How does gamma decay affect the structure of the atom?
Gamma decay is the release of energy. Gamma emissions are a way a nucleus dissipates energy after the rearrangement of nuclear particles. No actual changes in structure occur, simply a loss of energy.
As shown in this image, the atom does not structurally change, it just releases energy. Gamma decay never occurs alone, but rather accompanies alpha or beta decay, as those actually change the structure of the nucleus.