589 Matching Results

Search Results

Advanced search parameters have been applied.

Energy Dependence of High Moments for Net-proton Distributions

Description: High moments of multiplicity distributions of conserved quantities are predicted to be sensitive to critical fluctuations. To understand the effect of the non-critical physics backgrounds on the proposed observable, we have studied various moments of net-proton distributions with AMPT, Hijing, Therminator and UrQMD models, in which no QCD critical point physics is implemented. It is found that the centrality evolution of various moments of net-proton distributions can be uniformly described by a superposition of emission sources. In addition, in the absence of critical phenomena, some moment products of net-proton distributions, related to the baryon number susceptibilities in Lattice QCD calculations, are predicted to be constant as a function of the collision centrality. We argue that a non-monotonic dependence of the moment products as a function of the beam energy may be used to locate the QCD critical point.
Date: July 7, 2010
Creator: Luo, Xiaofeng; Mohanty, Bedangadas; Ritter, Hans Georg & Xu, Nu
Partner: UNT Libraries Government Documents Department

Influence of the deuteron energy on the testing volume of IFMIF and its impact on other parameters

Description: The influence of the energy of the deuteron beam on irradiation parameters of IFMIF is analyzed. The main purpose of this paper is to identify possible positive and negative impacts on irradiation parameters that an increase in the deuteron energy of the beam can cause. Several parameters of the facility, such as neutron generation rate, number of neutrons with energy above 20 MeV at the source and in the test assembly, volume with dpa rate above a threshold value, gas production, and gradient of the atomic displacement rate, are analyzed and conclusions are drawn based on the calculated values. It is shown that an increase in the deuteron energy to 40 MeV does not produce a significant negative impact for the elements analyzed, but instead is beneficial in producing nuclear responses more similar to a fusion environment than the lower deuteron energies.
Date: September 1, 1995
Creator: Gomes, I.C. & Smith, D.L.
Partner: UNT Libraries Government Documents Department

Thermal ablation of plasma-facing surfaces in tokamak disruptions: Sensitivity to particle kinetic energy

Description: Ablation damage to solid targets with high heat flux impulses is generally greater high-energy electron beam heat sources compared to low-energy plasma guns. This sensitivity to incoming particle kinetic energy is explored with computer modelling; a fast-running routine (DESIRE) is developed for initial scoping analysis and is found to be in reasonable agreement with several experiments on graphite and tungsten targets. If tokamak disruptions are characterized by particle energies less than {approximately}1 keV, then we expect plasma guns are a better analogue than electron beams for simulating disruption behavior and testing candidate plasma-facing materials.
Date: February 1, 1996
Creator: Ehst, D.A. & Hassanein, A.
Partner: UNT Libraries Government Documents Department

From Molecular Dynamics to Kinetic Rate Theory: A Simple Example of Multiscale Modeling

Description: Radiation damage formation in iron has been investigated using the method of molecular dynamics simulation. The MD simulations have been used to determine primary defect production parameters for cascade energies up to 50 keV at temperatures from 100 to 900K. The energy dependence of these parameters has been used to determine appropriate neutron-energy-spectrum averaged damage production cross sections for various irradiation environments. Two applications of these effective cross sections are discussed. The first is an evaluation of neutron energy spectrum effects in commercial fission reactor pressure vessels. The second example deals with the use of these cross sections in the source term of a kinetic model used to predict void swelling and microstructural evolution. The simulation of the primary damage event by MD involves times less than 100 ps and a size scale of a few tens of nm, while the kinetic simulation encompasses several years and macroscopic sizes. This use of the MD results to develop an improved source term for rate theory modeling provides a simple example of multiscale modeling.
Date: November 30, 1998
Creator: Greenwood, L.R. & Stoller, R.E.
Partner: UNT Libraries Government Documents Department

