Reactor neutrons, activation analysis

Moens, L, De Corte, F., De Wispelaere, A.. Hoste, J.. Simonits, A., Elek, A. and Szabo, E. (1984). ko- measurements and related nuclear data compilation for (n,y) reactor neutron activation analysis. J. Radioanai. Nucl. Chem. 82,385. 

Girardi, F., Guzzi, G. and Pauly, J. (1965) Reactor neutron activation analysis by the single comparator method. Anal. Chem., 37.1085-1092. 

Activation with reactor neutrons allows the determination of a wide range of metallic and non-metal lie elements. It can in general not be used for the determination of traces of carbon, nitrogen and oxygen. Among the elements considered in this book, boron can be determined by prompt methods based on the B(n,ay) i reaction (2), whereby the a-particles or y-rays emitted are measured during the irradiation. Phosphorus and sulphur can be determined by reactor neutron activation analysis as described in chapters VIII and IX. 

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. 

The concentration of Mn in steel can be determined by a neutron activation analysis using the method of external standards. A 1.000-g sample of an unknown steel sample and a 0.950-g sample of a standard steel known to contain 0.463% w/w Mn, are irradiated with neutrons in a nuclear reactor for 10 h. After a 40-min cooling period, the activities for gamma-ray emission were found to be 2542 cpm (counts per minute) for the unknown and 1984 cpm for the standard. What is the %w/w Mn in the unknown steel sample ... 

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 HFBR at Brookhaven National Laboratory is a heavy water moderated and cooled reactor designed to provide an intense beam of neutrons to the experimental area. In addition using thimbles i oiitaincd within the vessel, it provides isotopic production, neutron activation analysis, ami muiemi irradiations. It began operation in 1965 at a power of 40 MW to be upgraded to 60 MW m 19S2. 

This can result in a radioactive product from the A(n, t)A reaction where A is the stable element, n is a thermal neutron, A is the radioactive product of one atomic mass unit greater than A, and y is the prompt gamma ray resulting from the reaction. A is usually a beta and/or gamma emitter of reasonably long half-life. Where access to a nuclear reactor has been convenient, thermal neutron activation analysis has proven to be an extremely valuable nondestructive analytical tool and in many cases, the only method for performing specific analyses at high sensitivities... 

Attas, M. (1986), A Review of Neutron Activation Analysis, Reactor Technology Notes, no. 5. 

Tijoe, P.S., J.J.M. de Goeij, and M. de Bruin. 1977. Determination of Trace Elements in Dried Sea-Plant Homogenate (SP-M-1) and in Dried Copepod Homogenate (MA-A-1) by Means of Neutron Activation Analysis. Interuniv. Reactor Inst. Rept. 133-77-05, Delft, Nederlands 14 pp. 

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.)...

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 ... 

Due to the complexity and cost of the technique no water laboratory in the UK has its own facilities for carrying out neutron activation analysis. Instead, samples are sent to one of the organizations that possess the facilities, e.g. the Atomic Energy Research Establishment at Harwell or the Joint Manchester-Liverpool University Reactor located at Risley. 

A method has been developed for the determination of technetium-99 in mixed fission products by neutron activation analysis Tc is separated from most fission products by a cyclohexanone extraction from carbonate solution, the stripping into water by addition of CCI4 to the cylohexanone phase, and the adsorption on an anion exchange column. Induced Tc radioactivity is determined using X-ray spectrometry to measure the 540 and 591 keV lines. The sensitivity of the analysis under these conditions is approximately 5 ng. The method has been successfully applied to reactor fuel solutions. 

All impactor and filter samples were analyzed for up to 45 elements by instrumental neutron activation analysis (INAA) as described by Heft ( ). Samples were irradiated simultaneously with standard flux monitors in the 3-MW Livermore pool reactor. The x-ray spectra of the radioactive species were taken with large-volume, high-resolution Ge(Li) spectrometer systems. The spectral data were transferred to a GDC 7600 computer and analyzed with the GAMANAL code (1 ), which incorporates a background-smoothing routine and fits the peaks with Gaussian and exponential functions. 

The concentration of silver nanoparticles and ions in solntions was determined by neutron activation analysis [15]. Samples were irradiated in the nuclear reactor at the Institute of Nuclear Physics, Tashkent, Uzbekistan. The product of nuclear reaction ° Ag(n,y)" Ag has the half-life Tj j=253 days. The silver concentration was determined by measnring the intensity of gamma radiation with the energy of 0.657 MeV and 0.884 MeV emitted by "" Ag. A Ge(Li) detector with a resolution of about 1.9 keV at 1.33 MeV and a 6,144-channel analyzer were used for recording gamma-ray quanta. 

