Activation analysis neutron sources

The isotope cahfomium-252 undergoes spontaneous fission generating neutrons. It serves as a convenient source of neutrons for neutron activation analysis, neutron moisture gages, and in the determination of water and oilbearing layers in well-logging. It is expected to have many other potential applications, including synthesis of other heavy isotopes. 

Mass balance measurements for 41 elements have been made around the Thomas A. Allen Steam Plant in Memphis, Tenn. For one of the three independent cyclone boilers at the plant, the concentration and flow rates of each element were determined for coal, slag tank effluent, fly ash in the precipitator inlet and outlet (collected isokinetically), and fly ash in the stack gases (collected isokinetically). Measurements by neutron activation analysis, spark source mass spectroscopy (with isotope dilution for some elements), and atomic adsorption spectroscopy yielded an approximate balance (closure to within 30% or less) for many elements. Exceptions were those elements such as mercury, which form volatile compounds. For most elements in the fly ash, the newly installed electrostatic precipitator was extremely efficient. 

Califomium-252 is an intense neutron source. One gram emits 2.4 x 1012 neutrons per second. This isotope shows promise for applications in neutron activation analysis, neutron radiography, and as a portable source for field use in mineral prospecting and oil well logging. 

Neutrons are easy to produce. Being electrically neutral they easily invade the nuclear domain. For these reasons and because they react with most elements, neutrons are almost exclusively used in activation analysis. Neutrons can be obtained by means of nuclear reactors, particle accelerators, and from isotopic sources. 

When Cf is used as a neutron source, the data listed in Table 11.2 are useful. Practical applications of Cf make use of the spontaneous-fission neutrons generated by this isotope. Neutrons from Cf sources have been useful in such areas as neutron activation analysis, neutron radiography (complements x-ray radiography), and medical therapy. These neutron sources are most useful where access to nuclear reactors is not possible, not convenient, and/or where a lower neutron flux is adequate. For example, portable neutron activation analysis systems have been designed for use in deep-sea exploration for minerals. Various sizes and forms of Cf sources have been designed for medical applications, both for external irradiation and internal implantation. How extensive the practical application of Cf may become will be determined by the success of experiments using this nuclide. 

All the possible applications of Cf neutron sources (neutron radiography, mineral exploration, marine exploration, oil well logging, process control analysis, and, of course, neutron activation analysis) are reported in Californium-252 Progress , a bulletin issued regularly by the U.S.A.E.C. Ricci and Handley have reported favourable results of the use of a 0.37 mg Cf for activation analysis. The source produced thermal, epi-thermal, and fast neutron fluxes of 9.3 x 10 , 9.4 x 10, and ca. 10 cm s respectively, normalized to 1 mg Cf. The limits of detection for many elements using thermal and fast reactions were estimated, these ranging from 0.11 mg of Au to 3.7 g of Pb by the ° Pb(n,n ) Pb reaction. Trombka et al. used a 125 fig source for the in situ analysis of extended soil seunples using both NaI(Tl) and Ge(Li) spectroscopy to measure capture y radiation the elements Mn, Ti, Si, Fe, H, and Ca were all identified. 

The chemical composition of particulate pollutants is determined in two forms specific elements, or specific compounds or ions. Knowledge of their chemical composition is useful in determining the sources of airborne particles and in understanding the fate of particles in the atmosphere. Elemental analysis yields results in terms of the individual elements present in a sample such as a given quantity of sulfur, S. From elemental analysis techniques we do not obtain direct information about the chemical form of S in a sample such as sulfate (SO/ ) or sulfide. Two nondestructive techniques used for direct elemental analysis of particulate samples are X-ray fluorescence spectroscopy (XRF) and neutron activation analysis (NAA). 

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. 

Radioactivity. Methods based on the measurement of radioactivity belong to the realm of radiochemistry and may involve measurement of the intensity of the radiation from a naturally radioactive material measurement of induced radioactivity arising from exposure of the sample under investigation to a neutron source (activation analysis) or the application of what is known as the isotope dilution technique. 

Individual sources of 252Cf are currently available in quantities up to 10—50mgs of the element. Such sources, when contained in a suitable hydrogenous moderator, can provide thermal neutron outputs adequate for the activation analysis of many elements in the fraction of a percent wt range... 

This section will deal briefly with some aspects of expls safety peculiar to neutron activation analysis expts. We are concerned here with a) the possible effect of the ionizing radiation dose on the energetic material which will cause it to be more sensitive or hazardous to normal handling as an expl, and b) the potential direct expl hazards involved in the physical and mechanical transportation of samples to and horn the irradiation source and in a nuclear counting system... 

