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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Grain boundary enhanced UN and U3Si2 pellets with improved oxidation resistance

A method of forming a water resistant boundary on a fissile material for use in a water cooled nuclear reactor is described. The method comprises mixing a powdered fissile material selected from the group consisting of UN and U 3 Si 2 with an additive selected from oxidation resistant materials having a melting or softening point lower than the sintering temperature of the fissile material, pressing the mixed fissile and additive materials into a pellet, sintering the pellet to a temperature greater than the melting point of the additive. Alternatively, if the melting point of the oxidation resistant particles is greater than the sintering temperature of UN or U 3 Si 2 , then the oxidation resistant particles can have a particle size distribution less than that of the UN or U 3 Si 2 .

Lahoda, Edward J.↗
DOE OSTI2012

The relative variational model - A topological view of matter and its properties: UO{sub 2}{sup {+-}x} density

Formal definitions of convergence, connected-ness and continuity were established to characterize and describe the crystalline solid and its properties as a unified notion in the topological space. The crystalline solid is a previously empty space that has been filled with atoms and phonons, i.e., the crystal is built with packages of matter and energy in a regular and orderly repetitive pattern along three orthogonal dimensions of the space. The spatial occupation of the atom in the crystal structure is determined by its mean vibrational volume. Thus, the changes of volume and the changes of internal energy are intrinsically linked. In fact, physical and material properties are the interdependent and bijective quantifications associated with variations of the internal energy. These properties are modeled by means of an intrinsic and invariable form function: the Relative Variational Model. In this paper, the lattice parameter and specific mass of UO{sub 2}{sup {+-}x} are depicted in dependence on the variations of the stoichiometry in the band of -0.016 {<=} x and <0.25 and temperature from 0 K up to melting point. (authors)

36 MATERIALS SCIENCE↗
NASA NTRS2005

Microwave and Millimeter Wave Imaging Using Synthetic Aperture Focusing and Holographical Techniques

Microwave and millimeter wave nondestructive testing and evaluation (NDT&E) methods have shown great potential for determining material composition in composite structures, determining material thickness or debond thickness between two layers, and determining the location and size of flaws, defects, and anomalies. The same testing methods have also shown great potential to produce relatively high-resolution images of voids inside Spray On Foam Insulation (SOFI) test panels using real focused methods employing lens antennas. An alternative to real focusing methods are synthetic focusing methods. The essence of synthetic focusing is to match the phase of the scattered signal to measured points spaced regularly on a plane. Many variations of synthetic focusing methods have already been developed for radars, ultrasonic testing applications, and microwave concealed weapon detection. Two synthetic focusing methods were investigated; namely, a) frequency-domain synthetic aperture focusing technique (FDSAFT), and b) wide-band microwave holography. These methods were applied towards materials whose defects were of low dielectric contrast like air void in SOFI. It is important to note that this investigation used relatively low frequencies from 8.2 GHz to 26.5 GHz that are not conducive for direct imaging of the SOFI. The ultimate goal of this work has been to demonstrate the capability of these methods before they are applied to much higher frequencies such as the millimeter wave frequency spectrum (e.g., 30-300 GHz).

Case, Joseph Tobias↗
DOE OSTI2013

Functionalization of multi-walled carbon nanotubes using water-assisted chemical vapor deposition

A simple and novel method, water-assisted chemical vapor deposition (CVD) was developed to functionalize multi-walled carbon nanotubes (MWCNTs) during the synthesis process. The functionalized MWCNTs were characterized using Raman spectroscopy, XPS, TGA, NH{sub 3}-TPD, SEM and HR-TEM. It was found that new defects are introduced and the amount of acidic groups is increased on the MWCNT surface during the water-assisted CVD process. The amount of C-OH and C-O group on the MWCNT surface is found to be increased from 21.1% to 42% with water vapor assistance. Density functional theory (DFT) was employed to study the chemical behavior of water vapor molecule on the catalyst particle surface of Ni(1 1 1) cluster. Based on the experimental and DFT simulation results, a mechanism for functionalization of MWCNTs by water-assisted CVD is proposed. - Graphical abstract: Water is adsorbed and activated on Ni surface, then dissociated into OH and O species, followed by part of OH and O species desorbed from the surface. Finally, the desorbed OH and O species oxidize the unsaturated carbon atoms of carbon nanotubes, form defects and oxygen-containing groups. Highlights: Black-Right-Pointing-Pointer MWCNTs were functionalized by water-assisted CVD method. Black-Right-Pointing-Pointer Defects and weak-medium acidic sites were created on the MWCNT sidewalls. Black-Right-Pointing-Pointer Oxygen-containing groups in functionalized MWCNT were increased from 21.1% to 42%. Black-Right-Pointing-Pointer A mechanism for the influence of water vapor on MWCNTs was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

