Nucleus neutron activation analysis

All the techniques discussed here involve the atomic nucleus. Three use neutrons, generated either in nuclear reactors or very high energy proton ajccelerators (spallation sources), as the probe beam. They are Neutron Diffraction, Neutron Reflectivity, NR, and Neutron Activation Analysis, NAA. The fourth. Nuclear Reaction Analysis, NRA, uses charged particles from an ion accelerator to produce nuclear reactions. The nature and energy of the resulting products identify the atoms present. Since NRA is performed in RBS apparatus, it could have been included in Chapter 9. We include it here instead because nuclear reactions are involved. 

The y particle is emitted virtually instantaneously on the capture of the neutron, and is known as a prompt y - it can be used analytically, in a technique known as prompt gamma neutron activation analysis (PGNAA), but only if such y s can be measured in the reactor during irradiation. Under the conditions normally used it would be lost within the nuclear reactor. In this reaction, no other prompt particle is emitted. The isotope of sodium formed (24Na) is radioactively unstable, decaying by beta emission to the element magnesium (the product nucleus in Figure 2.13), as follows ... 

The number of protons is unique to the element but most elements can exist with two or more different numbers of neutrons in their nucleus, giving rise to different isotopes of the same element. Some isotopes are stable, but some (numerically the majority) have nuclei which change spontaneously - that is, they are radioactive. Following the discovery of naturally radioactive isotopes around 1900 (see Section 10.3) it was soon found that many elements could be artificially induced to become radioactive by irradiating with neutrons (activation analysis). This observation led to the development of a precise and sensitive method for chemical analysis. 

Neutron Activation Analysis This technique permits the quantitative and qualitative identification of elements. It is based on the conversion of a stable atomic nucleus into a radioactive nucleus by bombarding it with neutrons. The radiation emitted by the radioactive nuclei is then measured [154]. The advantages of NAA include [16, 154] ... 

The fundamental principle behind analysis by activation analysis is activation or excitation of an atomic nucleus by exposure to radiation such as neutrons, protons or high-energy photons with subsequent measurement of emitted sub-atomic particles or radiation. The most common aspect of the technique involves activation with neutrons in a nuclear reactor and measurement of delayed emitted gamma rays, denoted neutron activation analysis, either instrumental neutron activation analysis (INAA) or neutron activation followed by radiochemical separation (RNAA) in which the element of interest is chemically separated from the matrix after irradiation to provide for better, unimpeded counting. 

RM Reference Material RNA ribonucleic acid (structural element of the cytoplasm and cell nucleus), consisting of D-ribose sugar, the nitrogenous bases adenine, guanine, cytosine and uracil. There are three different types transfer RNA, messenger RNA and ribosomal RNA RNAA radiochemical neutron activation analysis (post irradiation radiochemical separation)... 

The neutron-activation-analysis limit of detection for arsenic is listed as 2 x 10" g for 1-hour irradiation in a neutron flux of 10 n/(cm sec). Using the value of 4.3 x 10" cm as the cross-section of the arsenic nucleus for neutron capture, calculate the disintegrations per second expected from As after irradiation for this period of time. 

One type of biotransformation of Cr(VI) yields DNA bound Cr(III) products (170). Neutron activation analysis of the Cr distribution between different cellular fractions following the uptake of [ °Cr04] by yeast cells revealed the highest Cr concentrations in the DNA fraction (48%), followed by RNA (34%) and protein (6%) fractions (199). Recently, this was supported by scanning micro-SRIXE analyses (employing a 0.3 pm-diameter focused X-ray beam) of thin-sectioned chromate-treated V79 cells that showed localization of Cr in P- and Zn-rich regions (which is characteristic of the cell nucleus) (91,... 

