Nitrogen detection by means of a broad resonance at 9.3 MeV in 14N(α,α)14N elastic backscattering

Because of recent interest in using high energy helium ion backscattering to measure the nitrogen content in heavy substrates, we have determined the differential cross sections for the 14N (α, α)14N non-Rutherford elastic scattering in the energy region 9.1-9.6 MeV at a laboratory scattering angle of 177deg. A broad (Γ ≅ 200 keV) resonance around 9.3 MeV was found. The cross section was ≅ 480mb/sr, about 190 times higher than Rutherford scattering. The resonance, allowing a depth resolution of 40-50 nm, has been used to probe an implanted nitrogen layer in stainless steel and a thick (≅ 4.5μm)TiN coating on the surface of a high speed steel (HSS) drill bit. For quantitative analysis of nitrogen content a computer simulation method based on fitting the low energy Rutherford portion of the backscattering spectrum is proposed to extract the pseudo-Rutherford surface height of the heavy elements in substrates without knowing their non-Rutherford cross sections at such high energies. (orig.)