Houyin; Cao, Bin

    2016-03-01

    Deuterium pressure in deuterium-helium mixture gas is successfully measured by a common quadrupole mass spectrometer (model: RGA200) with a resolution of ˜0.5 atomic mass unit (AMU), by using varied ionization energy together with new developed software and dedicated calibration for RGA200. The new software is developed by using MATLAB with the new functions: electron energy (EE) scanning, deuterium partial pressure measurement, and automatic data saving. RGA200 with new software is calibrated in pure deuterium and pure helium 1.0 × 10-6-5.0 × 10-2 Pa, and the relation between pressure and ion current of AMU4 under EE = 25 eV and EE = 70 eV is obtained. From the calibration result and RGA200 scanning with varied ionization energy in deuterium and helium mixture gas, both deuterium partial pressures (PD2) and helium partial pressure (PHe) could be obtained. The result shows that deuterium partial pressure could be measured if PD2 > 10-6 Pa (limited by ultimate pressure of calibration vessel), and helium pressure could be measured only if PHe/PD2 > 0.45, and the measurement error is evaluated as 15%. This method is successfully employed in EAST 2015 summer campaign to monitor deuterium outgassing/desorption during helium discharge cleaning.

  2. Adsorption of helium on isolated C60 and C70 anions

    NASA Astrophysics Data System (ADS)

    Harnisch, Martina; Weinberger, Nikolaus; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2015-08-01

    Adsorption of helium on free, negatively charged fullerenes is studied in this work. Helium nanodroplets have been doped with fullerenes and ionised by electron attachment. For suitable experimental conditions, C-60 and C-70 anions are found to be complexed with a large number of helium atoms. Prominent anomalies in the ion abundances indicate the high stability of the commensurate 1×1 phase in which all hollow adsorption sites are occupied by one atom each. The adsorption energy for an additional helium atom is about 40% less than for atoms in the commensurate layer, similar to our previous findings for fullerene cations and in agreement with theoretical dissociation energies. Similarly, an anomaly in the adsorption energy occurs when 60 helium atoms are attached to C-60 or 65 to C-70. For C60, the anomaly coincides with the one observed for cationic complexes but for C70 it does not. Implications of these features are discussed in light of several theoretical studies of neutral and positively charged helium-fullerene complexes.

  3. Mass separation of deuterium and helium with conventional quadrupole mass spectrometer by using varied ionization energy.

    PubMed

    Yu, Yaowei; Hu, Jiansheng; Wan, Zhao; Wu, Jinhua; Wang, Houyin; Cao, Bin

    2016-03-01

    Deuterium pressure in deuterium-helium mixture gas is successfully measured by a common quadrupole mass spectrometer (model: RGA200) with a resolution of ∼0.5 atomic mass unit (AMU), by using varied ionization energy together with new developed software and dedicated calibration for RGA200. The new software is developed by using MATLAB with the new functions: electron energy (EE) scanning, deuterium partial pressure measurement, and automatic data saving. RGA200 with new software is calibrated in pure deuterium and pure helium 1.0 × 10(-6)-5.0 × 10(-2) Pa, and the relation between pressure and ion current of AMU4 under EE = 25 eV and EE = 70 eV is obtained. From the calibration result and RGA200 scanning with varied ionization energy in deuterium and helium mixture gas, both deuterium partial pressures (P(D2)) and helium partial pressure (P(He)) could be obtained. The result shows that deuterium partial pressure could be measured if P(D2) > 10(-6) Pa (limited by ultimate pressure of calibration vessel), and helium pressure could be measured only if P(He)/P(D2) > 0.45, and the measurement error is evaluated as 15%. This method is successfully employed in EAST 2015 summer campaign to monitor deuterium outgassing/desorption during helium discharge cleaning.

  4. Explosive Hydrogen and Helium Burning in Astrophysical Events.

    NASA Astrophysics Data System (ADS)

    Wallace, Richard Kent

    The nuclear energy generation and nucleosynthesis that occur in hydrogen-rich compositions at temperatures substantially greater than 10('8) K are examined in detail. At these high temperatures, a new kind of nucleosynthetic process (the "rp-process") involving the rapid capture of protons on seed nuclei (or on the products of helium burning in a situation with zero initial metallicity) can lead to the production of heavy elements up to and beyond the iron group with an accompanying energy generation rate greatly modified from that of the (beta)-limited CNO cycle customarily employed in such calculations. New nuclear reaction rates of interest are tabulated, and reaction network calculations are presented to illustrate the application of this process to exploding supermassive stars, accreting neutron stars, novae, and certain chaotic cosmologies. Implications for (gamma)-line astronomy and x-ray burst models are discussed. To further explore the importance of thermonuclear instabilities for accreting neutron stars, the evolution of a 1.41 M(,(CIRCLE)) neutron star accreting both solar and metal-deficient mixtures of hydrogen, helium, and heavy elements at rates ranging from about 10('-11) to 10('-10) M(,(CIRCLE)) per year is examined using a one-dimensional numerical model. The metal deficient compositions may result either from placement of the neutron star in a binary system with a Population II Red Giant or from gravitational settling of heavy ions in the accreted material. For such accretion rates and metallicities, hydrogen burning, mediated by the (beta)-limited CNO cycle, is stable and leads to the accumulation of a thick helium layer with mass 10('23) to 10('25) g and temperature 0.7 (LESSTHEQ) T(,8) (LESSTHEQ) 1.2. Helium ignition occurs under extremely degenerate circumstances and is catastrophically violent. In the lower mass helium shells this runaway is propagated as a convective deflagration; for the thicker layers a detonation front is set up which

  5. Superfluid Helium Tanker (SFHT) study

    NASA Technical Reports Server (NTRS)

    1988-01-01

    The accomplishments and recommendations of the two-phase Superfluid Helium Tanker (SFHT) study are presented. During the first phase of the study, the emphasis was on defining a comprehensive set of user requirements, establishing SFHT interface parameters and design requirements, and selecting a fluid subsystem design concept. During the second phase, an overall system design concept was constructed based on appropriate analyses and more detailed definition of requirements. Modifications needed to extend the baseline for use with cryogens other than SFHT have been determined, and technology development needs related to the recommended design have been assessed.

  6. Helium in Earth's Early Core

    NASA Astrophysics Data System (ADS)

    Jephcoat, A. P.; Bouhifd, M. A.; Heber, V.; Kelley, S. P.

    2006-12-01

    The high 3He/4He ratios for some ocean-island basalts, and more recent observations for solar components of the other rare gases (Ne, Ar and possibly Xe), continue to raise questions on primordial source reservoirs as well as on accretionary and incorporation processes of rare gases. A number of geochemical mantle models have been made to explain the observed 3He/4He ratios, the most popular of which has been an undegassed primordial reservoir. Isotope systematics of other radiogenic elements do not support such an isolated source and changes in the accepted models of mantle convection style have made it harder to rely on the deep mantle as a reservoir. The core has remained a particularly unfavourable location either because of difficulty in constructing a retention mechanism during planetary accretion or simply because of a lack of data: Partitioning studies at pressure are rare and complicated by the difficulty in reproducing not only absolute concentrations, but confinement of gas in high-pressure apparatus and post-run analysis. We present experiments on helium solubility and partitioning between molten silicates and Fe-rich metal liquids up to 16 GPa and 3000 K, with the laser-heated diamond-anvil cell, and the quenched run products analysed by ultra-violet laser ablation mass spectrometry (UVLAMP). Our results indicate a significantly higher partition coefficient for He between molten silicates and Fe-rich alloy liquids of about 10-2 at 16 GPa and 3000~K -- two orders of magnitude more helium is measured in the metal phase compared to the only previous data of Matsuda et al., (1993). The solubility mechanism is varied and involves a distinguishable bulk component and an apparent surface signature (that may be the result of the quench process). Whether surface effects are included or not, the early Earth's core would have incorporated non-negligible amounts of primordial helium if its segregation took place under mid-depth, magma-ocean conditions. The process

  7. Helium bubble bursting in tungsten

    SciTech Connect

    Sefta, Faiza; Juslin, Niklas; Wirth, Brian D.

    2013-12-28

    Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom “islands,” craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz.

  8. Crystal orientation effects on implantation of low-energy hydrogen, helium and hydrogen/helium mixtures in plasma-facing tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Linn, Brian C.

    The development of plasma-facing materials (PFM) is one of the major challenges in. realizing fusion reactors. Materials deployed in PFMs must be capable of withstanding the high-flux of low-energy hydrogen and helium ions omitted from the plasma. while not hindering the plasma. Tungsten is considered a promising candidate material due to desirable material properties including its high melting temperature, good thermal conductivity and relatively low physical and chemical sputtering yields. This thesis uses molecular dynamic simulations to investigate helium and hydrogen bombardment of tungsten and the underlying physical effects (e.g. sputtering, erosion, blistering). Non-cumulative and cumulative bombardment simulations of helium, hydrogen, and hydrogen/helium bombardment of tungsten were modeled using the molecular dynamics code LAMMPS. Two orientations of monocrystalline bcc tungsten surfaces were considered, (001) and (111). Simulations were performed for temperatures ranging from 600K up to 1500K and helium / hydrogen incident energies of 20eV to 100eV . The results of these simulations showed the effect of temperature and incident particle energy on retention rates and implantation/deposition profiles in tungsten.

  9. Elusive structure of helium trimers

    NASA Astrophysics Data System (ADS)

    Stipanović, Petar; Vranješ Markić, Leandra; Boronat, Jordi

    2016-09-01

    Over the years many He–He interaction potentials have been developed, some very sophisticated, including various corrections beyond the Born–Oppenheimer approximation. Most of them were used to predict properties of helium dimers and trimers, examples of exotic quantum states, whose experimental study proved to be very challenging. Recently, detailed structural properties of helium trimers were measured for the first time, allowing a comparison with theoretical predictions and possibly enabling the evaluation of different interaction potentials. The comparisons already made included adjusting the maxima of both theoretical and experimental correlation functions to one, so the overall agreement between theory and experiment appeared satisfactory. However, no attempt was made to evaluate the quality of the interaction potentials used in the calculations. In this work, we calculate the experimentally measured correlation functions using both new and old potentials, compare them with experimental data and rank the potentials. We use diffusion Monte Carlo simulations at T = 0, which give within statistical noise exact results of the ground state properties. All models predict both trimers 4He3 and 4He{}2{}3He to be in a quantum halo state.

  10. Elusive structure of helium trimers

    NASA Astrophysics Data System (ADS)

    Stipanović, Petar; Vranješ Markić, Leandra; Boronat, Jordi

    2016-09-01

    Over the years many He-He interaction potentials have been developed, some very sophisticated, including various corrections beyond the Born-Oppenheimer approximation. Most of them were used to predict properties of helium dimers and trimers, examples of exotic quantum states, whose experimental study proved to be very challenging. Recently, detailed structural properties of helium trimers were measured for the first time, allowing a comparison with theoretical predictions and possibly enabling the evaluation of different interaction potentials. The comparisons already made included adjusting the maxima of both theoretical and experimental correlation functions to one, so the overall agreement between theory and experiment appeared satisfactory. However, no attempt was made to evaluate the quality of the interaction potentials used in the calculations. In this work, we calculate the experimentally measured correlation functions using both new and old potentials, compare them with experimental data and rank the potentials. We use diffusion Monte Carlo simulations at T = 0, which give within statistical noise exact results of the ground state properties. All models predict both trimers 4He3 and 4He{}2{}3He to be in a quantum halo state.

  11. Helium-flow measurement using ultrasonic technique

    NASA Astrophysics Data System (ADS)

    Sondericker, J. H.

    1983-08-01

    The ideal cryogenic instrumentation for the colliding beam accelerator helium distribution system does not add pressure drop to the system, functions over the entire temperature range, has high resolution, and delivers accurate mass flow measurement data. The design and testing of an ultrasonic flowmeter which measures helium flow under different temperatures are described.

  12. Detection of Hydrogen and Helium with EPHIN

    NASA Astrophysics Data System (ADS)

    Gómez-Herrero, R.; Rodríguez-Frías, M. D.; del Peral, L.; Sequeiros, J.; Müller-Mellin, R.; Kunow, H.; Sierks, H.

    2001-08-01

    A Monte Carlo simulation code based on GEANT 3.21 has been used to follow the SOHO (Solar and Heliospheric Observatory)/EPHIN (Electron, Proton and Helium Instrument) response to the detection of hydrogen and helium nuclei. The geometrical factor dependence on the energy has been evaluated and the contamination of the EPHIN channels has been obtained.

  13. Stability of Helium Clusters during Displacement Cascades

    SciTech Connect

    Yang, Li; Zu, Xiaotao T.; Xiao, H. Y.; Gao, Fei; Heinisch, Howard L.; Kurtz, Richard J.; Wang, Zhiguo; Liu, K. Z.

