HR: 0800h
AN: SH51C-03    [Abstracts]
TI: Satellite Observations of Annihilation of Positrons Produced at the Sun, the Earth, and Center of our Galaxy
AU: * Share, G H
EM: share@astro.umd.edu
AF: Department of Astronomy, University of Maryland, College Park, Md 20742, United States
AU: * Share, G H
EM: share@astro.umd.edu
AF: Space Science Division, Naval Research Laboratory, Washington, DC 20375, United States
AU: Murphy, R J
EM: murphy@ssd5.nrl.navy.mil
AF: Space Science Division, Naval Research Laboratory, Washington, DC 20375, United States
AU: Lin, R P
EM: bobin@ssl.berkeley.edu
AF: Space Science Laboratory, University of California, Berkeley, CA 94720, United States
AB: Positrons are created in nuclear interactions that produce β ⁺-unstable nuclei and pi⁺ mesons. Satellites remotely observe positron production when they annihilate with electrons yielding the characteristic line at 511 keV. Radiation detectors such as the germanium diodes on the Ramaty High-Energy Solar Spectrocopic Imager (RHESSI) observe this line from positrons by nuclei activated in the spacecraft by proton interactions during transit through the Earth's radiation belts and from cosmic radiation. This forms an intense background for solar and astrophysical observations. RHESSI and other satellites have observed positron annihilation in over 50 solar flares. These measurements provide information on the temperature, density, and ionization state of solar atmosphere where the positrons annihilate. The measurements suggest that up to a few kg of positrons are produced in these flares. Detectable annihilation-line radiation is also emitted from the Earth's atmosphere in interactions of cosmic rays and solar energetic particles. An extended annihilation-line source has also been detected within about 10 degrees of the center of the Milky Way that is attributed to positrons released in radioactive decays of nuclei with long half-lives produced in supernovae, novae, and other stellar explosions. From 1980 to 1988 NASA's Solar Maximum Mission satellite also detected belts of positrons emitted by nuclear reactors onboard KOSMOS satellites and trapped temporarily in the Earth's magnetic field. This work was supported by NASA Supporting Research & Technology grants.
UR: http:www.astro.umd.edu/~share/
DE: 7514 Energetic particles (2114)
DE: 7519 Flares
DE: 7554 X-rays, gamma rays, and neutrinos
DE: 7984 Space radiation environment
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Joint Assembly