Neutron activation analysis nuclear processes

Neutron Activation Analysis Few samples of interest are naturally radioactive. For many elements, however, radioactivity may be induced by irradiating the sample with neutrons in a process called neutron activation analysis (NAA). The radioactive element formed by neutron activation decays to a stable isotope by emitting gamma rays and, if necessary, other nuclear particles. The rate of gamma-ray emission is proportional to the analyte s initial concentration in the sample. For example, when a sample containing nonradioactive 13AI is placed in a nuclear reactor and irradiated with neutrons, the following nuclear reaction results. 

Neutron activation analysis (NAA) is a supreme technique for elemental analysis (Section 8.6.1). Other nuclear analytical techniques, such as PIXE (Section 8.4.2) and RBS, also find application in investigations of diffusion processes [445]. 

Figure 2.13 Schematic diagram of the nuclear processes involved in neutron activation analysis. Prompt gamma neutron activation analysis (PGNAA) occurs within the reactor delayed gamma NAA (DGNAA) occurs at some remote site. (After Glascock, 1994 Fig. 1. John Wiley Sons Limited. Reproduced with permission.)...

Neutron activation analysis (NAA) A nuclear process whereby the elements in a material can be qualitatively and quantitatively determined. 

Many trace element studies of archaeological samples have used neutron activation analysis (NAA). Although this technique is not useful for all elements, it is very sensitive for many of those that have proved to be valuable indicators of geochemical processes (e.g., the rare earth elements). The precision of the actual measurements is usually high and easy to determine. Samples can be irradiated with little or no sample preparation, so there are few chances of contamination during the analysis. However, the limited number of nuclear reactors severely limits access to this type of analysis. When samples are sent to a distant laboratory for analysis, the critical interaction between archaeologist and analyst can be lost. 

Nuclear reactions can be used to help museum directors detect whether an artwork, such as the one shown in Figure 18, is a fake. The process is called neutron activation analysis. A tiny sample from the suspected forgery is placed in a machine. A nuclear reactor in the machine bombards the sample with neutrons. Some of the atoms in the sample absorb neutrons and become radioactive isotopes. These isotopes emit gamma rays as they decay. 

Analytical techniques used for clinical trace metal analysis include photometry, atomic absorption spectrophotometry (AAS), inductively coupled plasma optical emission (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS). Other techniques, such as neutron activation analysis (NAA) and x-ray fluorescence (XRF), and electrochemical methods, such as anodic stripping voltammetry (ASV), are used less commonly For example. NAA requires a nuclear irradiation facility and is not readily available and ASV requires completely mineralized solutions for analysis, which is a time-consuming process. 

Neutron activation analysis is one of a small number of methods capable of multi-elemental analysis of subnanogram quantities of contaminants in semiconductors and other materials. Milligram to gram-sized samples of silicon, quartz, graphite, or organic materials are nearly Ideal for the method. The physics of the processes involved is simple, and qualitative identification of components is an Integral part of the quantitative analysis. Except for the need for access to a nuclear reactor, the equipment required is readily available commercially, and is comparable in cost and complexity to that used in other advanced analytical techniques. 

Several investigators have used neutron activation analysis (NAA) to determine the aluminium content of biological specimens both with and without some chemical processing. Instrumental neutron activation analysis involves the bombardment of a sample with neutrons and the measurement of the radioactivity induced by nuclear reactions. No chemical processing is required. Upon activation Al (100% isotopic abundance) forms the radioactive AI nuclide by a (n,y) reaction. There are a number of attractive features in this technique which include excellent sensitivity with relative independence from matrix effects and interferences. Also, there is relative freedom from contamination since the sample is analyzed directly with minimal handling. One major problem is the need to... 

Challenge Archeologists sometimes use a procedure called neutron activation analysis to identify elements in artifacts. The figure at right shows one type of reaction that can occur when an artifact is bombarded with neutrons. If the product of the process is cadmium-110, what was the target and unstable isotope Write balanced nuclear equations... 

Activation analysis is the other field of radiochemical analysis that has become of major importance, particularly neutron activation analysis. In this method nuclear transformations are carried out by irradiation with neutrons. The nature and the intensity of the radiation emitted by the radionuclides formed are characteristic, respectively, of the nature and concentrations of the atoms irradiated. Activation analysis is one of the most sensitive methods, an important tool for the analysis of high-purity materials, and lends itself to automation. The technique was devised by Hevesy, who with Levi in 1936 determined dysprosium in yttrium by measuring the radiation of dysprosium after irradiation with neutrons from a Po-Be neutron source. At the time the nature of the radiation was characterized by half-life, and the only available neutron sources were Po-Be and Ra-Be, which were of low efficiency. Hevesy s paper was not followed up for many years. The importance of activation analysis increased dramatically after the emergence of accelerators and reactors in which almost all elements could be activated. Hevesy received the 1943 Nobel prize in chemistry for work on the use of isotopes as tracers in the study of chemical processes . 

Surface and bottom seawater samples from three locations in the Kattegat and Baltic Sea were analyzed for and in both iodide and iodate species, and total inorganic iodine by neutron activation analysis using nuclear reactions of l(n,y) I and I(n,y) I (Hou et al. 2001). Levels of 2.3 x 10 mol/1 for and 7 x 10 mol/1 for are obtained. Therefore, these isotopes of iodine are promising tracers of physical and biochemical process in the ocean, and research about the chemical speciation of and in ocean will be developed. ... 

Many elements become radioactive when exposed to neutron bombardment inside a nuclear reactor. This is the basis of an extremely sensitive analytical method neutron activation analysis (NAA). The induced radioactivity is examined by y-ray measurement With computerized data processing it is possible to measure more than thirty elements simultaneously without chemical processing. For many elements and applications, NAA offers sensitivities of the order of parts per biUion (pbb). Neutron activation analysis was discovered in 1936 when Hevesy and Levi found that samples containing certain rare earth elements became highly radioactive after exposure to a source of neutrons. 

Although following similar nuclear reaction schemes, nuclear analytical methods (NAMs) comprise bulk analysing capability (neutron and photon activation analysis, NAA and PAA, respectively), as well as detection power in near-surface regions of solids (ion-beam analysis, IB A). NAMs aiming at the determination of elements are based on the interaction of nuclear particles with atomic nuclei. They are nuclide specific in most cases. As the electronic shell of the atom does not participate in the principal physical process, the chemical bonding status of the element is of no relevance. The general scheme of a nuclear interaction is ... 

Limitations may be imposed on activation analysis by conflicting nuclear processes. These have been mentioned above as becoming of increasing importance in neutron activation when the particle energy increases above that necessary to bring about the required interaction. 

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