Robert E. Steiner

Consideration of a millisecond pulsed glow discharge time-of-flight mass spectrometer for concurrent elemental and molecular analysis

The glow discharge ionization source operated in the pulsed (or modulated) power mode offers unique characteristics not available from its steady state counterpart. It has been well established that higher instantaneous power densities are obtainable without compromising the sample integrity when pulsed plasmas are implemented. This operating parameter affords higher sputter yields and lower limits of detection relative to the steady state plasmas. Of special interest are the discrete temporal regions associated with the modulated plasma. The presence of these time regimes offers temporal selectivity, allowing the collection of analytical data in a region where the contribution from background and contaminant species is minimized. These regions are characterized by strikingly different ionization mechanisms. Acquisition of data during each of these temporal regimes provides both molecular and elemental information. In this work the potential use of the pulsed glow discharge for collecting concurrent molecular and elemental information was explored. This task was accomplished using time-of-flight mass spectrometry (TOFMS). TOFMS has a significantly high throughput and duty cycle, making it ideally suited for rapid acquisition of spectra. This characteristic allows data acquisition during each of these temporal regions for each discharge pulse power cycle, affording concurrent elemental and molecular detection. p-Xylene was used as a test molecule for these studies.

Validation of reference materials for uranium radiochronometry in the frame of nuclear forensic investigations

The results of a joint effort by expert nuclear forensic laboratories in the area of age dating of uranium, i.e. the elapsed time since the last chemical purification of the material are presented and discussed. Completely separated uranium materials of known production date were distributed among the laboratories, and the samples were dated according to routine laboratory procedures by the measurement of the (230)Th/(234)U ratio. The measurement results were in good agreement with the known production date showing that the concept for preparing uranium age dating reference material based on complete separation is valid. Detailed knowledge of the laboratory procedures used for uranium age dating allows the identification of possible improvements in the current protocols and the development of improved practice in the future. The availability of age dating reference materials as well as the evolvement of the age dating best-practice protocol will increase the relevance and applicability of age dating as part of the tool-kit available for nuclear forensic investigations.

Round-robin 230Th–234U age dating of bulk uranium for nuclear forensics

In an inter-laboratory measurement comparison study, four laboratories determined 230Th–234U model ages of uranium certified reference material NBL U050 using isotope dilution mass spectrometry. The model dates determined by the participating laboratories range from 9 March 1956 to 19 October 1957, and are indistinguishable given the associated measurement uncertainties. These model ages are concordant with to slightly older than the known production age of NBL U050.

Characterization of an improved thermal ionization cavity source for mass spectrometry

A new thermal ionization source for use with a quadrupole mass spectrometer has been designed and characterized. The new source provides significant advantages over the previously reported prototype source and traditional filament-type thermal ionization sources. The operational interface between the source and the quadrupole mass spectrometer has been redesigned. A vacuum interlock, a translational stage, and an adjustable insertion probe are added to improve the source performance. With these modifications, the source is easier to operate while maximizing sample throughput. In this work, the performance of the newly developed source is examined. The ionization efficiencies are measured with a quadrupole mass spectrometer. The efficiency values obtained with this system are comparable to those obtained from a large scale isotope separator. The relationships among the ionization potential, vapor pressure, and measured ionization efficiency results are discussed. The crucible lifetime has been quantitatively estimated by measuring the crucible sputtering rate. Diagnostic studies of the new source show that the crucible position is a crucial parameter for sensitivity and performance. Stability tests demonstrate that the source can be run several weeks at a fixed emission current without significant degradation.

Polyatomic interferences on high precision uranium isotope ratio measurements by MC-ICP-MS: Applications to environmental sampling for nuclear safeguards

Modern mass spectrometry and separation techniques have made measurement of major uranium isotope ratios a routine task; however accurate and precise measurement of the minor uranium isotopes remains a challenge as sample size decreases. One particular challenge is the presence of isobaric interferences and their impact on the accuracy of minor isotope 234U and 236U measurements. We present techniques used for routine U isotopic analysis of environmental nuclear safeguards samples and evaluate polyatomic interferences that negatively impact accuracy as well as methods to mitigate their impacts.

