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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

OSSE observations of galactic 511 keV annihilation radiation

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory has performed several observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron annihilation radiation. Preliminary analysis of data collected during the observation of the galactic center region over the period 13-24 Jun. 1991, indicates the presence of a 511 keV line and positronium continuum superimposed on a power-law continuum. The line of flux was found to be (2.7 +/- 0.5) x 10(exp -4) gamma/sq cm sec, with a positronium fraction of (0.9 +/- 0.2). The 3(sigma) upper limit to daily variations in the 511 keV line flux from the mean during the observation interval is 3 x 10(exp -4) gamma/sq cm sec. If all of the observed annihilation radiation is assumed to originate from the x-ray source 1E 1740.7-2942, the corresponding 511 keV line flux would be (3.0 +/- 0.6) x 10(exp -4) gamma/sq cm sec. The 3(sigma) upper limit for 511 keV line emission from the x-ray binary GX1+4 is 6 x 10(exp -4) gamma/sq cm sec. Results from the galactic plane observations at galactic longitudes of 25 degrees (16-21 Aug. 1991) and 339 degrees (6-11 Sep. 1991) suggest that the emission is concentrated near the galactic center. The observations and the preliminary results are described.

Purcell, W. R.↗
NASA NTRS1993

Compton-backscattered annihilation radiation from the Galactic Center region

On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.

Smith, D. M.↗
NASA NTRS1993

Search for extraterrestrial intelligence/high resolution microwave survey team member

This semiannual status report describes activities conducted by the Principal Investigator during the first half of this third year of the NASA High Resolution Microwave Survey (HRMS) Investigator Working Group (IWG). As a (HRMS) Team Member with primary interest in the Sky Survey activity, this investigator attended IWG meetings at NASA/Ames and U.C.-Santa Cruz in Apr. and Aug. 1992, and has traveled independently to NRAO/Kitt Peak, Arizona (April 1993) and Woodbury, Georgia (July 1993). During the July 1993 visit to the Georgia Tech Research Corporation/Woodbury Research Facility, an experiment was conducted to study the effects of interference from C-band (3.7 - 4.2 GHz) geostationary spacecraft on the Sky Survey operation in that band. At the first IWG meeting in April of this year, results of a SETI observation conducted at the 203 GHz positronium hyperfine resonance using the NRAO facility at Kitt Peak, AZ, were presented, as well as updates on the development of the spaceborne RFI data bases developed for the project. At the second meeting, results of the study of interference from C-band geostationary spacecraft were presented. Likewise, a presentation was made at the accompanying 1993 Bioastronomy Symposium describing the SETI observation at the positronium hyperfine resonance.

Steffes, Paul G.↗
NASA NTRS1994

The annihilation of positrons in the cold phase of the interstellar medium revisited

The positron cross sections in H and H2 media are reevaluated, taking into account new experimental results. Using a Monte Carlo simulation, we find a positronium fraction before thermalization of 0.90 for H2, in good agreement with the previous experimental result given by Brown et al. (1986). For H we obtain an upper limit of 0.98. We study the behavior of the charge exchange annihilation in a cold phase (molecular cloud). We calculate a formula for the slowing-down time t, before annihilation lasting Delta t, via charge exchange, of a positron beam with a given energy for different medium densities and initial energies. An upper limit of 0.7 MeV for the initial energy of the positrons, annihilating in the molecular cloud G0.86 - 0.08 near the gamma ray source positronium and gives new time constraints on their possible observation.

Wallyn, P.↗
DOE OSTI2020

Demonstration of o-Ps detection with a cylindrical array of NaI detectors

Ortho-positronium (o-Ps) is a bound state of an electron and positron that can provide a means of searching for new physics. We searched and identified o-Ps in our cylindrical array of NaI(Tl) scintillators, developing a technique for tagging on o-Ps with any one of the 24 bars in the array. With high angular efficiency and this new technique, such an experimental setup could be used in a fundamental symmetries search. In particular, we explore the possibility of using such a setup with a search for CP- or CPT-violation in o-Ps.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

In-situ characterization of free-volume holes in polymer thin films under controlled humidity conditions with an atmospheric positron probe microanalyzer

A pulsed, slow positron beam, with a diameter of 200 {mu}m, was extracted into air through a thin SiN window of an atmospheric positron probe microanalyzer (PPMA), and used to measure the ortho-positronium lifetimes {tau} in polyvinyl alcohol and polycaprolactam sub-{mu}m-thick films. By measuring the variation of {tau} as a function of relative humidity, the effect of water molecules on the hole sizes, deduced from {tau}, was examined for the films with consideration to the chain mobility. The results demonstrate the usefulness of the atmospheric PPMA to the in-situ characterization of nanoscopic holes in thin films under practical conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Molecular structure calculations: A unified quantum mechanical description of electrons and nuclei using explicitly correlated Gaussian functions and the global vector representation

