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Estimate of the 9Be(n,el) Cross-section Uncertainties for the ENDL99 and ENDF/B-VII Evaluations

Description: Uncertainties for the ENDL99 and ENDF/B-VII evaluations of the {sup 9}Be (n, el) cross section have been estimated for incident neutron energies up to 20 MeV. The uncertainties were obtained by extracting the spread of the experimental data about the evaluations, using a sophisticated procedure to ensure smoothness of the uncertainty as a function of energy. The technique used to obtain the uncertainties is described briefly in this report, and the resulting error bands are given for the two evaluations.
Date: July 30, 2007
Creator: Younes, W & Pruet, J
Partner: UNT Libraries Government Documents Department

Initial Design Calculations for a Detection System that will Observe Resonant Excitation of the 680 keV state in 238U

Description: We present calculations and design considerations for a detection system that could be used to observe nuclear resonance fluorescence in {sup 238}U. This is intended as part of an experiment in which a nearly monochromatic beam of light incident on a thin foil of natural uranium resonantly populates the state at 680 keV in {sup 238}U. The beam of light is generated via Compton upscattering of laser light incident on a beam of relativistic electrons. This light source has excellent energy and angular resolution. In the current design study we suppose photons emitted following de-excitation of excited nuclei to be observed by a segmented array of BGO crystals. Monte Carlo calculations are used to inform estimates for the design and performance of this detector system. We find that each detector in this array should be shielded by about 2 cm of lead. The signal to background ratio for each of the BGO crystals is larger than ten. The probability that a single detector observes a resonant photon during a single pulse of the light source is near unity.
Date: January 26, 2007
Creator: Pruet, J. & Hagmann, C.
Partner: UNT Libraries Government Documents Department

On the Use of Rossi Alpha Critical Assembly Measurements for Validating and Constraining Nuclear Data

Description: Critical assemblies are exquisitely sensitive to details of the microscopic nuclear reactions that govern neutron multiplication. For this reason experimental studies of critical assemblies represent a cornerstone in the process of validating nuclear data. Several different characteristics of a critical system can be measured. The most commonly considered is the so-called effective k eigenvalue, k{sub eff}. Another well-measured property of these systems is {alpha}{sub 0}, the inverse e-folding time of the neutron population in the absence of {beta}-delayed neutrons. Through Monte Carlo calculations and appear to perturbation theory they show that for fast critical systems {alpha}{sub 0} and k{sub eff} can be viewed as lying on a single straight line for any reasonable assumptions about the underlying nuclear data. This means that the two quantities provide the same constraint on nuclear data. In principle, {alpha}{sub 0} could be associated with a very small uncertainty, and this would make the measurements for neutron multiplication rates more useful than k{sub eff} for constraining nuclear data. In practice, though, uncertainties in k{sub eff} and {alpha}{sub 0} are dominated by uncertainties in the representation of the critical system, and not by pure measurement errors for these quantities. This, together with the linear relation between {alpha}{sub 0} and k{sub eff}, implies that the two measured quantities provide exactly the same constraint on nuclear data. They do not consider other measured or inferred characteristics of critical assemblies, such as neutron generation times or spectral indices, that may be valuable in the validation process.
Date: March 7, 2007
Creator: Pruet, J & Sleaford, B
Partner: UNT Libraries Government Documents Department

Photon Production through Multi-step Processes Important in Nuclear Fluorescence Experiments

Description: The authors present calculations describing the production of photons through multi-step processes occurring when a beam of gamma rays interacts with a macroscopic material. These processes involve the creation of energetic electrons through Compton scattering, photo-absorption and pair production, the subsequent scattering of these electrons, and the creation of energetic photons occurring as these electrons are slowed through Bremsstrahlung emission. Unlike single Compton collisions, during which an energetic photon that is scattered through a large angle loses most of its energy, these multi-step processes result in a sizable flux of energetic photons traveling at large angles relative to an incident photon beam. These multi-step processes are also a key background in experiments that measure nuclear resonance fluorescence by shining photons on a thin foil and observing the spectrum of back-scattered photons. Effective cross sections describing the production of backscattered photons are presented in a tabular form that allows simple estimates of backgrounds expected in a variety of experiments. Incident photons with energies between 0.5 MeV and 8 MeV are considered. These calculations of effective cross sections may be useful for those designing NRF experiments or systems that detect specific isotopes in well-shielded environments through observation of resonance fluorescence.
Date: October 26, 2006
Creator: Hagmann, C & Pruet, J
Partner: UNT Libraries Government Documents Department