Neutron activation analysis (NAA), based on the interaction of the object material with fast neutrons, has been used in the identification and determination of the content of elements present in pigments, coins and alloys, stone, glass, and pottery [26]. Multi-elemental analysis (about 20 elements) can be performed on small samples off less than 5 mg, with sensitivities in the ppm range. The requirement of a nuclear reactor, the handling of radioactive materials, and the time-consuming procedures required for preparing the samples are the main drawbacks of this technique. 

During the late 1960s and early 1970s, neutron activation analysis provided a new way to measure bulk chemical composition. Neutron activation analysis utilizes (n,y) reactions to identify elements. A sample is placed in a nuclear reactor where thermal neutrons are captured by atoms in the sample and become radioactive. When they decay, the radioactive isotopes emit characteristic y-rays that are measured to determine abundances. Approximately 35 elements are routinely measured by neutron activation analysis. A number of others produce radioactive isotopes that emit y-rays, but their half-lives are too short to be useful. Unfortunately, silicon is one of these elements. Other elements do not produce y-ray-emitting isotopes when irradiated with neutrons. There are two methods of using neutron activation to determine bulk compositions, instrumental neutron activation analysis (INAA) and radiochemical neutron activation analysis (RNAA). 

The minor and trace elements in coals are currently determined by several techniques, the most popular of which are optical emission and atomic absorption spectroscopy. Neutron activation analysis is also an excellent technique for determining many elements, but it requires a neutron source, usually an atomic reactor. In addition, x-ray fluorescence spectroscopy, electron spectroscopy for chemical analyses (ESCA), and spark source mass spectroscopy have been successfully applied to the analyses of some minor and trace elements in coal. 

Increased environmental concern has accelerated research on the analysis of trace elements in fuels in many university and governmental facilities. Because instruments such as mass spectrometers and nuclear reactors for neutron activation analysis are available, much of this research uses sophisticated instrumentation and techniques. However, the wet chemistry laboratory is still the only available source of chemical... 

Methods and technology were developed and used at the NASA Plum Brook Reactor (PBR) to analyze trace elements in pollution-related samples by instrumental neutron activation analysis (INAA). This work is significant because it demonstrates that INAA is a useful analytic tool for monitoring trace elements in a variety of sample matrices related to environmental protection. In addition to coal, other samples analyzed for trace elements included fly ash, bottom ash, crude oil, fuel oil, residual oil, gasoline, jet fuel, kerosene, filtered air particulates, various ores, stack... 

Until now, little attention has been given to the analysis of ancient copper alloys with LA-ICP-MS. This type of material is usually analyzed with fast or instrumental neutron activation analysis (FNAA or INAA), particle induced X-ray emission (PIXE), X-ray fluorescence (XRF), inductively coupled plasma-atomic emission spectrometry or inductively coupled plasma-atomic absorption spectrometry (ICP-AES or ICP-AAS). Some of these techniques are destructive and involve extensive sample preparation, some measure only surface compositions, and some require access to a cyclotron or a reactor. LA-ICP-MS is riot affected by any of these inconveniences. We propose here an analytical protocol for copper alloys using LA-ICP-MS and present its application to the study of Matisse bronze sculptures. 

Instrumental neutron activation analysis was conducted at the University of Missouri Research Reactor (MURR). Samples of approximately 50-100 mg were subjected to long and short irradiations using the same methodology used on pottery and other materials with appropriate reference standards (23). The analysis provided abundances of 33 elements for 72 samples. 

Neutron activation analysis involves the exposure of the sample to high neutron flux densities in a nuclear reactor, but is a very sensitive method for certain metals, as illustrated by the following data on detection limits (ng) Fe, 3200 Zn, 420 Co, 12 Ni, 7 Na, <0.1 Cu, 0.035 Mn, 0.001. 

Neutron activation analysis (NAA) technique has also been used for determining low levels of barium in human blood (Olehy et al. 1966). This technique is based on the interaction of the nuclei of individual barium atoms with neutron irradiation, resulting in the emission of x-rays (photons). Detection limits of 7 pg barium/L of erythrocyte and 66 pg barium/L of plasma were obtained (Olehy et al. 1966). The advantages of the NAA technique are its nondestructive nature of sample and minimum sample manipulation. Disadvantages of this technique include its high costs and a nuclear reactor may not be readily available to many laboratories. 

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