Neutron Production in Solar Flares by Reactions of Accelerated ³He

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.