    2007-02-01

    The interaction of displacement cascades with helium-vacancy clusters is investigated using molecular dynamics simulations. The He-vacancy clusters initially consist of 20 vacancies with a Helium-to-vacancy ratio ranging from 0.2 to 3. The primary knock-on atom (PKA) energy, Ep, varies from 2 keV to 10 keV, and the PKA direction is chosen such that a displacement cascade is able to directly interact with a helium-vacancy cluster. The simulation results show that the effect of displacement cascades on a helium-vacancy cluster strongly depends on both the helium-to-vacancy ratio and the PKA energy. For the same PKA energy, the size of helium-vacancy clusters increases with the He/V ratio, but for the same ratio, the cluster size changes more significantly with increasing PKA energy. It has been observed that the He-vacancy clusters can be dissolved when the He/V ratio less than 1, but they are able to re-nucleate during the thermal spike phase, forming small He-V nuclei. When the He/V ratio is larger than 1, the He-V clusters can absorb a number of vacancies produced by displacement cascades, forming larger He-V clusters. These results are discussed in terms of PKA energy, helium-to-vacancy ratio, number of vacancies produced by cascades, and mobility of helium atoms.

  14. LOX Tank Helium Removal for Propellant Scavenging

    NASA Technical Reports Server (NTRS)

    Chato, David J.

    2009-01-01

    System studies have shown a significant advantage to reusing the hydrogen and oxygen left in these tanks after landing on the Moon in fuel cells to generate power and water for surface systems. However in the current lander concepts, the helium used to pressurize the oxygen tank can substantially degrade fuel cell power and water output by covering the reacting surface with inert gas. This presentation documents an experimental investigation of methods to remove the helium pressurant while minimizing the amount of the oxygen lost. This investigation demonstrated that significant quantities of Helium (greater than 90% mole fraction) remain in the tank after draining. Although a single vent cycle reduced the helium quantity, large amounts of helium remained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient to reduce the helium to small (less than 0.2%) quantities. Two vent cycles may be sufficient since once the tank has been brought up to pressure after the second vent cycle the helium concentration has been reduced to the less than 0.2% level. The re-pressurization process seemed to contribute to diluting helium. This is as expected since in order to raise the pressure liquid oxygen must be evaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third vent cycle is not required).

  15. Helium Speech: An Application of Standing Waves

    ERIC Educational Resources Information Center

    Wentworth, Christopher D.

    2011-01-01

    Taking a breath of helium gas and then speaking or singing to the class is a favorite demonstration for an introductory physics course, as it usually elicits appreciative laughter, which serves to energize the class session. Students will usually report that the helium speech "raises the frequency" of the voice. A more accurate description of the…

  16. 30 CFR 256.11 - Helium.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... of and the right to extract helium from all gas produced from the leased area. (b) In case the United... helium extracted. The United States shall determine the amount of reasonable compensation. The United... substantial delays in the delivery of natural gas produced to the purchaser of that gas....

  17. 30 CFR 256.11 - Helium.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... the United States, under section 12(f) of the Act, of the ownership of and the right to extract helium... other loss for which he is not reasonably compensated, except for the value of the helium extracted. The... delivery of natural gas produced to the purchaser of that gas....

  18. Paramagnetic Attraction of Impurity-Helium Solids

    NASA Technical Reports Server (NTRS)

    Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

    2003-01-01

    Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

  19. Helium, Carbon, and Helium Isotopes in the Northern Lau Basin

    NASA Astrophysics Data System (ADS)

    Lupton, J. E.; Butterfield, D. A.; Lilley, M. D.; Resing, J.; Embley, R. W.; Arculus, R. J.; Rubin, K. H.; Evans, L.; Greene, R.

    2009-12-01

    Helium isotope ratios in hydrothermal fluids and volcanic rocks in the northern Lau Basin show a complex pattern reflecting influences from diverse mantle sources, including the Samoan hotspot, the Tofua Arc, and mid-ocean ridge (MOR)-type upper mantle. The Samoan Islands represent a “high 3He” hotspot with 3He/4He ratios up to 38 Ra (where Ra is the 3He/4He ratio in air, 1.39 x 10-6) [Farley et al, 1992; Jackson et al., 2007]. In contrast to the 3He-rich helium in Samoa, typical back-arc spreading centers have MOR-type helium values of 7-9 Ra, while volcanic arcs have lower ratios of 5-7 Ra. In the northwestern part of the Lau Basin, basalt samples from the Northwest Lau Spreading Center and the Rochambeau Rifts have 3He/4He varying from 11 to 28 Ra, far above typical back-arc or MOR values. These elevated 3He/4He ratios indicate that the Samoan hotspot signal has somehow penetrated southward into the northern Lau Basin, presumably through a tear in the subducting Pacific Plate. In the northeastern Lau Basin, 3He/4He ratios in hydrothermal fluids from two sites on the Northeast Lau Spreading Center have 3He/4He of 8.0 and 8.7 Ra. These are MOR-type values typical for a back-arc spreading center. At the actively erupting West Mata volcano, vent fluids have 3He/4He of 7.3 Ra, while farther east at Volcano P analysis of water-column plume samples gave a value of 6.7 Ra for the estimated end-member 3He/4He value. This decrease in 3He/4He going toward the east indicates increasing arc influence with increasing proximity to the Tofua Arc. This interpretation is supported by the C/3He ratios in the hydrothermal fluids, which average 1-3 x 109 at vent sites on the NELSC (typical MOR values) and increase to a typical arc value of 2 x 1010 at West Mata. Analyses of volcanic rocks from the eruption sites on the NELSC and West Mata are in progress and should help to further define these variations.

  20. Gemini helium closed cycle cooling system

    NASA Astrophysics Data System (ADS)

    Lazo, Manuel; Galvez, Ramon; Rogers, Rolando; Solis, Hernan; Tapia, Eduardo; Maltes, Diego; Collins, Paul; White, John; Cavedoni, Chas; Yamasaki, Chris; Sheehan, Michael P.; Walls, Brian

    2008-07-01

    The Gemini Observatory presents the Helium Closed Cycle Cooling System that provides cooling capacity at cryogenic temperatures for instruments and detectors. It is implemented by running three independent helium closed cycle cooling circuits with several banks of compressors in parallel to continuously supply high purity helium gas to cryocoolers located about 100-120 meters apart. This poster describes how the system has been implemented, the required helium pressures and gas flow to reach cryogenic temperature, the performance it has achieved, the helium compressors and cryocoolers in use and the level of vibration the cryocoolers produce in the telescope environment. The poster also describes the new technology for cryocoolers that Gemini is considering in the development of new instruments.

  1. An efficient cooling loop for connecting cryocooler to a helium reservoir

    SciTech Connect

    Taylor, C.E.; Abbott, C.S.R.; Leitner, D.; Leitner, M.; Lyneis, C.M.

    2003-09-21

    The magnet system of the VENUS ECR Ion Source at LBNL has two 1.5-watt cryocoolers suspended in the cryostat vacuum. Helium vapor from the liquid reservoir is admitted to a finned condenser bolted to the cryocooler 2nd stage and returns as liquid via gravity. Small-diameter flexible tubes allow the cryocoolers to be located remotely from the reservoir. With 3.1 watts load, the helium reservoir is maintained at 4.35 K, 0.05K above the cryocooler temperature. Design, analysis, and performance are presented.

  2. Thermodynamics and phase separation of dense fully-ionized hydrogen-helium fluid mixtures

    NASA Technical Reports Server (NTRS)

    Stevenson, D. J.

    1975-01-01

    The free energy of a hydrogen-helium fluid mixture is evaluated for the temperatures and densities appropriate to the deep interior of a giant planet such as Jupiter. The electrons are assumed to be fully pressure-ionized and degenerate. In this regime, an appropriate first approximation to the ionic distribution functions can be found by assuming hard sphere interactions. Corrections to this approximation are incorporated by means of the perturbation theory of Anderson and Chandler. Approximations for the three-body interactions and the nonlinear response of the electron gas to the ions are included. It is predicted that a hydrogen-helium mixture, containing 10% by number of helium ions, separates into hydrogen-rich and helium-rich phases below about 8000 K, at the pressures relevant to Jupiter (4-40 Megabars). It is also predicted that the alloy occupies less volume per ion than the separated phases. The equations of state and other thermodynamic derivatives are tabulated. Implications of these results are discussed.

  3. On the stability of cationic complexes of neon with helium--solving an experimental discrepancy.

    PubMed

    Bartl, Peter; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2013-10-21

    Helium nanodroplets are doped with neon and ionized by electrons. The size-dependence of the ion abundance of HenNex(+), identified in high-resolution mass spectra, is deduced for complexes containing up to seven neon atoms and dozens of helium atoms. Particularly stable ions are inferred from anomalies in the abundance distributions. Two pronounced anomalies at n = 11 and 13 in the HenNe(+) series confirm drift-tube data reported by Kojima et al. [T. M. Kojima et al., Z. Phys. D, 1992, 22, 645]. The discrepancy with previously published spectra of neon-doped helium droplets, which did not reveal any abundance anomalies [T. Ruchti et al., J. Chem. Phys., 1998, 109, 10679-10687; C. A. Brindle et al., J. Chem. Phys., 2005, 123, 064312], is most likely due to limited mass resolution, which precluded unambiguous analysis of contributions from different ions with identical nominal mass. However, calculated dissociation energies of HenNe(+) reported so far do not correlate with the present data, possibly because of challenges in correctly treating the linear, asymmetric [He-Ne-He](+) ionic core in HenNe(+). Anomalies identified in the distributions of HenNex(+) for x > 1, including prominent ones at He12Ne2(+) and He14Ne2(+), may help to better understand solvation of Ne(+) and Nex(+) in helium.

  4. Optical Forces on Metastable Helium

    NASA Astrophysics Data System (ADS)

    Corder, Christopher Scott

    Optical forces using lasers allow precise control over the motion of atoms. The bichromatic optical force (BF) is unique in its large magnitude and velocity range, arising from the absorption and stimulated emission processes. These properties were used to transversely collimate a beam of metastable helium (He*) using the 23S - 23P transition. The collimation created a very bright beam of He*, allowing experiments of neutral atom lithography. The He* beam was used to pattern material surfaces using a resist-based lithography technique, where the pattern was determined by either mechanical or optical masks. The optical masks produced features with a separation of half the wavelength of the light used. Patterning was successfully demonstrated with both IR and UV optical masks. The etched pattern resolution was ˜ 100 nm and limited by the material surface. Further experiments were performed studying the ability of the bichromatic force to cool. The finite velocity range of the BF allows estimation of a characteristic cooling time which is independent of the excited state lifetime, only depending on the atomic mass and optical transition energy. Past experiments, including the helium collimation used for neutral atom lithography, have demonstrated that the BF can collimate and longitudinally slow atomic beams, but required long interaction times that included many spontaneous emission (SE) events. The effect of SE can be mitigated, and is predicted to not be necessary for BF cooling. Since the BF cooling time is not related to the excited state lifetime, a transition can be chosen such that the cooling time is shorter than the SE cycle time, allowing direct laser cooling on atoms and molecules that do not have cycling transitions. Experiments using the helium 2 3S-3P transition were chosen because the BF cooling time (285 ns) is on the order of the average SE cycle time (260 ns). Numerical simulations of the experimental system were run predicting compression of the

  5. FINAL TECHNICAL REPORT FOR DE-FG02-05ER64097 Systems and Methods for Injecting Helium Beams into a Synchrotron Accelerator

    SciTech Connect

    Bush, David A

    2008-09-30

    A research grant was approved to fund development of requirements and concepts for extracting a helium-ion beam at the LLUMC proton accelerator facility, thus enabling the facility to better simulate the deep space environment via beams sufficient to study biological effects of accelerated helium ions in living tissues. A biologically meaningful helium-ion beam will be accomplished by implementing enhancements to increase the accelerator's maximum proton beam energy output from 250MeV to 300MeV. Additional benefits anticipated from the increased energy include the capability to compare possible benefits from helium-beam radiation treatment with proton-beam treatment, and to provide a platform for developing a future proton computed tomography imaging system.

  6. Electronic Structure of Helium Atom in a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.

    2016-03-01

    Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India

  7. Krypton and helium irradiation damage in neodymium-zirconolite

    NASA Astrophysics Data System (ADS)

    Gilbert, M.; Davoisne, C.; Stennett, M.; Hyatt, N.; Peng, N.; Jeynes, C.; Lee, W. E.

    2011-09-01

    A leading candidate for the immobilisation of actinides, zirconolite's suitability as a potential ceramic host for plutonium disposition, both in storage and geological disposal, has been the subject of much research. One key aim of this study is to understand the effects of radiation damage and noble gas accommodation within the zirconolite material. To this end, a series of ex situ irradiations have been performed on polycrystalline (Ca 0.8Nd 0.2)Zr(Ti 1.8Al 0.2)O 7 zirconolite samples. Zirconolite samples, doped with Nd 3+ (as a Pu surrogate) on the Ca-site and charge-balanced by substituting Al 3+ onto the Ti-site, were irradiated with 36Kr + (2 MeV) ions at fluences of 1 × 10 14 and 5 × 10 15 cm -2 and 4He + (200 keV) ions at fluences of 1 × 10 14, 5 × 10 15 and 1 × 10 17 cm -2 to simulate the impact of alpha decay on the microstructure. Microstructural analysis revealed no damage present at the lower Kr + fluence, but that the higher 36Kr + fluence rendered the zirconolite completely amorphous. Similarly, evidence of helium accumulation was only seen at the highest 4He + fluence (1 × 10 17 cm -2). Monte Carlo simulations using the TRIM code predict the highest concentration of helium accumulating at a depth of 720 nm, in good agreement with the experimental observations.