Contraband Detection with Nuclear Resonance Fluorescence: Feasibility and Impact

Description: In this report they show that cargo interrogation systems developed to thwart trafficking of illicit nuclear materials could also be powerful tools in the larger fight against contraband smuggling. In particular, in addition to detecting special nuclear materials, cargo scanning systems that exploit nuclear resonance fluorescence to detect specific isotopes can be used to help find: chemical weapons; some drugs as well as some chemicals regulated under the controlled substances act; precious metals; materials regulated under export control laws; and commonly trafficked fluorocarbons.
Date: January 3, 2007
Creator: Pruet, J & Lange, D
Partner: UNT Libraries Government Documents Department

Updated Evaluations for Americium Isotopes

Description: Here we describe evaluations for Am isotopes that will be included in the next release of ENDL. Current ENDL99 evaluations for these isotopes are quite outdated and almost entirely undocumented. Because Am is important for several DNT applications, and because quality evaluations are either readily available or easily calculated, the effort to update ENDL seems warranted. Results from good existing evaluations are adopted whenever possible. To this end we devote the next section of this report to a consideration of the availability of evaluations The quality of different evaluations as well as comparisons against experiments are also presented and used to motivate our choice of adopted data sets. Plans for modifying and improving adopted evaluations are also discussed. For {sup 240}Am there are no existing evaluations. To fill this gap, we are providing a new Am evaluation based on calculations with the statistical model reaction codes TALYS and EMPIRE. This evaluation is described below. The ENDF/B-VI formatted file containing this evaluation is given in the appendix.
Date: September 22, 2005
Creator: Brown, D A & Pruet, J
Partner: UNT Libraries Government Documents Department

T-REX Design Considerations for Detection of Concealed 238U

Description: Here they outline considerations that might inform choices for the design of a laser/linac-based light source used to detect {sup 238}U via excitation of the resonance at 680.11 keV in this isotope. They assume that the principal concern is speed of interrogation and not, e.g., how much radiological dose is imparted during a scan. It is found that if the photon detectors used in the system have an energy resolution better than or comparable to that of the interrogation beam, then to a first approximation the light source should be designed to have the highest possible specific fluence (photons per unit energy per unit time). there is also a weak dependence of scan time on the number of photons emitted per pulse of the light source. A simple formula describing the tradeoff between specific fluence and number of photons per pulse is presented.
Date: February 7, 2006
Creator: Pruet, J & McNabb, D P
Partner: UNT Libraries Government Documents Department

Nucleosynthesis in Early Supernova Winds II: The Role of Neutrinos

Description: One of the outstanding unsolved riddles of nuclear astrophysics is the origin of the so called ''p-process'' nuclei from A = 92 to 126. Both the lighter and heavier p-process nuclei are adequately produced in the neon and oxygen shells of ordinary Type II supernovae, but the origin of these intermediate isotopes, especially {sup 92,94}Mo and {sup 96,98}Ru, has long been mysterious. Here we explore the production of these nuclei in the neutrino-driven wind from a young neutron star. We consider such early times that the wind still contains a proton excess because the rates for {nu}{sub e} and positron captures on neutrons are faster than those for the inverse captures on protons. Following a suggestion by Froehlich et al. (2005), they also include the possibility that, in addition to the protons, {alpha}-particles, and heavy seed, a small flux of neutrons is maintained by the reaction p({bar {nu}}{sub e}, e{sup +})n. This flux of neutrons is critical in bridging the long waiting points along the path of the rp-process by (n,p) and (n,{gamma}) reactions. Using the unmodified ejecta histories from a recent two-dimensional supernova model by Janka, Buras, and Rampp (2003), they find synthesis of p-rich nuclei up to {sup 102}Pd. However, if the entropy of these ejecta is increased by a factor of two, the synthesis extends to {sup 120}Te. Still larger increases in entropy, that might reflect the role of magnetic fields or vibrational energy input neglected in the hydrodynamical model, result in the production of numerous r-, s-, and p-process nuclei up to A {approx} 170, even in winds that are proton-rich.
Date: November 4, 2005
Creator: Pruet, J; Hoffman, R; Woosley, S; Janka, H & Buras, R
Partner: UNT Libraries Government Documents Department

