Editing Neutron activation analysis (section)

{{Short description|Method used for determining the concentrations of elements in many materials}}
{{Science with neutrons}}

'''Neutron activation analysis''' ('''NAA''') is a [[nuclear reaction|nuclear]] process used for determining the concentrations of [[chemical element|elements]] in many materials. NAA allows discrete [[Sampling (statistics)|sampling]] of elements as it disregards the chemical form of a sample, and focuses solely on atomic nuclei. The method is based on [[neutron activation]] and thus requires a [[neutron source]]. The sample is bombarded with [[neutron]]s, causing its constituent elements to form radioactive isotopes. The [[radiation|radioactive emissions]] and radioactive decay paths for each element have long been studied and determined. Using this information, it is possible to study [[emission spectrum|spectra]] of the emissions of the radioactive sample, and determine the concentrations of the various elements within it. A particular advantage of this technique is that it does not destroy the sample, and thus has been used for the analysis of works of art and historical artifacts. NAA can also be used to determine the [[Radioactive decay#Rates|activity]] of a radioactive sample.

If NAA is conducted directly on irradiated samples it is termed '''instrumental neutron activation analysis''' ('''INAA'''). In some cases, irradiated samples are subjected to [[separation process|chemical separation]] to remove interfering species or to concentrate the radioisotope of interest; this technique is known as '''radiochemical neutron activation analysis''' ('''RNAA''').

NAA can perform non-destructive analyses on solids, liquids, suspensions, slurries, and gases with no or minimal preparation. Due to the penetrating nature of incident neutrons and resultant gamma rays, the technique provides a true bulk analysis. As different radioisotopes have different half-lives, counting can be delayed to allow interfering species to decay eliminating interference. Until the introduction of [[ICP-AES]] and [[PIXE]], NAA was the standard analytical method for performing multi-element analyses with minimum detection limits in the sub-[[Parts per notation|ppm]] range.<ref name="pollard" /> [[Accuracy]] of NAA is in the region of 5%, and relative [[Accuracy and precision|precision]] is often better than 0.1%.<ref name="pollard" /> There are two noteworthy drawbacks to the use of NAA; even though the technique is essentially non-destructive, the irradiated sample will remain radioactive for many years after the initial analysis, requiring handling and disposal protocols for low-level to medium-level radioactive material; also, the number of suitable activation nuclear reactors is declining; with a lack of irradiation facilities, the technique has declined in popularity and become more expensive.