SU-F-T-366: Dosimetric Parameters Enhancement of 120-Leaf Millennium MLC Using EGSnrc and IAEA Phase-Space Data

Purpose: Recently, the multileaf collimators (MLC) have become an important part of any LINAC collimation systems because they reduce the treatment planning time and improves the conformity. Important factors that affects the MLCs collimation performance are leaves material composition and their thickness. In this study, we investigate the main dosimetric parameters of 120-leaf Millennium MLC including dose in the buildup point, physical penumbra as well as average and end leaf leakages. Effects of the leaves geometry and density on these parameters are evaluated Methods: From EGSnrc Monte Carlo code, BEAMnrc and DOSXYZnrc modules are used to evaluate the dosimetric parameters of a water phantom exposed to a Varian xi for 100cm SSD. Using IAEA phasespace data just above MLC (Z=46cm) and BEAMnrc, for the modified 120-leaf Millennium MLC a new phase space data at Z=52cm is produces. The MLC is modified both in leaf thickness and material composition. EGSgui code generates 521ICRU library for tungsten alloys. DOSXYZnrc with the new phase space evaluates the dose distribution in a water phantom of 60×60×20 cm3 with voxel size of 4×4×2 mm3. Using DOSXYZnrc dose distributions for open beam and closed beam as well as the leakages definition, end leakage, average leakage and physical penumbra are evaluated. Results: A new MLC with improved dosimetric parameters is proposed. The physical penumbra for proposed MLC is 4.7mm compared to 5.16 mm for Millennium. Average leakage in our design is reduced to 1.16% compared to 1.73% for Millennium, the end leaf leakage suggested design is also reduced to 4.86% compared to 7.26% of Millennium. Conclusion: The results show that the proposed MLC with enhanced dosimetric parameters could improve the conformity of treatment planning.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Accelerating self-consistent field iterations in Kohn-Sham density functional theory using a low-rank approximation of the dielectric matrix

We present an efficient preconditioning technique for accelerating the fixed-point iteration in real-space Kohn-Sham density functional theory (DFT) calculations. The preconditioner uses a low-rank approximation of the dielectric matrix (LRDM) based on Gâteaux derivatives of the residual of fixed-point iteration along appropriately chosen direction functions. We develop a computationally efficient method to evaluate these Gâteaux derivatives in conjunction with the Chebyshev filtered subspace iteration procedure, an approach widely used in large-scale Kohn-Sham DFT calculations. Further, we propose a variant of LRDM preconditioner based on adaptive accumulation of low-rank approximations from previous self-consistent field iterations, and also extend the LRDM preconditioner to spin-polarized Kohn-Sham DFT calculations. We demonstrate the robustness and efficiency of the LRDM preconditioner against other widely used preconditioners on a range of benchmark systems with sizes ranging from ~100 to 1100 atoms (~500–20,000 electrons). The benchmark systems include various combinations of metal-insulating-semiconducting heterogeneous material systems, nanoparticles with localized d orbitals near the Fermi energy, nanofilm with metal dopants, and magnetic systems. In all benchmark systems, the LRDM preconditioner converges robustly within 20–30 iterations. In contrast, other widely used preconditioners show slow convergence in many cases, as well as divergence of the fixed-point iteration in some cases. Lastly, we demonstrate the computational efficiency afforded by the LRDM method, with up to 3.4-fold reduction in computational cost for the total ground-state calculation compared to other preconditioners.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Self-learning quantum Monte Carlo method in interacting fermion systems

