The Development of Models and Simulations for Solar Neutron and Gamma Ray Events

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In Chapter 1 we described the initial concept and predictions of expected fluxes of neutrons and gamma-rays from solar flares. In Chapters 2–4, as well as in Chapters 6–10 are described a lot of solar neutron and gamma-ray observations. As underlined Hua and Lingenfelter (1987a), comparisons of these observations with theoretical calculations have provided the first direct determination of the number and energy spectra of accelerated particles in flares. These comparisons have also shown (Ramaty et al. 1982; Murphy and Ramaty 1984) that the nuclear interactions are caused primarily by accelerated particles that remain trapped in the magnetic fields of the flare region and interact as they slow down in the solar atmosphere, rather than by accelerated particles that eventually escape into interplanetary space. For if the escaping particles were responsible for the observed gamma-ray line emission, they would have been greatly enriched in spallation products, such as D, T, Li, Be, and B, which were not observed (McGuire et al. 1977, 1979) in the flare particles in interplanetary space. With the exception of few flares from which neutrons were measured directly, the number and energy spectrum of the accelerated particles were all determined from measurements of the integrated flux, or fluence, in the 2.223 MeV line and the 4–7 MeV band. The bulk of the emission in the 4–7 MeV band is from the two strongest nuclear deexcitation lines in 12C and 160, as has been shown (Ramaty et al. 1977; Ibragimov and Kocharov 1977a, b). Measurements of the fluence, rather than the flux, are needed because the time histories of the two lines differ significantly. The time history of the nuclear deexcitation line emission in the 4–7 MeV band follows almost instantaneously the time dependence of the accelerated particle interaction rate while that of the 2.223 MeV line is delayed by the neutron thermalization and capture times.