Laser Induced Breakdown Spectroscopy Diagnostics for Nuclear Debris

This paper demonstrates the suitability of Laser -Induced Breakdown Spectroscopy (LIBS) for nuclear debris analysis by presenting LIBS elemental maps of surrogate nuclear debris and isotopic measurements of lithium, a nuclear fuel, via LIBS and chemometrics

Laser-Induced Plasma Analysis for Surrogate Nuclear Debris

This work identifies analytical lines in laser-induced plasma for chemical analyses of major elements found in surrogate nuclear debris. These lines are evaluated for interferences and signal strength to insure they would be useful to measure relative concentrations. Compact, portable instruments are employed and can be included as part of a mobile nuclear forensics laboratory for field screening of nuclear debris and contamination. The average plasma temperature is measured using the well-established Boltzmann plot technique, and plasma\u27s average electron density is determined using empirical formulae based on Stark broadening of the H-alpha line. These measurements suggest existence of partial local thermal equilibrium

An analytic-deliberative process for the selection and deployment of radiation detection systems for shipping ports and border crossings

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Includes bibliographical references (p. 53-55).Combating the threat of nuclear smuggling through shipping ports and border crossings has been recognized as a national priority in defending the US against nuclear terrorism. In light of the SAFE Port act of 2006, the Domestic Nuclear Detection Office (DNDO) has been charged with the responsibility of providing the Customs and Border Protection Agency (CBP) with the capability to conduct 100% radiological screening of all containers entering the country. In an attempt to meet this mandate, the DNDO has conducted a typical government acquisition procedure to develop and acquire radiation portal monitors (RPMs) capable of passive gamma-ray spectroscopy that would allow 100% radiological screening without detrimental affects on the stream of commerce through the terminals. However, the Cost-Benefit Analysis (CBA) supporting the DNDO decision-making process has been criticised and has delayed the program significantly. We propose an Analytic-Deliberative Process (ADP) as an alternative to CBA for this application. We conduct a case study with four DNDO stakeholders using the ADP proposed by the National Research Council in the context of environmental remediation and adapted by the MIT group and compare the results to those derived from DNDO's CBA. The process involves value modeling using an objectives hierarchy and the analytic hierarchy process. Value functions are derived and expected outcomes for the decision options are elicited from the stakeholders. The process results in a preference ranking of the decision options in order of value to each stakeholder. The analytical results are then used to structure a deliberation in which the four stakeholders use both the analytical results and any pertinent information outside the analysis to form a consensus.(cont.) The final decision of both the CBA and ADP models show good agreement and demonstrate the validity of both methods. However, the ADP format is better at explicitly capturing and quantifying subjective influences affecting the final decision. This facilitates discussion and leads to faster consensus building.by Michael B. Shattan.S.M

Quantitative Analysis of Cerium-Gallium Alloys Using a Hand-Held Laser Induced Breakdown Spectroscopy Device

A hand-held laser-induced breakdown spectroscopy device was used to acquire spectral emission data from laser-induced plasmas created on the surface of cerium-gallium alloy samples with Ga concentrations ranging from 0–3 weight percent. Ionic and neutral emission lines of the two constituent elements were then extracted and used to generate calibration curves relating the emission line intensity ratios to the gallium concentration of the alloy. The Ga I 287.4-nm emission line was determined to be superior for the purposes of Ga detection and concentration determination. A limit of detection below 0.25%was achieved using a multivariate regression model of the Ga I 287.4-nm line ratio versus two separate Ce II emission lines. This LOD is considered a conservative estimation of the technique’s capability given the type of the calibration samples available and the low power (5 mJ per 1-ns pulse) and resolving power (λ/∆λ= 4000) of this hand-held device. Nonetheless, the utility of the technique is demonstrated via a detailed mapping analysis of the surface Ga distribution of a Ce-Ga sample, which reveals significant heterogeneity resulting from the sample production process

Measurement of Electron Density and Temperature from Laser-induced Nitrogen Plasma at Elevated Pressure (1–6 bar)

Laser-induced plasmas experience Stark broadening and shifts of spectral lines carrying spectral signatures of plasma properties. In this paper, we report time-resolved Stark broadening measurements of a nitrogen triplet emission line at 1–6 bar ambient pressure in a pure nitrogen cell. Electron densities are calculated using the Stark broadening for different pressure conditions, which are shown to linearly increase with pressure. Additionally, using a Boltzmann fit for the triplet, the electron temperature is calculated and shown to decrease with increasing pressure. The rate of plasma cooling is observed to increase with pressure. The reported Stark broadening based plasma diagnostics in nitrogen at high pressure conditions will be significantly useful for future studies on high-pressure combustion and detonation applications.Abstract © OSA

