nice post. You should, however, include a some more sources of radiation into your list.
There are high energy particles from outer space and the sun entering the atmosphere (primary radiation), mainly protons and neutrons. There are also cosmic showers created by high energy particles hitting nuclei (oxygen, nitrogen) of the atmosphere, causing huge showers of secondary particles e.g. electrons, muons, pions, kaons and so on.
Cosmic showers are the most important contribution to the radiation in an airplane. They are also the reason why the dose of radiation is higher at high altitudes.
(Alpha, Beta and Gamma ray are usually associated with the decay of a single atom.)