Event-by-Event Study of Prompt Neutrons from 239Pu

Description: Employing a recently developed Monte Carlo model, we study the fission of {sup 240}Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies of less than 2 MeV.
Date: January 15, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
Partner: UNT Libraries Government Documents Department

Alternative Approach to Nuclear Data Representation: Building the infrastructure to support QMU and next-generation simulations

Description: The nuclear data infrastructure currently relies on punch-card era formats designed some five decades ago. Though this system has worked well, recent interest in non-traditional and complicated physics processes has demanded a change. Here we present an alternative approach under development at LLNL. In this approach data is described through collections of distinct and self-contained simple data structures. This structure-based format is compared with traditional ENDF and ENDL, which can roughly be characterized as dictionary-based representations.
Date: January 17, 2006
Creator: Pruet, J; Brown, D A; Beck, B & McNabb, D P
Partner: UNT Libraries Government Documents Department

Nucleosynthesis in Early Neutrino Driven Winds

Description: Two recent issues related to nucleosynthesis in early proton-rich neutrino winds are investigated. In the first part we investigate the effect of nuclear physics uncertainties on the synthesis of {sup 92}Mo and {sup 94}Mo. Based on recent experimental results, we find that the proton rich winds of the model investigated here can not be the only source of the solar abundance of {sup 92}Mo and {sup 94}Mo. In the second part we investigate the nucleosynthesis from neutron rich bubbles and show that they do not contribute to the nucleosynthesis integrated over both neutron and proton-rich bubbles and proton-rich winds.
Date: January 9, 2008
Creator: Hoffman, R; Fisker, J; Pruet, J; Woosley, S; Janka, H & Buras, R
Partner: UNT Libraries Government Documents Department

Calculation of 239Pu fission observables in an event-by-event simulation

Description: The increased interest in more exclusive fission observables has demanded more detailed models. We describe a new computational model, FREYA, that aims to meet this need by producing large samples of complete fission events from which any observable of interest can then be extracted consistently, including any interesting correlations. The various model assumptions are described and the potential utility of the model is illustrated. As a concrete example, we use formal statistical methods, experimental data on neutron production in neutron-induced fission of {sup 239}Pu, along with FREYA, to develop quantitative insights into the relation between reaction observables and detailed microscopic aspects of fission. Current measurements of the mean number of prompt neutrons emitted in fission taken together with less accurate current measurements for the prompt post-fission neutron energy spectrum, up to the threshold for multi-chance fission, place remarkably fine constraints on microscopic theories.
Date: March 31, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
Partner: UNT Libraries Government Documents Department

