Neutron activation analysis (NAA) is a nuclear analytical method that utilises the specific properties of nuclear reactions, thereby enabling simultaneous determination of numerous elements in environmental samples. There are several possible techniques, differing in input radiation: i) Neutron Activation Analysis (NAA), ii) Charged-Particle Activation Analysis (CPAA) and iii) Photon Activation Analysis (PAA).

Due to its sensitivity, versatility and high reliability, NAA is the most prominent of all the activation techniques (AAS, AES-ICP, ICP-MS, XRF, PIXE, etc.). It enables multielemental analysis of macroscopic samples (up to 10-12 g of the element in a gram of sample) and the determination of a relatively large number of elements (approximately 70% of the elements in the periodic table have suitable characteristics for NAA).

Several different variations of absolute methods and activation analyses have been developed, which approximately four decades ago led to the introduction of the k0-standardisation method of NAA. This is a “quasi” absolute method that usually uses compound nuclear constants k0 and Q0 which are experimentally determined for each nuclide. These constants are in general use and are relatively independent of irradiation and counting devices. The k0-library today contains nuclear data for 144 radionuclides, which enables the determination of 68 elements in an unknown sample.

The Department of Environmental Sciences at the Jožef Stefan Institute (JSI) has been using the k0-method of NAA for routine analyses for approximately 25 years. The KayWin commercial software is used for the determination of elemental concentrations from the analysed gamma spectra. The k0-method has been optimized for the determination of major, minor and trace elements in environmental samples using the 250 kW TRIGA Mark II reactor and measurement of induced gamma activities on absolutely calibrated HPGe detectors. The method has been successfully used in numerous intercomparison studies and characterisation of reference materials of different origin (biological, environmental, industrial, geological materials, etc.) prepared by IRMM, BAM, IAEA, NIST, etc. Last not least, the k0-NAA was applied in various CCQM-KC intercomparison studies demonstrating calibration and measurement capability (CMC) on national level in the field of Metrology in Chemistry for the amount of substance: Chemical and trace elements in the organic and inorganic materials. Some applications of the k0-method of NAA will be presented and discussed.