2,536 Matching Results

Search Results

Advanced search parameters have been applied.

Relativistic Models of the Structure of Light Nuclei

Description: In this talk, I will discuss how relativistic meson theory is developed and applied to the description of few nucleon systems, and show how the ideas which emerge from this discussion provide a natural, theoretical foundation for the Dirac treatment of proton-nucleus scattering.
Date: January 1, 1985
Creator: Gross, Franz
Partner: UNT Libraries Government Documents Department

Electromagnetic Studies in Nuclei

Description: This talk is devoted to a brief review of the experimental program for the new generation of multi GeV continuous beam electron accelerator facilities. First, the kinematic variables used in electron scattering are reviewed, three experiments which are representative of previous work in this field are described, and some comparisons are made between electron and hadronic probes. The main part of the talk then describes seven experiemnts proposed for the future. These are concerned with the structure of light nuclei, the structure of mesons, and baryons, the influence of the nuclear medium on hadronic interaction, and the weak interactions.
Date: March 1, 1985
Creator: Gross, Franz
Partner: UNT Libraries Government Documents Department

Polarization Phenomena in Electromagnetic Interactions at Intermediate Energies

Description: Recent results of polarization measurements in electromagnetic interactions at intermediate energies are discussed. Prospects of polarization experiments at the new CW electron accelerators, as well as on upgraded older machines are outlined. It is concluded that polarization experiments will play a very important role in the study of the structure of the nucleon and of light nuclei.
Date: July 1, 1990
Creator: Burkert, Volker
Partner: UNT Libraries Government Documents Department

Observation of an Antimatter Hypernucleus

Description: Nuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons - composed of an antiproton, antineutron, and antilambda hyperon - produced by colliding gold nuclei at high energy. Our analysis yields 70 {+-} 17 antihypertritons ({sub {bar {Lambda}}}{sup 3}{bar H}) and 157 {+-} 30 hypertritons ({sub {Lambda}}{sup 3}H). The measured yields of {sub {Lambda}}{sup 3}H ({sub {bar {Lambda}}}{sup 3}{bar H}) and {sup 3}He ({sup 3}{ovr He}) are similar, suggesting an equilibrium in coordinate and momentum space populations of up, down, and strange quarks and antiquarks, unlike the pattern observed at lower collision energies. The production and properties of antinuclei, and nuclei containing strange quarks, have implications spanning nuclear/particle physics, astrophysics, and cosmology.
Date: July 5, 2010
Creator: Collaboration, STAR & Abelev, Betty
Partner: UNT Libraries Government Documents Department

Electromagnetic and Weak transitions in light nuclei

Description: Recent advances in the study of the p -- d radiative and mu -- {sup 3}He weak capture processes by our group are presented and discussed. The trinucleon bound and scattering states have been obtained from variational calculations by expanding the corresponding wave functions in terms of correlated hyper-spherical harmonic functions. The electromagnetic and weak transition currents include one- and two-body operators. The accuracy achieved in these calculations allows for interesting comparisons with experimental data.
Date: September 1, 2002
Creator: Viviani, M.; Marcucci, L.E.; Kievsky, A.; Rosati, S. & Schiavilla, R.
Partner: UNT Libraries Government Documents Department

Interaction, currents and the electromagnetic structure of light nuclei

Description: The authors discuss the traditional model of the nucleus as a system of nucleons interacting via effective interactions and currents, and present results obtained within this framework for the electromagnetic structure of the ground- and low-lying-states of A=3-6 nuclei.
Date: June 1, 1998
Creator: L.E. Marcucci, R. Schiavilla
Partner: UNT Libraries Government Documents Department

Studies of nuclear processes at the Triangle Universities Nuclear Laboratory. Final report