High Energy Nuclear Database: A Testbed for Nuclear Data Information Technology

Description: We describe the development of an on-line high-energy heavy-ion experimental database. When completed, the database will be searchable and cross-indexed with relevant publications, including published detector descriptions. While this effort is relatively new, it will eventually contain all published data from older heavy-ion programs as well as published data from current and future facilities. These data include all measured observables in proton-proton, proton-nucleus and nucleus-nucleus collisions. Once in general use, this database will have tremendous scientific payoff as it makes systematic studies easier and allows simpler benchmarking of theoretical models for a broad range of experiments. Furthermore, there is a growing need for compilations of high-energy nuclear data for applications including stockpile stewardship, technology development for inertial confinement fusion, target and source development for upcoming facilities such as the International Linear Collider and homeland security. This database is part of a larger proposal that includes the production of periodic data evaluations and topical reviews. These reviews would provide an alternative and impartial mechanism to resolve discrepancies between published data from rival experiments and between theory and experiment. Since this database will be a community resource, it requires the high-energy nuclear physics community's financial and manpower support. This project serves as a testbed for the further development of an object-oriented nuclear data format and database system. By using ''off-the-shelf'' software tools and techniques, the system is simple, robust, and extensible. Eventually we envision a ''Grand Unified Nuclear Format'' encapsulating data types used in the ENSDF, ENDF/B, EXFOR, NSR and other formats, including processed data formats.
Date: April 18, 2007
Creator: Brown, D A; Vogt, R; Beck, B & Pruet, J
Partner: UNT Libraries Government Documents Department

Spectra Observed Following Cargo Interrogation

Description: The authors present calculations of photon spectra observed following irradiation of bare HEU, HEU embedded in steel and wood cargos, and steel and wood alone. These spectra might be useful starting points for statistical detection efforts aimed at determining whether fissile material is present in a cargo. Detailed comparisons between calculations and experiments are presented and overall quite good (small {chi}{sup 2}) agreement is found. they do not present a complete solution to the problem of determining whether a given spectrum contains contributions from post-fission photons. However, it is shown that a brute-force fitting of observed spectra in terms of a few calculated ''basis'' spectra gives meaningful predictions about the presence of {sup 235}U in cargo. Though this may not be the most powerful method, it does give well defined confidence limits and seems to have strong predictive power.
Date: November 15, 2005
Creator: Pruet, J; Prussin, S; Descalle, M & Hall, J
Partner: UNT Libraries Government Documents Department

Neutron and Photon Transport in Sea-Going Cargo Containers

Description: Factors affecting sensing of small quantities of fissionable material in large sea-going cargo containers by neutron interrogation and detection of {beta}-delayed photons are explored. The propagation of variable-energy neutrons in cargos, subsequent fission of hidden nuclear material and production of the {beta}-delayed photons, and the propagation of these photons to an external detector are considered explicitly. Detailed results of Monte Carlo simulations of these stages in representative cargos are presented. Analytical models are developed both as a basis for a quantitative understanding of the interrogation process and as a tool to allow ready extrapolation of the results to cases not specifically considered here.
Date: February 9, 2005
Creator: Pruet, J; Descalle, M; Hall, J; Pohl, B & Prussin, S G
Partner: UNT Libraries Government Documents Department

Translated ENDF formatted data at LLNL

Description: The LLNL Computational Nuclear Physics (CNP) Group announces the release of translated ENDF/BVI, ENDF/B-VII, JEFF-3.1, JENDL-3.3 and other neutron incident evaluated reaction data libraries to LLNL users.
Date: June 29, 2006
Creator: Brown, D A; Beck, B; Hedstrom, G & Pruet, J
Partner: UNT Libraries Government Documents Department

Alternative Approach to Nuclear Data Representation

Description: This paper considers an approach for representing nuclear data that is qualitatively different from the approach currently adopted by the nuclear science community. Specifically, they examine a representation in which complicated data is described through collections of distinct and self contained simple data structures. This structure-based representation is compared with the ENDF and ENDL formats, which can be roughly characterized as dictionary-based representations. A pilot data representation for replacing the format currently used at LLNL is presented. Examples are given as is a discussion of promises and shortcomings associated with moving from traditional dictionary-based formats to a structure-rich or class-like representation.
Date: July 27, 2005
Creator: Pruet, J; Brown, D; Beck, B & McNabb, D P
Partner: UNT Libraries Government Documents Department

Test Suite for Nuclear Data I: Deterministic Calculations for Critical Assemblies and Replacement Coefficients

