Positron‐Emitter Production in Solar Flares from 3 He Reactions

Abstract

We treat in detail positron production from the decay of radioactivenuclei produced in nuclear reactions of accelerated 3He.Because of their large cross sections and low threshold energies, thesereactions can significantly contribute to positron production in solarflares with accelerated-particle compositions enriched in3He. The addition of these 3He reactions extendsearlier calculations of positron production by accelerated protons andα-particles. 3He reactions not only add significantlyto the total positron yield in flares, but can also yield a positrondepth distribution that peaks higher in the solar atmosphere. We discussthe impact these reactions have on the analysis of the annihilation lineobserved with RHESSI from the 2002 July 23 flare. A significantcontribution from 3He reactions expands the utility of theannihilation line as a sensitive tool for investigating the structure ofthe flaring solar atmosphere.