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Assessment of Nuclear Resonance Fluorescence for Spent Nuclear Fuel Assay

Description: In nuclear resonance fluorescence (NRF) measurements, resonances are excited by an external photon beam leading to the emission of gamma rays with specific energies that are characteristic of the emitting isotope. NRF promises the unique capability of directly quantifying a specific isotope without the need for unfolding the combined responses of several fissile isotopes as is required in other measurement techniques. We have analyzed the potential of NRF as a non-destructive analysis technique for quantitative measurements of Pu isotopes in spent nuclear fuel (SNF). Given the low concentrations of 239Pu in SNF and its small integrated NRF cross sections, the main challenge in achieving precise and accurate measurements lies in accruing sufficient counting statistics in a reasonable measurement time. Using analytical modeling, and simulations with the radiation transport code MCNPX that has been experimentally tested recently, the backscatter and transmission methods were quantitatively studied for differing photon sources and radiation detector types. Resonant photon count rates and measurement times were estimated for a range of photon source and detection parameters, which were used to determine photon source and gamma-ray detector requirements. The results indicate that systems based on a bremsstrahlung source and present detector technology are not practical for high-precision measurements of 239Pu in SNF. Measurements that achieve the desired uncertainties within hour-long measurements will either require stronger resonances, which may be expressed by other Pu isotopes, or require quasi-monoenergetic photon sources with intensities that are approximately two orders of magnitude higher than those currently being designed or proposed.This work is part of a larger effort sponsored by the Next Generation Safeguards Initiative to develop an integrated instrument, comprised of individual NDA techniques with complementary features, that is fully capable of determining Pu mass in spent fuel assemblies.
Date: June 30, 2011
Creator: Quiter, Brian; Ludewigt, Bernhard & Ambers, Scott
Partner: UNT Libraries Government Documents Department

Using Visual Analytics to Maintain Situation Awareness in Astrophysics

Description: We present a novel collaborative visual analytics application for cognitively overloaded users in the astrophysics domain. The system was developed for scientists needing to analyze heterogeneous, complex data under time pressure, and then make predictions and time-critical decisions rapidly and correctly under a constant influx of changing data. The Sunfall Data Taking system utilizes severalnovel visualization and analysis techniques to enable a team of geographically distributed domain specialists to effectively and remotely maneuver a custom-built instrument under challenging operational conditions. Sunfall Data Taking has been in use for over eighteen months by a major international astrophysics collaboration (the largest data volume supernova search currently in operation), and has substantially improved the operational efficiency of its users. We describe the system design process by an interdisciplinary team, the system architecture, and the results of an informal usability evaluation of the production system by domain experts in the context of Endsley?s three levels of situation awareness.
Date: July 1, 2008
Creator: Aragon, Cecilia R.; Poon, Sarah S.; Aldering, Gregory S.; Thomas, Rollin C. & Quimby, Robert
Partner: UNT Libraries Government Documents Department

Transmission Nuclear Resonance Fluorescence Measurements of 238U in Thick Targets

Description: Transmission nuclear resonance fluorescence measurements were made on targets consisting of Pb and depleted U with total areal densities near 86 g/cm2. The 238U content n the targets varied from 0 to 8.5percent (atom fraction). The experiment demonstrates the capability of using transmission measurements as a non-destructive technique to identify and quantify the presence of an isotope in samples with thicknesses comparable to he average thickness of a nuclear fuel assembly. The experimental data also appear to demonstrate the process of notch refilling with a predictable intensity. Comparison of measured spectra to previous backscatter 238U measurements indicates general agreement in observed excited states. Two new 238U excited states and possibly a third state have also been observed.
Date: August 31, 2010
Creator: Quiter, Brian J.; Ludewigt, Bernhard A.; Mozin, Vladimir V.; Wilson, Cody & Korbly, Steve
Partner: UNT Libraries Government Documents Department

EIGHT-TESLA SYNCHROTRON DIPOLES -- DESIGN ALTERNATIVES

Description: Superconducting accelerator bending magnets in the 4 to 5 tesla field range have been, or are being, developed for the LBL ESCAR, FNAL Doubler, and BNL ISABELLE projects and can be considered as state-of-the-art. We are now engaged in a program to develop accelerator dipoles with significantly enhanced performance, into the 8-tesla range. Analytical design studies, based on idealized configurations, have been done to trace the dependence of stresses within the coil and overall magnet size on the magnet aperture, coil current density, central magnetic field, structural ring stress, and magnetic induction in the iron flux-return yoke. Our development program includes: (1) Development and measurement at 4.2 K, of coil structures consistent with the requirements of the analytical design studies; (2) Superfluid helium II at 1.8 K and at atmospheric pressure, large magnets as well as conductors will be tested; (3) Development and evaluation of aluminum stabilization and various A-15 superconductors; and (4) Tests of various model dipoles with instrumentation to measure mechanical motion.
Date: March 1, 1979
Creator: Gilbert, W. S.; Lambertson, G. R. & Meuser, R. B.
Partner: UNT Libraries Government Documents Department

