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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Recent experimental results of two-proton correlated emission from the excited states of {sup 17,18}Ne and {sup 28,29}S

Two-proton emissions from the excited states of {sup 17,18}Ne and {sup 28,29}S were investigated by the radioactive beams bombarding on the {sup 197}Au target via the Coulomb excitation. The complete-kinematics measurements were actualized by the stacks of silicon-strip detectors and CsI+PIN array detectors. The invariant mass of final systems as well as the relative momentum, opening angle, and relative energy of the two emitted protons were reconstructed under the framework of relativistic kinematics. The mechanisms of two-proton emission were analyzed in a simple schematic model. With the help of Monte-Carlo simulations, the two protons emitted from the 6.15 MeV excited state of {sup 18}Ne and the excited states around 10 MeV of {sup 29}S, respectively, exhibit prominent features of {sup 2}He decay. While for the other states, no obvious diproton emissions were observed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Two-proton sequential decay from excited states of {sup 18}Ne

Two-proton radioactivity from {sup 18}Ne is discussed in terms of sequential decay. The widths for one-proton emission from excited states are calculated, which include spectroscopic factors, obtained from a Shell-model calculation with realistic interactions. The widths show that two-proton emission from the 1{sup -} state of {sup 18}Ne at 7.94 MeV, is most likely to go through sequential decay. The same mechanism is discussed for other excited states at higher energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Precise measurement of the {sup 19}Ne half-life

We describe a high-precision measurement of the half-life of the T = 1/2 nucleus {sup 19}Ne, performed at TRIUMF, Canada's National Laboratory for Nuclear and Particle Physics, Vancouver, Canada. Some implications of this measurement related to tests of the Standard Model are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Initial commissioning results with the NSCL Electron Beam Ion Trap

The ReA reaccelerator is being added to the National Superconducting Cyclotron Laboratory (NSCL) fragmentation facility in order to provide exotic rare-isotope beams, not available at the Isotope Separation On-Line facilities, in the several-MeV/u energy range. The first stage of the NSCL reaccelerator complex, consisting of an EBIT charge breeder, a room-temperature radiofrequency quadrupole (RFQ) accelerator, and superconducting linear accelerator modules, has been completed and is being put into operation. Commissioning of the EBIT has started by extracting charge-bred residual gas ions, ions created from a Ne gas jet directed across the EBIT's electron beam and ions captured from an external test ion source. Charge-bred ions from the Ne gas jet have been extracted as a pulse and accelerated through the RFQ and the two cryomodules.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Ne{sup +} ion sputtering effect on amorphous Ga-In-Zn-O thin-film surface investigated by high-resolution XPS

The effect of Ne{sup +} ion sputtering on amorphous Ga-In-Zn-O (a-GIZO) thin films was investigated by using surface-sensitive, synchrotron-radiation-based, high-resolution X-ray photoelectron spectroscopy (XPS). a-GIZO thin films having different compositions (Ga{sub 2}O{sub 3}:In{sub 2}O{sub 3}:ZnO = 1:1:1, 2:2:1, 3:2:1, 4:2:1) were investigated. It was found out that the amounts of the In and Zn contents relative to that of Ga decreased noticeably after sufficient sputtering, and that there occurred a subgap state above the valence band maximum and metallic states at the In 3d and 4d core levels as well as at the Fermi edge.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Production of high intensity Beta beams at the ISOLDE facility

We discuss a design study devoted to a construction of the Beta beams facility at CERN, a next generation European facility aiming for a production of pure and collimated ultra-relativistic beam of electron (anti)neutrinos with help of accelerated {beta}-decaying radioactive ions circulating in a storage decay ring. This high intense source of (anti)neutrinos directed towards a remote underground neutrino detector will allow to measure neutrino oscillations with high accuracy offering a unique chance for establishing a value of the {beta}{sub 13} mixing angle and CP violating phase. Recently, a significant progress have been achieved on the conceptual design of high power targets required for a production and an extraction of two baseline isotopes, {sup 6}He and {sup 18}Ne, at the unexampled rate of several 10{sup 13} ions/s. There is a possibility to produce these isotopes using the so-called Isotope Separation On Line (ISOL) method at the ISOLDE facility (CERN). The {sup 6}He production is realized by taking advantage of the {sup 9}Be(n,{alpha}){sup 6}He reaction and with help of spallation neutrons and porous BeO target material. The production of {sup 18}Ne through the {sup 19}F(p,2n){sup 18}Ne reaction at required intensities is even more challenging. Currently, a molten salt (NaF) loop target is proposed for a production of high rate of {sup 18}Ne required for the Beta beams project. The progress on the design study associated with new data and plans for future is briefly presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Transport and emittance study for 18 GHz superconducting-ECR ion source at RCNP