Neutron Activation Analysis X-Ray Fluorescence Particle-Induced X-Ray Emission Particle-Induced Nuclear Reaction Analysis Rutherford Backscattering Spectrometry Spark Source Mass Spectrometry Glow Discharge Mass Spectrometry Electron Microprobe Analysis Laser Microprobe Analysis Secondary Ion Mass Analysis Micro-PIXE... 

Silvery white, artificial element that is also generated by intensive bombardment of plutonium with neutrons. It is a strong ("hot") neutron emitter and is used in microgram quantities in nuclear medicine. This reliable neutron source is also used in industry and science (for activation analysis). 

Williams-Thorpe, O., S. E. Warren, and J. G. Nandis (1997), Characterization of obsidian sources and artefacts from central and eastern Europe, using instrumental neutron activation analysis, in Korek, J. (ed.), Proc. Int. Conf. Lithic Raw Material Characterization, Budapest and Siimeg, 1996, Budapest. 

WVGES has not had analytical laboratory facilities since the 1970 s so contract geochemical analyses are a necessity. After considering a variety of sources for analytical work including both university and government laboratories, we decided to use a commercial lab, located in Ontario, which specializes in analyses for the mineral exploration industry (they have since expanded into the environmental field as well). For the sake of consistency, each sample is analyzed using the same set of techniques, a combination of Instrumental Neutron Activation Analysis (INAA) and Selective Extraction-Ignition Coupled Plasma spectroscopy that yield results for 49 elements - Au, Ag, As, Ba, Br, Ca, Co, Cr, Cs, Fe, Hf, Hg, Ir, Mo, Na, Ni, Rb, Sb, Sc, Se, Sn, Sr, Ta, Th, U, W, Zn, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Cu, Pb, Mn, Cd,... 

It was not until the application of neutron activation analysis (NAA) that the problem of overlapping sources could be tackled. NAA is a highly sensitive and essentially non-destructive technique, although samples have to be taken which remain radioactive for some time after analysis. The use of NAA in characterizing obsidian was first demonstrated in the early 1970s (Aspinall... 

Allen, R.O., Luckenbach, A.H. and Holland, C.G. (1975). The application of instrumental neutron activation analysis to a study of prehistoric steatite artifacts and source material. Archaeometry 17 69-83. 

Activation analysis requires the use of a powerful source of neutrons as the activator and is suitable only for elements which form an isotope whose half-life is longer than the isotopes of other elements which may be produced. 

Cluster analysis Is used to determine the particle types that occur in an aerosol. These types are used to classify the particles in samples collected from various locations and sampling periods. The results of the sample classifications, together with meteorological data and bulk analytical data from methods such as instrunental neutron activation analysis (INAA). are used to study emission patterns and to screen samples for further study. The classification results are used in factor analysis to characterize spatial and temporal structure and to aid in source attribution. The classification results are also used in mass balance comparisons between ASEM and bulk chemical analyses. Such comparisons allow the combined use of the detailed characterizations of the individual-particle analyses and the trace-element capability of bulk analytical methods. 

With analytical methods such as x-ray fluorescence (XRF), proton-induced x-ray emission (PIXE), and instrumental neutron activation analysis (INAA), many metals can be simultaneously analyzed without destroying the sample matrix. Of these, XRF and PEXE have good sensitivity and are frequently used to analyze nickel in environmental samples containing low levels of nickel such as rain, snow, and air (Hansson et al. 1988 Landsberger et al. 1983 Schroeder et al. 1987 Wiersema et al. 1984). The Texas Air Control Board, which uses XRF in its network of air monitors, reported a mean minimum detectable value of 6 ng nickel/m (Wiersema et al. 1984). A detection limit of 30 ng/L was obtained using PIXE with a nonselective preconcentration step (Hansson et al. 1988). In these techniques, the sample (e.g., air particulates collected on a filter) is irradiated with a source of x-ray photons or protons. The excited atoms emit their own characteristic energy spectrum, which is detected with an x-ray detector and multichannel analyzer. INAA and neutron activation analysis (NAA) with prior nickel separation and concentration have poor sensitivity and are rarely used (Schroeder et al. 1987 Stoeppler 1984). 

First, we analyzed samples for a large number of elements to Identify any elements, regardless of toxicity or typical concentration, that would provide signals for the presence of material from certain types of sources. Both ambient samples and particles from sources were analyzed by Instrumental neutron activation analysis (INAA), by which one can often measure about 35 elements In Individual samples (17), As the Important elements Pb, N1 and Cd are not consistently, If ever, observed by INAA, they were often measured by other methods. As INAA Is sensitive to very small amounts of obscure elements, we have obtained reliable data for elements such as Ga, Hf, Sc, In, W and many rare earths which pose no known health hazard at present levels and contribute Insignificant amounts of mass to TSP. However, as discussed below, many trace elements have already been shown to be Important In receptor... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

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