776 Matching Results

Search Results

Advanced search parameters have been applied.

A Measurement of the muon neutrino charged current quasielastic interaction and a test of Lorentz violation with the MiniBooNE experiment

Description: The Mini-Booster neutrino experiment (MiniBooNE) at Fermi National Accelerator Laboratory (Fermilab) is designed to search for {nu}{sub {mu}} {yields} {nu}{sub e} appearance neutrino oscillations. Muon neutrino charged-current quasi-elastic (CCQE) interactions ({nu}{sub {mu}} + n {yields} {mu} + p) make up roughly 40% of our data sample, and it is used to constrain the background and cross sections for the oscillation analysis. Using high-statistics MiniBooNE CCQE data, the muon-neutrino CCQE cross section is measured. The nuclear model is tuned precisely using the MiniBooNE data. The measured total cross section is {sigma} = (1.058 {+-} 0.003 (stat) {+-} 0.111 (syst)) x 10{sup -38} cm{sup 2} at the MiniBooNE muon neutrino beam energy (700-800 MeV). {nu}{sub e} appearance candidate data is also used to search for Lorentz violation. Lorentz symmetry is one of the most fundamental symmetries in modern physics. Neutrino oscillations offer a new method to test it. We found that the MiniBooNE result is not well-described using Lorentz violation, however further investigation is required for a more conclusive result.
Date: December 1, 2008
Creator: Katori, Teppei & U., /Indiana
Partner: UNT Libraries Government Documents Department


Description: The EMPIRE code system is being extended to cover the resolved and unresolved resonance region employing proven methodology used for the production of new evaluations in the recent Atlas of Neutron Resonances. Another directions of Empire expansion are uncertainties and correlations among them. These include covariances for cross sections as well as for model parameters. In this presentation we concentrate on the KALMAN method that has been applied in EMPIRE to the fast neutron range as well as to the resonance region. We also summarize role of the EMPIRE code in the ENDF/B-VII.0 development. Finally, large scale calculations and their impact on nuclear model parameters are discussed along with the exciting perspectives offered by the parallel supercomputing.
Date: April 22, 2007
Partner: UNT Libraries Government Documents Department


Description: New evaluations for the tungsten isotopes {sup 180,182,183,184,186}W in the neutron energy range up to 60 MeV were produced. In the resonance range only minor adjustments to the resonance parameters were made due to a lack of adequate experimental data. Evaluations in the fast energy region were based on nuclear model calculations using the EMPIRE-2.19 code. Recently derived dispersive coupled-channel optical model potentials for W and Ta isotopes were instrumental to achieve a very good description of the available microscopic cross-section database. Model covariance data were generated with the Monte Carlo technique to produce a prior estimate for the covariance matrix. Experimental data were introduced through the GANDR system. The evaluated files were tested on selected fusion neutronics benchmarks and showed marked improvement compared to other existing evaluations.
Date: April 22, 2007
Partner: UNT Libraries Government Documents Department

Covariance matrices for nuclear cross sections derived from nuclear model calculations.

Description: The growing need for covariance information to accompany the evaluated cross section data libraries utilized in contemporary nuclear applications is spurring the development of new methods to provide this information. Many of the current general purpose libraries of evaluated nuclear data used in applications are derived either almost entirely from nuclear model calculations or from nuclear model calculations benchmarked by available experimental data. Consequently, a consistent method for generating covariance information under these circumstances is required. This report discusses a new approach to producing covariance matrices for cross sections calculated using nuclear models. The present method involves establishing uncertainty information for the underlying parameters of nuclear models used in the calculations and then propagating these uncertainties through to the derived cross sections and related nuclear quantities by means of a Monte Carlo technique rather than the more conventional matrix error propagation approach used in some alternative methods. The formalism to be used in such analyses is discussed in this report along with various issues and caveats that need to be considered in order to proceed with a practical implementation of the methodology.
Date: January 10, 2005
Creator: Smith, D. L.
Partner: UNT Libraries Government Documents Department