Nd-Fe-B undulator design for CESR

Description: It is proposed to build a Nd-Fe-B based undulator on CESR ring which would provide pseudomonochromatic tunable radiation in the hard x-ray range from 4 to 15 keV. Such an intense radiation source opens unlimited possibilities for doing exciting science in material science and condensed matter physics. Here, we present the design goals for such an undulator and discuss the influence of various parameters that govern the properties of radiation from undulators. The analysis of these results leads us to select the specific design parameters of the undulator that will meet the radiation needs of the experimental program.
Date: October 14, 1986
Creator: Shenoy, G.K.; Viccaro, P.J. & Kim, S.
Partner: UNT Libraries Government Documents Department

Undulator tunability and ring-energy

Description: An Undulator has two properties which make it an extremely attractive source of electromagnetic radiation. The first is that the radiation is concentrated in a number of narrow energy bands known as harmonics of the device. The second characteristic is that under favorable operating conditions, the energy of these harmonics can be shifted or {open_quotes}tuned{close_quotes} over an energy interval which can be as large as two or three times the value of the lowest energy harmonic. Both the photon energy of an undulator as well as its tunability are determined by the period, {lambda}, of the device, the magnetic gap, G (which is larger than the minimum aperture required for injection and operation of the storage ring), and the storage ring energy, E{sub R}. Given the photon energy, E{sub p}, the above parameters ultimately define the limits of operation or tunability of the undulator.
Date: September 1, 1996
Creator: Viccaro, P.J. & Shenoy, G.K.
Partner: UNT Libraries Government Documents Department

Point Defect Cluster Formation in Iron Displacement Cascades Up to 50 keV

Description: The results of molecular dynamics displacement cascade simulations in iron at energies up to 50 keV and temperatures of 100, 600, and 900K are summarized, with a focus on the characterization of interstitial and vacancy clusters that are formed directly within the cascade. The fraction of the surviving point defects contained in clusters, and the size distributions of these in-cascade clusters have been determined. Although the formation of true vacancy clusters appears to be inhibited in iron, a significant degree of vacancy site correlation was observed. These well correlated arrangements of vacancies can be considered nascent clusters, and they have been observed to coalesce during longer term Monte Carlo simulations which permit short range vacancy diffusion. Extensive interstitial clustering was observed. The temperature and cascade energy dependence of the cluster size distributions are discussed in terms of their relevance to microstructural evolution and mechanical property changes in irradiated iron-based alloys.
Date: November 30, 1998
Creator: Stoller, R.E.
Partner: UNT Libraries Government Documents Department

Characterization of laser-produced fusion plasmas with thomson scattering

Description: Thomson scattering has been developed at the Nova laser facility as a direct and accurate diagnostic to characterize inertial confinement fusion plasmas. Measurements from methane-filled, ignition relevant hohlraums apply the theory for two ion species plasmas, which has been tested in separate open geometry experiments, to obtain electron and ion temperatures. The experimental data provide a benchmark for two-dimensional hydrodynamic simulations using LASNEX, which is presently in use to predict he performance of future megajoule laser- driven hohlraums of the National Ignition Facility (NIF). The data are consistent with modeling using significantly inhibited heat transport at the peak of the drive. Furthermore, we find that stagnating plasma regions on the hohlraum axis are well described by the calculations. The result implies that stagnation in gas-filled hohlraums occurs too late to directly affect the capsule implosion in ignition experiments.
Date: July 9, 1997
Creator: Glenzer, S.H.; Back, C.A.; Suter, L.J.; MacGowan, B.J.; Landen, O.L.; Lindl, J.D. et al.
Partner: UNT Libraries Government Documents Department

Energy and rapidity dependence of beauty production at Tevatron

Description: The CDF and D0 experiments have measured bb production in pp interactions at {radical}s = 1800 GeV and 630 GeV (the energy at which the previous measurement was performed by the UAl experiment). The Tevatron measurements are used to evaluate, for the first time, the center-of-mass energy and rapidity dependence of b-quark production cross section measured with the same detectors. Preliminary results from these measurements are presented and compared with the next-to-leading order QCD predictions.
Date: September 1, 1997
Creator: Ba, M.M.
Partner: UNT Libraries Government Documents Department

Study of neutron-proton interaction in the 300--700 MeV energy region. Final progress report, July 1991--August 1994

