Overview of Neutron Activation Analysis Overview of Neutron Activation Analysis

This chapter provides a comprehensive overview of physical principles, procedures, proprieties, and some scientific achievements of neutron activation analysis. The most scientific events organized by the International Scientific Committees ICAA and k 0 -ISC are also reported.


Properties
The analytical techniques based on neutron activation are classified according to energy of incoming neutrons, elastic and inelastic neutron scattering, and neutron capture reactions as well as its combination such as thermal NAA (TNAA), epithermal NAA (ENAA), prompt gamma NAA (PGNAA), fast NAA (FNAA), and 14-MeV INAA a form of FNAA based on reactions with 14-MeV neutrons that are produced by neutron generators. These techniques have big application potential since they could provide data about large number of elements simultaneously. Figure 1 presents more than 65 elements that may be analyzed using neutron activation analysis method. For most elements, NAA is an extremely sensitive method for analysis. The potential benefits of NAA include the multielement capability and the fact that non-destructive analyses can be performed.

ICAA, k 0 -ISC, and scientific events
The objectives of the International Committee on Activation analysis of ICAA are to improve and promote the application of nuclear methods of chemical analysis. The International Committee on Activation Analysis (ICAA) is organized exclusively for scientific and educational purposes, and specifically to coordinate the series of international conferences entitled Modern Trends in Activation Analysis (MTAA). The official ICAA website (http://www.icaamtaa.org) provides information on their activities, membership, etc. [10].

Advanced Technologies and Applications of Neutron Activation Analysis
The k 0 -International Scientific Committee was originally mainly involved in the organization of the k 0 -Workshops and the accepting and reviewing of the papers presented there. The mandate of the k 0 -ISC is to promote the development and application of the k 0 -method of neutron activation analysis, k 0 -NAA. Examples of the k 0 -ISC's promotion of the development and application of the k 0 method include the coordination of the k 0 -Workshops, maintenance and improvement of the recommended k 0 -Nuclear Database, through the k 0 -Nuclear Data Subcommittee, and the maintenance of the k 0 website to give information and to allow k 0users to contact members of the k 0 -ISC.
George de Hevesy (1885-1966) received the Nobel Prize for Chemistry in 1943 for his work on the use of isotopes as tracers in the study of chemical processes. The Hevesy Medal as illustrated in Figure 2 is the premier international award of excellence honoring outstanding achievements in radioanalytical and nuclear chemistry as illustrated. Table 1 presents the list of the laureates of George de Hevesy award during the period 1968-2018 [10].

Nuclear data
The authors F. De Corte and A. Simonits published in 2003, the recommended nuclear data for use in the k 0 -standardization of neutron activation analysis [3]. In 2010, De Corte described in his paper "Towards an international authoritative system for coordination and management of a unique recommended k 0 -NAA database" the constitution of the nuclear data library [25]. As indicated in the paper, "the 2012 recommended k 0 database", R. Javimovic et al. established the k 0 database in the form of an accessible excel file freely downloadable at http:// www.kayzero.com/k0naa/News/News.html [26].

Neutron activation systems
Database from the IAEA's Research Reactor Database (RRDB) provides information with respect to the status of the world's research reactors. More than half of the 241 operational RRs worldwide performing neutron activation analysis distributed over 59 member states [31]. The highest roles of NAA have been identified as the most suitable opportunity for research, education and training, and commercialization of RR services. For that, NAA groups focused their efforts on the development and modernization of neutron activation analysis process including irradiation devices, gamma-ray spectrometers, and data analyzing instruments [31][32][33][34][35].  Table 2. List of the past international conferences on modern trends in activation analysis, MTAA (1961-2015) [10].
Overview of Neutron Activation Analysis http://dx.doi.org/10.5772/intechopen.85461 laboratories, under the framework of IAEA projects using IPE (International Plant-analytical Exchange) and ISE (International Soil-analytical Exchange) samples provided by the accredited organism such WEPAL [32].
Neutron activation analysis has traditionally been used mainly for the characterization of geological, environmental, and biological materials. However, other analysis techniques have emerged to replace NAA for many of those applications, and NAA now thrives mainly because of its unique advantage, the high penetrating power of neutrons and gamma rays, leading to ease of use in many instances where no sample preparation is required. In addition, NAA practitioners have innovated to provide fast, accurate, and reliable analyses of various matrices posing great difficulties for other techniques. Some of the applications made possible by these innovations are listed here.
In the medical field, it has often been hypothesized that a lack of selenium in the body may lead to increased risk for certain cancers. To measure the body's selenium status, toenails have been found to be a good indicator of the selenium status over a period of several months prior to the taking of the sample. Several NAA laboratories [37][38][39] have measured Se in toenails using the very short-lived Se-77m, half-life 17.5 s. This required the development of fast pneumatic sample transfer systems with accurate control of irradiation and decay times as well as accurate correction of counting losses when the count-rate is changing during the counting period. The results of studies [37][38][39] using thousands of samples sometimes revealed an association between lower Se levels and increased cancer risk, while in others, no significant difference in Se level was observed between the controls and subjects who developed certain forms of cancer.
A knowledge of the levels of trace elements in plastics may be useful from several points of view, as it may reveal the presence of toxic elements such as Cd [36], or information on the production process through the presence of catalyst residues, it may permit differentiating new plastics from those containing recycled material with flame retardants Br and Sb, and it may help decide the suitability of plastics for insulation of high-voltage electrical cables [37] or cables used in the nuclear industry [38]. Plastic samples of 100 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.
Pure selenium used for photographic film must be very low in chlorine; an upper limit of 2 μg/g is tolerable. Achieving this sensitivity by INAA is difficult because Cl is detected by 37 min half-life Cl-38 with gamma rays at 1642 and 2167 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-38 gamma rays, discriminating gamma-ray spectrometry [40] has been used. A 10 mm thick lead plate was placed between sample and detector. To reduce the uncertainty of the calculated area of the barely visible 2167 keV peak, samples were counted for 30 m at the maximum tolerable count rate, which gave between 10 and 30% dead-time, and the peak fit was carried out using maximum predetermined information: the peak position and width were fixed relative to nearby strong Se peaks. 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. For 100 mg samples with very high rare-earth concentrations, NAA results accurate to better than 5% were achieved for 13 rare-earth elements [43].
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. The chemical element Ca, K, Na, Br, Rb, and Zn have been determined in six kinds of baby formula milk using k0-NAA technique. 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. As an example of the existing stakeholder's needs are mainly to evaluate the whole blood and hair correlation factor of Na and K, Fe, and Zn of patients suffering from Alzheimer and psoriasis pathologies and normal controls using INAA and k 0 -NAA techniques. According to the gender and age consideration, the results obtained in these studies have been discussed [45,46]. For quality control and quality assurance, the biological matrix NIST1566b Ouster Tissue), IAEA A13 (animal blood) were analyzed simultaneously with the samples. Three statistical parameters Z-score, U-score, and bias were determined and discussed. For more details about the basic theory of NAA, recent developments and technologies and potential applications of neutron activation analysis performed at the author's laboratory and nuclear facilities, the interested reader should refer to the works discussed in Chapters 2-6.