A heavy ion (5.5 MeV Ni 3+) beam was applied for PIXE (particle induced X-ray emission) analysis of iron implanted into a silicon wafer with energy of 343 keV. The implanted fluences ranged from 1 × 10 13 to 7.3 × 10 15 ions/cm 2. In order to compare with conventional PIXE analysis by light ions, a 2 MeV proton beam was also employed. It was found that the nickel probe has a few times larger cross sections for Fe K α X-ray production than the proton, while the background level around the Fe K α D-ray energy was a few tens times less than in the case of the proton. It was concluded that the detection limit of iron near the surface of the silicon wafer was improved very much by using the MeV nickel probe. This is because molecular orbital effects took place between Fe and Ni atoms due to very close level matching and relatively low energy of incident nickel (∼0.1 MeV/amu) that induced low background levels.