Description: The authors concluded their program to establish the trends of isospin mixing in nuclei ranging from {sup 12}C to {sup 40}Ca. This program revealed a systematic variation in the proton reduced widths from one A = 4N nucleus to the next as T = 0 nuclei were bombarded by protons and T = 3/2 states were populated in the compound system. In few-body physics, their program of studies of D-state properties of light nuclei ({sup 3}H, {sup 3}He, and {sup 4}He) resulted in precise determinations of the {eta} parameters for {sup 3}He and {sup 3}H which agreed well with theoretical predictions and served as an important constraint on theoretical calculations. The D{sub 2} parameter determination for {sup 4}He, carried out in collaboration with researchers at Munich and Lisbon, was not as precise but did indicate that {sup 4}He has significant deformation. A program was initiated during this period to measure the ratio of asymptotic D- to S-state normalization constant ({eta}) for {sup 6}Li at Florida State University using the ({sup 6}Li,d) reaction. They determined that the {eta} parameter for {sup 6}Li is extremely small, contrary to expectations.
Date: March 1, 2000
Partner: UNT Libraries Government Documents Department

Nuclear forces and chiral theories

Description: Recent successes in ab initio calculations of light nuclei (A=2-6) will be reviewed and correlated with the dynamical consequences of chiral symmetry. The tractability of nuclear physics evinced by these results is evidence for that symmetry. The relative importance of three-nucleon forces, four-nucleon forces, multi-pion exchanges, and relativistic corrections will be discussed in the context of effective field theories and dimensional power counting. Isospin violation in the nuclear force will also be discussed in this context.
Date: September 1, 1995
Creator: Friar, J.L.
Partner: UNT Libraries Government Documents Department

PRELIMINARY CROSS SECTION AND NU-BAR COVARIANCES FOR WPEC SUBGROUP 26

Description: We report preliminary cross section covariances developed for the WPEC Subgroup 26 for 45 out of 52 requested materials. The covariances were produced in 15- and 187-group representations as follows: (1) 36 isotopes ({sup 16}O, {sup 19}F, {sup 23}Na, {sup 27}Al, {sup 28}Si, {sup 52}Cr, {sup 56,56}Fe, {sup 58}Ni, {sup 90,91,92,94}Zr, {sup 166,167,168,170}Er, {sup 206,207,208}Pb, {sup 209}Bi, {sup 233,234,236}U, {sup 237}Np, {sup 238,240,241,242}Pu, {sup 241,242m,243}Am, {sup 242,243,244,245}Cm) were evaluated using the BNL-LANL methodology. For the thermal region and the resolved and unresolved resonance regions, the methodology has been based on the Atlas-Kalman approach, in the fast neutron region the Empire-Kalman method has been used; (2) 6 isotopes ({sup 155,156,157,158,160}Gd and {sup 232}Th) were taken from ENDF/B-VII.0; and (3) 3 isotopes ({sup 1}H, {sup 238}U and {sup 239}Pu) were taken from JENDL-3.3. For 6 light nuclei ({sup 4}He, {sup 6,7}Li, {sup 9}Be, {sup 10}B, {sup 12}C), only partial cross section covariance results were obtained, additional work is needed and they do not report the results here. Likewise, the cross section covariances for {sup 235}U, which they recommend to take from JENDL-3.3, will be included once the multigroup processing is successfully completed. Covariances for the average number of neutrons per fission, total {nu}-bar, are provided for 10 actinides identified as priority by SG26. Further work is needed to resolve some of the issues and to produce covariances for the full set of 52 materials.
Date: January 31, 2007
Creator: ROCHMAN,D.
Partner: UNT Libraries Government Documents Department

Ab Initio and Ab Exitu No-Core Shell Model

Description: We outline two complementary approaches based on the no core shell model (NCSM) and present recent results. In the ab initio approach, nuclear properties are evaluated with two-nucleon (NN) and three-nucleon interactions (TNI) derived within effective field theory (EFT) based on chiral perturbation theory (ChPT). Fitting two available parameters of the TNI generates good descriptions of light nuclei. In a second effort, an ab exitu approach, results are obtained with a realistic NN interaction derived by inverse scattering theory with off-shell properties tuned to fit light nuclei. Both approaches produce good results for observables sensitive to spin-orbit properties.
Date: October 2, 2007
Creator: Vary, J P; Navratil, P; Gueorguiev, V G; Ormand, W E; Nogga, A; Maris, P et al.
Partner: UNT Libraries Government Documents Department