Nuclear reactions with 11C and 14O radioactive ion beams

Description: Radioactive ion beams (RIBs) have been shown to be a useful tool for studying proton-rich nuclides near and beyond the proton dripline and for evaluating nuclear models. To take full advantage of RIBs, Elastic Resonance Scattering in Inverse Kinematics with Thick Targets (ERSIKTT), has proven to be a reliable experimental tool for investigations of proton unbound nuclei. Following several years of effort, Berkeley Experiments with Accelerated Radioactive Species (BEARS), a RIBs capability, has been developed at the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. The current BEARS provides two RIBs: a 11C beam of up to 2x108 pps intensity on target and an 14O beam of up to 3x104 pps intensity. While the development of the 11C beam has been relatively easy, a number of challenges had to be overcome to obtain the 14O beam. The excellent 11C beam has been used to investigate several reactions. The first was the 197Au(11C,xn)208-xnAt reaction, which was used to measure excitation functions for the 4n to 8n exit channels. The measured cross sections were generally predicted quite well using the fusion-evaporation code HIVAP. Possible errors in the branching ratios of ?? decays from At isotopes as well as the presence of incomplete fusion reactions probably contribute to specific overpredictions. 15F has been investigated by the p(14O,p)14O reaction with the ERSIKTT technology. Several 14O+p runs have been performed. Excellent energy calibration was obtained using resonances from the p(14N,p)14N reaction in inverse kinematics, and comparing the results to those obtained earlier with normal kinematics. The differences between 14N+p and 14O+p in the stopping power function have been evaluated for better energy calibration. After careful calibration, the energy levels of 15F were fitted with an R-matrix calculation. Spins and parities were assigned to the two observed resonances. This new measurement of the 15F ground state supports the ...
Date: December 9, 2004
Creator: Guo, Fanqing
Partner: UNT Libraries Government Documents Department

New yttrium evaluated cross sections and impact on 88-Y(n,2n)87-Y radchem

Description: We evaluate new n+{sup 89}Y radchem cross sections using recent LANSCE/GEANIE measurements and GNASH nuclear model calculations, together with previous measurements at Livermore by Dietrich et al. A quantification of margins and uncertainties (QMU) analysis leads to evaluated cross sections for the (n,2n) population of the {sup 88}Y ground state and m1, m2 isomers, together with uncertainties. Our new results agree with historic radchem database cross sections within a few percent below 15 MeV (with larger differences above 15 MeV) and they therefore provide a validation of the historic Arthur work that is used in LANL simulation codes. Since the (n,2n) cross sections to the {sup 88}Y g.s. and m1, m2 isomers impact the average {sup 88}Y(n,2n){sup 87}Y cross section at leading-order, we determine the new 14.1 MeV average {sup 88}Y(n,2n){sup 87}Y cross section (crucially important for radchem). Our new 14 MeV average {sup 88}Y(n,2n){sup 87}Y cross section is 1107 mb ({+-} 4%) which agrees with the value obtained from the historic Arthur cross section data to 0.7%.
Date: March 4, 2004
Creator: White, M; Kawano, T; Fotiadis, N; Devlin, M; Nelson, R; Garrett, P et al.
Partner: UNT Libraries Government Documents Department

Competing degrees of freedom in nuclear structure theory. Final Report for 1999-2002

Description: The central focus of this research was the interplay between three generic classes of degrees of freedom relevant to nuclear structure theory: single-particle degrees of freedom, collective degrees of freedom, and statistical degrees of freedom, which can be thought of as an incoherent mean field or a thermal bath.
Date: July 4, 2003
Creator: Johnson, Calvin W.
Partner: UNT Libraries Government Documents Department


Description: We review in this talk various SUSY SO(10) models. Specifically, we discuss how small neutrino masses are generated in and generic predictions of different SO(10) models. A comparison of the predictions of these models for sin{sup 2} {theta}{sub 13}is given.
Date: June 5, 2003
Partner: UNT Libraries Government Documents Department

