Production of neutrons and gamma rays by nuclear interactions in solar flares

In recent years, the possibility has been discussed by various authors that solar neutrons and 2.2-MeV gamma rays are produced by the nuclear interactions of flare-accelerated particles with solar material. In this paper, it is emphasized that the ratio of neutrons to 2.2-MeV gamma rays depends significantly on the direction of motion of the flare-accelerated particles with respect to the solar atmosphere. For the direction of motion of flare-accelerated particles, we shall consider three cases: (a) isotropic motion, (b) upward-directed motion towards the corona, (c) downward-directed motion towards the photosphere. These flare-accelerated particles would interact with the solar atmosphere to produce neutrons with energies above several MeV. Some of the neutrons will escape into space through the corona, while some will be slowed down in the denser atmosphere and captured by the atmospheric protons with the emission of 2.2-MeV gamma rays.According to the calculations in this paper, the ratio of neutrons to 2.2-MeV gamma rays for case (b) is 10–20 times that for (a) or (c). The value for case (c) is twice that for case (a). For the expected solar neutron intensity, the values for (b) and (c) are ~10−6 and 4 × 10−2 of that for (a), respectively.