  8. Helium and neon abundances and compositions in cometary matter.

    PubMed

    Marty, Bernard; Palma, Russell L; Pepin, Robert O; Zimmermann, Laurent; Schlutter, Dennis J; Burnard, Peter G; Westphal, Andrew J; Snead, Christopher J; Bajt, Sasa; Becker, Richard H; Simones, Jacob E

    2008-01-01

    Materials trapped and preserved in comets date from the earliest history of the solar system. Particles captured by the Stardust spacecraft from comet 81P/Wild 2 are indisputable cometary matter available for laboratory study. Here we report measurements of noble gases in Stardust material. Neon isotope ratios are within the range observed in "phase Q," a ubiquitous, primitive organic carrier of noble gases in meteorites. Helium displays 3He/4He ratios twice those in phase Q and in Jupiter's atmosphere. Abundances per gram are surprisingly large, suggesting implantation by ion irradiation. The gases are probably carried in high-temperature igneous grains similar to particles found in other Stardust studies. Collectively, the evidence points to gas acquisition in a hot, high ion-flux nebular environment close to the young Sun.

  9. Helium and Neon Abundances and Compositions in Cometary Matter

    SciTech Connect

    Marty, B; Palma, R L; Pepin, R O; Zimmmermann, L; Schlutter, D J; Burnard, P G; Westphal, A J; Snead, C J; Bajt, S; Becker, R H; Simones, J E

    2007-10-15

    Materials trapped and preserved in comets date from the earliest history of the solar system. Particles captured by the Stardust spacecraft from comet Wild 2 are indisputable cometary matter available for laboratory study. Here they report measurements of noble gases in Stardust material. neon isotope ratios are within the range observed in 'phase Q', a ubiquitous, primitive organic carrier of noble gases in meteorites. Helium displays {sup 3}He/{sup 4}He ratios twice those in phase Q and in Jupiter's atmosphere. Abundances per gram are surprisingly large, suggesting implantation by ion irradiation. The gases are carried in high temperature igneous grains similar to particles found in other Stardust studies. Collectively the evidence points to gas acquisition in a hot, high ion flux nebular environment close to the young Sun.

  10. Helium Saturation of Liquid Propellants

    NASA Technical Reports Server (NTRS)

    Yavrouian, A. H.; Moran, Clifford M.

    1990-01-01

    The research is in three areas which are: (1) techniques were devised for achieving the required levels of helium (He) saturation in liquid propellants (limited to monomethylhydrazine (MMH) and nitrogen tetroxide (NTO)); (2) the values were evaluated for equilibrium solubilities of He in liquid propellants as currently used in the industry; and (3) the He dissolved in liquid propellants were accurately measured. Conclusions drawn from these studies include: (1) Techniques for dissolving He in liquid propellants depending upon the capabilities of the testing facility (Verification of the quantity of gas dissolved is essential); (2) Until greater accuracy is obtained, the equilibrium solubility values of He in MMH and NTO as cited in the Air Force Propellant Handbooks should be accepted as standard (There are still enough uncertainties in the He saturation values to warrant further basic experimental studies); and (3) The manometric measurement of gas volume from a frozen sample of propellant should be the accepted method for gas analysis.

  11. Atom lithography with metastable helium

    SciTech Connect

    Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold

    2010-02-15

    A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

  12. Analysis of the Effect of Time, Temperature, and Fuel Age on Helium Release from 238-Plutonium Dioxide Fuel

    NASA Astrophysics Data System (ADS)

    Barklay, Chadwick D.; Kramer, Daniel P.; Ruhkamp, Joseph D.

    2005-02-01

    The compound 238-plutonium dioxide has been employed over the last several decades as the fuel of choice in fabricating nuclear powered thermal to electrical converters. The alpha decay of 238-plutonium results in the generation of helium ions as a function of time. While the quantity of helium formed within the fuel can be easily calculated, its diffusion and/or release mechanism as a function of time, temperature, fuel quantity and age needs to be characterized. Within the scope of this paper the principle interest centers on determining the expected quantity of helium that will be released from solid 238-plutonium dioxide fuel forms enclosed within a primary containment vessel (PCV) under Hypothetical Accident Conditions (HAC) as described in 10 CFR 71.73(4). Once the quantity of helium released during HAC has been determined, the partial pressure increase due to the helium release can be calculated for a given shipping configuration. This partial pressure increase due to helium release during HAC for a selected shipping configuration can then be used to determine if the structural integrity of the package will be maintained or compromised during HAC. However, it is important to recognize that helium release is not a function of a particular shipping package, but as shall be demonstrated is a function of time, temperature, and fuel quantity and age.

  13. Analysis of the Effect of Time, Temperature, and Fuel Age on Helium Release from 238-Plutonium Dioxide Fuel

    SciTech Connect

    Barklay, Chadwick D.; Kramer, Daniel P.; Ruhkamp, Joseph D.

    2005-02-06

    The compound 238-plutonium dioxide has been employed over the last several decades as the fuel of choice in fabricating nuclear powered thermal to electrical converters. The alpha decay of 238-plutonium results in the generation of helium ions as a function of time. While the quantity of helium formed within the fuel can be easily calculated, its diffusion and/or release mechanism as a function of time, temperature, fuel quantity and age needs to be characterized. Within the scope of this paper the principle interest centers on determining the expected quantity of helium that will be released from solid 238-plutonium dioxide fuel forms enclosed within a primary containment vessel (PCV) under Hypothetical Accident Conditions (HAC) as described in 10 CFR 71.73(4). Once the quantity of helium released during HAC has been determined, the partial pressure increase due to the helium release can be calculated for a given shipping configuration. This partial pressure increase due to helium release during HAC for a selected shipping configuration can then be used to determine if the structural integrity of the package will be maintained or compromised during HAC. However, it is important to recognize that helium release is not a function of a particular shipping package, but as shall be demonstrated is a function of time, temperature, and fuel quantity and age.

  14. Weldability of helium-containing stainless steels using a YAG laser

    NASA Astrophysics Data System (ADS)

    Kawano, S.; Nakahigashi, S.; Uesugi, K.; Nakamura, H.; Kono, W.; Fukuya, K.; Kano, F.; Hasegawa, A.; Abe, K.

    1998-10-01

    Bead-on-plate welding experiments using a 400 W YAG laser were conducted on SUS304 stainless steels implanted with helium ions of 0.5, 5 and 50 appm uniformly to a depth of 0.25 mm. High heat input welding at 20 kJ/cm caused surface grain boundary cracking in the heat-affected zone at 50 appm He. Cross-sectional observations after etching in oxalic acid solution revealed that bubble growth at grain boundaries in the heat-affected zone was enhanced at higher heat input and at higher helium concentrations. Bubble growth was negligible for the laser welding condition of 1 kJ/cm even at 50 appm He. The results suggest that YAG laser welding is a promising welding technique for stainless steels containing high amounts of helium.

  15. Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets

    SciTech Connect

    Krasnokutski, Serge A.; Huisken, Friedrich

    2015-02-28

    Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al–He{sub n} vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (∼400 cm{sup −1}). However, using the same laser wavelength, we were unable to detect any Al{sub n} photoion with n larger than two.

  16. Rotational Action Spectroscopy via State-Selective Helium Attachment

    NASA Astrophysics Data System (ADS)

    Kluge, Lars; Stoffels, Alexander; Brünken, Sandra; Asvany, Oskar; Schlemmer, Stephan

    2015-06-01

    Helium atoms can attach to molecular cations via ternary collision processes forming weakly bound (≈ 1 kcal/mol) He-M^+ complexes. We developed a novel sensitive action spectroscopic scheme for molecular ions based on an observed rotational state dependency of the He attachment process [1]. A detailed account of the underlying kinetics will be presented on the example of the CD^+ ion, where our studies indicate a decrease of around 50% for the rotational state dependent ternary He attachment rate coefficient of the J=1 level with respect to the J=0 level. Experiments are performed on mass-selected ions stored in a temperature-variable (T≥ 3.9~K) cryogenic rf 22-pole ion trap in the presence of a high number density of He (≈ 1015 cm-3) [2]. Rotational spectra of the bare ions are recorded by measuring the change in the number of formed He-M^+ complexes after a certain storage time as a function of excitation wavelength. Here we will also present the first measurements of the rotational ground state transitions of CF^+ (J=1-0, hfs resolved) and NH_3D^+ (J_K=1_0-0_0), recorded in this way. [1] Brünken et al., ApJL 783, L4 (2014) [2] Asvany et al., Applied Physics B 114, 203 (2014)

  17. Helium-3 and diffuse Helium-4 emissions prior the 2014-15 Fogo eruption, Cape Verde

    NASA Astrophysics Data System (ADS)

    Asensio-Ramos, María; Padrón, Eleazar; Dionis, Samara; Sumino, Hirochika; Fernandes, Paulo; Melián, Gladys V.; Barrancos, José; Hernández, Pedro A.; Rodríguez, Fátima; Silva, Sónia; Pérez, Nemesio M.; Padilla, Germán; Bandomo, Zuleyka; Cabral, Jeremias; Calvo, David; Pereira, José Manuel; Semedo, Helio

    2015-04-01

    On November 23, 2014 a new volcanic eruption started at the southwestern flank of Pico do Fogo volcano (Fogo Island, Cape Verde) after 19 years of the last eruptive event. Helium-3 emission from fumarole discharges and diffuse helium-4 degassing studies have been carried out regularly at the summit crater of Pico do Fogo since May 2007 until March 2014. The first published data on helium isotopes and diffuse helium-4 degassing from Pico do Fogo volcano is related to the field work performed on February 2010 which shows already relatively high helium-3 emission, 8.53 ± 0.9 R/RA (being R and RA the sample and atmospheric 3He/4He isotope ratio, respectively), and diffuse helium-4 degassing rate, 4.2 ± 0.2 kg d-1 (Dionis et al., 2015). During the eight year period 2007-2014, helium-4 emission rate was measured yearly at 50 different sampling sites selected in the surface environment of the summit crater of Pico do Fogo (0.14 km2) following the Darcy's law, and assuming that helium-4 emission is mainly governed by convection. The distribution of the sampling sites was carefully chosen to homogeneously cover the target area, allowing the computation of the total helium-4 emission by sequential Gaussian simulation (sGs). In addition, helium-3 emission was measured in the fumarole gases following the method described by Sumino et al. (2001). During the eight year period, convective helium-4 emission ranged between 1.2 and 5.7 kg d-1, and helium-3 emission between 7.73 and 8.82 R/RA. Both helium-4 and helium-3 emission showed significant increases on February 2010, suggesting a potential magma intrusion into the volcanic system of Pico do Fogo. However, the highest observed values of both parameters were observed on November, 2013 (helium-3 emission) and on March 2014 (diffuse helium-4 emission) suggesting a second magma intrusion giving rise to the volcanic eruption on November 23, 2014. As was observed in other volcanic systems (Padrón et al., 2013), helium degassing

  18. Helium refrigeration considerations for cryomodule design

    SciTech Connect

    Ganni, V.; Knudsen, P.

    2014-01-29

    Many of the present day accelerators are based on superconducting radio frequency (SRF) cavities, packaged in cryo-modules (CM), which depend on helium refrigeration at sub-atmospheric pressures, nominally 2 K. These specialized helium refrigeration systems are quite cost intensive to produce and operate. Particularly as there is typically no work extraction below the 4.5-K supply, it is important that the exergy loss between this temperature level and the CM load temperature(s) be minimized by the process configuration choices. This paper will present, compare and discuss several possible helium distribution process arrangements to support the CM loads.

  19. Apparatus and method for determining the gas permeability and flux of helium through the materials and coatings

    NASA Astrophysics Data System (ADS)

    Barchenko, V. T.; Lisenkov, A. A.; Vinogradov, M. L.

    2014-11-01

    Apparatus and method for measuring flow of helium through the materials and coatings, obtained by ion-plasma technologies, are developed and tested. The apparatus for the measurement is designed on the basis of a helium leak detector TI1-14, produced by JSC "Zavod Izmeriter, that provides a minimum detectable flow of helium 7.10-13 Pa.m3/s. The purpose of the study is the creating apparatus and method to determine gas permeability and helium flux through new materials and coatings to create the hermetic devices with special properties. This devices are made from polymer coated with metals, and they should replace full metals device analogues in the field of aerospace engineering.

  20. The statistical equilibrium of hydrogen and helium in a radiation field, with an application to interpreting Wolf-Rayet spectra

    NASA Technical Reports Server (NTRS)

    Bhatia, A. K.; Underhill, A. B.

