The use of neutron activation analysis to characterize archaeological specimens (e.g., pottery, obsidian, chert, basalt and limestone) and to relate the artifacts to sources through their chemical signatures is a well-established application of the method. Over the past decade, large databases of chemical fingerprints for clays, obsidian, chert and basalt have been accumulated through analysis of approximately thirty elements in each of more than 42,000 specimens. The combination of these databases with powerful multivariate statistical methods (i.e., principal components analysis, factor analysis, discriminant analysis, and Mahalanobis distance probabilities) allows many archaeological materials to be sourced with a high degree of confidence. The sourcing information can help archaeologists reconstruct the habits of prehistoric peoples. For example, the "fingerprinting" of obsidian artifacts by NAA is a nearly 100 percent successful method for determining prehistoric trade routes since sources of obsidian are easily differentiated from one another through their chemical compositions.
Possible Applications for NAA
Many agricultural processes and their consequences, such as fertilization and herbicidal and pesticidal control, are influenced by surface and sub-surface movement, percolation and infiltration of water. Stable activatable tracers, such as bromide, analyzed by NAA, have allowed the soil scientist to quantify the distribution of agricultural chemicals under a wide variety of environmental and land use influences. In soil science (ca. 1970), the use of bromide ion (Br-)in various forms (e.g. KBr, NaBr, SrBr2) was introduced as a non-reactive stable tracer in solute transport studies normally moving freely with the flux of water without substantial chemical or physical interactions with the soil. Typically, Br- is extracted from soil and quantified using either a bromide selective electrode (sensitivity is ~10 µg mL or by high-performance liquid chromatography (sensitivity is ~0.010 µg/mL). Where the sensitivity is adequate, the selective conductivity method, which is simple, affordable and fast, is preferred. More recently (ca. 1990), workers have reported that 20% of Br- tracers, at low groundwater pH, may be absorbed by iron oxides and kaolinite when present in the alluvial aquifer. We investigated the use of epithermal neutron activation analysis (ENAA) as a means of measuring Br- directly in soil samples without an extraction. ENAA was chosen because of its high theoretical advantage factor over aluminum (i.e. ~20), the principal interfering soil constituent, calculated for the 79Br(n,γ)80Br reaction compared to 27Al(n,γ)28Al. Br- was measured (sensitivity is ~0.050 µg/g) in one gram soil samples from a five-second irradiation (φth = 2.5 x 1012 n/cm²/sec) using a BN capsule.
Analysis of rock specimens by neutron activation analysis assists geochemists in research on the processes involved in the formation of different rocks through the analysis of the rare earth elements REEs and other trace elements. About 30 elements can be measured routinely in almost any geological sample.
An additional 15-20 elements can be measured by applying specialized procedures. In addition to modeling geochemical processes, other applications include location of ore deposits and tracking elements of environmental importance. For example, the discovery of anomalously high iridium concentrations in 65-million-year old limestone deposits from Italy and Denmark could only have been accomplished by NAA. The NAA findings support the theory that extinction of the dinosaurs occurred soon after the impact of a large meteorite with the earth.
Study of Uranium and Thorium Redistribution due to Ore Processing
In the 10 years between 1948 and 1958 uranium ore mining in the United States expanded from a cumulative total of 38,000 tons to 5.2 million tons involving more than 400 mines. Ores from these mines were chemically processed at an estimated 50 to 100 sites. These activities have resulted in the contamination of hundreds of square miles of surface and subsurface soils, and their corresponding ground waters, with uranium-238, thorium-232 and their radioactive daughters. In most cases these sites have various radioactive waste materials such as ore tailings, processing residues and leachates mixed with soil and generally covered with an uncontaminated soil layer several feet in thickness. In other cases the tailings or wastes have remained exposed and hence have been further distributed by wind and erosion. EBNAA has been developed as a methodology suitable for automation by which contaminated ore-processing sites can be characterized and their restoration monitored.
This work is being done in collaboration with both federal and state agencies. Fresh-water ecosystems in California have been grossly contaminated with selenium as a result of irrigation run-off from heavily used agricultural areas. The effect has been observed throughout most of the food chain. The objective of these studies is to evaluate the extent of the contamination and evaluate methodologies that might be efficacious in the reduction of selenium in these ecosystems.
