Search NASA⌕ Search

SEARCH · Search NASA

Results for “positron annihilation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Gamma ray lines from solar flares and cosmic transients

Gamma-ray line emission processes in solar flares and cosmic transients are reviewed and the implications of recent line observations are discussed. For solar flares, neutron, positron, and deexcitation line production is addressed, presenting results of new numerical calculations based on more detailed and accurate nuclear cross sections. The application of the theory is illustrated by considering the June 7, 1980 flare, and the structure of the interaction region is discussed. For gamma-ray bursts and transients, the processes of positron production and annihilation and nuclear line emission are emphasized. The possible origin of the gamma-ray lines observed in a longer duration transient which is a particularly strong gamma-ray line emitter is also considered.

Ramaty, R.↗
NASA NTRS1983

Relativistic thermal plasmas - Effects of magnetic fields

Processes and equilibria in finite, relativistic, thermal plasmas are investigated, taking into account electron-positron creation and annihilation, photon production by internal processes, and photon production by a magnetic field. Inclusion of the latter extends previous work on such plasmas. The basic relations for thermal, Comptonized synchrotron emission are analyzed, including emission and absorption without Comptonization, Comptonized thermal synchrotron emission, and the Comptonized synchrotron and bremsstrahlung luminosities. Pair equilibria are calculated, including approximations and dimensionless parameters, the pair balance equation, maximum temperatures and field strengths, and individual models and cooling curves.

Araki, S.↗
NASA NTRS1983

Positron-electron pairs in astrophysics; Proceedings of the Workshop, Greenbelt, MD, January 6-8, 1983

Astrophysical sources of positron-electron-pair annihilation radiation are characterized in reviews and reports of observational and theoretical investigations. Topics examined include gamma-ray lines from solar flares, gamma-ray bursts, pulsars, the Galactic center, active galaxies, and physical processes in relativistic and magnetized plasmas. Spectra, historgrams, graphs, and diagrams are provided.

Burns, M. L.↗
NASA NTRS1992

Unthermalized positrons in gamma ray burst sources

The spectra of the broadening 0.511 MeV annihilation line produced by high temperatures was calculated in the case of unthermalized plasma; i.e., T sub e(+) is not = T sub e(-). The flattening in the spectrum of the annihilation lines for large differences of electron and positron temperatures is a strong indication that the observed features of the hard tailed spectrum of the gamma bursts can be well described by annihilation of unthermalized positrons. It is proposed that the charge separation occurring in Eddington limited accretion onto a neutron star or the one photon pair production in strong magnetic fields as a mechanism for the production of unthermalized positrons in the sources of gamma bursts. From the best fit of experimental spectra by the model, the parameters of sources for which the regions with different plasma temperatures can exist is evaluated.

Tkaczyk, W.↗
NASA NTRS1983

The Origin of the Galactic Annihilation Radiation

Observations of the e(+)-e(-) annihilation radiation from the galactic center are reviewed and the implications of these and other observations on the positron production process, the annihilation region and the fundamental nature of the galactic center source are discussed.

Lingenfelter, R. E.↗
DOE OSTI2023

Annihilation-gamma-based diagnostic techniques for magnetically confined electron–positron pair plasma

Efforts are underway to magnetically confine electron–positron pair plasmas to study their unique behaviour, which is characterized by significant changes in plasma time and length scales, supported waves and unstable modes. However, use of conventional plasma diagnostics presents challenges with these low-density and annihilating matter–antimatter plasmas. To address this problem, we propose to develop techniques based on the distinct emission provided by annihilation. This emission exhibits two spatial correlations: the distance attenuation of isotropic sources and the back-to-back propagation of momentum-preserving 2 $\gamma$ annihilation. We present the results of our analysis of the $\gamma$ emission rate and the spatial profile of the annihilation in a magnetized pair plasma from direct pair collisions, from the formation and decay of positronium as well as from transport processes. In order to demonstrate the effectiveness of annihilation-based techniques, we tested them on annular $\gamma$ emission profiles produced by a $\beta ^+$ radioisotope on a rotating turntable. Direct and positronium-mediated annihilation result in overlapping volumetric $\gamma$ sources, and the 2 $\gamma$ emission from these volumetric sources can be tomographically reconstructed from coincident counts in multiple detectors. Transport processes result in localized annihilation where field lines intersect walls, limiters or internal magnets. These localized sources can be identified by the fractional $\gamma$ counts on spatially distributed detectors.

Physics↗
NASA NTRS1974

Gamma-ray lines from novae

An appropriate gamma-ray telescope could detect the gamma-rays associated with radioactive decays. The observable lines would be the annihilation radiation following the positron emission of N-13, O-14, O-15, and Na-22 and the 2.312-MeV line emitted following the O-14 decay and the 1.274-MeV line emitted following the Na-22 decay. The experimental possibility should be borne in mind for the occurrence of novae within a few kiloparsecs.

Clayton, D. D.↗
NASA NTRS2004

High Energy Astrophysics Tests of Lorentz Invariance Violation

Observations of the multi-TeV spectra of the Mkn 501 and other nearby BL Lac objects exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz invariance violation. Such constraints have important implications for some quantum gravity and large extra dimension models. A much smaller amount of Lorentz invariance violation has potential implications for understanding the spectra of ultrahigh energy cosmic rays.

