Conversion electron Mo¨ssbauer spectroscopy has been used to study irradiation effects in the near surface region of type 304 stainless steel after 40 keV helium ion bombardment; a ferromagnetic phase in the paramagnetic matrix was observed after the irradiation to 8×1017ion/cm2at 200 °C. The amount of ferromagnetic phase was found to increase with increasing helium ion fluence.