The Use of Radiotracers to Study the Fate of Hazardous Elements in Waste Material/Coal-Char Admixtures under Gasification: An Emerging Waste Management Technology
With an increasing emphasis being placed on the cleanup of hazardous waste sites from past technological operations, science has had to come up with ideas on how to simultaneously decompose and stabilize a variety of mixed wastes which include radioactive materials. The most difficult of all wastes to cleanup is mixed waste. These may contain organic materials (dichlorobenzene, naphthalene, etc) along with hazardous elements (cadmium, mercury,plutonium, thorium, uranium and other transuranics).
Current waste destruction technology relies on oxidation of the waste (incineration); an alternative is the storage of this waste. Both have drawbacks. Incineration requires high temperatures and the resulting high fuel costs and volatilization of some hazardous components. Storage costs are proportional to the amount of space taken up by the waste and the regulations surrounding the waste, therefore, long term storage of some existing radioactive waste is unacceptable without volume reduction and stabilization.
A process developed at MU, ChemChar gasification, helps minimize these problems. ChemChar gasification using a coal char (a triple reverse burn coal product which is very porous) acts as both a surface for chemical reactions and a sequestering agent of hazardous elements. Initially the process uses the char as an absorber of the waste stream which is mixed on a 2:1 weight ratio (char: waste). A flame front is established which moves opposite the direction of oxygen flow and in the flame front organics are decomposed and other species tend to be chemically reduced. The volatile organics are carried off and trapped later while the immobile metals, metalloids and some non-metals are sequestered on the char for final disposal or other disposition. The gasification process also results in volume reduction, partitioning of potentially usable organic solvents and the production of a gas that could be used as an energy source. The objective of the MURR component of this project is to develop a procedure by which radiotracers can be used to determine the fates of hazardous elements during gasification in support of the use of gasification as a means of decomposing, stabilizing and reducing the volume of hazardous mixed wastes including radioactive wastes resulting from the nuclear weapons program. To date the fates of arsenic, strontium, cadmium, cesium, mercury, uranium, thorium, neptunium and protactinium, chlorine (as an organochloride) and phosphorus (as organophosphorus surrogates for military wastes) have been studied in this reducing atmosphere using MURR produced radiotracers.
Semiconductor Materials and Other High-purity Materials
Neutron Activation Analysis (NAA) is used to measure trace- and ultra trace-element concentrations of impurities and/or dopants in semiconductors and other high-purity materials. The behavior of semiconductor devices is strongly influenced by the presence of impurity elements either added intentionally (doping with B, P, As, Au, etc.) or contaminants remaining due to incomplete purification of the semiconductor material during device manufacture. Small quantities of impurities present at concentrations below 1 ppb can have a significant effect on the quality of semiconductor devices. The objective of the client is to demonstrate that a chemical or material meets or exceeds purity requirements required by the end user. In some instances the MURR Nuclear Analysis Group conducts a multi-element qualitative and quantitative analysis which then is used as the certificate of analysis for that substance. In other cases the NA staff work with clients to establish purification factors at various stages in the production process of high-purity materials such as silicon or, the efficacy of cleaning and leaching procedures. In still other cases we are ask to demonstrate that a specific impurity or set of impurities is below the level of technical or regulatory concern. NAA is the elemental analysis method of choice for these projects because of the limited sample handling required and the high sensitivity for many elements of interest. For more information about this application of NAA, see the MURR Analytical Chemistry Group's page on NAA of Semiconductor Materials
In-situ Radiotracers for Dosage-Form Testing
Over the last several years there has been a growing interest in the use of in-situ radiotracers to test new pharmaceuticals and dosage forms being developed for commercial distribution. This work has been done in collaboration with several pharmaceutical companies and university research centers. The in-situ radiotracers are produced through carefully designed irradiations done at the MURR and used in laboratory, animal, and in a few cases, human experiments. These methodologies offer significant advantages in the evaluation of encapsulations, time release, clearance and the distribution of the pharmaceutical in animal and human models.