Results from the First {sup 249}Cf + {sup 48}Ca Experiment

Description: The present paper reports the results of an attempt aimed at the synthesis of element 118 in the reaction {sup 249}Cf({sup 48}Ca,3n){sup 294}118. The experiment was performed employing the Dubna Gas-filled Recoil Separator and the U400 heavy-ion cyclotron at FLNR, JINR, Dubna. In the course of a 2300-hour irradiation of an enriched {sup 249}Cf target (0.23 mg/cm{sup 2}) with a beam of 245-MeV {sup 48}Ca ions, we accumulated a total beam dose of 2.5 x 10{sup 19} ions. We detected two events that may be attributed to the formation and decay of nuclei with Z=118. For one event, we observed a decay chain of two correlated {alpha}-decays with corresponding energies and correlation times of E{sub {alpha}1} = 11.65 {+-} 0.06 MeV, t{sub {alpha}1} = 2.55 ms and E{sub {alpha}2} = 10.71 {+-} 0.17 MeV, t{sub {alpha}2} = 42.1 ms and, finally, a spontaneous fission with the sum of the kinetic energies of the fission fragments E{sub tot} = 207 MeV (TKE {approx} 230 MeV) and t{sub SF} = 0.52 s. In the second event chain, the recoil nucleus decayed into two fission fragments with E{sub tot} = 223 MeV (TKE {approx} 245 MeV) 3.16 ms later, without intervening {alpha} decays. The probabilities that these events were caused by the chance correlations of unrelated signals are negligible. Both events were observed at an excitation energy of the compound nucleus {sup 297}118 of E* = 30.0 {+-} 2.4 MeV, close to the expected maximum of the 3n-evaporation channel. The relationship between the decay energy Q{sub {alpha}} and decay period T{sub {alpha}} shows that sequential {alpha}-transitions in the first event correspond to the decay chain with Z = 118{_}116{_}114. Decay characteristics of the newly observed nuclides are compared with radioactive decay properties of the even-even isotopes with Z = 116, 114 and 112 ...
Date: February 3, 2003
Creator: Oganessian, Y T; Utyonkov, V K; Lobanov, Y V; Abdullin, F S; Polyakov, A N; Shirokovsky, I V et al.
Partner: UNT Libraries Government Documents Department

Gamma-ray production cross sections from neutron interactions with iron.

Description: The initial purpose of this experiment was to provide a consistent data base of neutron-induced gamma-ray production cross sections over a large energy range for use in estimating elemental composition of the martian surface by observing gamma rays produced by cosmic ray interactions on the planet's surface [Bo02]. However, these data should be useful for other projects such as oil-well logging, accelerator transmutation of nuclear waste, shielding calculations, gamma-ray heating for nuclear reactors and verification of nuclear model calculations and databases. The goal of the measurements was to collect data on the strongest gamma rays from many samples of interest. Because of the available beam time this meant that many of the measurcments were rather short. Despite the short running time the large samples used and the good beam intensity resulted in very satisfactory results. The samples, chosen mainly as common constituents of rock and soil and measured in the same few week period, include: B&, BN, C, Al, Mg, Si, S, Cay Ti, Cr, Mn, and Fe. Be was also used as a neutron scatterer that only produces one gamma ray (478 keV from 7Li) with appreciable intensity. Thus Be can serve as a measure of neutron-induced backgrounds. In this first paper we present results for Fe.
Date: January 1, 2002
Creator: Nelson, R. O. (Ronald O.); Laymon, C. M. (Charles M.); Wender, S. A. (Stephen A.); Drake, D. M. (Darrell M.); Drosg, Manfred; Bobias, S. G. (S. George) et al.
Partner: UNT Libraries Government Documents Department

High Precision Spectroscopy of Lambda-Hypernuclei by (e, e' K{sup +}) reaction and gamma-ray measurement

Description: Hypernuclei, with one nucleon converted into a hyperon and coupled back to the residual nuclear core, provide a new probe to study the hyperon-nucleon interaction and an additional strangeness degree of freedom to test the limit of our conventional nuclear models in solving the many body system. The First Lambda electroproduction experiment E89009(HNSS) at JLAB focusing on the Lambda hypernuclear spectroscopy in p-shell achieved the best resolution( FWHM: 500-600 keV) ever reached in this field. The unnatural parity (spin-flip) states were observed for the first time on the 12 / Lambda B missing mass spectrum. The detailed hypernuclear structure of 9 / Lambda Be produced through (k{sup -}, pi{sup -}) reaction in BNL-AGS, was studied with the hypernuclear gamma-ray spectroscopy by using a large acceptance germanium detector (Hyperball) in experiment E-930.
Date: August 1, 2001
Creator: Zhu, Xiaofeng
Partner: UNT Libraries Government Documents Department