As the upgrade program of the azimuthally varying field (AVF) cyclotron is at the cyclotron facility of the RCNP, Osaka University for the improvement of the quality, stability, and intensity of accelerated beams, an 18 GHz superconducting (SC) ECR ion source has been installed to increase beam currents and to extend the variety of ions, especially for highly charged heavy ions which can be accelerated by RCNP AVF cyclotron. The production development of several ions such as B, O, N, Ne, Ar, Ni, Kr, and Xe has been performed by Yorita et al.[Rev. Sci. Instrum. 79, 02A311(2008); 81, 02A332 (2010)]. Further studies for the beam transport have been done in order to improve the beam current more for injection of cyclotron. The effect of field leakage of AVF main coil is not negligible and additional steering magnet has been installed and then beam transmission has been improved. The emittance monitor has also been developed for the purpose of investigating correlation between emittance of beam from ECR ion sources and injection efficiency. The monitor consists with BPM82 with rotating wire for fast measurement for efficient study.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Experimental investigation on focusing characteristics of a He-Ne laser using circular Fresnel zone plate for high-precision alignment of linear accelerators

We experimentally investigate the focusing characteristics of a He-Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than {+-}30 {mu}m. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in GaAs using coherent acoustic phonon spectroscopy

We report the results of coherent acoustic phonon spectroscopy analysis of band-edge optical modification of GaAs irradiated with 400 keV Ne{sup ++} for doses between 10{sup 11}-10{sup 13} cm{sup -2}. We relate this optical modification to the structural damage density as predicted by simulation and verified by ion channeling analysis. Crystal damage is observed to cause optical modification that reduces the amplitude of the optoacoustic signal. The depth-dependent nature of the optoacoustic measurement allows us to determine optical damage cross-sections along the ion track, which are found to vary as a function of position along the track. Unexpectedly, we find that this optical modification is primarily dependent on the structural damage density and insensitive to the specific defect configuration along the ion track, suggesting that a simple model of defect density along the track is sufficient to characterize the observed optical changes. The extent of optical modification is strongly probe frequency-dependent as the frequency is detuned from the GaAs band edge. As determined from the experimental measurements, the spatial extent of optical modification exceeds the spatial extent of the structural disorder by an order of magnitude.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Temperature diagnostics of ECR plasma by measurement of electron bremsstrahlung

The x-ray bremsstrahlung spectrum emitted by the electron population in a 14.5 GHz ECR plasma source has been measured using a NaI(Tl) detector, and hence the electron temperature of the higher energy electron population in the plasma has been determined. The x-ray spectra for Ne and Ar gases have been systematically studied as a function of inlet gas pressure from 7 Multiplication-Sign 10{sup -7} mbar to 7 Multiplication-Sign 10{sup -5} mbar and for input microwave power {approx}1 W to {approx}300 W. At the highest input power and optimum pressure conditions, the end point bremsstrahlung energies are seen to reach {approx}700 keV. The estimated electron temperatures (T{sub e}) were found to be in the range 20 keV-80 keV. The T{sub e} is found to be peaking at a pressure of 1 Multiplication-Sign 10{sup -5} mbar for both gases. The T{sub e} is seen to increase with increasing input power in the intermediate power region, i.e., between 100 and 200 W, but shows different behaviour for different gases in the low and high power regions. Both gases show very weak dependence of electron temperature on inlet gas pressure, but the trends in each gas are different.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

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

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.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach

A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Spectral lines behavior of Be I and Na I isoelectronic sequence in Debye plasma environment