    1986-01-01

    The interpretation of the intensities of the hydrogen and helium emission lines in O and Wolf-Rayet spectra in terms of the abundance of hydrogen relative to helium requires information regarding the distribution of hydrogen and helium atoms and ions over their several energy states. In addition, some estimate is needed regarding the transmission of the radiation through the stellar mantle. The present paper provides new information concerning the population of the energy levels of hydrogen and helium when statistical equilibrium occurs in the presence of a radiation field. The results are applied to an interpretation of the spectra of four Wolf-Rayet stars, taking into account the implications for interpreting the spectra of O stars, OB supergiants, and Be stars.

  1. Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR

    NASA Astrophysics Data System (ADS)

    Schmitz, O.; Ida, K.; Kobayashi, M.; Bader, A.; Brezinsek, S.; Evans, T. E.; Funaba, H.; Goto, M.; Mitarai, O.; Morisaki, T.; Motojima, G.; Nakamura, Y.; Narushima, Y.; Nicolai, D.; Samm, U.; Tanaka, H.; Yamada, H.; Yoshinuma, M.; Xu, Y.; TEXTOR, the; LHD Experiment Groups

    2016-10-01

    The ability to exhaust helium as the fusion born plasma impurity is a critical requirement for burning plasmas. We demonstrate in this paper that resonant magnetic perturbation (RMP) fields can be used to actively manipulate helium exhaust characteristics. We present results from puff/pump studies at TEXTOR as example for a tokamak with a pumped limiter and from the Large Helical Device (LHD) with the closed helical divertor as example for a heliotron/stellarator device. For LHD, the effective helium confinement time τ p,\\text{He}\\ast is a factor of 7-8 higher in the low and high density regimes explored when compared to TEXTOR discharges. This is attributed to ion root impurity transport which is one particular impurity transport regime assessed experimentally at LHD and which facilitates helium penetration to the plasma core. However, when an edge magnetic island is induced by externally applied RMP fields, τ p,\\text{He}\\ast is decreased by up to 30% and hence τ p,\\text{He}\\ast values closer to those of TEXTOR can be established. The combination of TEXTOR and LHD results suggest that a magnetic island induced by the RMP field in the plasma source region is an important ingredient for improving helium exhaust. The reduction in τ p,\\text{He}\\ast seen is caused by a combination of improved helium exhaust due to an enhanced coupling to the pumping systems, increased outward transport and a reduced fueling efficiency for the helium injected and recycling from the wall elements.

  2. 21 CFR 868.1640 - Helium gas analyzer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Helium gas analyzer. 868.1640 Section 868.1640...) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Diagnostic Devices § 868.1640 Helium gas analyzer. (a) Identification. A helium gas analyzer is a device intended to measure the concentration of helium in a...

  3. 21 CFR 868.1640 - Helium gas analyzer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Helium gas analyzer. 868.1640 Section 868.1640...) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Diagnostic Devices § 868.1640 Helium gas analyzer. (a) Identification. A helium gas analyzer is a device intended to measure the concentration of helium in a...

  4. 21 CFR 868.1640 - Helium gas analyzer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Helium gas analyzer. 868.1640 Section 868.1640...) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Diagnostic Devices § 868.1640 Helium gas analyzer. (a) Identification. A helium gas analyzer is a device intended to measure the concentration of helium in a...

  5. 21 CFR 868.1640 - Helium gas analyzer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Helium gas analyzer. 868.1640 Section 868.1640...) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Diagnostic Devices § 868.1640 Helium gas analyzer. (a) Identification. A helium gas analyzer is a device intended to measure the concentration of helium in a...

  6. Observation of the antimatter helium-4 nucleus.

    PubMed

    2011-05-19

    High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high-energy accelerator of heavy nuclei provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (4He), also known as the anti-α (α), consists of two antiprotons and two antineutrons (baryon number B = -4). It has not been observed previously, although the α-particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent level. Antimatter nuclei with B < -1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by a factor of about 1,000 with each additional antinucleon. Here we report the observation of 4He, the heaviest observed antinucleus to date. In total, 18 4He counts were detected at the STAR experiment at the Relativistic Heavy Ion Collider (RHIC; ref. 6) in 10(9) recorded gold-on-gold (Au+Au) collisions at centre-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, providing an indication of the production rate of even heavier antimatter nuclei and a benchmark for possible future observations of 4He in cosmic radiation.

  7. Observation of the antimatter helium-4 nucleus.

    PubMed

    2011-05-19

    High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high-energy accelerator of heavy nuclei provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (4He), also known as the anti-α (α), consists of two antiprotons and two antineutrons (baryon number B = -4). It has not been observed previously, although the α-particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent level. Antimatter nuclei with B < -1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by a factor of about 1,000 with each additional antinucleon. Here we report the observation of 4He, the heaviest observed antinucleus to date. In total, 18 4He counts were detected at the STAR experiment at the Relativistic Heavy Ion Collider (RHIC; ref. 6) in 10(9) recorded gold-on-gold (Au+Au) collisions at centre-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, providing an indication of the production rate of even heavier antimatter nuclei and a benchmark for possible future observations of 4He in cosmic radiation. PMID:21516103

  8. Fractionated dose of 35-MEV fast neutrons and hypoxic tumor cell survival curve.

    PubMed

    U, R; Evans, J C; Cavanaugh, P J; Abramson, N; Thompson, T T; Wheless, D M

    1975-06-01

    The determination of the RBE for the MANTA fast neutrons produced by NRL is inprogress, with the model system using tumor cell population kinetic response patterns assayed in vitro after irradiation in vivo. Ascites tumor cells BW-5147 were irradiated with a clinically usable fast neutron beam from the NRL cyclotron, which is produced by accelrating deuterons to 35 MeV and using htem to bombard a thick berylliumtarget. The comparison of dose-effect relationships was made for doses ranging from30 to 1000 rads. The doses required for an isoeffect on BW-5147 hypoxic tumor cell survival and impairment of its reproductive capacity from fast neutron exposure were not different wheither it was given a single dose or the same dose given in three fractions separated by long recovery periods in situ. No intracellular repair of sublethal injury when the dose was given in three fractions, although the hypoxic BWp5147 tumor cells haveno effective reoxygenation or repopulation in this time interval. The RBE for the fast neutron beam is 4 relative to x rays for fractionated doses at the surviving fractionlevel of 0.6-0.7, while the RBE IS 2.5 FOR SINGLE DOSES. However, at a surviving fraction of 0.1, the RBE is 1.9 for single and 2.8 for fractionated doses. Analysis of thedaily cell population rate or mitotic delay between the two types of radiations at a similiar level of survival.

  9. Helium release and microstructural changes in Er(D,T)2-x3Hex films).

    SciTech Connect

    Gelles, D. S.; Browning, James Frederick; Snow, Clark Sheldon; Banks, James Clifford; Mangan, Michael A.; Rodriguez, Mark Andrew; Brewer, Luke N.; Kotula, Paul Gabriel

    2007-12-01

    Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface region and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.

  10. Non-equilibrium Helium Ionization in an MHD Simulation of the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Golding, Thomas Peter; Leenaarts, Jorrit; Carlsson, Mats

    2016-02-01

    The ionization state of the gas in the dynamic solar chromosphere can depart strongly from the instantaneous statistical equilibrium commonly assumed in numerical modeling. We improve on earlier simulations of the solar atmosphere that only included non-equilibrium hydrogen ionization by performing a 2D radiation-magnetohydrodynamics simulation featuring non-equilibrium ionization of both hydrogen and helium. The simulation includes the effect of hydrogen Lyα and the EUV radiation from the corona on the ionization and heating of the atmosphere. Details on code implementation are given. We obtain helium ion fractions that are far from their equilibrium values. Comparison with models with local thermodynamic equilibrium (LTE) ionization shows that non-equilibrium helium ionization leads to higher temperatures in wavefronts and lower temperatures in the gas between shocks. Assuming LTE ionization results in a thermostat-like behavior with matter accumulating around the temperatures where the LTE ionization fractions change rapidly. Comparison of DEM curves computed from our models shows that non-equilibrium ionization leads to more radiating material in the temperature range 11-18 kK, compared to models with LTE helium ionization. We conclude that non-equilibrium helium ionization is important for the dynamics and thermal structure of the upper chromosphere and transition region. It might also help resolve the problem that intensities of chromospheric lines computed from current models are smaller than those observed.

  11. Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

    NASA Astrophysics Data System (ADS)

    Changizian, P.; Zhang, H. K.; Yao, Z.

    2015-12-01

    This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni+/He+) irradiation. The 1 MeV Ni+ ions with the damage rate of 10-3 dpa/s as well as 15 keV He+ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ‧ (Ni3 (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2-5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 <1 1 1> Frank loops in the size of 10-20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.

  12. Calculated Regenerator Performance at 4 K with HELIUM-4 and HELIUM-3

    NASA Astrophysics Data System (ADS)

    Radebaugh, Ray; Huang, Yonghua; O'Gallagher, Agnes; Gary, John

    2008-03-01

    The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K deviates considerably from an ideal gas. As a result, losses in the regenerator, given by the time-averaged enthalpy flux, are increased and are strong functions of the operating pressure and temperature. Helium-3, with its lower boiling point, behaves somewhat closer to an ideal gas in this low temperature range and can reduce the losses in 4 K regenerators. An analytical model is used to find the fluid properties that strongly influence the regenerator losses as well as the gross refrigeration power. The thermodynamic and transport properties of helium-3 were incorporated into the latest NIST regenerator numerical model, known as REGEN3.3, which was used to model regenerator performance with either helium-4 or helium-3. With this model we show how the use of helium-3 in place of helium-4 can improve the performance of 4 K regenerative cryocoolers. The effects of operating pressure, warm-end temperature, and frequency on regenerators with helium-4 and helium-3 are investigated and compared. The results are used to find optimum operating conditions. The frequency range investigated varies from 1 Hz to 30 Hz, with particular emphasis on higher frequencies.

  13. Helium Dilution Cryocooler for Space Applications

    NASA Technical Reports Server (NTRS)

    Roach, Pat; Hogan, Robert (Technical Monitor)

    2001-01-01

    NASA's New Millenium Program Space Technology presents the Helium Dilution Cryocooler for Space Applications. The topics include: 1) Capability; 2) Applications; and 3) Advantages. This paper is in viewgraph form.

  14. Helium and Enhanced Image of the Sun

    NASA Video Gallery

    This video blinks between an image in Helium and an enhanced image. The original image is from AIA on SDO and the enhanced image was created at the LM Solar and Astrophysics Laboratory (LMSAL) by D...

  15. Helium Find Thaws the Cold Fusion Trail.

    ERIC Educational Resources Information Center

    Pennisi, E.

    1991-01-01

    Reported is a study of cold fusion in which trace amounts of helium, possible evidence of an actual fusion reaction, were found. Research methodology is detailed. The controversy over the validity of experimental results with cold fusion are reviewed. (CW)

  16. Commissioning of a new helium pipeline

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Center Director Roy Bridges addresses the audience at the commissioning of a new high-pressure helium pipeline at Kennedy Space Center that will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. The nine-mile- long buried pipeline will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad. Others at the ceremony were Jerry Jorgensen, pipeline project manager, Space Gateway Support (SGS); Col. Samuel Dick, representative of the 45th Space Wing; Ramon Lugo, acting executive director, JPMO; David Herst, director, Delta IV Launch Sites; Pierre Dufour, president and CEO, Air Liquide America Corporation; and Michael Butchko, president, SGS.

  17. Commissioning of a new helium pipeline

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Jerry Jorgensen welcomes the audience to the commissioning of a new high-pressure helium pipeline at Kennedy Space Center. Jorgensen, with Space Gateway Support (SGS), is the pipeline project manager. To the right is Ramon Lugo, acting executive director, JPMO. Others at the ceremony were Center Director Roy Bridges; Col. Samuel Dick, representative of the 45th Space Wing; David Herst, director, Delta IV Launch Sites; Pierre Dufour, president and CEO, Air Liquide America Corporation; and Michael Butchko, president, SGS. The pipeline will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. The nine-mile-long buried pipeline will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad.

  18. Commissioning of a new helium pipeline

    NASA Technical Reports Server (NTRS)

    2000-01-01

    At the commissioning of a new high-pressure helium pipeline at Kennedy Space Center, Ramon Lugo, acting executive director, JPMO , presents a plaque to Center Director Roy Bridges. The pipeline will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. Others at the ceremony were Jerry Jorgensen, pipeline project manager, Space Gateway Support (SGS); Col. Samuel Dick, representative of the 45th Space Wing; David Herst, director, Delta IV Launch Sites; Pierre Dufour, president and CEO, Air Liquide America Corporation; and Michael Butchko, president, SGS. The nine-mile-long buried pipeline will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad.

  19. Development of charcoal sorbents for helium cryopumping

    SciTech Connect

    Sedgley, D.W.; Tobin, A.G.