We present the self-learning Monte Carlo method is a powerful general-purpose numerical method recently introduced to simulate many-body systems. In this work, we extend it to an interacting fermion quantum system in the framework of the widely used determinant quantum Monte Carlo. This method can generally reduce the computational complexity and moreover can greatly suppress the autocorrelation time near a critical point. This enables us to simulate an interacting fermion system on a $100 × 100$ lattice even at the critical point and obtain critical exponents with high precision.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Impact of Point Defects on Electronic Structure in Y₂Ti₂O₇

With many technologies and applications downscaling to nanometer dimensions, the influence of single point defects on electronic structure has shown an increasingly profound impact on optical and electrical properties, and advancing fundamental understanding is critical to defect engineering and control of materials properties. In the present study, first-principles calculations based on density functional theory (DFT) are carried out to study the effects of Ti point defects on the electronic structure of Y₂Ti₂O₇. In the literature, it has been demonstrated that conventional DFT tends to produce delocalized holes and electrons in defective oxide materials due to insufficient cancellation of the self-interaction energy and underestimation of the band gap, which results in an incorrect description of the electronic structure of the system. In an effort to better understand the accuracy of DFT in describing the behavior of Y₂Ti₂O₇ with point defects, the calculated results obtained from DFT and DFT+U methods are compared, including the geometrical distortion, the localization of the defect states and the position of the defect levels in the band gap. Using DFT, distorted geometries around the Ti vacancy and interstitial are found, along with localized oxygen holes and Ti electrons, both of which compare well with the DFT+U results, suggesting that the conventional DFT can be used to describe the localization of the Ti defects in Y₂Ti₂O₇. One major difference in the DFT and DFT+U calculations is the energy position of the defect levels, for which DFT+U results in the states positioned deep in the band gap. Since the DFT+U method suffers from the dependence of the results on the empirical parameter U and no experimental results on the energy position of the defect states are available to tune this U value, care must be taken in applying DFT+U to electronic structure calculations of Y₂Ti₂O₇ with point defects. Based on the DFT method, the most preferred charge state is determined by the formation energies for charged point defects. Moving the Fermi level across the band gap has slight effects on the charge state, and the Ti vacancy and interstitial are found to be in 24 and +4 charge states, respectively.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2011

Cryoplasty Versus Conventional Angioplasty in Femoropopliteal Arterial Recanalization: 3-Year Analysis of Reintervention-Free Survival by Treatment Received

Purpose: To compare long-term efficacy of cryoplasty therapy versus conventional angioplasty in the treatment of peripheral arterial atherosclerotic stenosis on the basis of our 3-year clinical experience. Materials and Methods: From January 2006 to December 2008, a total of 155 patients with 192 lesions of the femoropopliteal sector were randomized to receive either cryoplasty or conventional balloon angioplasty. The primary study end point was lesion target patency. Follow-up with clinical evaluation of patient's symptoms, ankle-brachial index, and Doppler ultrasound was scheduled at 1, 6, 9, 12, 24, and 36 months. Results: For the cryoplasty group (n = 86), technical immediate success was achieved in 74.4% of lesions. Rate of significant dissection was 13.5% and rate of stent placement of 22%. In the long term, target lesion patency rate at 6 months was 59.4%, with rates of 55.9, 52.6, and 49.1% at 1, 2, and 3 years, respectively. For the conventional angioplasty group (n = 69), the immediate technical success rate was 83.7%. Rate of significant dissection was 19%, and rate of stent placement was 72.9%. Patency rates at 6 months and at 1, 2, and 3 years were 71.5, 61.2, 60, and 56%, respectively. Conclusion: Compared with conventional angioplasty, cryoplasty showed good immediate success rates with lower stent placement rates. During the 3-year follow-up, patency rates tended to equalize between the two modalities.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Surfactant-assisted synthesis of hybrid lithium iron phosphate nanoparticles for enhancing electrochemical performance

