The Annihilation of Positrons in the Cold Phase of the Interstellar Medium Revisited
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1994
- DOI:
- 10.1086/173753
- Bibcode:
- 1994ApJ...422..610W
- Keywords:
-
- Abundance;
- Cold Gas;
- Elementary Particles;
- Interstellar Matter;
- Ionization Cross Sections;
- Molecular Clouds;
- Nuclear Fusion;
- Positron Annihilation;
- Astronomical Models;
- Charge Exchange;
- Computerized Simulation;
- Hydrogen;
- Mathematical Models;
- Monte Carlo Method;
- Positronium;
- Astrophysics;
- ELEMENTARY PARTICLES;
- ISM: ATOMS;
- NUCLEAR REACTIONS;
- NUCLEOSYNTHESIS;
- ABUNDANCES