Neutron Activation Analysis
Cerium Labs uses Neutron Activation Analysis (NAA) to measure the bulk elemental composition of samples that are particularly difficult to dissolve (e.g., poly silicon used in photovoltaic solar cells) since little or no sample preparation is necessary. Samples are irradiated with neutron flux from a research reactor to convert impurities into their radioactive isotopes. These isotopes decay with emission of characteristic gamma rays that are detected and analyzed using a gamma ray spectrometer. While the energy of the gamma ray identifies the element (e.g., 1332 keV gamma ray shows presence of Co), its intensity allows quantification using a known reference material. One advantage of the NAA for a silicon matrix is that, while Si converts into radioactive 31Si, it has a short half-life (only 2.6 hours) while the half lives of the impurities are long (e.g., Au is 2.7 days). Therefore a very low background and high sensitivity measurement of the elements can be realized after the decay of the 31Si radioactivity.
Typically NAA bulk analysis at ppb to ppt levels can be completed in one week turn time. A typical list of elements includes Ag, As, Au, Ba, Br, Ce, Co, Cr, Cu, Fe, Ir, K, La, Mo, Na, Ni, Sb, W, Zn. Organic samples such as polymer, tissue and biological materials can be analyzed for trace elements with equally low detection limits.