The positronium fraction before thermalization in helium

Details The positronium fraction before thermalization in helium The positronium fraction before thermalization in helium

Jun 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...92..545c&link_type=abstract

The Astrophysical Journal Supplement Series, vol. 92, no. 2, p. 545-547

Astronomy and Astrophysics

Astrophysics

5

Atomic Interactions, Cosmochemistry, Helium, Interstellar Matter, Nuclear Astrophysics, Particle Production, Positronium, Thermalization (Energy Absorption), Abundance, Ionization, Monte Carlo Method, Positrons

Scientific paper

Positron interactions with the matter of various media have been studied for a long time in astrophysics, expecially since the 511 keV line was detected in the direction of the Galactic center (Johnson, Harnden, & Haymes 1972) and confirmed by gamma-ray line experiments. The abundance of helium in the interstellar medium (the second most important atom after hydrogen) makes the study of the interaction of positrons in that medium a subject of great interest in astrophysics. The positronium fraction before thermalization in helium has already been measured in the laboratory (f1 = 80.7% +/- 0.5%; Brown & Leventhal 1986). The experimental value of the positronium fraction in molecular hydrogen (f1 = 89.7% +/- 0.3%; Brown & Leventhal 1986) has also been evaluated by a Monte Carlo simulation (Bussard, Ramaty, & Drachman 1979) (93%), and recently a reevaluation based on recent measurements of cross sections has been calculated by Wallyn et al. (1993)(90%). Theoretical calculations have already been done (Bussard, Ramaty, & Drachman 1979), (95%) and reevaluated (Wallyn et al. 1993) (98%) for the positronium fraction in atomic hydrogen. We pursue this investigation with helium atoms and obtain 78%. Our result is in excellent agreement with the experimental value of Brown & Leventhal (1986). Astrophysical implications will be emphasized.

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