Towards a Real-time Transient Classification Engine

Description: Temporal sampling does more than add another axis to the vector of observables. Instead, under the recognition that how objects change (and move) in time speaks directly to the physics underlying astronomical phenomena, next-generation wide-field synoptic surveys are poised to revolutionize our understanding of just about anything that goes bump in the night (which is just about everything at some level). Still, even the most ambitious surveys will require targeted spectroscopic follow-up to fill in the physical details of newly discovered transients. We are now building a new system intended to ingest and classify transient phenomena in near real-time from high-throughput imaging data streams. Described herein, the Transient Classification Project at Berkeley will be making use of classification techniques operating on"features" extracted from time series and contextual (static) information. We also highlight the need for a community adoption of a standard representation of astronomical time series data (i.e.,"VOTimeseries").
Date: February 22, 2008
Creator: Nugent, Peter E.; Bloom, Josh; Starr, Dan; Butler, Nat; Nugent, Peter; Rischard, M. et al.
Partner: UNT Libraries Government Documents Department

K-corrections and spectral templates of Type Ia supernovae

Description: With the advent of large dedicated Type Ia supernova (SN Ia) surveys, K-corrections of SNe Ia and their uncertainties have become especially important in the determination of cosmological parameters. While K-corrections are largely driven by SN Ia broadband colors, it is shown here that the diversity in spectral features of SNe Ia can also be important. For an individual observation, the statistical errors from the inhomogeneity in spectral features range from 0.01 (where the observed and rest-frame filters are aligned) to 0.04 (where the observed and rest-frame filters are misaligned). To minimize the systematic errors caused by an assumed SN Ia spectral energy distribution (SED), we outline a prescription for deriving a mean spectral template time series that incorporates a large and heterogeneous sample of observed spectra. We then remove the effects of broadband colors and measure the remaining uncertainties in the K-corrections associated with the diversity in spectral features. Finally, we present a template spectroscopic sequence near maximum light for further improvement on the K-correction estimate. A library of ~;;600 observed spectra of ~;;100 SNe Ia from heterogeneous sources is used for the analysis.
Date: March 20, 2007
Creator: Nugent, Peter E.; Hsiao, E.Y.; Conley, A.; Howell, D.A.; Sullivan, M.; Pritchet, C.J. et al.
Partner: UNT Libraries Government Documents Department

Object Classification at the Nearby Supernova Factory

Description: We present the results of applying new object classification techniques to the supernova search of the Nearby Supernova Factory. In comparison to simple threshold cuts, more sophisticated methods such as boosted decision trees, random forests, and support vector machines provide dramatically better object discrimination: we reduced the number of nonsupernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaining a reasonable false positive rate in the automated transient alert pipelines of upcoming large optical surveys.
Date: December 21, 2007
Creator: Aragon, Cecilia R.; Bailey, Stephen; Aragon, Cecilia R.; Romano, Raquel; Thomas, Rollin C.; Weaver, B. A. et al.
Partner: UNT Libraries Government Documents Department

Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra

Description: We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its dispersion using high signal-to-noise ratio Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40percent of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high-quality local spectra. The mean UV spectrum of our z~;;=0.5 SNe Ia and its dispersion is tabulated for use in future applications. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes.
Date: February 28, 2008
Creator: Nugent, Peter E; Ellis, R.S.; Sullivan, M.; Nugent, P.E.; Howell, D.A.; Gal-Yam, A. et al.
Partner: UNT Libraries Government Documents Department

Application of High-performance Visual Analysis Methods to Laser Wakefield Particle Acceleration Data

Description: Our work combines and extends techniques from high-performance scientific data management and visualization to enable scientific researchers to gain insight from extremely large, complex, time-varying laser wakefield particle accelerator simulation data. We extend histogram-based parallel coordinates for use in visual information display as well as an interface for guiding and performing data mining operations, which are based upon multi-dimensional and temporal thresholding and data subsetting operations. To achieve very high performance on parallel computing platforms, we leverage FastBit, a state-of-the-art index/query technology, to accelerate data mining and multi-dimensional histogram computation. We show how these techniques are used in practice by scientific researchers to identify, visualize and analyze a particle beam in a large, time-varying dataset.
Date: August 28, 2008
Creator: Rubel, Oliver; Prabhat, Mr.; Wu, Kesheng; Childs, Hank; Meredith, Jeremy; Geddes, Cameron G.R. et al.
Partner: UNT Libraries Government Documents Department

Quantitative comparison between Type Ia supernova spectra at low and high redshifts: A case study

Description: We develop a method to measure the strength of the absorption features in type Ia supernova (SN Ia) spectra and use it to make a quantitative comparisons between the spectra of type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 = z = 0.912) SNe Ia observed by the Supernova Cosmology Project. Through measurements of the strengths of these features and of the blueshift of theabsorption minimum in Ca ii H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z< 0.15). One supernova in our high redshift sample, SN 2002fd at z = 0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.
Date: March 24, 2008
Creator: Supernova Cosmology Project
Partner: UNT Libraries Government Documents Department