Stecker, F. W.↗
NASA NTRS2004

High Energy Astrophysics Tests of Lorentz Invariance Violation

Observations of the multi-TeV spectra of the nearby BL Lac objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker & Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz violation. We will show that such constraints have important implications for some quantum gravity models and large extra dimension models. We will also discuss the potentially important effects of a smaller Lorentz violation which is consistent with these constraints on the propagation and spectra of ultrahigh energy cosmic rays.

Stecker, Floyd W.↗
NASA NTRS2007

A Neutron Detector for the Electron Calorimeter (ECAL) Long Duration Balloon Experiment

The highest energy measurements of cosmic ray electrons extend just beyond 1 TeV. High energy electrons are of particular interest because energy losses during interstellar propagation insure that they arrive primarily from nearby sources. This may produce observable structure in their spectrum. Further, it is predicted that electrons and positrons result from the annihilation of many exotic particles deposited as dark matter candidates. These electrons may appear as excesses in the cosmic ray electron spectrum from 200 GeV to 1000 GeV. A new long duration balloon experiment, ECAL, is being planned to provide direct cosmic ray electron measurements from approx.50 GeV to >1 TeV. To make these measurements ECAL must discriminate strongly against showers from protons and heavier ions. One of the techniques used to make this discrimination may be based on measuring the secondary neutrons produced by events in the instrument. The neutron detector configuration and technique will be discussed along with its expected performance based on Monte Carlo simulations.

Adams, J. H., Jr.↗
NASA NTRS1975

Time dependences of the 0.51 and 2.2 MeV lines in solar flares

The time dependence of the 0.51 MeV line in solar flares is determined by the following factors: variation with time of the rate of nuclear reactions which produce the positron emitters; mean lives of the positron emitters; slowing-down of the positrons which depends on the ambient density and magnetic field; and annihilation or positronium formation times of the positrons with free or bound electrons. The discussion is limited to the observed intensity-time profile of a 0.35-8 MeV gamma-ray emission and of a 0.51-MeV line calculated for three different ambient densities in the annihilation region. Major conclusions are that (1) MeV electrons and protons of at least 30 MeV/nuc have similar time dependences and hence a common origin in the flare region, which support a two-phase acceleration model in solar flares; and (2) the delayed character of the 0.51-MeV emission is clearly defined, where at a time when the rate of nuclear reactions is zero, there still is considerable 0.51-MeV emission.

Ramaty, R.↗
NASA NTRS1987

Neutrino pair energy deposition in supernovae

The role of neutrino-antineutrino annihilation (producing an electron-positron pair) in delayed type II supernova explosions is investigated theoretically. The assumptions and analysis of Goodman et al. (1987) are examined in detail, with a focus on the need for a large density gradient at the edge of the neutrinosphere. It is found that the neutrino annihilation mechanism cannot contribute significantly to the energy of the explosion.

Cooperstein, J.↗
DOE OSTI2020

Hazma: a python toolkit for studying indirect detection of sub-GeV dark matter

With several proposed MeV gamma-ray telescopes on the horizon, it is of paramount importance to perform accurate calculations of gamma-ray spectra expected from sub-GeV dark matter annihilation and decay. We present hazma, a python package for reliably computing these spectra, determining the resulting constraints from existing gamma-ray data, and prospects for upcoming telescopes. For high-level analyses, hazma comes with several built-in dark matter models where the interactions between dark matter and hadrons have been determined in detail using chiral perturbation theory. Additionally, hazma provides tools for computing spectra from individual final states with arbitrary numbers of light leptons and mesons, and for analyzing custom dark matter models. hazma can also produce electron and positron spectra from dark matter annihilation, enabling precise derivation of constraints from the cosmic microwave background

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Limits on dark matter annihilation from the shape of radio emission in M31

Well-motivated models of dark matter often result in a population of electrons and positrons within galaxies produced through dark matter annihilation — usually in association with gamma rays. As they diffuse through galactic magnetic fields, these e ± produce synchrotron radio emission. The intensity and morphology of this signal depends on the properties of the interstellar medium through which the e ± propagate. Using observations of the Andromeda Galaxy (M31) to construct a model of the gas, magnetic fields, and starlight, we set constraints on dark matter annihilation to b$\overline{b}$ using the morphology of 3.6 cm radio emission. As the emission signal at the center of M31 is very sensitive to the diffusion coefficient and dark matter profile, we base our limits on the differential flux in the region between 0.9 – 6.9 kpc from the center. We exclude annihilation cross sections ≳ 3 × 10 −25 cm 3 /s in the mass range 10 – 500 GeV, with a maximum sensitivity of 7 × 10 −26 cm 3 /s at 20 – 40 GeV. Though these limits are weaker than those found in previous studies of M31, they are robust to variations of the diffusion coefficient.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Annihilation physics of exotic galactic dark matter particles

Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

Stecker, F. W.↗
NASA NTRS1976

Radiation mechanisms and magnetospheric structure of pulsars

A model of pulsars is outlined. Key early considerations were those which led to the identification of pulsars with neutron stars, the Goldreich-Julian model of pulsar magnetospheres, and the recognition that, in a pulsar magnetosphere, a high energy gamma ray may annihilate to produce an electron-positron pair. Arguments that suggest that pulsar magnetospheres may contain large masses of plasma, a suggestion which has important implications concerning the structure of the magnetosphere, are considered along with observational data which support a magnetosphere model based on that idea rather than the Goldreich-Julian model.

Sturrock, P. A.↗