Description: Researchers at Los Alamos National Laboratory are considering the possibility of using the Low Energy Demonstration Accelerator (LEDA), constructed at LANSCE for the Accelerator Production of Tritium program (APT), as a neutron source. Evaluated nuclear data are needed for the p+{sup 7}Li reaction, to predict neutron production from thin and thick lithium targets. In this report we describe evaluation methods that make use of experimental data, and nuclear model calculations, to develop an ENDF-formatted data library for incident protons with energies up to 150 MeV. The important {sup 7}Li(p,n{sub 0}) and {sup 7}Li(p,n{sub 1}) reactions are evaluated from the experimental data, with their angular distributions represented using Lengendre polynomial expansions. The decay of the remaining reaction flux is estimated from GNASH nuclear model calculations. This leads to the emission of lower-energy neutrons and other charged particles and gamma-rays from preequilibrium and compound nucleus decay processes. The evaluated ENDF-data are described in detail, and illustrated in numerous figures. We also illustrate the use of these data in a representative application by a radiation transport simulation with the code MCNPX.
Date: November 1, 2000
Creator: MASHNIK, S. & AL, ET
Partner: UNT Libraries Government Documents Department

Alternate Approach to the 239Pu(n,2n) Cross Section

Description: Using existing experimental data for neutron-induced total, elastic, inelastic, reaction and fission cross sections, as well as results from nuclear model calculations and evaluations from nuclear reaction data libraries, we derived an estimate for the cross sections for the {sup 235}U(n,2n) and {sup 239}Pu(n,2n) reactions for the neutron energy range from threshold to approximately 12 MeV. In effect, our approach is based on subtracting the fission and inelastic cross sections from the total reaction cross section where the difference is expected to yield the (n,2n) cross section. In addition to this subtraction approach, a ratio method and a differential method have also been explored. For {sup 235}U(n,2n), as a test case, we arrive at a cross section consistent with previous measurements, and for {sup 239}Pu(n,2n) we obtain a peak value of 400 {+-} 60 mb for the incident neutron energy range of 10 {le} E{sub n} {le} 12 MeV.
Date: September 1, 2000
Creator: Anderson, J D; Bauer, R W; Becker, J A; Dietrich, F S & McNabb, D P
Partner: UNT Libraries Government Documents Department

Ternary particles with extreme N/Z ratios from neutron-induced fission

Description: The existing ternary fission models can well reproduce the yields of the most abundant light charged particles. However, these models tend to significantly overestimate the yields of ternary particles with an extreme N/Z ratio: {sup 3}He, {sup 11}Li, {sup 14}Be, etc. The experimental yields of these isotopes were investigated with the recoil separator LOHENGRIN down to a level of 10{sup {minus}10} per fission. Results from the fissioning systems {sup 233}U (n{sub th}, f), {sup 235}U(n{sub th},f), {sup 239}Pu(n{sub th},f) {sup 241}Pu(n{sub th},f) and {sup 245}Cm(n{sub th},f) are presented and the implications for the ternary fission models are discussed.
Date: May 16, 2000
Creator: Koster, U.; Faust, H.; Friedrichs, T.; Oberstedt, S.; Fioni, G.; Grob, M. et al.
Partner: UNT Libraries Government Documents Department

The 239 Pu(n,2n)238Pu cross section: preliminary calculations

Description: The primary motivation for the present work is to provide theoretical values for the ratio of the partial <sup>239</sup>Pu(n,2nx{gamma})<sup>238</sup>Pu to total <sup>239</sup> Pu(n,2n)<sup>238</sup>Pu cross section for several discrete gamma transitions. Results and conclusions of preliminary calculations from threshold to 20 MeV are presented. Calculations are based on theoretical models with parameters obtained from the literature or from our ad hoc systematics. Optical model cross sections and transmission coefficients were determined using the coupled-channels method. The calculations included a preequilibrium component followed by multiple particle and gamma-ray emissions. Fission competition was included at all stages of de-excitation. Suggestions for further verifications and possible improvements are provided.
Date: March 12, 1999
Creator: Chen, H.; Reffo, G.; Ross, M. A. & White, R. M.
Partner: UNT Libraries Government Documents Department

Experimental test of nuclear magnetization distribution and nuclear structure models

