premise: Gamma radiation is generated by radioactivity, the decay of radioactive (unstable) atoms both in Earth's crust and in the atmosphere, and in reactions caused by cosmic ray collisions with atmospheric constituents, as well as by the decay of elementary particles produced by these collisions.
hypothesis: Radioactive atoms, nuclear explosions, and stars produce gamma rays
hypothesis_graph_structure: Radioactive atoms, nuclear explosions, and stars<>produce<>gamma rays