Hybrid nanoparticles of LiFePO{sub 4} with carbon and lithium phosphates were synthesized through organic-inorganic co-assembly procedure using a triblock copolymer (F108 or P123). We found that the triblock copolymers play a critical role in controlling size of hybrid particle and the degree of crystallinity of the inorganic nanostructures. The hybrid using P-123 had more graphitic carbon which resulted in fast electron mobility. Also, magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed that the crystallinity of the hybrid using P123 is higher than that using F108 which is not measurable in X-ray diffraction. Electrochemical performance of the hybrid using P123 as a cathode material in Li-ion batteries showed superior rate capability at 20 C of charging rate and 2 C of discharging rate without capacity loss, in which discharge capacity was 102 mAh/g. - Graphical abstract: Hybrid nanoparticles were synthesized through organic-inorganic co-assembly based on synthetic procedure of mesoporous materials. P123-LFP showed superior high-rate capability at a 20 C charging rate and 2 C discharging rate without capacity loss in Li-ion battery. Highlights: Black-Right-Pointing-Pointer LiFePO{sub 4} nanohybrids are synthesized through the organic-inorganic co-assembly method. Black-Right-Pointing-Pointer Copolymers (F108 or P123) serve as structure directing agents and a carbon source. Black-Right-Pointing-Pointer P123 produces more graphitic carbon and higher crystalline nanohybrids. Black-Right-Pointing-Pointer Nanohybrids using P123 show superior rate capability in Li-ion battery.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Novel hetero-bilayered materials for photovoltaics

The recently synthesized GaS and MoSe 2 nanosheets have been used as appropriate substrates for other layered materials, e.g. silicene/GaS heterosheets akin to graphene/BN systems. Here, we have performed a comprehensive first-principles study of the electronic and optical properties of two-dimensional (2D) GaS/MoSe 2 hetero-bilayers based on density functional theory (DFT). Here we found almost all proposed GaS/MoSe2 hetero-bilayers in the current study have an indirect band gap from the Γ point to the K point, except for one with a direct band gap at the K point. Tunable band gaps GaS/MoSe 2 hetero-bilayers can be controlled by strain modulation. State-of-the-art GW-Bethe–Salpeter method, accounting for electron-electron and electron-hole interactions, has been employed to compute accurate absorbance spectra for layered materials. Compared with its composing GaS and MoSe 2 monolayers, GaS/MoSe 2 hetero-bilayers show superior behavior on optical absorbance, indicating a stronger visible-light absorption and applications in solar energy harvesting. We foresee that the novel GaS/MoSe 2 hetero-bilayers would stimulate the fabrication of materials with unprecedented optical and physico-chemical properties that may apply in nanodevices and photovoltaic cells.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Kernel principal component analysis for stochastic input model generation

Highlights: {yields} KPCA is used to construct a reduced order stochastic model of permeability. {yields} A new approach is proposed to solve the pre-image problem in KPCA. {yields} Polynomial chaos is used to provide a parametric stochastic input model. {yields} Flow in porous media with channelized permeability is considered. - Abstract: Stochastic analysis of random heterogeneous media provides useful information only if realistic input models of the material property variations are used. These input models are often constructed from a set of experimental samples of the underlying random field. To this end, the Karhunen-Loeve (K-L) expansion, also known as principal component analysis (PCA), is the most popular model reduction method due to its uniform mean-square convergence. However, it only projects the samples onto an optimal linear subspace, which results in an unreasonable representation of the original data if they are non-linearly related to each other. In other words, it only preserves the first-order (mean) and second-order statistics (covariance) of a random field, which is insufficient for reproducing complex structures. This paper applies kernel principal component analysis (KPCA) to construct a reduced-order stochastic input model for the material property variation in heterogeneous media. KPCA can be considered as a nonlinear version of PCA. Through use of kernel functions, KPCA further enables the preservation of higher-order statistics of the random field, instead of just two-point statistics as in the standard Karhunen-Loeve (K-L) expansion. Thus, this method can model non-Gaussian, non-stationary random fields. In this work, we also propose a new approach to solve the pre-image problem involved in KPCA. In addition, polynomial chaos (PC) expansion is used to represent the random coefficients in KPCA which provides a parametric stochastic input model. Thus, realizations, which are statistically consistent with the experimental data, can be generated in an efficient way. We showcase the methodology by constructing a low-dimensional stochastic input model to represent channelized permeability in porous media.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Experimental Fabrication of Porous Additive Manufactured Material