Two elemental analyzer systems have been developed, the "Continuous On-line Nuclear Assay of Coal", CONAC, (Science Application, Inc., Palo Alto, CA) and "The Elemental Analyzer" (MDH Industries, Inc., Monrovia, CA). Both of these units are based upon the measurement of prompt gamma rays that are emitted from a nucleus following the capture of a neutron. This technique is commonly known as prompt neutron activation analysis, PNAA. 

In neutron activation analysis, an activation of a sample material is accomplished by placing the sample in some position within the neutron environment. At the time the sample is exposed to neutrons, a compound nucleus is formed as the result of the interaction of a neutron with the nucleus of a stable isotope of the element being determined. The compound nucleus i.e. the end-product of an excitation process caused by both the kinetic and binding energy of the neutron with the nucleus, instantaneously loses its excess energy by a transformation to a more stable isotope by emitting prompt radiations. As a result of this event, another stable nuclide or a radioactive isotope is formed. This radioisotope then becomes the activation, or isotopic, indicator of the element of interest. 

Neutron activation analysis (NAA) came into being in 1936 when George von Hevesy and Hilde Levi published a new principle [3] for making analysis A sample was exposed to a stream of neutrons from a radium-beryllium source, and some of the atoms in the sample captured a neutron in their nucleus and became radioactive the composition of the sample could now be inferred from the measurement of the amounts and properties of such radioactive indicators. 

Neutron activation analysis of iron in the human nucleus caudatus and putamen from patients aged 23 to 66 y resulted in 8.30 0.46 and 8.78 0.55 x 10" terms of element weight per unit dried tissue, respectively (HOck etal. 1975). 

Neutron activation analysis (NAA) is the general term used to describe a nuclear-based technique in which a solid or liquid sample is irradiated with neutrons. Capture or absorption of a neutron excites the nuclide that returns (promptly or after a delay) to ground state by emission of an energetic photon (gamma ray) and/or other particles from the nucleus (Figure 1.20). 

Neutron activation analysis is an analysis of elements in a sample based on the conversion of stable isotopes to radioactive isotopes by bombarding a sample with neutrons. Hnman hair contains trace amonnts of many elements. By determining the exact amoimts and the position of the elements in the hair shaft, you can identify whom the hair comes from (assiuning yon have a sample known to be that pCTSon s hair for comparison). Consider the analysis of human hair for arsenic, for example. When the natural isotope As is bombarded with neutrons, a metastable nucleus 3f"As is obtained. 

Neutron activation analysis (NAA) is one of the most important nuclear techniques for nanometallome quantification, as it can simultaneously measure more than 30 elements in a sample. The detection limits of NAA range from 10 to 10 gg In typically instrumental NAA, stable nuclides ( Z, the target nucleus) in the sample undergo neutron capture reactions in a flux of (incident) neutrons. The radioactive nuclides the compound nucleus)... 

In this example, the excited nucleus that is formed decays with the emission of a 7 ray with a distinctive energy. Neutron-activated nuclei may decay by other modes, however, such as j8 decay. The activity of the radioisotope formed is measured. This measurement, together with such factors as the rate of neutron bombardment, the half-life of the radioisotope, and the efficiency of the radiation detector, can be used to calculate the quantity of the element in the sample. The method is especially attractive because (1) trace quantities of elements can be determined (sometimes in parts per billion or less) (2) a sample can be tested without destroying it and (3) the sample can be in any state of matter, including biological materials. Neutron activation analysis has been used, for instance, to determine the authenticity of old paintings. Old masters formulated their own paints. Differences between formulations are easily detected through the trace elements they contain. 

NAA is the most common form of activation analysis. The activation reaction is induced by the interaction of a neutron with the nucleus of an analyte element. Depending on the energy of the incident neutron and the reaction cross sections of the target elements, different types of reactions can take place, leading to activation products as described in O Sect. 30.2. This reaction is commonly followed by the measurement of a nuclide-characteristic de-excitation step (radioactive decay). It is this characteristic gamma-ray decay that is commonly used in the detection and determination of the element of interest. 

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