In recent years there is a decided upswing in interest in the application of fast neutron activation analysis methodologies to certain problems, i.e., detection of contraband substances, use of steady-state and pulsing instruments of body compositions etc. The value of a method which can characterize major and minor elements in large samples is again recognized.
The enhancement factors possible by using reactor pulsing during neutron activation analysis have been shown to exceed 1.0 for half-lives shorter than 42 seconds. Studies published to date have applied the technique to pure elemental standards in order to evaluate the advantage. In addition, its use has been demonstrated for the analysis of several environmental samples. This paper describes experimental work performed in an effort to demonstrate the utilization of the technique on a wide range of real sample materials. The purpose of the investigation was to assess the value of the methodology to the neutron activation analysis program of our laboratory in support of university research. A series of sample matrices including reference materials, fossil fuels, geological specimen, ecologically important materials and animal and plant tissues have been subjected to pulsed neutron irradiation. Resulting gamma emissions were detected from samples after each irradiation. Representative spectral data are presented. Suitability of the technique for trace analysis are discussed.
Fast neutron generators are used at Texas A & M University to provide a supply of high energy neutrons for nuclear analytical measurements. A series of neutron activation analysis procedures have been developed for determining various major, minor and trace constituents in a variety of materials. These procedures are primarily developed to compliment our reactor based NAA program, thereby expanding the list of determinable elements to include those difficult or impossible to measure using thermal neutrons. A few typical methods are discussed. The unique implementation of the methodologies at Texas A & M are explained.
The TRIGA research reactor operated by the Nuclear Science Center (NSCR) for Texas A&M University has the capability of producing fast transient power pulses by pneumatic ejection of the transient control rod upward out of the core to a preset distance corresponding to the desired input reactivity. The NSCR has been recently relicensed to operate in this mode. An evaluation of linearity of radioactivation to reactivity insertion and integrated pulse energy is presented. Pulse/irradiation timing considerations have proven to be of paramount importance. Pulse shape variations have been shown to significantly effect specific activation, especially at low reactivity insertions. The design and construction of a rapid transfer system for pulsed irradiation activation analysis is discussed.
Detection of small quantities of uranium in silicon wafers has been carried out by neutron activation followed by observation
of fission product140La. Irradiations of about one week were made at a flux of 6·1014n cm−2 s−1 and the activity of the 1596 keV line was determined. Counting rates of as low as 1 count per minute have been observed.
This indicates uranium concentrations of about 5·1010 atoms per cubic centimeter of silicon or about 0.01 mg/g, assuming activity from other fissionable nuclides to be negligible.
Instrumental neutron activation analysis (INAA) was used to analyzed Nigerian bituminous coal and ash. Good statistical agreement (p
0.05) between the literature and reported elemental values of USGS AGV-1 sample was found. Many elements were determined in the coal with some enrichment in the coal ash. Arsenic was measured only in the ash while Hg was present only in the coal. Coal ashing at 800°C contributed to a loss of Hg in the ash. Al, Na, Mg, Ti, Fe, which are major elements were found in the coal as expected, with slight enrichment in the ash. Ca and Si were only obtained in the ash. High ash Al (14.9±0.19%) and Si (25.3±4.11%) levels are of concem due to possible cases of pneumononiosis from inhalation of the particulates. Graphical illustration of the lanthanide concentrations peaked at Ce with a decrease from Sm to Lu. U and Th were also present in the samples showing slight enhancement in the ash. Comparatively low coal elemental values, notably S(1.8%), highly advocate this coal as a good quality fuel-coal.
Fast neutron activation analysis (FNAA) has proven to be a useful technique for the estimation of non-metallic inclusions in metals, and is currently being used in industry, especially for the determination of oxygen in magnesium alloys. However, high levels of radioactivity induced in large metallic samples by irradiation in a neutron field give rise to matrix interferences which are significant at low oxygen concentrations. These interferences are due to coincidental summations that fall into the energy window used for quantitation of oxygen. This report explains technical details of newly developed experimental procedures and alterations of existing software which correct for the errors, thereby enhancing the potential for use of the method.
Instrumental Neutron Activation Analysis (INAA) was used to determine relative manufacturing locales of lead-glazed earthenwares recovered from four Spanish missions in Texas. Two principal clays were distinguished, one containing volcanic ash and one sand. The ceramics characterized by the volcanic ash were believed to have been manufactured in Mexico, while those containing sand were made in Texas. This distinctionis important because it suggests that the Indians at the Texas missions were manufacturing ceramics using Spanish technology such as lead-glazing.
Trace element partitioning was studied at a pulverized-lignite fired power plant in Texas. Concentrations of 41 elements were determined by neutron activation analysis (NAA) for lignite fuel and combustion effluents collected during 10 consecutive days. Elements studied were grouped into three classes according to their enrichment factors and the relationship between their concentrations and particle size. In general, the concentration enhancement in fly ash and the difference in enhancement between elements placed in different classes are shown to be less significant in this study than for other partitioning studies on higher rank coals.
A fast (14-MeV) neutron activation analysis procedure was employed to directly measure mass fractions of oxygen in coal samples. The procedure demonstrated sufficient precision and accuracy to determine a relative change of about 5% or more, in the oxygen mass fraction of about 12%. The procedure was applied to test samples of the newly developed SRM 1632c Trace Elements in Coal (Bituminous). The samples had been stored at three conditions: in liquid nitrogen vapor and at room temperature in the original containers packaged under argon, and for accelerated aging at 50 °C open to air. Following six months storage increments, duplicate samples of each of twelve bottles of the SRM were measured for each storage condition. In addition each sample was processed through ten separate analytical runs yielding a total of some 720 measurements per storage duration. Oxygen was determined by comparison to a primary standard potassium dichromate and the accuracy of the method was assessed through the analysis of replicate samples of three reference materials that are certified for oxygen content. The initial 6-months test period indicated uptake of oxygen in the open-air storage.