Fe-N films containing up to 70% alpha "-Fe16N2 were prepared by annealing N-implanted Fe layers on Si. Quantitative phase identification was performed by Mossbauer spectroscopy. The magnetic properties of the alpha " phase were deduced from magnetization measurements. The average magnetic moment per iron atom was about 15% higher than for pure alpha-Fe, which is in agreement with theoretical predictions. In contrast with earlier reports on alpha " grown by molecular beam epitaxy, the ion-beam-synthesized alpha " did not show giant magnetic moments.