Description: Models exist that ascribe the nuclear magnetic fields to the presence of a single nucleon whose spin is not neutralized by pairing it up with that of another nucleon; other models assume that the generation of the magnetic field is shared among some or all nucleons throughout the nucleus. All models predict the same magnetic field external to the nucleus since this is an anchor provided by experiments. The models differ, however, in their predictions of the magnetic field arrangement within the nucleus for which no data exist. The only way to distinguish which model gives the correct description of the nucleus would be to use a probe inserted into the nucleus. The goal of our project was to develop exactly such a probe and to use it to measure fundamental nuclear quantities that have eluded experimental scrutiny. The need for accurately knowing such quantities extends far beyond nuclear physics and has ramifications in parity violation experiments on atomic traps and the testing of the standard model in elementary particle physics. Unlike scattering experiments that employ streams of free particles, our technique to probe the internal magnetic field distribution of the nucleus rests on using a single bound electron. Quantum mechanics shows that an electron in the innermost orbital surrounding the nucleus constantly dives into the nucleus and thus samples the fields that exist inside. This sampling of the nucleus usually results in only minute shifts in the electron´┐Ż s average orbital, which would be difficult to detect. By studying two particular energy states of the electron, we can, however, dramatically enhance the effects of the distribution of the magnetic fields in the nucleus. In fact about 2% of the energy difference between the two states, dubbed the hyperfine splitting, is determined by the effects related to the distribution of ...
Date: February 26, 1999
Creator: Beirsdorfer, P; Crespo-Lopez-Urrutia, J R & Utter, S B
Partner: UNT Libraries Government Documents Department

Measurement of the deuteron elastic structure functions up to large momentum transfers

Description: The cross section for elastic electron-deuteron scattering was measured in JLab experiment 91-026. The deuteron elastic structure functions A(Q{sup 2}) and B(Q{sup 2}) have been extracted from this data. The final results for the ``electric'' structure function A(Q{sup 2}), in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 6.0 (GeV/c){sup 2} are presented. Preliminary results for the ``magnetic'' structure function B(Q{sup 2}) are presented in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 1.35 (GeV/c){sup 2}. These data are compared with theoretical predictions of both meson-nucleon and quark-gluon based models.
Date: February 1, 1999
Creator: de Jager, Kees
Partner: UNT Libraries Government Documents Department

Nuclear data for radiotherapy: Presentation of a new ICRU report and IAEA initiatives

Description: An ICRU report entitled ''Nuclear Data for neutron and Proton Radiotherapy and for Radiation Protection'' is in preparation. The present paper presents an overview of this report, along with examples of some of the results obtained for evaluated nuclear cross sections and kerma coefficients. These cross sections are evaluated using a combination of measured data and the GNASH nuclear model code for elements of importance for biological, dosimetric, beam modification and shielding purposes. In the case of hydrogen both R-matrix and phase-shift scattering theories are used. In the report neutron cross sections and kerma coefficients will be presented up to 100 MeV and proton cross sections up to 250 MeV. An IAEA Consultants' Meeting was also convened to examine the ''Status of Nuclear Data needed for Radiation Therapy and Existing Data Development Activities in Member States''. Recommendations were made regarding future endeavors.
Date: September 1, 1998
Creator: Chadwick, M.B.; Jones, D.T.L. & Barschall, H.H.
Partner: UNT Libraries Government Documents Department

Analysis of nucleon-induced fission cross sections of lead and bismuth at energies from 45 to 500 MeV

Description: In order to investigate the applicability of the Cascade-Exciton model (CEM) of nuclear reactions to fission cross sections and hoping to learn more about intermediate-energy fission, the authors use an extended version of the CEM, as realized in the code CEM95 to perform a detailed analysis of proton- and neutron-induced fission cross sections of {sup 209}Bi and {sup 208}Pb nuclei and of the linear momentum transfer to the fissioning nuclei in the 45--500 meV energy range.
Date: August 1, 1998
Creator: Prokofyev, A.V.; Mashnik, S.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

Magnetic radius of the deuteron

Description: The root-mean square radius of the deuteron magnetic moment distribution, r{sub Md}, is calculated for several realistic models of the NN-interaction. For the Paris potential the result is r{sub Md} = 2.312 {+-} 0.010 fm. The dependence of r{sub Md} on the choice of NN model, relativistic effects and meson exchange currents is investigated. The experimental value of r{sub Md} is also considered. The necessity of new precise measurements of the deuteron magnetic form factor at low values of Q{sup 2} is stressed.
Date: August 1, 1998
Creator: Afanasev, Andrei; Afanasev, V.D. & Trubnikov, S.V.
Partner: UNT Libraries Government Documents Department

Theory of neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date: August 1998
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department