We elaborate on the theory for the variational solution of the Schroedinger equation of small atomic and molecular systems without relying on the Born-Oppenheimer paradigm. The all-particle Schroedinger equation is solved in a numerical procedure using the variational principle, Cartesian coordinates, parameterized explicitly correlated Gaussian functions with polynomial prefactors, and the global vector representation. As a result, non-relativistic energy levels and wave functions of few-particle systems can be obtained for various angular momentum, parity, and spin quantum numbers. A stochastic variational optimization of the basis function parameters facilitates the calculation of accurate energies and wave functions for the ground and some excited rotational-(vibrational-)electronic states of H{sub 2}{sup +} and H{sub 2}, three bound states of the positronium molecule, Ps{sub 2}, and the ground and two excited states of the {sup 7}Li atom.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

AEgIS experiment commissioning at CERN

The AEgIS Experiment is an international collaboration based at CERN whose aim is to perform the first direct measurement of the gravitational acceleration g of antihydrogen in the gravitational field of the Earth. Cold antihydrogen will be produced with a pulsed charge exchange reaction in a cylindrical Penning trap where antiprotons will be cooled to 100mK. The cold antihydrogen will be produced in an excited Rydberg state and subsequently formed into a beam. The deflection of the antihydrogen beam will be measured by using Moire deflectometer gratings. After being approved in late 2008, AEgIS started taking data in a commissioning phase early 2012. This report presents an overview of the AEgIS experiment, describes its current status and shows the first measurements on antiproton catching and cooling in the 5 T Penning catching trap. We will also present details on the techniques needed for the 100mK antihydrogen production, such as pulsed positronium production and its excitation with lasers.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Positron interactions with water–total elastic, total inelastic, and elastic differential cross section measurements

Utilising a high-resolution, trap-based positron beam, we have measured both elastic and inelastic scattering of positrons from water vapour. The measurements comprise differential elastic, total elastic, and total inelastic (not including positronium formation) absolute cross sections. The energy range investigated is from 1 eV to 60 eV. Comparison with theory is made with both R-Matrix and distorted wave calculations, and with our own application of the Independent Atom Model for positron interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Positron annihilation characteristics in mesostructural silica films with various porosities

Porous silica films with various porosities were prepared via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structure-directing agent. Doppler broadening of positron annihilation radiation (DBAR) spectra were collected for the prepared films using a variable energy slow positron beam. Different linear relationships between positron annihilation line shape parameters S and W are found for the as-deposited films and calcined ones, indicative of the decomposition of the copolymer porogen in the as-deposited films upon calcination. This also reveals the variation of positron annihilation sites as a function of F127 loading or porosity. Strong correlations between positronium 3γ annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Short and medium range order in two-component silica glasses by positron annihilation spectroscopy

The dependence of chemical composition on the average sizes of subnanometer-scale intrinsic structural open spaces surrounded by glass random networks in two-component silica-based glasses was investigated systematically using positronium (Ps) confined in the open spaces. The average sizes of the open spaces for SiO{sub 2}-B{sub 2}O{sub 3} and SiO{sub 2}-GeO{sub 2} glasses are only slightly dependent on the chemical compositions because the B{sub 2}O{sub 3} and GeO{sub 2} are glass network formers that are incorporated into the glass network of the base SiO{sub 2}. However, the open space sizes for all SiO{sub 2}-R{sub 2}O (R = Li, Na, K) glasses, where R{sub 2}O is a glass network modifier that occupies the open spaces, decrease rapidly with an increase in the R{sub 2}O concentration. Despite the large difference in the ionic radii of the alkali metal (R) atoms, the open space sizes decrease similarly for all the alkali metal atoms studied. This dependence of the chemical composition on the open space sizes in SiO{sub 2}-R{sub 2}O observed by Ps shows that the alkali metal atoms do not randomly occupy the structural open spaces, but filling of the open spaces by R{sub 2}O proceeds selectively from the larger to the smaller open spaces as the R{sub 2}O concentrations are increased.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Exciton complexes in low dimensional transition metal dichalcogenides

We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter α, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of α is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The spectrum of darkonium in the Sun

Dark matter that gets captured in the Sun may form positronium-like bound states if it self-interacts via light dark photons. In this case, dark matter can either annihilate to dark photons or recombine in bound states which subsequently also decay to dark photons. The fraction of the dark photons that leave the Sun without decaying to Standard Model particles have a characteristic energy spectrum which is a mixture of the direct annihilation process, the decays of ortho- and para- bound states and the recombination process. The ultimate decay of these dark photons to positron-electron pairs (via kinetic mixing) outside the Sun creates a distinct signal that can either identify or set strict constraints on dark photon models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Symmetry and boundness of four-particle coulomb systems