    1984-01-01

    Testing of the cryogenically cooled charcoal using fusion-compatible binders for pumping helium has shown promising results. The program demonstrated comparable or improved performance with these binders compared to the charcoal (type and size) using an epoxy binder.

  20. How hot are your ions in TWAVE ion mobility spectrometry?

    PubMed

    Merenbloom, Samuel I; Flick, Tawnya G; Williams, Evan R

    2012-03-01

    Effective temperatures of ions during traveling wave ion mobility spectrometry (TWIMS) analysis were measured using singly protonated leucine enkephalin dimer as a chemical thermometer by monitoring dissociation of the dimer into monomer, as well as the subsequent dissociation of monomer into a-, b-, and y-ions, as a function of instrumental parameters. At fixed helium cell and TWIMS cell gas flow rates, the extent of dissociation does not vary significantly with either the wave velocity or wave height, except at low (<500 m/s) wave velocities that are not commonly used. Increasing the flow rate of nitrogen gas into the TWIMS cell and decreasing the flow rate of helium gas into the helium cell resulted in greater dissociation. However, the mobility distributions of the fragment ions formed by dissociation of the dimer upon injection into the TWIMS cell are nearly indistinguishable from those of fragment ions formed in the collision cell prior to TWIMS analysis for all TWIMS experiments. These results indicate that heating and dissociation occur when ions are injected into the TWIMS cell, and that the effective temperature subsequently decreases to a point at which no further dissociation is observed during the TWIMS analysis. An upper limit to the effective ion temperature of 449 K during TWIMS analysis is obtained at a helium flow rate of 180 mL/min, TWIMS flow rate of 80 mL/min, and traveling wave height of 40 V, which is well below previously reported values. Effects of ion heating in TWIMS on gas-phase protein conformation are presented.

  1. Cosmogenic helium in a terrestrial igneous rock

    NASA Technical Reports Server (NTRS)

    Kurz, M. D.

    1986-01-01

    New helium isotopic measurements on samples from the Kula formation of Haleakala volcano of Hawaii are presented that are best explained by an in situ cosmogenic origin for a significant fraction of the He-3. Results from crushing and stepwise heating experiments, and consideration of the exposure age of the sample at the surface and the cosmic ray fluxes strongly support this hypothesis. Although crustal cosmogenic helium has been proposed previously, this represents its first unambiguous identification in a terrestrial sample.

  2. Trace organic impurities in gaseous helium

    NASA Technical Reports Server (NTRS)

    Schehl, T. A.

    1973-01-01

    A program to determine trace organic impurities present in helium has been initiated. The impurities were concentrated in a cryogenic trap to permit detection and identification by a gas chromatographic-mass spectrometric technique. Gaseous helium (GHe) exhibited 63 GC flame ionization response peaks. Relative GC peak heights and identifications of 25 major impurities by their mass spectra are given. As an aid to further investigation, identities are proposed for 16 other components, and their mass spectra are given.

  3. High efficiency pump for space helium transfer

    NASA Technical Reports Server (NTRS)

    Hasenbein, Robert; Izenson, Michael G.; Swift, Walter L.; Sixsmith, Herbert

    1991-01-01

    A centrifugal pump was developed for the efficient and reliable transfer of liquid helium in space. The pump can be used to refill cryostats on orbiting satellites which use liquid helium for refrigeration at extremely low temperatures. The pump meets the head and flow requirements of on-orbit helium transfer: a flow rate of 800 L/hr at a head of 128 J/kg. The overall pump efficiency at the design point is 0.45. The design head and flow requirements are met with zero net positive suction head, which is the condition in an orbiting helium supply Dewar. The mass transfer efficiency calculated for a space transfer operation is 0.99. Steel ball bearings are used with gas fiber-reinforced teflon retainers to provide solid lubrication. These bearings have demonstrated the longest life in liquid helium endurance tests under simulated pumping conditions. Technology developed in the project also has application for liquid helium circulation in terrestrial facilities and for transfer of cryogenic rocket propellants in space.

  4. Sonic helium detectors in the Fermilab Tevatron

    SciTech Connect

    Bossert, R.J.; /Fermilab

    2006-01-01

    In the Fermilab Tevatron cryogenic system there are many remotely located low-pressure plate relief valves that must vent large volumes of cold helium gas when magnet quenches occur. These valves can occasionally stick open or not reseat completely, resulting in a large helium loss. As such, the need exists for a detector to monitor the relief valve's discharge area for the presence of helium. Due to the quantity needed, cost is an important factor. A unit has been developed and built for this purpose that is quite inexpensive. Its operating principle is based on the speed of sound, where two closely matched tubes operate at their acoustic resonant frequency. When helium is introduced into one of these tubes, the resulting difference in acoustic time of flight is used to trigger an alarm. At present, there are 39 of these units installed and operating in the Tevatron. They have detected many minor and major helium leaks, and have also been found useful in detecting a rise in the helium background in the enclosed refrigerator buildings. This paper covers the construction, usage and operational experience gained with these units over the last several years.

  5. Advanced helium magnetometer for space applications

    NASA Technical Reports Server (NTRS)

    Slocum, Robert E.

    1987-01-01

    The goal of this effort was demonstration of the concepts for an advanced helium magnetometer which meets the demands of future NASA earth orbiting, interplanetary, solar, and interstellar missions. The technical effort focused on optical pumping of helium with tunable solid state lasers. We were able to demonstrate the concept of a laser pumped helium magnetometer with improved accuracy, low power, and sensitivity of the order of 1 pT. A number of technical approaches were investigated for building a solid state laser tunable to the helium absorption line at 1083 nm. The laser selected was an Nd-doped LNA crystal pumped by a diode laser. Two laboratory versions of the lanthanum neodymium hexa-aluminate (LNA) laser were fabricated and used to conduct optical pumping experiments in helium and demonstrate laser pumped magnetometer concepts for both the low field vector mode and the scalar mode of operation. A digital resonance spectrometer was designed and built in order to evaluate the helium resonance signals and observe scalar magnetometer operation. The results indicate that the laser pumped sensor in the VHM mode is 45 times more sensitive than a lamp pumped sensor for identical system noise levels. A study was made of typical laser pumped resonance signals in the conventional magnetic resonance mode. The laser pumped sensor was operated as a scalar magnetometer, and it is concluded that magnetometers with 1 pT sensitivity can be achieved with the use of laser pumping and stable laser pump sources.

  6. Helium bubble formation in ultrafine and nanocrystalline tungsten under different extreme conditions

    SciTech Connect

    El-atwani, O.; Hattar, Khalid Mikhiel; Hinks, J. A.; Greaves, G.; Harilal, S. S.; Hassanein, A.

    2014-12-25

    We investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. Moreover, at energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. Finally, we discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.

  7. Helium bubble formation in ultrafine and nanocrystalline tungsten under different extreme conditions

    DOE PAGES

    El-atwani, O.; Hattar, Khalid Mikhiel; Hinks, J. A.; Greaves, G.; Harilal, S. S.; Hassanein, A.

    2014-12-25

    We investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. Moreover,more » at energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. Finally, we discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.« less

  8. Non-local thermodynamic equilibrium effects on isentropic coefficient in argon and helium thermal plasmas

    SciTech Connect

    Sharma, Rohit; Singh, Kuldip

    2014-03-15

    In the present work, two cases of thermal plasma have been considered; the ground state plasma in which all the atoms and ions are assumed to be in the ground state and the excited state plasma in which atoms and ions are distributed over various possible excited states. The variation of Zγ, frozen isentropic coefficient and the isentropic coefficient with degree of ionization and non-equilibrium parameter θ(= T{sub e}/T{sub h}) has been investigated for the ground and excited state helium and argon plasmas at pressures 1 atm, 10 atm, and 100 atm in the temperature range from 6000 K to 60 000 K. For a given value of non-equilibrium parameter, the relationship of Zγ with degree of ionization does not show any dependence on electronically excited states in helium plasma whereas in case of argon plasma this dependence is not appreciable till degree of ionization approaches 2. The minima of frozen isentropic coefficient shifts toward lower temperature with increase of non-equilibrium parameter for both the helium and argon plasmas. The lowering of non-equilibrium parameter decreases the frozen isentropic coefficient more emphatically in helium plasma at high pressures in comparison to argon plasma. The increase of pressure slightly reduces the ionization range over which isentropic coefficient almost remains constant and it does not affect appreciably the dependence of isentropic coefficient on non-equilibrium parameter.

  9. Heavy ion therapy: Bevalac epoch

    SciTech Connect

    Castro, J.R.

    1993-10-01

    An overview of heavy ion therapy at the Bevelac complex (SuperHILac linear accelerator + Bevatron) is given. Treatment planning, clinical results with helium ions on the skull base and uveal melanoma, clinical results with high-LET charged particles, neon radiotherapy of prostate cancer, heavy charged particle irradiation for unfavorable soft tissue sarcoma, preliminary results in heavy charged particle irradiation of bone sarcoma, and irradiation of bile duct carcinoma with charged particles and-or photons are all covered. (GHH)

  10. Helium and Neon in Comets

    NASA Technical Reports Server (NTRS)

    Jewitt, David

    1996-01-01

    Two comets were observed with EUVE in late 1994. Both comet Mueller and comet Borrelly are short-period comets having well established orbital elements and accurate ephemerides. Spectra of 40 ksec were taken of each. No evidence for emission lines from either Helium or Neon was detected. We calculated limits on the production rates of these atoms (relative to solar) assuming a standard isotropic outflow model, with a gas streaming speed of 1 km/s. The 3-sigma (99.7% confidence) limits (1/100,000 for He, 0.8 for Ne) are based on a conservative estimate of the noise in the EUVE spectra. They are also weakly dependent on the precise pointing and tracking of the EUVE field of view relative to the comet during the integrations. These limits are consistent with ice formation temperatures T greater than or equal to 30 K, as judged from the gas trapping experiments of Bar-Nun. For comparison, the solar abundances of these elements are He/O = 110, Ne/O = 1/16. Neither limit was as constraining as we had initially hoped, mainly because comets Mueller and Borrelly were intrinsically less active than anticipated.

  11. Pulsating Helium Atmosphere White Dwarfs

    NASA Astrophysics Data System (ADS)

    Provencal, Judith; Montgomery, Michael H.; Bischoff-Kim, Agnes; Shipman, Harry; Nitta, Atsuko; Whole Earth Telescope Collaboration

    2015-08-01

    The overwhelming majority of all stars currently on the main sequence as well as those from earlier generations will or have ended their stellar lives as white dwarf stars. White dwarfs are rich forensic laboratories linking the history and future evolution of our Galaxy. Their structure and atmospheric composition provide evidence of how the progenitors lived, how they evolved, and how they died. This information reveals details of processes governing the behavior of contemporary main sequence stars. Combined with their distribution in luminosity/temperature, white dwarfs strongly constrain models of galactic and cosmological evolution.GD358 is among the brightest (mv =13.7) and best studied of the pulsating white dwarfs. This helium atmoshere pulsator (DBV) has an extensive photometric database spanning 30 years, including nine multisite Whole Earth Telescope campaigns. GD358 exhibits a range of behaviors, from drastic changes in excited pulsation modes to variable multiplet splittings. We use GD358 as a template for an examination of the DBV class, combining photometric results with recent COS spectroscopy. The results present new questions concerning DB formation and evolution.

  12. Imaging using accelerated heavy ions

    SciTech Connect

    Chu, W.T.

    1982-05-01

    Several methods for imaging using accelerated heavy ion beams are being investigated at Lawrence Berkeley Laboratory. Using the HILAC (Heavy-Ion Linear Accelerator) as an injector, the Bevalac can accelerate fully stripped atomic nuclei from carbon (Z = 6) to krypton (Z = 34), and partly stripped ions up to uranium (Z = 92). Radiographic studies to date have been conducted with helium (from 184-inch cyclotron), carbon, oxygen, and neon beams. Useful ranges in tissue of 40 cm or more are available. To investigate the potential of heavy-ion projection radiography and computed tomography (CT), several methods and instrumentation have been studied.

  13. Rotational relaxation of molecular ions in a buffer gas

    NASA Astrophysics Data System (ADS)

    Pérez-Ríos, Jesús; Robicheaux, F.

    2016-09-01

    The scattering properties regarding the rotational degrees of freedom of a molecular ion in the presence of a buffer gas of helium are investigated. This study is undertaken within the framework of the infinite-order sudden approximation for rotational transitions, which is shown to be applicable to a large variety of molecular ions in a buffer gas of helium at fairly low temperatures. The results derived from the present approach have potential applications in cold chemistry and molecular quantum logic spectroscopy.

  14. Simulation of alpha decay of actinides in iron phosphate glasses by ion irradiation

    NASA Astrophysics Data System (ADS)

    Dube, Charu L.; Stennett, Martin C.; Gandy, Amy S.; Hyatt, Neil C.

