SH51C-01
Modeling of the Interstellar Antiproton Flux on the Basis of the Leaky-Box Propagation Model
Numerous modeling of the galactic antiproton flux originated from interactions of Cosmic Rays with interstellar matter has shown that the calculated flux is lower than the antiproton flux observed near the Earth. To assess this discrepancy, in our modeling we have made an effort to eliminate all possible uncertainties in the parameters of antiproton flux calculation, and we have used modern nuclear reaction computer code accounting for antiparticle behavior. Common uncertainties include the incomplete knowledge of cross sections for antiproton production, the corresponding spectral limitations, the precise knowledge of annihilation and scattering, and the limitations on the antiproton propagation models for the heliosphere. In this presentation we show results of simulation of antiproton (pbar) production in (p,A) and (pbar,A) reactions and the influence of the latter on the interstellar antiproton flux. The antiproton yield was simulated on the basis of nuclear reaction Multy Stage Dynamical Model computer code (Dementyev et al). The interstellar antiproton flux is calculated for the Leaky-box propagation model including accounting for the tertiary antiprotons produced by secondary antiprotons in nuclear reactions with the interstellar gas. Tertiaries were calculated on the base of Tan et al., approximation and using the MSDM code. The tertiary antiproton spectral shape obtained with MSDM approximation differs modestly from the shape with the Tan and Ng approximation. However, this difference affects only the antiproton spectrum at E < 0.1 GeV, i.e. in the energy range where at present direct measurements are absent. The calculated flux was modulated within the heliosphere for periods of minimum and maximum solar activity accordingly to (Moskalenko et al.), and it agrees quite well with the BESS experimental results obtained in the minimum solar activity and also with BESS (2000) results in epoch near the maximum solar activity. Dementyev, A.V. et al., Radiation Measurements, 30, 553, 1999. Tan, L.C.,et al., Phys. Rev., D26, 1179-1182, 1983. Moskalenko, I.V., et al., Ap.J. (565), 280-296, 2002.
SH51C-02
Radiation Belts of Antiparticles in Planetary Magnetospheres
The Earth's radiation belts could be populated, besides with electrons and protons, also by antiparticles, such as positrons (Basilova et al., 1982) and antiprotons (pbar). Positrons are born in the decay of pions that are directly produced in nuclear reactions of trapped relativistic inner zone protons with the residual atmosphere at altitudes in the range of about 500 to 3000 km over the Earth's surface. Antiprotons are born by high energy (E > 6 GeV) cosmic rays in p+p - p+p+p+ pbar and in p+p - p+p+n+nbar reactions. The trapping and storage of these charged anti-particles in the magnetosphere result in radiation belts similar to the classical Van Allen belts of protons and electrons. We describe the mathematical techniques used for numerical simulation of the trapped positron and antiproton belt fluxes. The pion and antiproton yields were simulated on the basis of the Russian nuclear reaction computer code MSDM, a Multy Stage Dynamical Model, Monte Carlo code, (i.e., Dementyev and Sobolevsky, 1999). For estimates of positron flux there we have accounted for ionisation, bremsstrahlung, and synchrotron energy losses. The resulting numerical estimates show that the positron flux with energy >100 MeV trapped into the radiation belt at L=1.2 is of the order ~1000 m-2 s-1 sr-1, and that it is very sensitive to the shape of the trapped proton spectrum. This confined positron flux is found to be greater than that albedo, not trapped, mixed electron/positron flux of about 50 m-2 s-1 sr-1 produced by CR in the same region at the top of the geomagnetic field line at L=1.2. As we show in report, this albedo flux also consists mostly of positrons. The trapped antiproton fluxes produced by CR in the Earth's upper rarified atmosphere were calculated in the energy range from 10 MeV to several GeV. In the simulations we included a mathematic consideration of the radial diffusion process, both an inner and an outer antiproton source, losses of particles due to ionization process, annihilation, and nuclear interactions with the ambient matter. We have found that the Earth's antiproton belt possesses about 6-60 times larger antiproton fluxes compared to the galactic fluxes in interplanetary space during minimum and maximum solar activity at all energies in confinement zone. The radiation belt antiproton fluxes are spread into a wider L-shell range than its generation location around L=1.2. This is due to diffusion processes, and it demonstrates that radial diffusion as a relatively significant process for antimatter, even in the inner magnetosphere. Antimatter accumulated in the magnetospheres of solar system bodies may be of significance for space travel. It could be used as a propulsion for space missions to the outer planets and beyond. Antimatter has an energy density more than ten orders of magnitude higher than the best chemical propellants currently used in rocket systems. References: Basilova, R. N., A.A. Gusev, G.I. Pugacheva , Geom. and Aeronom. V. 22, p. 671-673, 1982.Chen, J., T. Dementyev, A.V., Sobolevsky, N.M. Radiation Measurements, 30, 553, 1999.
SH51C-03
Satellite Observations of Annihilation of Positrons Produced at the Sun, the Earth, and Center of our Galaxy
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.
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