Problem 28. Consider the process A* + A+), and A* is stationary (at rest). This is the process that an excited atom emits a photon and goes back to the ground state atom A. Assume that the excited atom has a rest mass M6. Show that v-mi (loro) hvo (4.3.14) = 1 2M where v is the photon frequency if the recoil is taken into account, and vo is the photon frequency if the recoil is not taken into account.