Interactions of charged, accelerated particles in the solar atmosphere, and the generation of secondary energetic particles and radiation: pioneer results -- The events of August 1972 and the discovery of solar gamma-radiation -- The events of June 1980 and June 1982, and the discovery of solar neutrons -- Space probe observations of solar neutron and gamma ray events -- Solar neutron propagation in the Earth's atmosphere, and the sensitivity of neutron monitors and other ground based detectors to solar neutrons -- Statistical investigations of solar neutron events on the basis of ground observations -- Observations of solar neutron events by ground based detectors, and their interpretation -- The solar neutron decay phenomenon -- Gamma rays from solar energetic particle interactions with the Sun's atmosphere -- Positron generation in the nuclear interactions of flare energetic particles in the solar atmosphere -- The development of models and simulations for solar neutron and gamma ray events.