Scattering cross section as a function of rest frame energy for exciting an electron in initial Landau level n_i = 0 with spin −1/2 to level n_f with n_i ≤ n_f ≤ 6 and final spin −1/2 within a magnetic field of strength B = 0.0385 B_crit, resulting in a fundamental cyclotron resonance at ~20 keV. The solid, dashed, and dotted lines show cross sections for μ = cosϑ = 0.1,0.5,0.9, corresponding to angles between the path of the incoming photon and the B-field of , 60°, and , respectively.