Nuclear industries can benefit from materials that can perform well mechanically and thermally in high temperature and corrosion environments. Functionally graded materials (FGM) are materials manufactured with complex spatial, structural, and chemical compositions, creating components predesigned with tailored microstructural and mechanical properties. Porosity-graded FGMs are designed to introduce pores into a component’s structure as a mechanism to increase bulk or surface material performance, such as stress accommodation and negative thermal conductivity. Additive manufacturing (AM) techniques such as laser energy net shape (LENS) and wire arc additive manufacturing (WAAM), excel in high energy density, point-to-point metal deposition, and present in combination with other combinatorial approaches, exciting methods to manufacture porous FGM components. This project is also examining plasma jet printing as another means for method evaluations for smaller scale graded components. This study explores AM FGM process parameters and combinatorial fabrication methodologies for stainless steel components functionally graded in porosity levels. Preliminary characterization results are provided to attest the feasibility of the combinational fabrication techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Molecular dynamics simulations of solid state recrystallization I: Observation of grain growth in annealed iron nanoparticles

Molecular dynamics simulations of solid state recrystallization and grain growth in iron nanoparticles containing 1436 atoms were carried out. During the period of relaxation of supercooled liquid drops and during thermal annealing of the solids they froze to, changes in disorder were followed by monitoring changes in energy and the migration of grain boundaries. All 27 polycrystalline nanoparticles, which were generated with different grain boundaries, were observed to recystallize into single crystals during annealing. Larger grains consumed the smaller ones. In particular, two sets of solid particles, designated as A and B, each with two grains, were treated to generate 18 members of each set with different thermal histories. This provided small ensembles (of 18 members each) from which rates at which the larger grain engulfed the smaller one, could be determined. The rate was higher, the smaller the degree of misorientation between the grains, a result contrary to the general rule based on published experiments, but the reason was clear. Crystal A, which happened to have a somewhat lower angle of misorientation, also had a higher population of defects, as confirmed by its higher energy. Accordingly, its driving force to recrystallize was greater. Although the mechanism of recrystallization is commonly called nucleation, our results, which probe the system on an atomic scale, were not able to identify nuclei unequivocally. By contrast, our technique can and does reveal nuclei in the freezing of liquids and in transformations from one solid phase to another. An alternative rationale for a nucleation-like process in our results is proposed. - Graphical Abstract: Time dependence of energy per atom in the quenching of liquid nanoparticles A-C of iron. Nanoparticle C freezes directly into a single crystal but A and B freeze to solids with two grains. A and B eventually recrystallize into single crystals. Highlights: Black-Right-Pointing-Pointer Solid state material synthesis. Black-Right-Pointing-Pointer Experimental study of nucleation in condensed materials. Black-Right-Pointing-Pointer Computation Study of nucleation in condensed materials. Black-Right-Pointing-Pointer Observation of recrystallization in atomic detail.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Metal forming and working of stabilized nanocrystalline Cu-Ta for electrical contacts

The commercialization of nanocrystalline metals and alloys is currently entering a renaissance period. Many of the processing and consolidation challenges that have haunted them are now more fully understood, opening the doors for stabilized nanocrystalline metals to be produced on a bulk scale. While challenges remain, the increased volume at which these materials are being supplied is for the first time allowing for investigations into more traditional methods of metal working, such as extruding, rolling, forming, and forging. Recently, the manufacturing science has been developed to allow nanocrystalline Cu-Ta alloys to progress to this point. This article therefore builds upon the last decade of evolutionary progression within the family of stabilized nanocrystalline Cu-Ta alloys by presenting some of the first findings related to scaled powder synthesis, production of billets, thin sheets, and foils. Here, the mechanical performance and physical properties relevant to forming electrical contacts and pins including, tensile, J-integral fracture toughness, Charpy Impact, bi-axial tension, and conductivity are reported. This introductory investigation into forming such a novel material, provides evidence to these alloys potential at bridging the gap between being a scientific curiosity to that of a real engineering material.

