Christopher G. Worley

Quantification of Large Scale Micro-X-Ray Fluorescence Elemental Images:

Niobium is commonly alloyed with uranium to prevent surface oxidation, and determining how the niobium concentration is distributed throughout a sample is useful in explaining observed material properties. The niobium concentration distribution was determined across the surface of depleted uranium samples using micro-X-ray fluorescence (MXRF). To date, MXRF has been employed primarily as a qualitative tool for determining relative differences in elemental concentrations across a sample surface. Here, a process was developed to convert qualitative MXRF niobium distribution images from depleted uranium samples into images displaying concentration values. Thus, MXRF was utilized to determine elemental concentrations across a surface in a manner similar to that of the established method of electron microprobe X-ray analysis (EMPA). However, MXRF can provide such information from relatively large sample areas many cm2 in size that are too large to examine by the higher spatial resolution technique of EMPA. Although the sample surfaces were polished to the same degree as the standards, little or no sample preparation should be necessary for sample systems where a high energy analyte XRF line can be used for imaging.

Application of Micro-XRF for Nuclear Materials Characterization and Problem Solving

Micro-X-ray fluorescence (MXRF) used for >> 20 years To date MXRF has been underutilized for nuclear materials (NM) spatially-resolved elemental characterization. Scanning electron microscopy (SEM) with EDX much more common for NM characterization at a micro scale. But MXRF fills gap for larger 10s microns to cm{sup 2} scales. Will present four interesting NM applications using MXRF. Demonstrated unique value of MXRF for various plutonium applications. Although SEM has much higher resolution, MXRF clearly better for these larger scale samples (especially non-conducting samples). MXRF useful to quickly identify insoluble particles in Pu/Np oxide. MXRF vital to locating HEPA filter Pu particles over cm{sup 2} areas which were then extracted for SEM morphology and particle size distribution analysis. MXRF perfect for surface swipes which are far too large for practical SEM imaging, and loose residue would contaminate SEM vacuum chamber. MXRF imaging of ER Plutonium metal warrants further studies to explore metal elemental heterogeneity.

DETECTION OF VISIBLE AND LATENT FINGERPRINTS BY MICRO-X-RAY FLUORESCENCE

Numerous methods are available to forensic scientists for detecting fingerprints in which the prints are treated with various agents to enhance the visual contrast between the print and the surface. In the present work, the spatial elemental imaging capabilities of micro-X-ray fluorescence (MXRF) were used to visualize fingerprint patterns based on inorganic elements present in the prints. A major advantage of using MXRF is that the prints are left unaltered for other analyses such as DNA extraction or for archiving. Most of the fingerprints which were examined were imaged from the potassium and chlorine present in the print residue. Among the various prints studied, lower count rates were also observed in the elemental maps of Ca, Al, Na, Mg, Si, P, S, and the X-ray source scatter. A sebaceous oily fingerprint left by one subject was successfully imaged by MXRF, but sebaceous prints left by a different person were undetectable, indicating print elemental composition may be person and/or diet dependent. Prints containing substances that might be found in real world cases were also visualized including sweat, lotion, saliva, and sunscreen.

OPTIMIZATION OF A DRIED RESIDUE SPECIMEN PREPARATION METHOD FOR QUANTIFYING ANALYTES IN PLUTONIUM METAL USING WDXRF

A novel method for preparing thin films was investigated for quantifying gallium and iron in plutonium solutions using WDXRF. This technique was developed to eliminate the potential for radioactive liquid to leak into the spectrometer, decrease specimen preparation time, and minimize waste. Samples were cast in µL quantities onto Kapton, and a surfactant was added to disperse the solution uniformly across the Kapton. After drying the specimens, they were sealed in a cell for analysis. Results to date indicate the method can provide a relative precision of ~0.5% for gallium and ~2% for iron, which is more than sufficient for routine sample analyses.

What’s that yellow powder? A nuclear forensic case study

In this paper the utilization of three analytical chemistry techniques including gamma spectrometry, XRF, and ICP-MS/OES is described for performing nuclear forensic analyses on an unknown powder. We have demonstrated that each method was unique in providing specific material characteristics, yet they were also complementary for extracting useful nuclear forensic signatures. It is the integral effort of all three analytical chemistry tools in the nuclear forensic tool box that ultimately allowed us to reveal the identity of the unknown nuclear material as Nb2O5 mixed with ~ 9% HEU.