    2016-03-01

    A surrogate approach of ion beam irradiation is employed to simulate alpha decay of actinides in iron phosphate nuclear waste glasses. Bismuth and helium ions of different energies have been selected for simulating glass matrix modification owing to radiolysis and ballistic damage due to recoil atoms. Structural modification and change in coordination number of network former were probed by employing Reflectance Fourier-Transform Infrared (FT-IR), and Raman spectroscopies as a consequence of ion irradiation. Depolymerisation is observed in glass sample irradiated at intermediate energy of 2 MeV. Helium blisters of micron size are seen in glass sample irradiated at low helium ion energy of 30 keV.

  15. Partial cross sections of helium satellites at medium photon energies

    SciTech Connect

    Wehlitz, R.; Sellin, I.A.; Hemmers, O.

    1997-04-01

    Still of current interest is the important role of single ionization with excitation compared to single ionization alone. The coupling between the electrons and the incoming photon is a single-particle operator. Thus, an excitation in addition to an ionization, leading to a so-called satellite line in a photoelectron spectrum, is entirely due to electron-electron interaction and probes the electron correlation in the ground and final state. Therefore the authors have undertaken the study of the intensity of helium satellites He{sup +}nl (n = 2 - 6) relative to the main photoline (n = 1) as a function of photon energy at photon energies well above threshold up to 900 eV. From these results they could calculate the partial cross-sections of the helium satellites. In order to test the consistency of their satellite-to-1s ratios with published double-to-single photoionization ratios, the authors calculated the double-to-single photoionization ratio from their measured ratios using the theoretical energy-distribution curves of Chang and Poe and Le Rouzo and Dal Cappello which proved to be valid for photon energies below 120 eV. These calculated double-to-single ionization ratios agree fairly well with recent ion measurements. In the lower photon energy range the authors ratios agree better with the ratios of Doerner et al. while for higher photon energies the agreement is better with the values of Levin et al.

  16. Digging gold: keV He+ ion interaction with Au

    PubMed Central

    Veligura, Vasilisa; Hlawacek, Gregor; Berkelaar, Robin P; Zandvliet, Harold J W; Poelsema, Bene

    2013-01-01

    Summary Helium ion microscopy (HIM) was used to investigate the interaction of a focused He+ ion beam with energies of several tens of kiloelectronvolts with metals. HIM is usually applied for the visualization of materials with extreme surface sensitivity and resolution. However, the use of high ion fluences can lead to significant sample modifications. We have characterized the changes caused by a focused He+ ion beam at normal incidence to the Au{111} surface as a function of ion fluence and energy. Under the influence of the beam a periodic surface nanopattern develops. The periodicity of the pattern shows a power-law dependence on the ion fluence. Simultaneously, helium implantation occurs. Depending on the fluence and primary energy, porous nanostructures or large blisters form on the sample surface. The growth of the helium bubbles responsible for this effect is discussed. PMID:23946914

  17. The solar flare iron line to continuum ratio and the coronal abundances of iron and helium

    NASA Technical Reports Server (NTRS)

    Mckenzie, D. L.

    1975-01-01

    Narrow band Ross filter measurements of the Fe 25 line flux around 0.185 nm and simultaneous broadband measurements during a solar flare were used to determine the relationship between the solar coronal abundances of iron and helium. The Fe 25 ion population was also determined as a function of time. The proportional counter and the Ross filter on OSO-7 were utilized. The data were analyzed under the separate assumptions that (1) the electron density was high enough that a single temperature could characterize the continuum spectrum and the ionization equilibrium, and that (2) the electron density was low so that the ion populations trailed the electron temperature in time. It was found that the density was at least 5x10 to the 9th power, and that the high density assumption was valid. It was also found that the iron abundance is 0.000011 for a helium abundance of 0.2, relative to hydrogen.

  18. Method and means of reducing erosion of components of plasma devices exposed to helium and hydrogen isotope radiation

    DOEpatents

    Kaminsky, Manfred S.; Das, Santosh K.; Rossing, Thomas D.

    1977-01-25

    Surfaces of components of plasma devices exposed to radiation by atoms or ions of helium or isotopes of hydrogen can be protected from damage due to blistering by shielding the surfaces with a structure formed by sintering a powder of aluminum or beryllium and its oxide or by coating the surfaces with such a sintered metal powder.

  19. Model for describing non-equilibrium helium plasma energy level population

    NASA Astrophysics Data System (ADS)

    Kavyrshin, D. I.; Chinnov, V. F.; Ageev, A. G.

    2015-11-01

    A new method for calculating the population of excited levels of helium atoms and ions is suggested. The method is based on direct solution of a system of balance equations for all energy levels for which it was possible to obtain process speed constants. The equations include terms for the processes of particle loss and income by excitation and deexcitation, ionization and recombination as well as losses due to diffusion and radiation. The challenge of solution of such large system is also discussed.

  20. [Effects of helium-neon laser on physico-chemical properties of the bile].

    PubMed

    Mansurov, Kh Kh; Dzhuraev, Kh Sh; Barakaev, S B; Kharina, T P; Pulatov, L I

    1990-08-01

    The influence of helium-neon laser radiation on bile physico-chemical characteristics in healthy subjects and in patients with the physico-chemical stage of gallstone disease was studied in vitro. This type of laser was found to induce positive therapeutic effects, such as: correction of hydrogen ion concentrations, surface tension and viscosity decrease and prolonged bile nucleation in patients with gallstone disease.

  1. Electron-impact ionization of interstellar hydrogen and helium at interplanetary shocks

    SciTech Connect

    Isenberg, P.A.; Feldman, W.C.

    1995-04-15

    The authors investigate the ionization of interstellar hydrogen and helium due to electron impact by shock-heated electrons. Taking the electron distributions measured at four interplanetary shocks at 1 AU, they show that the electrons in the downstream region of strong shocks can ionize interstellar atoms at rates matching or exceeding the nominal photoionization or charge-exchange rates. They suggest that this process may explain some puzzling observations of interstellar pickup ions made by the Ulysses spacecraft. 17 refs.

  2. Transparent Helium in Stripped Envelope Supernovae

    NASA Astrophysics Data System (ADS)

    Piro, Anthony L.; Morozova, Viktoriya S.

    2014-09-01

    Using simple arguments based on photometric light curves and velocity evolution, we propose that some stripped envelope supernovae (SNe) show signs that a significant fraction of their helium is effectively transparent. The main pieces of evidence are the relatively low velocities with little velocity evolution, as are expected deep inside an exploding star, along with temperatures that are too low to ionize helium. This means that the helium should not contribute to the shaping of the main SN light curve, and thus the total helium mass may be difficult to measure from simple light curve modeling. Conversely, such modeling may be more useful for constraining the mass of the carbon/oxygen core of the SN progenitor. Other stripped envelope SNe show higher velocities and larger velocity gradients, which require an additional opacity source (perhaps the mixing of heavier elements or radioactive nickel) to prevent the helium from being transparent. We discuss ways in which similar analysis can provide insights into the differences and similarities between SNe Ib and Ic, which will lead to a better understanding of their respective formation mechanisms.

  3. TRANSPARENT HELIUM IN STRIPPED ENVELOPE SUPERNOVAE

    SciTech Connect

    Piro, Anthony L.; Morozova, Viktoriya S.

    2014-09-01

    Using simple arguments based on photometric light curves and velocity evolution, we propose that some stripped envelope supernovae (SNe) show signs that a significant fraction of their helium is effectively transparent. The main pieces of evidence are the relatively low velocities with little velocity evolution, as are expected deep inside an exploding star, along with temperatures that are too low to ionize helium. This means that the helium should not contribute to the shaping of the main SN light curve, and thus the total helium mass may be difficult to measure from simple light curve modeling. Conversely, such modeling may be more useful for constraining the mass of the carbon/oxygen core of the SN progenitor. Other stripped envelope SNe show higher velocities and larger velocity gradients, which require an additional opacity source (perhaps the mixing of heavier elements or radioactive nickel) to prevent the helium from being transparent. We discuss ways in which similar analysis can provide insights into the differences and similarities between SNe Ib and Ic, which will lead to a better understanding of their respective formation mechanisms.

  4. Thermal Performance of the XRS Helium Insert

    NASA Technical Reports Server (NTRS)

    Breon, Susan R.; DiPirro, Michael J.; Tuttle, James G.; Shirron, Peter J.; Warner, Brent A.; Boyle, Robert F.; Canavan, Edgar R.

    1999-01-01

    The X-Ray Spectrometer (XRS) is an instrument on the Japanese Astro-E satellite, scheduled for launch early in the year 2000. The XRS Helium Insert comprises a superfluid helium cryostat, an Adiabatic Demagnetization Refrigerator (ADR), and the XRS calorimeters with their cold electronics. The calorimeters are capable of detecting X-rays over the energy range 0.1 to 10 keV with a resolution of 12 eV. The Helium Insert completed its performance and verification testing at Goddard in January 1999. It was shipped to Japan, where it has been integrated with the neon dewar built by Sumitomo Heavy Industries. The Helium Insert was given a challenging lifetime requirement of 2.0 years with a goal of 2.5 years. Based on the results of the thermal performance tests, the predicted on-orbit lifetime is 2.6 years with a margin of 30%. This is the result of both higher efficiency in the ADR cycle and the low temperature top-off, more than compensating for an increase in the parasitic heat load. This paper presents a summary of the key design features and the results of the thermal testing of the XRS Helium Insert.

  5. Helium release from radioisotope heat sources

    SciTech Connect

    Peterson, D.E.; Early, J.W.; Starzynski, J.S.; Land, C.C.

    1984-05-01

    Diffusion of helium in /sup 238/PuO/sub 2/ fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel.

  6. BASG thermomechanical pump helium 2 transfer tests

    NASA Technical Reports Server (NTRS)

    Mills, G. L.; Newell, D. A.; Urbach, A. R.

    1990-01-01

    The purpose of the effort described was to perform experiments and calculations related to using a thermomechanical pump in the space-based resupply of the Space Infrared Telescope Facility (SIRTF) with Helium 2. Thermomechanical (fountain effect) pumps have long been suggested as a means for pumping large quantities of Helium 2. The unique properties of Helium 2 have made it useful for cooling space instruments. Several space science missions, including SIRTF, are now being planned which would benefit greatly from on-orbit resupply of Helium 2. A series of experiments were performed to demonstrate that large volumes of Helium 2 can be transferred with a thermomechanical pump at high flow rates and at high efficiency from one dewar to another through valves and lines that are similar to the plumbing arrangement that would be necessary to accomplish such a transfer on-orbit. In addition, temperature, pressure, and flow rate data taken during the tests were used to verify and refine a computer model which was developed.

  7. Commissioning of a new helium pipeline

    NASA Technical Reports Server (NTRS)

    2000-01-01

    At the commissioning of a new high-pressure helium pipeline at Kennedy Space Center, participants cut the lines to helium-filled balloons. From left, they are Center Director Roy Bridges; Michael Butchko, president, SGS; Pierre Dufour, president and CEO, Air Liquide America Corporation; David Herst, director, Delta IV Launch Sites; Pamela Gillespie, executive administrator, office of Congressman Dave Weldon; and Col. Samuel Dick, representative of the 45th Space Wing. The nine-mile-long buried pipeline will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. It will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad. Others at the ceremony were Jerry Jorgensen, pipeline project manager, Space Gateway Support (SGS), and Ramon Lugo, acting executive director, JPMO.

  8. Commissioning of a new helium pipeline

    NASA Technical Reports Server (NTRS)

    2000-01-01

    At the commissioning of a new high-pressure helium pipeline at Kennedy Space Center, participants watch as helium-filled balloons take to the sky after their lines were cut. From left, they are Center Director Roy Bridges; Michael Butchko, president, SGS; Pierre Dufour, president and CEO, Air Liquide America Corporation; David Herst, director, Delta IV Launch Sites; Pamela Gillespie, executive administrator, office of Congressman Dave Weldon; and Col. Samuel Dick, representative of the 45th Space Wing. The nine-mile-long buried pipeline will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. It will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad. Others at the ceremony were Jerry Jorgensen, pipeline project manager, Space Gateway Support (SGS), and Ramon Lugo, acting executive director, JPMO.

  9. Homonuclear ionizing collisions of laser-cooled metastable helium atoms

    SciTech Connect

    Stas, R. J. W.; McNamara, J. M.; Hogervorst, W.; Vassen, W.

    2006-03-15

    We present a theoretical and experimental investigation of homonuclear ionizing collisions of laser-cooled metastable (2 {sup 3}S{sub 1}) helium atoms, considering both the fermionic {sup 3}He and bosonic {sup 4}He isotopes. The theoretical description combines quantum threshold behavior, Wigner's spin-conservation rule, and quantum-statistical symmetry requirements in a single-channel model, complementing a more complete close-coupling theory that has been reported for collisions of metastable {sup 4}He atoms. The model is supported with measurements (in the absence of light fields) of ionization rates in magneto-optically trapped samples that contain about 3x10{sup 8} atoms of a single isotope. The ionization rates are determined from measurements of trap loss due to light-assisted collisions combined with comparative measurements of the ion production rate in the absence and presence of trapping light. Theory and experiment show good agreement.