Description: The experimental program supported by the present grant is a continuation of the work supported under DOE Contract DE-AS05-76ER04449. More detailed discussion of the experimental apparatus and earlier activities can be found in annual reports for that contract and this grant. The primary objective of this program is investigation of the nucleon-nucleon (NN) interaction, in the medium-energy region, in both elastic and inelastic channels.
Date: August 1, 1994
Creator: Northcliffe, L.C. & Hiebert, J.C.
Partner: UNT Libraries Government Documents Department

The cost of transportation`s oil dependence

Description: Transportation is critical to the world`s oil dependence problem because of the large share of world oil it consumes and because of its intense dependence on oil. This paper will focus on the economic costs of transportation`s oil dependence.
Date: May 1, 1995
Creator: Greene, D.L.
Partner: UNT Libraries Government Documents Department

Remark on: the neutron spherical optical-model absorption.

Description: The energy-dependent behavior of the absorption term of the spherical neutron optical potential for doubly magic {sup 208}Pb and the neighboring {sup 209}Bi is examined. These considerations suggest a phenomenological model that results in an intuitively attractive energy dependence of the imaginary potential that provides a good description of the observed neutron cross sections and that is qualitatively consistent with theoretical concepts. At the same time it provides an alternative to some of the arbitrary assumptions involved in many conventional optical-model interpretations reported in the literature and reduces the number of the parameters of the model.
Date: June 30, 2007
Creator: Smith, A. B.
Partner: UNT Libraries Government Documents Department

Bremstrahlung versus Monoenergetic Photons for Photonuclear Inspection Applications

Description: Bremsstrahlung sources have been utilized for various non-intrusive inspection or interrogation applications for over 100 years - with the primary focus being radiographic imaging. In the last several decades, it has become evident that photons of energy greater than 6 MeV can also provide useful photonuclear information that can extend the capabilities and information available from active inspections. These energetic inspection photons can be produced as a continuum of energies (i.e., bremsstrahlung distribution) or as a set of one or more discrete photon energies (i.e., monoenergetic distribution). This paper will discuss the photonuclear process and its energetic photon energy dependence, will discuss the photonuclear role in nuclear material detection, will present applicable photon sources along with their field deployment status, and highlight some advantages and disadvantages of bremsstrahlung and monoenergetic photons sources.
Date: June 1, 2008
Creator: Jones, Dr. James L.
Partner: UNT Libraries Government Documents Department

Particle Correlations with the PHENIX Experiment

Description: Results of identical pion correlations from the first year of data collection with the PHENIX detector at RHIC ({radical}S{sub NN} = 130 GeV) are presented. PHENIX has good particle identification using an electromagnetic calorimeter for timing, leading to identified pions from .2 to 1 GeV/c. This extends the range of previously measured correlation radii at this energy to (k{sub T}) = 633MeV/c. The beam energy dependence of the HBT radii are studied in depth and no significant dependence of the transverse radii is present. The longitudinal correlation length has a moderate energy dependence. Furthermore, theoretical predictions of R{sub out}/R{sub side} severely underpredict the measured ratio, which is consistent with unity for all k{sub T}. The implications of these results are considered.
Date: January 20, 2002
Creator: Johnson, S C
Partner: UNT Libraries Government Documents Department

Extracting longitudinal shower development information from crystal calorimetry plus tracking

Description: We present an approach to derive longitudinal shower development information from the longitudinally unsegmented BABAR electromagnetic calorimeter by using tracking information. Our algorithm takes advantage of the good three-dimensional tracking resolution of BABAR, which provides an independent geometric constraint on the shower as measured in the BABAR crystal calorimeter. We show that adding the derived longitudinal shower development information to standard particle identification algorithms significantly improves the low-momentum separation of pions from electrons and muons. We also verify that the energy dependence of the electromagnetic shower development we measure is consistent with the prediction of a standard electromagnetic shower model.
Date: November 1, 2007
Creator: Brown, David; Brown, D.N.; Ilic, J. & Mohanty, G.B.
Partner: UNT Libraries Government Documents Department

