Suppose a $_{88}^{226}Ra$ nucleus at rest and in ground state undergoes $\alpha$-decay to a $_{86}^{222}Rn$ nucleus in its excited state. The kinetic energy of the emitted $\alpha$ particle is found to be 4.44 MeV. $_{86}^{222}Rn$ nucleus then goes to its ground state by $\gamma$-decay. The energy of the emitted $\gamma$ photon is ............ keV. [Given : atomic mass of $_{86}^{226}Ra$= 226.005 u, atomic of $_{86}^{222}Rn$= 222.000 u, atomic mass of $\alpha$ particle = 4.000 u, 1 u = 931 MeV/e2, c is speed of the light]