Neutron Production in Solar Flares by Reactions of Accelerated 3He

Abstract

Abstract Previously, we showed that 3He is enhanced in the ion population accelerated in large solar flares, with a 3He/4He ratio of >0.1; i.e., several orders of magnitude larger than the accepted coronal value. We also showed that when 3He is enhanced, its nuclear reactions with elements of the solar atmosphere can significantly impact both positron production (and the subsequent positron-annihilation line) and the gamma-ray de-excitation-line spectrum. Both the 2.223 MeV neutron-capture line and escaping neutrons are important additional flare observables. Neutron production from reactions of 3He with heavy elements of the solar atmosphere are not currently included in our neutron-production code, and the reliable and consistent analysis of all available solar-flare data requires that neutron-production calculations include these reactions. We evaluate the neutron-production cross sections for these reactions and include them in the code. We then explore how the neutron observables (the escaping-neutron yield and spectrum and the flux of the neutron-capture line) are affected by 3He reactions. We find that neutron production by accelerated 3He reactions with heavy elements is similar to that by accelerated 4He and so will be significant only for accelerated 3He/4He ratios greater than 1.