Analytical Chemistry and Materials Characterization Results for Debris Recovered from Nitrate Salt Waste Drum S855793

Solid debris was recovered from the previously-emptied nitrate salt waste drum S855793. The bulk sample was nondestructively assayed for radionuclides in its as-received condition. Three monoliths were selected for further characterization. Two of the monoliths, designated Specimen 1 and 3, consisted primarily of sodium nitrate and lead nitrate, with smaller amounts of lead nitrate oxalate and lead oxide by powder x-ray diffraction. The third monolith, Specimen 2, had a complex composition; lead carbonate was identified as the predominant component, and smaller amounts of nitrate, nitrite and carbonate salts of lead, magnesium and sodium were also identified. Microfocused x-ray fluorescence (MXRF) mapping showed that lead was ubiquitous throughout the cross-sections of Specimens 1 and 2, while heteroelements such as potassium, calcium, chromium, iron, and nickel were found in localized deposits. MXRF examination and destructive analysis of fragments of Specimen 3 showed elevated concentrations of iron, which were broadly distributed through the sample. With the exception of its high iron content and low carbon content, the chemical composition of Specimen 3 was within the ranges of values previously observed in four other nitrate salt samples recovered from emptied waste drums.

Waste reduction process improvements in the analysis of plutonium by x-ray fluorescence: results from multiple data sets

To minimize waste, improve process safety, and minimize costs, modifications were implemented to a method for quantifying gallium in plutonium metal using wavelength dispersive X-ray fluorescence. These changes included reducing sample sizes, reducing ion exchange process volumes, using cheaper reagent grade acids, eliminating the use of HF acid, and using more robust containment film for sample analysis. Relative precision and accuracy achieved from analyzing multiple aliquots from a single parent sample were {approx}0.2% and {approx}0.1% respectively. The same precision was obtained from analyzing a total of four parent materials, and the average relative accuracy from all the samples was 0.4%, which is within programmatic uncertainty requirements.

Improvements in XRF specimen preparation using the dried residue method: Gallium in plutonium metal

Preparing dry specimens from liquid samples for XRF analysis avoids introducing caustic or hazardous liquids into the instrument. Several modifications were made to a dried residue specimen preparation method for quantifying gallium in plutonium metal in order to improve the method accuracy and precision. Ion exchange chromatography was utilized to remove the plutonium prior to casting the dried residue specimens. This coupled with several other changes improved the method relative error from ~5% to less than 1%. These results are sufficient for routine sample analysis and are almost comparable to results from the established process using liquid specimens. However, the analysis of radioactive liquid specimens is unnecessary for quantifying the plutonium gallium content using this dried residue approach.

F25 Improvements in XRF Specimen Preparation Using the Dried Residue Method: Gallium in Plutonium

Preparing dry specimens from liquid samples for XRF analysis avoids introducing caustic or hazardous liquids into the instrument. Several modifications were made to a dried residue specimen preparation method for quantifying gallium in plutonium metal in order to improve the method accuracy and precision. Ion exchange chromatography was utilized to remove the plutonium prior to casting the dried residue specimens. This coupled with several other changes improved the method relative error from ~5% to less than 1%. These results are sufficient for routine sample analysis and are almost comparable to results from the established process using liquid specimens. However, the analysis of radioactive liquid specimens is unnecessary for quantifying the plutonium gallium content using this dried residue approach. INTRODUCTION Gallium is alloyed with plutonium in manufacturing nuclear weapons, and quantifying the gallium content accurately is an essential step in the manufacturing process. WDXRF is a proven method for quantifying the gallium. The established XRF specimen preparation method involves an aqueous dissolution process in which chromatography is implemented to remove the plutonium[1,2]. Recently, an alternate dried residue specimen casting process was developed to eliminate the need to analyze liquid radioactive specimens[2-4]. In the aqueous method, the eluted gallium solution from the chromatography step is analyzed by XRF using zinc as an internal standard. Although excellent precision and accuracy are achieved with this method, the liquid specimens are radioactive due to residual amounts of plutonium as well as trace americium and uranium. Thus, the potential exists for radioactive solution to leak inside the instrument. A common method for preconcentrating trace elements to improve XRF detection limits is to cast a sample solution in microliter sized spots that are then dried[5-10]. In the current work, a dried residue casting process was used to prepare dry specimens from liquid samples. A sample is dissolved and then cast in microliter sized drops on Kapton film. After the drops dry, the specimen is sealed inside a cup and analyzed. The primary advantage for this method is that no radioactive liquids are introduced into the instrument. Also, since no acidic solutions are analyzed, the instrument steel cups are not corroded from the acid vapors. Previous studies have demonstrated the viability of this dried residue process[2,4]. However, the average relative precision and accuracy achieved in quantifying gallium in a set of plutonium test samples was approximately 4% and 5% respectively[2]. These results were adequate for a quick, Copyright ©JCPDS International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume 47. 98

Determining analyte concentrations in plutonium metal by x-ray fluorescence using a dried residue method

Accurately determining the concentration of certain elements in plutonium is of vital importance in manufacturing nuclear weapons. X-ray fluorescence (XRF) provides a means of obtaining this type of elemental information accurately, quickly, with high precision, and often with little sample preparation. In the present work, a novel method was developed to analyze the gallium concentration in plutonium samples using wavelength-dispersive XRF. A description of the analytical method will be discussed.