36 MATERIALS SCIENCE↗
DOE OSTI2011

O K-energy loss near-edge structure change induced by tantalum impurity in monoclinic hafnium oxide

The present paper reports the energy loss near-edge structure (ELNES) study of monoclinic HfO{sub 2} (m-HfO{sub 2}) and tantalum doped m-HfO{sub 2} (Ta{sub 0.1}Hf{sub 0.9}O{sub 2}) thin films prepared by radio frequency magnetron co-sputtering method. A change in the O K-ELNES spectra was observed as the amount of dopant increases. In order to precise the common features and the differences as a function of Ta defect nature (substitutional or interstitial) in HfO{sub 2}, the O K-ELNES were commented with respect to density functional theory calculations implemented in Vienna ab initio simulation package code. The calculated Ta doped HfO{sub 2} band structure showed that substitutional tantalum is the dominant defect and the spectral differences between doped and non-doped HfO{sub 2} are mainly originated from the change in the local cation distribution around the oxygen atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Theory of spiral structure.

The question whether the galactic spiral arms are material objects or wave patterns is discussed. A semiempirical approach is adopted in presenting the concept of density waves. The theory of density waves is considered, giving attention to a survey of theoretical developments by analytical methods, the implication of a spiral pattern of density waves, spirals with moderately small pitch angle, and the origin and permanence of galactic spirals. The theoretical aspects discussed are tested against more detailed observations in the Milky Way system. It is pointed out that the density wave concept introduced by Lindblad, including the material concentration of both gas and stars, is the essential basis for the spiral structure of disk-shaped galaxies.

Lin, C. C.↗
DOE OSTI2014

Identification of Leakage Spectra from Neutron Activation in Glass/Cherenkov Detectors - Paper 96

Oak Ridge National Laboratory has developed a new detector system concept that can be deployed in major US cities to identify the leakage spectrum of a nuclear weapon detonation. The detector is based on a small piece of glass that has been doped with an element that has a high activation cross section and creates a radioactive activation product with a reasonable length half-life. The decay of the activation product(s) after exposure creates Cherenkov light which can propagate to a photomultiplier and can be turned into a count-rate signal. The signal from each glass in each detector in a city can be individually analyzed to determine the amount of activation products produced in the initial exposure. Several activation products can be determined in a single glass if the half-lives are not the same. With a known source location and a detailed 3D model of a city, neutron transport simulations can be made by using a library of known sources to predict the activation amounts each source would have made in the glass detectors. A simple comparison of the measured activation amounts and the predicted activation amounts can identify the source spectrum contained in the library that is the best match. Choosing dopants with a large range in the threshold energy for the activation reactions can help to differentiate the spectra in the library. The method of matching the measured activation amounts to the predicted activation amounts to identify the source spectrum is similar to the analysis used for the passive Activation Foil Integrated Detector System (AFIDS), also developed at Oak Ridge National Laboratory. In AFIDS, wires or foils of known mass and isotopic composition are deployed before and then collected after exposure. Counting gammas in a nearby laboratory determines the activation amounts. The glass/Cherenkov system is active - it uses a battery-powered detector to count flashes of Cherenkov light and to communicate its count rates to a remote location for further analysis. Work has been performed in several areas, including glass making, automated detection and communication systems and software tools for analysis of the signal and source spectrum identification. Bell and Boatner have developed phosphate glasses that incorporate elements with high capture cross sections, and Hayward has simulated the response with Geant4 and measured the response with isotopic gamma sources. This paper will focus on the software tools for determining the activation amounts from the Cherenkov count-rate signal and finding the best matching source spectrum. A test problem in an urban environment is used to demonstrate the potential of a spectrum identification system using neutron activation. The analysis methods developed to identify the neutron leakage spectra from Cherenkov light given off by neutron activation in doped glasses work well. The calculation used to unfold the count-rate information into the number of actual activation products uses robust algorithms that can also compute associated uncertainties. These uncertainties and the known uncertainties of the glass tube material compositions are incorporated into the matching analysis to determine which of the source spectra in the library best matches the measured activation data. Any measurement method used to identify a neutron source spectrum relies at some point on a comparison against known sources; no identification method is definitive. Detection systems measure some physical aspect of the source, not its serial number. Many systems measure the physical aspect to determine that the source has some property, and then leave it to experts to determine which potential sources share that property. The analysis system presented here incorporates the comparison into the analysis itself. The statistical tests show which of the known library sources match the measured data the best and whether that match is a good match. If the best match still does not fit the measured data well (a very high χ{sup 2} value), that indicates the true source is not one of the sources in the library. This is still valuable information for decision makers. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