  10. Effect of helium implantation on SiC and graphite

    NASA Astrophysics Data System (ADS)

    Guo, Hong-Yan; Ge, Chang-Chun; Xia, Min; Guo, Li-Ping; Chen, Ji-Hong; Yan, Qing-Zhi

    2015-03-01

    Effects of helium implantation on silicon carbide (SiC) and graphite were studied to reveal the possibility of SiC replacing graphite as plasma facing materials. Pressureless sintered SiC and graphite SMF-800 were implanted with He+ ions of 20 keV and 100 keV at different temperatures and different fluences. The He+ irradiation induced microstructure changes were studied by field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Project supported by the ITER-National Magnetic Confinement Fusion Program, China (Grant Nos. 2010GB109000, 2011GB108009, and 2014GB123000) and the National Natural Science Foundation of China (Grant No. 11075119).

  11. Photodissociation of alkyl iodides in helium nanodroplets. III. Recombination

    SciTech Connect

    Braun, Andreas; Drabbels, Marcel

    2007-09-21

    The recombination of fragments resulting from the photodissociation of (fluorinated) alkyl iodides in helium nanodroplets at a wavelength of 266 nm has been investigated by means of ion imaging techniques. It is found that in the case of CH{sub 3}I an appreciable fraction of the fragments recombine in the aftermath of the photolysis. The proposed mechanism involves a complete translational relaxation of both photofragments inside the nanodroplets followed by geminate recombination of the fragments. In contrast with CH{sub 3}I, no recombination is observed for CF{sub 3}I. This is attributed to the larger masses and the different initial kinetic energies of the fragments produced by the photolysis of CF{sub 3}I, which strongly diminishes the fragment thermalization efficiency.

  12. Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

    NASA Astrophysics Data System (ADS)

    Carbone, Emile A. D.; Schregel, Christian-Georg; Czarnetzki, Uwe

    2016-10-01

    In this paper, we discuss the experimental results presented in Schregel et al (2016 Plasma Sources Sci. Technol. 25 054003) on a high pressure micro-discharge operated in helium and driven by nanosecond voltage pulses. A simple global plasma chemistry model is developed to describe the ions, excited atomic and molecular species dynamics in the ignition and early afterglow regimes. The existing experimental data on high pressure helium kinetics is reviewed and critically discussed. It is highlighted that several inconsistencies in the branching ratio of neutral assisted associative and dissociative processes currently exist in the literature and need further clarification. The model allows to pinpoint the mechanisms responsible for the large amounts of Rydberg molecules produced in the discharge and for the helium triplet metastable state in the afterglow. The main losses of electrons are also identified. The fast quenching of excited He (n  >  3) states appears to be a significant source of Rydberg molecules which has been previously neglected. The plasma model finally draws a simplified, but still accurate description of high pressure helium discharges based on available experimental data for ion and neutral helium species.

  13. Toward Optimized Surface δ-Profiles of Nitrogen-Vacancy Centers Activated by Helium Irradiation in Diamond.

    PubMed

    Fávaro de Oliveira, Felipe; Momenzadeh, S Ali; Antonov, Denis; Scharpf, Jochen; Osterkamp, Christian; Naydenov, Boris; Jelezko, Fedor; Denisenko, Andrej; Wrachtrup, Jörg

    2016-04-13

    The negatively charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution. This provides insights into the efficiency of vacancy diffusion and recombination paths concurrent to the formation of NV centers. It was found that the range of efficient formation of NV centers is limited only to approximately 10 to 15 nm (radius) around the initial ion track of irradiating helium atoms. Using this information we demonstrate the fabrication of nanometric-thin (δ) profiles of NV centers for sensing external spins at the diamond surface based on a three-step approach, which comprises (i) nitrogen-doped epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy helium irradiation and thermal annealing, and (iii) controlled layer thinning by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to 50 μs are demonstrated at depths of less than 5 nm in material with 1.1% of (13)C (depth estimated by spin relaxation (T1) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.

  14. Development of a high vacuum sample preparation system for helium mass spectrometer

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Das, N. K.; Mallik, C.; Bhandari, R. K.

    2012-11-01

    A high vacuum sample preparation system for the 3He/4He ratio mass spectrometer (Helix SFT) has been developed to remove all the gaseous constituents excluding helium from the field gases. The sample preparation system comprises of turbo molecular pump, ion pump, zirconium getter, pipettes and vacuum gauges with controller. All these are fitted with cylindrical SS chamber using all metal valves. The field samples are initially treated with activated charcoal trap immersed in liquid nitrogen to cutoff major impurities and moisture present in the sample gas. A sample of 5 ml is collected out of this stage at a pressure of 10-2 mbar. This sample is subsequently purified at a reduced pressure of 10-7 mbar before it is injected into the ion source of the mass spectrometer. The sample pressure was maintained below 10-7 mbar with turbo molecular vacuum pumps and ion pumps. The sample gas passes through several getter elements and a cold finger with the help of manual high vacuum valves before it is fed to the mass spectrometer. Thus the high vacuum sample preparation system introduces completely clean, dry and refined helium sample to the mass spectrometer for best possible analysis of isotopic ratio of helium.

  15. Feasibility of lunar Helium-3 mining

    NASA Astrophysics Data System (ADS)

    Kleinschneider, Andreas; Van Overstraeten, Dmitry; Van der Reijnst, Roy; Van Hoorn, Niels; Lamers, Marvin; Hubert, Laurent; Dijk, Bert; Blangé, Joey; Hogeveen, Joel; De Boer, Lennaert; Noomen, Ron

    With fossil fuels running out and global energy demand increasing, the need for alternative energy sources is apparent. Nuclear fusion using Helium-3 may be a solution. Helium-3 is a rare isotope on Earth, but it is abundant on the Moon. Throughout the space community lunar Helium-3 is often cited as a major reason to return to the Moon. Despite the potential of lunar Helium-3 mining, little research has been conducted on a full end-to-end mission. This abstract presents the results of a feasibility study conducted by students from Delft University of Technology. The goal of the study was to assess whether a continuous end-to-end mission to mine Helium-3 on the Moon and return it to Earth is a viable option for the future energy market. The set requirements for the representative end-to-end mission were to provide 10% of the global energy demand in the year 2040. The mission elements have been selected with multiple trade-offs among both conservative and novel concepts. A mission architecture with multiple decoupled elements for each transportation segment (LEO, transfer, lunar surface) was found to be the best option. It was found that the most critical element is the lunar mining operation itself. To supply 10% of the global energy demand in 2040, 200 tons of Helium-3 would be required per year. The resulting regolith mining rate would be 630 tons per second, based on an optimistic concentration of 20 ppb Helium-3 in lunar regolith. Between 1,700 to 2,000 Helium-3 mining vehicles would be required, if using University of Wisconsin’s Mark III miner. The required heating power, if mining both day and night, would add up to 39 GW. The resulting power system mass for the lunar operations would be in the order of 60,000 to 200,000 tons. A fleet of three lunar ascent/descent vehicles and 22 continuous-thrust vehicles for orbit transfer would be required. The costs of the mission elements have been spread out over expected lifetimes. The resulting profits from Helium

  16. Laser spectroscopic measurement of helium isotope ratios.

    SciTech Connect

    Wang, L.-B.; Mueller, P.; Holt, R. J.; Lu, Z.-T.; O'Connor, T. P.; Sano, Y.; Sturchio, N.; Univ. of Illinois; Univ. of Tokyo; Univ. of Illinois at Chicago

    2003-06-13

    A sensitive laser spectroscopic method has been applied to the quantitative determination of the isotope ratio of helium at the level of {sup 3}He/{sup 4}He = 10{sup -7}--10{sup -5}. The resonant absorption of 1083 nm laser light by the metastable {sup 3}He atoms in a discharge cell was measured with the frequency modulation saturation spectroscopy technique while the abundance of {sup 4}He was measured by a direct absorption technique. The results on three different samples extracted from the atmosphere and commercial helium gas were in good agreement with values obtained with mass spectrometry. The achieved 3{sigma} detection limit of {sup 3}He in helium is 4 x 10{sup -9}. This demonstration required a 200 {mu}L STP sample of He. The sensitivity can be further improved, and the required sample size reduced, by several orders of magnitude with the addition of cavity enhanced spectroscopy.

  17. Thermodynamic properties of hydrogen-helium plasmas

    NASA Technical Reports Server (NTRS)

    Nelson, H. F.

    1971-01-01

    The thermodynamic properties of an atomic hydrogen-helium plasma are calculated and tabulated for temperatures from 10,000 to 100,000 K as a function of the mass fraction ratio of atomic hydrogen. The tabulation is for densities from 10 to the minus 10th power to 10 to the minus 6th power gm/cu cm and for hydrogen mass fraction ratios of 0, 0.333, 0.600, 0.800, and 1.0, which correspond to pure helium, 50 percent hydrogen per unit volume, 75 percent hydrogen per unit volume, 89 percent hydrogen per unit volume, and pure hydrogen plasmas, respectively. From an appended computer program, calculations can be made at other densities and mass fractions. The program output agrees well with previous thermodynamic property calculations for limiting cases of pure hydrogen and pure helium plasmas.

  18. Ages of globular clusters and helium diffusion

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian; Sarajedini, Ata; Demarque, Pierre

    1992-01-01

    Evolutionary tracks have been calculated with alpha-enhanced compositions which cover the entire globular cluster metallicity range and have constructed isochrones which include the effects of microscopic diffusion of helium. The turnoff magnitudes from the isochrones were combined with the theoretical RR Lyrae magnitudes from Lee to determine the ages of 32 Galactic globular clusters using the magnitude difference between the turnoff and horizontal branch. It is found that including the effects of helium diffusion has a negligible effect on the derived ages of globular clusters. Regardless of the inclusion of helium diffusion, a significant age spread of 5 Gyr among the globular clusters is found. The oldest globular clusters studied here are 17 +/- 2 Gyr old.

  19. SCREW COMPRESSOR CHARACTERISTICS FOR HELIUM REFRIGERATION SYSTEMS

    SciTech Connect

    Ganni, Venkatarao; Knudsen, Peter; Creel, Jonathan; Arenius, Dana; Casagrande, Fabio; Howell, Matt

    2008-03-01

    The oil injected screw compressors have practically replaced all other types of compressors in modern helium refrigeration systems due to their large displacement capacity, minimal vibration, reliability and capability of handling helium's high heat of compression.At the present state of compressor system designs for helium systems, typically two-thirds of the lost input power is due to the compression system. Therefore it is important to understand the isothermal and volumetric efficiencies of these machines to help properly design these compression systems to match the refrigeration process. This presentation summarizes separate tests that have been conducted on Sullair compressors at the Superconducting Super-Collider Laboratory (SSCL) in 1993, Howden compressors at Jefferson Lab (JLab) in 2006 and Howden compressors at the Spallation Neutron Source (SNS) in 2006. This work is part of an ongoing study at JLab to understand the theoretical basis for these efficiencies and their loss

  20. Helium Speech: An Application of Standing Waves

    NASA Astrophysics Data System (ADS)

    Wentworth, Christopher D.

    2011-04-01

    Taking a breath of helium gas and then speaking or singing to the class is a favorite demonstration for an introductory physics course, as it usually elicits appreciative laughter, which serves to energize the class session. Students will usually report that the helium speech "raises the frequency" of the voice. A more accurate description of the phenomenon requires that we distinguish between the frequencies of sound produced by the larynx and the filtering of those frequencies by the vocal tract. We will describe here an experiment done by introductory physics students that uses helium speech as a context for learning about the human vocal system and as an application of the standing sound-wave concept. Modern acoustic analysis software easily obtained by instructors for student use allows data to be obtained and analyzed quickly.

  1. Helium corona-assisted air discharge

    SciTech Connect

    Jiang Nan; Gao Lei; Ji Ailing; Cao Zexian

    2011-10-15

    Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb--for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

  2. The prospects of a subnanometer focused neon ion beam.

    PubMed

    Rahman, F H M; McVey, Shawn; Farkas, Louis; Notte, John A; Tan, Shida; Livengood, Richard H

    2012-01-01

    The success of the helium ion microscope has encouraged extensions of this technology to produce beams of other ion species. A review of the various candidate ion beams and their technical prospects suggest that a neon beam might be the most readily achieved. Such a neon beam would provide a sputtering yield that exceeds helium by an order of magnitude while still offering a theoretical probe size less than 1-nm. This article outlines the motivation for a neon gas field ion source, the expected performance through simulations, and provides an update of our experimental progress. PMID:21796647

  3. The prospects of a subnanometer focused neon ion beam.

    PubMed

    Rahman, F H M; McVey, Shawn; Farkas, Louis; Notte, John A; Tan, Shida; Livengood, Richard H

    2012-01-01

    The success of the helium ion microscope has encouraged extensions of this technology to produce beams of other ion species. A review of the various candidate ion beams and their technical prospects suggest that a neon beam might be the most readily achieved. Such a neon beam would provide a sputtering yield that exceeds helium by an order of magnitude while still offering a theoretical probe size less than 1-nm. This article outlines the motivation for a neon gas field ion source, the expected performance through simulations, and provides an update of our experimental progress.