This project is being done in collaboration with the Harvard Medical School stemming from the rather striking findings reported in JAMA (December, 1996) showing a significant protective effect due to a 200 microgram/day supplement of selenium against cancers of the colon, lung and prostate. One specific aim of the project is to evaluate the relationship between selenium status and cancer of the colon and prostate in the Physicians Health Study. As proposed, this is a five-year study using prospectively collected blood samples as the biologic monitor of selenium status. If fully funded, this would be the largest prospective case-control study to date of selenium status and incidence of prostate cancer. Over the five years 2470 prostate cancer cases and 850 colon cancer cases are anticipated.
A Cohort Study of the Relationship Between Diet, Molecular Markers, and Cancer Risk: the Canadian Study of Diet, Lifestyle and Health
A pilot study to characterize the nail as a biologic monitor for the dietary intake for selenium in Canada has been undertaken to extend our work to the major Canadian provinces. Suspected selenium determinants such as smoking, use of dietary supplements, age and gender will be statistically evaluated in a population of over 700 subjects. Results will be compared with our earlier study of a female population drawn from 11 states in the U.S. The objective of this work is to expand the collaborative MURR nutritional epidemiology program, that has enjoyed good success in the U.S., to Canada. This pilot will serve as a basis for two grant applications that will be submitted to the National Cancer Institute of Canada and the Canadian Research Council. The work is being done in collaboration with the Faculty of Medicine, University of Toronto.
This study is being done in collaboration with the Northern California Cancer Center, Stanford University and the University of California, San Francisco. Asian women who have immigrated to the U.S. west coast experience a significantly increased incidence of thyroid cancer which is hypothesized to be a consequence of their substantial change in diet. Specifically, iodine intake is substantially increased and may stress a hypersensitive thyroid --a condition observed in many of these subjects presumably due to chronically low iodine intakes prior to immigration. MURR is responsible for two specific aims: characterizing the nail as a biologic monitor for iodine; and to measure iodine in nails obtained in a nested case-control study of thyroid cancer. In these subjects, the use of iodine-containing contrast agents can confound analytical interpretations of any biologic monitor. From our work we have found that biologic monitors from subjects exposed to iodine-containing contrast agents will be influenced by the exposure for over a year. Consequently, these subjects should be screened out of nested case-control studies having an iodine hypothesis. The case-control comparison is blinded to our laboratory and will be evaluated beginning in 1999.
This study is being done in collaboration with Dartmouth Medical School. There is some evidence that higher than normal intakes of arsenic may increase the risk of non-melanoma skin cancer. This hypothesis is being studied in a New Hampshire population routinely ingesting comparatively high levels of arsenic in their drinking water supplies which are typically wells serving a single residence or just a few residences. We have shown that the arsenic concentration in nails is directly correlated with drinking-water arsenic levels. An NAA procedure to measure arsenic in nails has been developed and applied in this nested pseudo-prospective case-control study. Over 1000 samples have been analyzed over the last 2 years which is approximately the midpoint of the project. The case-control status will remain blind to our laboratory until the project is concluded.
In this study, being conducted in collaboration with Johns Hopkins University, School of Hygiene and Public Health, we are investigating the relationship of dietary and occupational exposures to selenium, cadmium and zinc and the incidence of prostate cancer. This is the most extensive study to date in which we have the opportunity to compare two biologic monitors, nails and blood sera or plasma, in a nested case-control study having a specific disease outcome.
Mineral characterization studies with the knockout gene cystic fibrosis (CF) mouse model have been done in collaboration with the MU Department of Veterinary Biomedical Science. Bone and tooth mineralization differences between CF and normal mice were studied using NAA to measure Ca, Mg, P, Na, K, F, Cl, Br and Mn. NAA was also used to measure mineralization differences in the whole-body of the CF and normal mouse.
In support of the MU Department of Child Health we have studied calcium absorption in pig and lamb models using Ca-47 produced and processed at the MURR from an enriched Ca-46 target. In support of human studies with low birth-weight infants, juvenile rheumatoid arthritics and cystic methodology, based on stable isotopes measured via NAA, has been developed to measure true absorption of calcium from experimental diets.