Practical application of thermal ionization mass spectrometry for the determination of plutonium for the LANL Bioassay Program (LA-UR-00-1697)

Utilization of thermal ionization mass spectrometry as a routine analytical service provided to the Los Alamos National Laboratory Bioassay Program has evolved significantly since its implementation just over three years ago. Converting this unique research tool designed to support nuclear weapons testing to a quasi-production mode for the routine analysis of ~300 urine samples/year for ultra-low levels of plutonium has required resolution of numerous practical issues. These issues include clean-room sample preparation, adequate tracer recovery, customer specified turn-around times, throughput, water and urine blank values, statistical data reduction, and quality control and performance evaluation sample requirements.

US-DOE and CIAE international cooperation in age-dating uranium standards

In 2014 the United States Department of Energy and the China Institute of Atomic Energy collaborated in a study measuring the model ages of uranium certified reference materials. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL), and the Chinese Institute of Atomic Energy (CIAE) determined 230Th–234U model ages for uranium certified reference materials U010 and U850. The aim of this work was to collaborate with CIAE and compare methods for measuring the age of bulk uranium materials using the 230Th–234U radiochronometer. Accurate results for age-dating depend on the accurate calibration of the tracer materials (e.g., 229Th and 233U) used for the isotope dilution mass spectrometry (IDMS) analyses. To facilitate inter-comparison of results, samples of a 230Th standard reference material were distributed to each laboratory for 229Th tracer inter-calibration. The resulting 230Th–234U model ages from this collaboration for U010 ranged from March 1956 to January 1959, which agree with the known material production date of June 5th, 1958. The determined model ages for U850 were from December 1955 to October 1957, which agree with the material production date of December 31, 1957. All three laboratories used independent methods to determine model ages for uranium standards that agree with known production ages and with previously reported results.

New determination of the 229Th half-life

A new determination of the 229Th half-life was made based on measurements of the 229Th massic activity of a high-purity solution for which the 229Th molality had previously been measured. The 229Th massic activity was measured by direct comparison with SRM 4328C using 4παβ liquid scintillation counting, NaI counting, and standard addition liquid scintillation counting. The massic activity was confirmed by isotope dilution alpha spectrometry measurements. The calculated 229Th half-life is (7825 ± 87) years (k = 2), which is shorter than the three most recent half-life determinations but is consistent with these values within uncertainties.

Determination of Volatility and Element Fractionation in Glassy Fallout Debris by SIMS

The purpose of this report is to characterize glassy fallout debris using the Trinity Test and then characterize the U-isotopes of U3O8 reference materials that contain weaponized debris.

Keeping the Momentum and Nuclear Forensics at Los Alamos National Laboratory

LANL has 70 years of experience in nuclear forensics and supports the community through a wide variety of efforts and leveraged capabilities: Expanding the understanding of nuclear forensics, providing training on nuclear forensics methods, and developing bilateral relationships to expand our understanding of nuclear forensic science. LANL remains highly supportive of several key organizations tasked with carrying forth the Nuclear Security Summit messages: IAEA, GICNT, and INTERPOL. Analytical chemistry measurements on plutonium and uranium matrices are critical to numerous programs including safeguards accountancy verification measurements. Los Alamos National Laboratory operates capable actinide analytical chemistry and material science laboratories suitable for nuclear material and environmental forensic characterization. Los Alamos National Laboratory uses numerous means to validate and independently verify that measurement data quality objectives are met. Numerous LANL nuclear facilities support the nuclear material handling, preparation, and analysis capabilities necessary to evaluate samples containing nearly any mass of an actinide (attogram to kilogram levels).