Aspects of Graviton Detection: Graviton Emission and Absorption by   Atomic Hydrogen
  Graviton absorption cross sections and emission rates for hydrogen are calculated by both semi-classical and field theoretic methods. We point out several mistakes in the literature concerning spontaneous emission of gravitons and related phenomena, some of which are due to a subtle issue concerning gauge invariance of the linearized interaction Hamiltonian. 
Stephen Boughn, Tony Rothman