The problem of boundness of a{sup +}b{sup +}c{sup -}d{sup -} four-particle Coulomb systems (quadrions) is studied versus the masses of the particles involved. Inequalities that make it possible to deduce that, if some reference quadrions form a bound state, the same is true for a large number of quadrions formed by particles having various masses were derived. A compendium of calculations for energies of reference systems that possess various symmetries [positronium molecules (e{sup +}e{sup +}e{sup -}e{sup -}) and quadrions of the a{sup +}b{sup +}b{sup -}b{sup -}, a{sup +}b{sup +}a{sup --}, and a{sup +}a{sup +}b{sup -}c{sup -} types] is given, and groups of bound asymmetric quadrions corresponding to them are determined. An inequality for kinetic energies of particles that makes it possible to find out, by using asymmetric reference systems, whether specific quadrions are bound is obtained. It is shown that the boundness of many quadrions is ensured by the boundness of respective three-particle systems. The entire body of the present results permits proving that, of the total number of 406 quadrions containing electrons, muons, pions, kaons, protons, deuterons, and tritons and their antiparticles, 227 quadrions are bound.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Hamiltonian anomalies of bound states in QED

The Bound State in QED is described in systematic way by means of nonlocal irreducible representations of the nonhomogeneous Poincare group and Dirac's method of quantization. As an example of application of this method we calculate triangle diagram Para-Positronium {yields} {gamma}{gamma}. We show that the Hamiltonian approach to Bound State in QED leads to anomaly-type contribution to creation of pair of parapositronium by two photon.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

e + e - Plasma Photon Source

This note addresses the idea of a photon source that is based on an e + e - plasma created by co-propagating beams of e + and e - . The plasma has a well-defined temperature, and the thermal distribution of the charged particles is used to average over the relative velocity cross section multiplied by the relative velocity. Two relevant cross sections are the direct “free-free” annihilation of e + e - pairs in the plasma, and the radiative recombination of e + e - pairs into positronium (Ps) which subsequently undergoes annihilation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Influence of Water, Vacuum, and Temperature on Surface Conditions of a Zeolite‐based Molecular Sieve

Molecular sieves such as zeolite-based materials are ubiquitous in industrial separation processes. However, there is a significant gap in understanding the surface properties and adsorption mechanisms for commercial zeolites, as most research focuses on pure zeolite powders rather than industrially relevant forms. Here, this work addresses this gap in understanding by employing advanced characterization techniques, including positron annihilation spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, liquid nitrogen sorption, and Fourier-transform infrared spectroscopy, to investigate the adsorption and desorption behavior of water in commercial zeolite 13X. Our research reveals insights into the pore-filling mechanisms, the impact of material binders on adsorption properties, and the dynamics of hydration and drying processes for zeolites. Monitoring changes on a minute scale allowed the distinction between fast and slow processes leading to sample drying. The identification of positronium bound to Na + ions indicated that water molecules remain in the vicinity of Na + ions after air-drying zeolite 13X. These findings highlight the importance of various environmental conditions in restoring zeolite properties to baseline after hydration, with significant implications for optimizing industrial processes. This work sets the direction for further research aimed at developing more efficient and robust separation techniques.

Beads Binder↗
DOE OSTI2018

Effect of Cobalt Oxide Nanoparticles on the Nano-scale Free Volume and Optical Properties of Biodegradable CMC/PVA Films

Chemically prepared cobalt oxide nanoparticles (NPs) were added to biodegradable carboxymethyl cellulose (CMC) (20%)/polyvinyl alcohol (PVA) (80%) blend films. The structural properties of these films were investigated by X-ray diffraction, Fourier transformation infrared spectroscopy (FTIR) and differential thermal analysis (DTA). Co{sub 3}O{sub 4}/(CMC + PVA) films show a semi-crystalline structure and the degree of crystallinity decreases with adding Co{sub 3}O{sub 4} NPs. FTIR confirms the good interaction between the blend chains and Co{sub 3}O{sub 4} NPs. The melting temperature T{sub m} for CMC/PVA is about 212 °C then decreased with increasing Co{sub 3}O{sub 4} content, due to some decrease in the ordered association of the blend which results in a decrease in the blend crystallinity. Positron annihilation lifetime spectroscopy (PALS) measurements were carried out with a conventional fast–fast coincidence spectrometer. It was found that ortho-positronium lifetime τ{sub 3} and free volume V{sub f} increase while o-Ps intensity I{sub 3} still constant as Co{sub 3}O{sub 4} concentration increases. This is because adding Co{sub 3}O{sub 4} NPs encourages the formation of o-Ps. The swelling ratio SR% as a function of Co{sub 3}O{sub 4} concentration was also studied and its value increases with Co{sub 3}O{sub 4} addition. The optical study illustrated the decrease of the transmittance T of the films from 87 to 35.5% with increasing Co{sub 3}O{sub 4} content from 0 to 0.9 wt%. Also, both the direct and indirect optical band gaps of the films red-shifted from 4.05 to 3.75 eV and 3.3 to 2.75 eV, respectively. The influence of Co{sub 3}O{sub 4} on the refractive index of the films is also reported.

77 NANOSCIENCE AND NANOTECHNOLOGY↗