Determination of nitrogen in metallic phases using the 14N(d, pγ)15N nuclear reaction

Analysis of nitrogen in metallic materials using X-ray spectrometry (EDS, PIXE) is subjected to large errors due to two factors: the low nitrogen contents in the steels (usually below 0.3 wt.%) and the presence of interfering L-lines of the main metallic components (Fe, Cr, Ni, ...). These factors prevent the use of SEM, TEM, micro-PIXE and other microanalytical techniques for the quantitative determination of nitrogen in metallic phases, non-metallic inclusions, precipitates, etc. In this case the deuteron induced gamma-ray emission (DIGE or d-PIGE) is known to be a very suitable method. In this work we describe the methodology for the use of the 14N(d, pγ)15N nuclear reaction at a deuteron energy of 1.4 MeV to measure low nitrogen levels in steel, using both macro and microbeam analysis. DIGE experiments were performed in the universal chamber and in the scanning nuclear microprobe at the Centro Nacional de Aceleradores in Seville, using steel standards with nitrogen contents ranging between 0.008 and 0.35 wt.%. These results give a value for the detection limits for nitrogen in the steels of 0.001 wt.% for the macrobeam and 0.04 wt.%. for the microbeam. Results are applied, in combination with d-PIXE (or DIXE), RBS and electron imaging to the determination of the nitrogen partitioning ratio between α-Fe and γ-Fe in an austenitic-ferritic duplex stainless steel