Description: The authors describe tools developed by the Computational Nuclear Physics group for testing the quality of internally developed nuclear data and the fidelity of translations from ENDF formatted data to ENDL formatted data used by Livermore. These tests include S{sub n} calculations for the effective k value characterizing critical assemblies and for replacement coefficients of different materials embedded in the Godiva and Jezebel critical assemblies. For those assemblies and replacement materials for which reliable experimental information is available, these calculations provide an integral check on the quality of data. Because members of the ENDF and reactor communities use calculations for these same assemblies in their validation process, a comparison between their results with ENDF formatted data and their results with data translated into the ENDL format provides a strong check on the accuracy of translations. As a first application of the test suite they present a study comparing ENDL 99 and ENDF/B-V. They also consider the quality of the ENDF/B-V translation previously done by the Computational Nuclear Physics group. No significant errors are found.
Date: May 22, 2006
Creator: Pruet, J; Brown, D A & Descalle, M
Partner: UNT Libraries Government Documents Department

Effects of non-equilibrium particle distributions in deuterium-tritium burning

Description: We investigate the effects of non-equilibrium particle distributions resulting from rapid deuterium-tritium burning in plasmas using a Fokker-Planck code that incorporates small-angle Coulomb scattering, Brehmsstrahlung, Compton scattering, and thermal-nuclear burning. We find that in inertial confinement fusion environments, deviations away from Maxwellian distributions for either deuterium or tritium ions are small and result in 1% changes in the energy production rates. The deuterium and tritium effective temperatures are not equal, but differ by only about 2.5% near the time of peak burn rate. Simulations with high Z (Xe) dopants show that the dopant temperature closely tracks that of the fuel. On the other hand, fusion product ion distributions are highly non-Maxwellian, and careful treatments of energy-exchange between these ions and other particles is important for determining burn rates.
Date: August 18, 2009
Creator: Michta, D; Graziani, F; Pruet, J & Luu, T
Partner: UNT Libraries Government Documents Department

Description of ALARMA: the alarm algorithm developed for the Nuclear Car Wash

Description: The goal of any alarm algorithm should be that it provide the necessary tools to derive confidence limits on whether the existence of fissile materials is present in cargo containers. It should be able to extract these limits from (usually) noisy and/or weak data while maintaining a false alarm rate (FAR) that is economically suitable for port operations. It should also be able to perform its analysis within a reasonably short amount of time (i.e. {approx} seconds). To achieve this, it is essential that the algorithm be able to identify and subtract any interference signature that might otherwise be confused with a fissile signature. Lastly, the algorithm itself should be user-intuitive and user-friendly so that port operators with little or no experience with detection algorithms may use it with relative ease. In support of the Nuclear Car Wash project at Lawrence Livermore Laboratory, we have developed an alarm algorithm that satisfies the above requirements. The description of the this alarm algorithm, dubbed ALARMA, is the purpose of this technical report. The experimental setup of the nuclear car wash has been well documented [1, 2, 3]. The presence of fissile materials is inferred by examining the {beta}-delayed gamma spectrum induced after a brief neutron irradiation of cargo, particularly in the high-energy region above approximately 2.5 MeV. In this region naturally occurring gamma rays are virtually non-existent. Thermal-neutron induced fission of {sup 235}U and {sup 239}P, on the other hand, leaves a unique {beta}-delayed spectrum [4]. This spectrum comes from decays of fission products having half-lives as large as 30 seconds, many of which have high Q-values. Since high-energy photons penetrate matter more freely, it is natural to look for unique fissile signatures in this energy region after neutron irradiation. The goal of this interrogation procedure is a 95% success rate of ...
Date: November 28, 2006
Creator: Luu, T; Biltoft, P; Church, J; Descalle, M; Hall, J; Manatt, D et al.
Partner: UNT Libraries Government Documents Department