Shock Front Detachment during Pulsed Laser Ablation of Graphite

Pulsed laser ablation of pyrolytic graphite with a 5.7 J/cm2 frequency-doubled Nd:YAG laser in backgrounds of argon, nitrogen, and mixed gas at pressures from 3 to 180 Torr was performed to study the dynamics of the ablation shock wave and plume emissive contact front. White light schlieren shock wave imaging and optical emission imaging with a 2.88–40 ns gated ICCD camera was used to determine shock wave and emissive plume trajectories to find the location of shock detachment from the plume and for blast energy characterization by Sedov-Taylor theory. The shock detachment points are used to limit emissive contact front Sedov-Taylor fits to the portion of the plume which exhibits a shock-like trajectory, resulting in improved laser-plume coupling energy estimates compared to standard fits. The emissive plume expands with initial Mach numbers up to M ~ 54 at t = 62 ns, decreasing to M ~ 7 as the emission becomes too weak to detect after several microseconds. The shock wave expands with initial Mach numbers up to M ~ 55 at t = 62 ns, decreasing to M ~ 1 at t = 20 µs. The shock waves exhibit spherical shock fronts, but the dimensionality, n, decreases as pressure and mass of the background gas increase, while the plumes exhibit an opposite trend. The Sedov-Taylor energy released in the sudden ablation is typically 55–75% of the laser pulse energy. The detachment-limited blast energy calculations for the emissive plume agree to within 3–5% of the shock wave energy values. Shock detachment points are nearer the target at higher pressure and scale with the mean free path

Quantitative Analysis of Cerium-Gallium Alloys Using a Hand-Held Laser Induced Breakdown Spectroscopy Device

A hand-held laser-induced breakdown spectroscopy device was used to acquire spectral emission data from laser-induced plasmas created on the surface of cerium-gallium alloy samples with Ga concentrations ranging from 0–3 weight percent. Ionic and neutral emission lines of the two constituent elements were then extracted and used to generate calibration curves relating the emission line intensity ratios to the gallium concentration of the alloy. The Ga I 287.4-nm emission line was determined to be superior for the purposes of Ga detection and concentration determination. A limit of detection below 0.25% was achieved using a multivariate regression model of the Ga I 287.4-nm line ratio versus two separate Ce II emission lines. This LOD is considered a conservative estimation of the technique’s capability given the type of the calibration samples available and the low power (5 mJ per 1-ns pulse) and resolving power ( λ / Δ λ = 4000) of this hand-held device. Nonetheless, the utility of the technique is demonstrated via a detailed mapping analysis of the surface Ga distribution of a Ce-Ga sample, which reveals significant heterogeneity resulting from the sample production process

Applications of Portable LIBS for Actinide Analysis

A portable LIBS device was used for rapid elemental impurity analysis of plutonium alloys. This device demonstrates the potential for fast, accurate in-situ chemical analysis and could significantly reduce the fabrication time of plutonium alloys

Analytical comparisons of handheld LIBS and XRF devices for rapid quantification of gallium in a plutonium surrogate matrix

This work compares a portable laser-induced breakdown spectroscopy (LIBS) analyzer to a portable X-ray fluorescence (XRF) device for quantification of gallium (Ga) in a plutonium surrogate matrix of cerium (Ce) for the first time. Calibration methods are developed with spectra of Ce–Ga samples from both devices. Metrics such as limit of detection (LoD) and mean average percent error (MAPE) are examined to evaluate calibration performance. While the portable LIBS device can yield a nearly instantaneous analytical measurement, its accuracy is hampered by self-absorption. By employing a self-absorption correction and increasing gating delay, LIBS calibrations with errors in the low single percents and LoDs of 0.1% Ga were constructed. The XRF device produces calibrations with superlative sensitivity, yielding LoDs for gallium in the low tens of parts-per-million (ppm), two orders of magnitude lower than the corrected LIBS models. However, a clear trade-off of measurement fidelity is established between the instantaneous analysis of the LIBS device and the minutes-long XRF measurement yielding superior detection limits

Comparison of machine learning techniques to optimize the analysis of plutonium surrogate material via a portable LIBS device

The utilization of machine learning techniques has become commonplace in the analysis of optical emission spectra. These methods are often limited to variants of principal components analysis (PCA),partial-least squares (PLS), and artificial neural networks (ANNs). A plethora of other techniques exist and are well established in the world of data science, yet are seldom investigated for their use in spectroscopic problems. In this study, machine learning techniques were used to analyze optical emission spectra of laser-induced plasma from ceria pellets doped with silicon in order to predict silicon content. A boosted regression ensemble model was created, and its predictive accuracy was compared to that of traditional PCA, PLS, and ANN regression models. Boosted regression tree ensembles yielded fits with R-squared (R2) values as high as 0.964 and mean-squared errors of prediction (MSEPs) as low as 0.074, providing the most accurate predictive model. Neural networks performed with slightly lower R2 values and higher MSEPs compared to the ensemble methods, thus indicating susceptibility to overfitting