We report the plasma screening effect on the first ionization potential (IP) and [He]2s{sup 2} ({sup 1}S{sub 0}){yields}[He]2s2p/2s3p allowed ({sup 1}P{sub 1}) and inter-combination transitions ({sup 3}P{sub 1}) in some selected Be-like ions. In addition, we investigate the spectral properties of [Ne]3s ({sup 2}S{sub 1/2}){yields}[Ne]np ({sup 2}P{sub 1/2} and {sup 2}P{sub 3/2} for n = 3, 4) transitions in Ca X and Fe XVI ions (Na I isoelectronic sequence) and [He]3s({sup 2}S{sub 1/2}){yields}[He]np ({sup 2}P{sub 1/2} and {sup 2}P{sub 3/2} for n = 2, 3) transitions in Li, B II, and N IV (Li I isoelectronic sequence) under plasma environment. The state-of-the-art relativistic coupled cluster calculations using the Debye model of plasma for electron-nucleus interaction show that (a) the ionization potential decreases sharply with increasing plasma strength and (b) the gap between the [He]2s{sup 2} ({sup 1}S{sub 0}){yields}[He]2s2p({sup 1,3}P{sub 1}) energy levels increases with increasing plasma potential and nuclear charge. It is found that the [He]2s{sup 2} ({sup 1}S{sub 0}){yields}2s3p ({sup 1,3}P{sub 1}) transition energy decreases uniformly with increasing plasma potential and nuclear charge. In other words, the spectral lines associated with 2s-2p (i.e., {Delta}n=0, where n corresponds to principle quantum number) transitions in Be I isoelectronic sequence exhibit a blue-shift (except for Be I, B II, and the lowest inter-combination line in C III, which exhibit a red-shift), whereas those associated with 2s-3p (i.e., {Delta}n{ne}0) transitions are red-shifted. Similar trend is observed in Li I and Na I isoelectronic sequences, where spectral lines associated with {Delta}n=0 ({Delta}n{ne}0) are blue-shifted (red-shifted). The effect of Coulomb screening on the spectral lines of ions subjected to plasma is also addressed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

A new theoretical approach to thermonuclear radiative-capture reaction rate

We propose a new computational method for astrophysical reaction rate of radiative capture process, which does not require any solution of scattering problem. It is tested for twobody radiative caputure reaction {sup 16}O({alpha},{gamma}){sup 20}Ne and a comparison is made with an ordinary method solving two-body scattering problem. The method is shown to work well in practice and thus will be useful for problems in which an explicit construction of scattering solution is difficult such as the triple-alpha capture process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Some exploitations of the self-consistent QRPA approach with the Gogny force

Fully consistent axially-symmetric-deformed quasiparticle random phase approximation calculations have been performed with the D1S Gogny force. Giant resonances in exotic nuclei as well as in deformed Mg and Si isotopes have been studied. Dipole responses have been calculated in Ne isotopes and N=16 isotones to study the existence of soft dipole modes in exotic nuclei. The same formalism has been used to describe multipole responses up to octupole in the deformed and heavy nucleus {sup 238}U. Low energy spectroscopy of nickel isotopes has been studied, revealing 0{sup +} states which display a particular structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Studies of light neutron-excess systems from bounds to continuum

The generalized two-center cluster model (GTCM), which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, {sup 12}Be = {alpha}+{alpha}+4N. We discuss the change of the neutrons' configuration around two {alpha}-cores as a variation of an excitation energy. We show that the excess neutrons form various chemical-bondinglike configurations around two {alpha} cores in the unbound region above the {alpha} decay threshold. The possibility of the {alpha} cluster formation in the heavier neutron-excess system, {sup 28}Ne, is also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Fusion-fission and quasifission in the reactions with heavy ions leading to the formation of Hs

Mass and energy distributions of binary reaction products obtained in the reactions {sup 22}Ne+{sup 249}Cf,{sup 26}Mg+{sup 248}Cm,{sup 36}S+{sup 238}U and {sup 58}Fe+{sup 208}Pb leading to Hs isotopes have been measured. At energies below the Coulomb barrier the bimodal fission of Hs*, formed in the reaction {sup 26}Mg+{sup 248}Cm, is observed. In the reaction {sup 36}S+{sup 238}U the considerable part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier the symmetric fragments originate mainly from fusion-fission process for both reactions with Mg and S ions. In the case of the {sup 58}Fe+{sup 208}Pb reaction the quasifission process dominates at all measured energies. The pre- and post-scission neutron multiplicities as a function of the fragment mass have been obtained for the reactions studied.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Infrared characteristics of VO{sub 2} thin films for smart window and laser protection applications

Vanadium dioxide (VO{sub 2}) films with a low semiconductor-to-metal transition temperature of 45 Degree-Sign C were fabricated through direct current magnetron sputtering followed by a post-annealing. Atomic force microscopy measurements show that the VO{sub 2} grain size is about one hundred of nanometers. Infrared (IR) characteristic is well investigated by applying a He-Ne laser power intensity measurement, and the result reveals that the VO{sub 2} film exhibits excellent IR switching property. Furthermore, solar smart window and laser protection experiments demonstrate that the obtained VO{sub 2} thin film is a promising material for the application in related fields.

36 MATERIALS SCIENCE↗