Determination of nitrogen in reference materials by cold neutron prompt gamma-ray activation analysis

Accurate determination of nitrogen is difficult, especially at low concentrations. Nitrogen is most often determined in biological materials using the Kjeldahl procedure, which requires destruction of the sample and does not always yield total nitrogen. Prompt gamma-ray activation analysis (PGAA) has been used for the nondestructive measurement of total nitrogen; however, the sensitivity is poor when thermal neutrons are used. The use of cold neutrons and neutron guide tubes in PGAA have resulted in improved sensitivities and better detection limits for many elements. Because element sensitivities in cold neutron (CN) PGAA are greatly affected by neutron scattering by hydrogen, difficulties are encountered when applying the technique to the analysis of biological materials. However, studies have shown that this effect is minimized when thin (1- to 2-mm-thick) samples are analyzed.