  4. On the size and structure of helium snowballs formed around charged atoms and clusters of noble gases.

    PubMed

    Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2014-09-18

    Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ≤ x ≤ 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ≤ 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions.

  5. Ab Initio Simulations of Dense Helium Plasmas

    SciTech Connect

    Wang Cong; He Xiantu; Zhang Ping

    2011-04-08

    We study the thermophysical properties of dense helium plasmas by using quantum molecular dynamics and orbital-free molecular dynamics simulations, where densities are considered from 400 to 800 g/cm{sup 3} and temperatures up to 800 eV. Results are presented for the equation of state. From the Kubo-Greenwood formula, we derive the electrical conductivity and electronic thermal conductivity. In particular, with the increase in temperature, we discuss the change in the Lorenz number, which indicates a transition from strong coupling and degenerate state to moderate coupling and partial degeneracy regime for dense helium.

  6. Experiments with single electrons in liquid helium

    SciTech Connect

    Guo, W.; Jin, D.; Seidel, G. M.; Maris, H. J.

    2009-02-01

    We describe experiments we have performed in which we are able to image the motion of individual electrons moving in liquid helium 4. Electrons in helium form bubbles of radius {approx}19 A. We use the negative pressure produced by a sound wave to expand these bubbles to a radius of about 10 {mu}m. The bubbles are then illuminated with light from a flash lamp and their position recorded. We report on several interesting phenomena that have been observed in these experiments. It appears that the majority of the electrons that we detect result from cosmic rays passing through the experimental cell. We discuss this mechanism for electron production.

  7. Helium Microbeam Mixing of Bilayers.

    NASA Astrophysics Data System (ADS)

    Davis, John Baran

    This study is an experimental and theoretical investigation of room-temperature mixing of bilayers by micron-width He^+ ion beams. Bilayer targets, including Cu/Al, Cu/Si and Sb/Si, were irradiated at room temperature in the University at Albany's Dynamitron particle accelerator with 2-MeV He^+ ion beams ranging from 2 to 6 μm in width. At doses on the order of 10^ {19}/cm^2, RBS spectra revealed evidence of interface mixing in all targets to depths of several thousand A within the cylinder irradiated by the beam. Both RBS spectra and isometric RBS contour maps of the target also showed that mixing of the interface extends laterally well beyond the irradiated area. The interface mixing reaches a maximum in an annular region several times larger in diameter than the ion-beam. Standard theories of primary-recoil, secondary -cascade and thermal-spike mixing predicted interface widths two orders of magnitude smaller than observed for Cu/Al bilayers. Furthermore, He^+ irradiation of Cu/Al targets at liquid-nitrogen temperature did not produce interface mixing, further indicating that ballistic interpretations of the mixing are inadequate. Defect concentrations as a function of position and time were calculated by numerical solution of coupled rate equations for vacancies and interstitials in aluminum. The results of these calculations show that room-temperature He^+ mixing of Cu/Al results almost exclusively from interstitial migration. The numerically calculated concentration of interstitials within the damage cylinder was used to derive an approximate expression for interface width as a function of dose. Comparisons of these predicted values with the experimentally determined interface width as a function of dose agree, within uncertainties. In addition, the annular region observed on RBS maps is explained by the continued presence of a non-equilibrium concentration of interstitials after the ion beam is shut off. Interface mixing in Cu/Si targets, although

  8. Helium building no. 2 west and south sides. Looking 70 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Helium building no. 2 west and south sides. Looking 70 ENE. - Marine Corps Air Station Tustin, Helium Tank Building No. 1, Near intersection of Meffett Avenue & Maxfield Street, Tustin, Orange County, CA

  9. 8. ORIGINAL HELIUM COMPRESSOR, CIRCA 1957, BY HASKELL ENGINEERING, GLENDALE, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. ORIGINAL HELIUM COMPRESSOR, CIRCA 1957, BY HASKELL ENGINEERING, GLENDALE, CALIFORNIA. Looking north. - Edwards Air Force Base, Air Force Rocket Propulsion Laboratory, Helium Compression Plant, Test Area 1-115, intersection of Altair & Saturn Boulevards, Boron, Kern County, CA

  10. Helium building no. 2 east and north sides. Looking 270 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Helium building no. 2 east and north sides. Looking 270 W. - Marine Corps Air Station Tustin, Helium Tank Building No. 1, Near intersection of Meffett Avenue & Maxfield Street, Tustin, Orange County, CA

  11. 5. INTERIOR, LOOKING PAST HELIUM COMPRESSORS NO. 3 AND NO. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. INTERIOR, LOOKING PAST HELIUM COMPRESSORS NO. 3 AND NO. 2, TO NORTHEAST FRONT. - Edwards Air Force Base, Air Force Rocket Propulsion Laboratory, Helium Compression Plant, Test Area 1-115, intersection of Altair & Saturn Boulevards, Boron, Kern County, CA

  12. Adsorption of Helium Atoms on Two-Dimensional Substrates

    NASA Astrophysics Data System (ADS)

    Burganova, Regina; Lysogorskiy, Yury; Nedopekin, Oleg; Tayurskii, Dmitrii

    2016-01-01

    The study of the adsorption phenomenon of helium began many decades ago with the discovery of graphite as a homogeneous substrate for the investigation of physically adsorbed monolayer films. In particular, helium monoatomic layers on graphite were found to exhibit a very rich phase diagram. In the present work we have investigated the adsorption phenomenon of helium atoms on graphene and silicene substrates by means of density functional theory with Born-Oppenheimer approximation. Helium-substrate and helium-helium interactions were considered from first principles. Vibrational properties of adsorbed monolayers have been used to explore the stability of the system. This approach reproduces results describing the stability of a helium monolayer on graphene calculated by quantum Monte Carlo (QMC) simulations for low and high coverage cases. However, for the moderate coverage value there is a discrepancy with QMC results due to the lack of helium zero point motion.

  13. A helium liquefier using three 4 k pulse tube cryocoolers

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Oviedo, Abner

    2012-06-01

    We have developed a helium liquefier which can be used for recondensing/reliquefying helium vapor in a helium cryostat or liquefying helium gas in a storage dewar. The helium liquefier employs three 4 K pulse tube cryocoolers, Cryomech model PT415. Each PT415 has remote motor/rotary valve assembly to minimize vibration, providing ≥ 1.5W at 4.2K. The liquefier can liquefy room temperature helium gas with a liquefaction rate of 62 Liter/day. When installing it in the cryostat, it can recondense and reliquefy helium vapor with a rate of 78 L/day. The liquefier will be installed in a gravitational wave detector in Brazil to recondense/reliquefy the helium boil off from the cryostat.

  14. An efficient helium circulation system with small GM cryocoolers

    NASA Astrophysics Data System (ADS)

    Takeda, Tsunehiro; Okamoto, Masayoshi; Atsuda, Kazuhiro; Kobayashi, Akihiro; Owaki, Takashi; Katagiri, Keishi

    2008-01-01

    We developed a helium circulating system that re-liquefies all the evaporating helium gas and consumes far less power than conventional systems, because warm helium gas at about 40 K collected high above the surface of the liquid helium in the Dewar is used to keep the Dewar cold, and because cold helium gas just above the liquid helium surface is collected and re-liquefied while still cold. A special transfer tube with multi-concentric pipes was developed to make the system operate efficiently. The system can produce up to 35.5 l/D of liquid helium from the evaporated helium using two 1.5 W@4.2 K GM cryocoolers.

  15. 2. SOUTHEAST SIDE. HIGH PRESSURE HELIUM STORAGE TANKS AT LEFT. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. SOUTHEAST SIDE. HIGH PRESSURE HELIUM STORAGE TANKS AT LEFT. - Edwards Air Force Base, Air Force Rocket Propulsion Laboratory, Helium Compression Plant, Test Area 1-115, intersection of Altair & Saturn Boulevards, Boron, Kern County, CA

  16. The dynamics and helium distribution in hydrogen-helium fluid planets

    NASA Technical Reports Server (NTRS)

    Stevenson, D. J.; Salpeter, E. E.

    1977-01-01

    The simple case of a homogeneous planet without first-order phase transitions is considered and an investigation is conducted concerning a pure hydrogen planet in which a first-order phase transition takes place from fluid molecular hydrogen to fluid metallic hydrogen. Attention is also given to convection in the presence of a compositional gradient, the effects of helium insolubility in a cooling hydrogen-helium planet, a hydrogen-helium planet in its early evolution, and the case in which influence of phase transition occurs much later in the evolution of the planet.

  17. Determination of pitch angles of magnetic field lines in tokamak with obliquely injected helium beam

    NASA Astrophysics Data System (ADS)

    Mohri, Akihiro

    1987-04-01

    Pitch angles of magnetic field lines or q-profile in high density tokamaks can be determined by the method proposed here. Blobs of monoenergetic helium beam with different velocities are injected into the tokomak obliquely to the toroidal direction on a poloidal plane x. Produced He(+) ions move nearly along the magnetic field lines, and their front emitting a HeII line crosses a different sight plane and forms a curve on it. Optically measured shift of the curve from x leads to the distribution of pitch angle after correction of perpendicular drift motion of He(+) ions using the velocity dependence of the drift.

  18. The EUV Helium Spectrum in the Quiet Sun: A By-Product of Coronal Emission?

    NASA Technical Reports Server (NTRS)

    Andretta, Vincenzo; DelZanna, Giulio; Jordan, Stuart D.; Oegerle, William (Technical Monitor)

    2002-01-01

    In this paper we test one of the mechanisms proposed to explain the intensities and other observed properties of the solar helium spectrum, and in particular of its Extreme-Ultraviolet (EUV) resonance lines. The so-called Photoionisation-Recombination (P-R) mechanism involves photoionisation of helium atoms and ions by EUV coronal radiation, followed by recombination cascades. We present calibrated measurements of EUV flux obtained with the two CDS spectrometers on board SOHO, in quiescent solar regions. We were able to obtain an essentially complete estimate of the total photoionizing flux in the wavelength range below 504 A (the photoionisation threshold for He(I)), as well as simultaneous measurements with the same instruments of the intensities of the strongest EUV helium lines: He(II) lambda304, He(I) lambda584, and He(I) lambda537. We find that there are not enough EUV photons to account for the observed helium line intensities. More specifically, we conclude that He(II) intensities cannot be explained by the P-R mechanism. Our results, however, leave open the possibility that the He(I) spectrum could be formed by the P-R mechanism, with the He(II) lambda304 line as a significant photoionizating source.

  19. Electron diffraction of CBr4 in superfluid helium droplets: A step towards single molecule diffraction

    NASA Astrophysics Data System (ADS)

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-07-01

    We demonstrate the practicality of electron diffraction of single molecules inside superfluid helium droplets using CBr4 as a testing case. By reducing the background from pure undoped droplets via multiple doping, with small corrections for dimers and trimers, clearly resolved diffraction rings of CBr4 similar to those of gas phase molecules can be observed. The experimental data from CBr4 doped droplets are in agreement with both theoretical calculations and with experimental results of gaseous species. The abundance of monomers and clusters in the droplet beam also qualitatively agrees with the Poisson statistics. Possible extensions of this approach to macromolecular ions will also be discussed. This result marks the first step in building a molecular goniometer using superfluid helium droplet cooling and field induced orientation. The superior cooling effect of helium droplets is ideal for field induced orientation, but the diffraction background from helium is a concern. This work addresses this background issue and identifies a possible solution. Accumulation of diffraction images only becomes meaningful when all images are produced from molecules oriented in the same direction, and hence a molecular goniometer is a crucial technology for serial diffraction of single molecules.

  20. A comparison of hydrogen vs. helium glow discharge effects on fusion device first-wall conditioning

    SciTech Connect

    Dylla, H.F.

    1989-09-01

    Hydrogen- and deuterium-fueled glow discharges are used for the initial conditioning of magnetic fusion device vacuum vessels following evacuation from atmospheric pressure. Hydrogenic glow discharge conditioning (GDC) significantly reduces the near-surface concentration of simple adsorbates, such as H/sub 2/O, CO, and CH/sub 4/, and lowers ion-induced desorption coefficients by typically three orders of magnitude. The time evolution of the residual gas production observed during hydrogen-glow discharge conditioning of the carbon first-wall structure of the TFTR device is similar to the time evolution observed during hydrogen GDC of the initial first-wall configuration in TFTR, which was primarily stainless steel. Recently, helium GDC has been investigated for several wall-conditioning tasks on a number of tokamaks including TFTR. Helium GDC shows negligible impurity removal with stainless steel walls. For impurity conditioning with carbon walls, helium GDC shows significant desorption of H/sub 2/O, CO, and CO/sub 2/; however, the total desorption yield is limited to the monolayer range. In addition, helium GDC can be used to displace hydrogen isotopes from the near-surface region of carbon first-walls in order to lower hydrogenic retention and recycling. 38 refs., 6 figs.