Using the first-order Doppler-shift formula f= f₀ (1 + v/)c², calculate the energy shift of a 1 eV photon emitted from an iron atom moving toward you with energy (3/2)kT at T = 300 K. Compare this Doppler line broadening with the natural line width calculated in Example 5-9. Repeat the calculation for a 1 MeV photon from a nuclear transition.