Description: A new class of tunable, monochromatic {gamma}-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photoscience and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. A prototype, capable of producing > 10{sup 8} 0.7 MeV photons in a single shot, with a fractional bandwidth of 1%, and a repetition rate of 10 Hz, is currently under construction at LLNL; this system will be used to perform nuclear resonance fluorescence experiments. A new symmetrized S-band rf gun, using a Mg photocathode, will produce up to 1 nC of charge in an 8 ps bunch, with a normalized emittance modeled at 0.8 mm.mrad; electrons are subsequently accelerated up to 120 MeV to interact with a 500 mJ, 10 ps, 355 nm laser pulse and generate {gamma}-rays. The laser front end is a fiber-based system, using corrugated-fiber Bragg gratings for stretching, and drives both the frequency-quadrupled photocathode illumination laser and the Nd:YAG interaction laser. Two new technologies are used in the laser: a hyper-Michelson temporal pulse stacker capable of producing 8 ps square UV pulses, and a hyper-dispersion compressor for the interaction laser. Other key technologies, basic scaling laws, and recent experimental results will also be presented, along with an overview of future research and development directions.
Date: August 15, 2007
Creator: Hartemann, F V; Anderson, S G; Gibson, D J; Hagmann, C A; Johnson, M S; Jovanovic, I et al.
Partner: UNT Libraries Government Documents Department

Nuclear car wash status report, August 2005

Description: A large majority of US imports arrive at seaports in maritime cargo containers. The number of containers arriving is nearly 10 million per year, each with a cargo of up to 30 tons of various materials. This provides a vulnerable entry point for the importation of a nuclear weapon or its components by a terrorist group. Passive radiation sensors are being deployed at portals to detect radioactive material and portable instruments are carried by port personnel to augment detection. Those instruments can detect the neutrons and g-rays produced by {sup 240}Pu that is normally present in weapons grade plutonium in cases where cargo overburden is not too great. However, {sup 235}U produces almost no neutron output in its normal radioactive decay and its principal {gamma}-radiation is at 186 keV and is readily attenuated by small amounts of wood or packing materials. Impurities such as {sup 232}U, often present in reactor irradiated material at the 100-200 ppt level, can provide a detectable signal through significant cargo overburden but the wide variations among samples of HEU make this an unreliable means of detecting SNM. High quality radiography may be useful in determining that the majority of containers are clearly free of SNM. However, some containers will lead to ambiguous results from radiography and passive radiation sensing. For these reasons active neutron interrogation is proposed as a means to produce fission and thus greatly amplify the radiation output of fissionable material to facilitate its reliable detection even when well shielded by large cargo overburden. Historically, the fission signature utilized as the unique identifying feature of fissionable materials is the detection of delayed neutrons. However, these neutrons have very low yield {approx} 0.017 per fission in {sup 235}U, and their low energy results in very poor penetration of hydrogenous materials such as fuels, water, ...
Date: July 29, 2005
Creator: Prussin, S; Slaughter, D; Pruet, J; Descalle, M; Bernstein, A; Hall, J et al.
Partner: UNT Libraries Government Documents Department

Fiber-Based, Spatially and Temporally Shaped Picosecond UV Laser for Advanced RF Gun Applications

Description: The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has been specifically designed for advanced rf gun applications, with a special emphasis on the production of high-brightness electron beams for free-electron lasers and Compton scattering light sources. The laser pulse can be shaped to a flat-top in both space and time with a duration of 10 ps at full width of half-maximum (FWHM) and rise and fall times under 1 ps. The expected pulse energy is 50 {micro}J at 261.75 nm and the spot size diameter of the beam at the photocathode is 2 mm. A fiber oscillator and amplifier system generates a chirped pump pulse at 1047 nm; stretching is achieved in a chirped fiber Bragg grating. A single multi-layer dielectric grating based compressor recompresses the input pulse to 250 fs FWHM and a two stage harmonic converter frequency quadruples the beam. Temporal shaping is achieved with a Michelson-based ultrafast pulse stacking device with nearly 100% throughput. Spatial shaping is achieved by truncating the beam at the 20% energy level with an iris and relay-imaging the resulting beam profile onto the photocathode. The integration of the system, as well as preliminary laser measurements will be presented.
Date: June 8, 2007
Creator: Shverdin, M Y; Anderson, S G; Betts, S M; Gibson, D J; Hartemann, F V; Hernandez, J E et al.
Partner: UNT Libraries Government Documents Department