The energy dependence of the total charm cross section

Description: We discuss the energy dependence of the total charm cross section and some of its theoretical uncertainties including the quark mass, scale choice and the parton densities. We compare the next-to-leading order calculation of the total cross section with results obtained using PYTHIA.
Date: October 18, 2007
Creator: Vogt, R
Partner: UNT Libraries Government Documents Department


Description: Among the goals of the MINOS experiment are the test of the {nu}{sub {mu}} {yields} {nu}{sub {tau}} oscillation and the search for sub-dominant {nu}{sub {mu}} {yields} {nu}{sub {tau}} oscillations. The former proceeds by a {nu}{sub {mu}} ''disappearance'' analysis while the latter would involve the ''appearance'' of {nu}{sub e} interactions in a predominantly {nu}{sub {mu}} beam. The disappearance of muon neutrinos is described by P({nu}{sub {mu}} {yields} {mu}{sub {mu}}) = 1 - sin{sup 2} 2{theta}{sub 23} sin{sup 2} (1.27 {Delta} m{sub 23}{sup 2} L/E) in the two-flavor approximation where {theta}{sub 23} is the angle between the second row and third column of the neutrino mixing matrix, {Delta}m{sub 23}{sup 2} = m{sub 2}{sup 2}-m{sub 3}{sup 2} (eV{sup 2}), L is the neutrino flight distance in km and E is the neutrino energy in GeV. A generic disappearance experiment compares a measured muon neutrino energy spectrum at a fixed baseline to the known energy spectrum of muon neutrino beam to extract the oscillation parameters sin{sup 2} 2{theta} which controls the overall magnitude of the disappearance and {Delta}m{sup 2} which controls the energy dependence.
Date: October 26, 2006
Creator: JAFFE,D.E.
Partner: UNT Libraries Government Documents Department

Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

Description: We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at {radical}s{sub NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < {eta} < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 {+-} 0.1 and 1.2 {+-} 0.1 for {radical}s{sub NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of {eta} - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department


Description: The results of cross-section measurements for the reactions {sup 209}Bi({sup 12}C,X)Au, E = 4.8 and 25.2 GeV and {sup 209}Bi({sup 20}Ne,X)Au, E = 8.0 GeV are reported. The observed yields of the gold isotopes show a similar dependence on mass number for each reaction, differing slightly in the position of the centroid of the distribution. As the projectile energy increases, the inferred excitation energy of the primary residues remains the same or decreases slightly. This observation is in agreement with the predictions of the intranuclear cascade model of relativistic heavy ion collisions.
Date: July 1, 1980
Creator: Aleklett, K.; Morrissey, D.J.; Loveland, W.; McGaughey, P.L. & Seaborg, g.T.
Partner: UNT Libraries Government Documents Department

System size, energy and centrality dependence of strange hadron elliptic flow at STAR

Description: The elliptic flow (v{sub 2}) pattern in terms of hadron mass and transverse momentum p{sub T} is qualitatively described for p{sub T} < 2 GeV/c by ideal hydrodynamics in Au + Au collisions at RHIC. In addition, for p{sub T} = 2-6 GeV/c the measured v{sub 2} follow a universal scaling by the number of quarks explained by quark coalescence/recombination models. These observations suggest that a partonic collectivity develops in the matter in early stage of heavy ion collisions. Centrality as well as system size and energy dependence of the v{sub 2} is important to shed light on the underlying collision dynamics in heavy ion collisions. We present the measurements of centrality dependence of v{sub 2} at {radical}s{sub NN} = 200 and 62.4 GeV in Au + Au and Cu + Cu collisions for K{sub S}{sup 0}, {phi}, {Lambda}, {Xi} and {Omega} at STAR experiment. We focus on the recent Cu + Cu results and discuss the centrality dependence of v{sub 2} as well as the number of quark scaling as a function of transverse kinetic energy at different system size and energies. We also discuss the eccentricity scaled v{sub 2} for identified hadrons and implications that ideal hydrodynamical limit has not been reached at RHIC.
Date: December 21, 2008
Creator: Masui, Hiroshi
Partner: UNT Libraries Government Documents Department