What is neutron activation analysis

Neutron activation analysis NAA is an analytical technique that relies on the measurement of gamma rays emitted from a sample that was irradiated by neutrons. The rate at which gamma rays are emitted from an element in a sample is directly proportional to the concentration of that element. The major advantages of NAA are that:. The process for analyzing samples by NAA involves irradiating them with a neutron source.

Neutrons are captured by elements in the sample to produce unstable radioactive isotopes radionuclides. Beta particles, and in most cases gamma rays, are emitted from the radionuclides as they decay. The energies of these gamma rays are, in general, distinct for a specific nuclide and the rate at which these photons are emitted with a particular energy can be measured using high—resolution semiconductor detectors.

Because the production and decay rate of gamma radiation are dependent on the half—life of the nuclide, elemental measurements can be optimized by varying the irradiation and the decay times i. The most common procedure for NAA involves encapsulating the samples and suitable standards in heat—sealed polyethylene or quartz vials and simultaneously irradiating them. Ideally, the samples are irradiated in a "lazy susan" facility that revolves around the core thereby ensuring that the samples and standards experience the same neutron fluence.

Following sequential decay periods, each standard sample is analyzed utilizing high resolution germanium detectors coupled to a multi—channel analyzer system. Gamma ray counts accumulated in an energy region above the background counts produce photopeaks. After counting analysis is complete, these data are processed using sophisticated computer programs that smooth the spectral data and determine the net areas of gamma ray photopeaks.

The program then translates the area into count rates counts per minute or cpm. These programs are capable of resolving overlapping and complex photopeak energy regions. The principal error in the analysis of materials by NAA is the counting statistic error, which is based on the signal to background ratio at the gamma ray energy region of interest.

A one sigma error for a photopeak area determination is approximately equal to the square root of the total counts background plus net counts divided by the net counts. Plastic samples of mg mass are appropriate for some applications but several NAA laboratories have innovated to be able to analyze routinely and quickly samples up to 4 g mass which, for certain trace elements, are more representative of the original material, and in special cases, even larger samples may be analyzed using large-sample NAA.

The problem of the growth of fungus or mold on wood or paper products used in humid environments, wood for windows, cardboard on wallboard used in basements, and wrappers for bars of soap stored in bathrooms, has been remediated by the application of fungicides containing heavy elements like copper and iodine.

Regular quality control measurements are needed to ensure that the right amount of fungicide has been applied. NAA is ideally suited for this as there is no sample preparation and methods have been developed [ 39 ] for large representative samples, at least 6 cm 2 for wood samples cut from the surface of the board and 60 cm 2 for paper, and the NAA results are independent of penetration depth. To successfully provide a fast and reliable service for industry, the reactor and staff must be available when needed; the service must be given high priority.

Achieving this sensitivity by INAA is difficult because Cl is detected by 37 min half-life Cl with gamma rays at and keV which suffer interference from the much more intense low-energy gamma rays emitted by several short-lived Se isotopes produced by neutron irradiation of Se.

In order to reduce the detection efficiency for the interfering low-energy gamma rays relative to the high-energy Cl gamma rays, discriminating gamma-ray spectrometry [ 40 ] has been used.

A 10 mm thick lead plate was placed between sample and detector. A similar discriminating gamma-ray spectrometry technique was used [ 41 ] for the determination of vanadium in materials with high content of titanium, barium, and strontium. To satisfy the increasing demand for rare-earth elements used in the electronics industry, new rare-earth mines are opening along with their associated refineries and the development of refining techniques.

This development requires the measurement of rare-earth concentrations in the ore and products at all stages of refinement. The great sensitivity of NAA for most rare-earth elements has made it an excellent method for measuring rare-earths at low concentrations in rocks, sediments, soils, and plants.

However, at the high concentrations found in ores and refinery products, the high neutron absorption cross-sections cause a severe neutron self-shielding problem even with small samples.

This problem has recently been solved [ 42 ] with the development of an accurate neutron self-shielding model coupled with accurate gamma attenuation calculations for the low energy gamma rays of Ce, Nd, Sm, Dy, Ho, and Tm. The correction calculation is iterative, using the raw NAA-measured rare-earth concentrations in each sample as input and then simultaneously adjusting the neutron self-shielding factors and the gamma attenuation coefficients according to the models.

The use of nuclear analytical techniques is most practical to analyze a variety of samples in different fields related to life sciences in particular food product for humans.

The objective of this research is to point out the research results of content and nutritional importance of individual essential elements that are present in various milks and dairy products. Recently, an extensively studied on nutrients and heavy metals concentration in food overall the world.

In the last years, several brands of milk powder for categories child and adult have been studied by using the k 0 -INAA technique [ 44 ]. As complementary work for dairy products, it is very important to evaluate the consumption of the commercial baby formula milk for the first and the second age in Algeria.

Results obtained in this work show a good agreement with concentration values given by producers [ 9 ]. Relevance of activation analysis is driven by its stakeholders. According to the gender and age consideration, the results obtained in these studies have been discussed [ 45 , 46 ]. Three statistical parameters Z-score, U-score, and bias were determined and discussed.

The author wants to express her deep conviction and my gratitude with regard to the role promoting nuclear research and development, one of such importance, which Mr M. The author would like to thank Prof. Kennedy retired from the Engineering Physics Department, Polytechnique, Montreal, Canada for his comments and suggestions.

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MNRC provides help with sample preparation, data analysis, and report preparation. Unlike other analytical techniques, neutron activation analysis is a non-destructive method and often samples can be returned to the customer within days to weeks after their irradiation. Furthermore, the chemical form of the sample does not interfere with the assay of various individual elements. Solid samples are generally preferred, however, liquid samples can be assayed.