Stellar Astrophysics and a Fundamental Description of Thermonuclear Reactions ? 04-ERD-058 Final Report

Description: Report on the progress achieved in 04-ERD-058. The primary goal of the project was to investigate new methods to provide a comprehensive understanding of how reactions between light nuclei proceed in hot, dense environments, such as stellar interiors. The project sought to develop an entirely new theoretical framework to describe the dynamics of nuclear collisions based on the fundamental nuclear interactions. Based on the new theoretical framework, new computational tools were developed to address specific questions in nuclear structure and reactions. A full study of the true nature of the three-nucleon interaction was undertaken within the formalism of effective field theory. We undertook a preliminary theoretical study of the quantum corrections to electron screening in thermal plasmas to resolve a discrepancy exhibited in previous theoretical approaches.
Date: February 22, 2007
Creator: Ormand, W E; Navratil, P & Libby, S B
Partner: UNT Libraries Government Documents Department

Hyperon-nucleon bound states and electroproduction of strangeness on light nuclei.

Description: The A(e,e{prime}K{sup +})Y X reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at a beam energy of 3.245 GeV for {sup 1}H, {sup 2}H, {sup 3}He and {sup 4}He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations including {Lambda}, {Sigma}{sup 0}, {Sigma}{sup -} hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for {Lambda}-hypernuclear bound states is seen for {sup 3,4}He targets.
Date: June 25, 2002
Creator: Dohrmann, F.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J. et al.
Partner: UNT Libraries Government Documents Department

Quantum Monte Carlo calculations for light nuclei

Description: Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 have been made using a realistic Hamiltonian that fits NN scattering data. Results for more than two dozen different (J{sup {pi}}, T) p-shell states, not counting isobaric analogs, have been obtained. The known excitation spectra of all the nuclei are reproduced reasonably well. Density and momentum distributions and various electromagnetic moments and form factors have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.
Date: October 1, 1997
Creator: Wiringa, R.B.
Partner: UNT Libraries Government Documents Department

Monte Carlo calculations of nuclei

Description: Nuclear many-body calculations have the complication of strong spin- and isospin-dependent potentials. In these lectures the author discusses the variational and Green`s function Monte Carlo techniques that have been developed to address this complication, and presents a few results.
Date: October 1, 1997
Creator: Pieper, S.C.
Partner: UNT Libraries Government Documents Department

In-beam gamma-ray spectrometric measurements of multi-body breakup reactions for E{sub n} between threshold and 40 MeV

Description: A system for in-beam gamma-ray spectrometric measurements to study inelastic neutron scattering has been extended to increasing incident neutron energies to study multi-body breakup reactions on light and medium-weight elements. The (n,2n{gamma}) cross sections are generally the largest; however, reactions of the types (n,{alpha}{gamma}), (n,np{gamma}) and (n,3n{gamma}) have been observed. In addition to improved understanding of reaction channels studied by other techniques, this method provides data for some reactions, e.g. {sup 56}Fe(n,3n){sup 54}Fe, which have not been observed previously.
Date: April 1995
Creator: Dickens, J. K. & Larson, D. C.
Partner: UNT Libraries Government Documents Department

Nuclear scales

Description: Nuclear scales are discussed from the nuclear physics viewpoint. The conventional nuclear potential is characterized as a black box that interpolates nucleon-nucleon (NN) data, while being constrained by the best possible theoretical input. The latter consists of the longer-range parts of the NN force (e.g., OPEP, TPEP, the {pi}-{gamma} force), which can be calculated using chiral perturbation theory and gauged using modern phase-shift analyses. The shorter-range parts of the force are effectively parameterized by moments of the interaction that are independent of the details of the force model, in analogy to chiral perturbation theory. Results of GFMC calculations in light nuclei are interpreted in terms of fundamental scales, which are in good agreement with expectations from chiral effective field theories. Problems with spin-orbit-type observables are noted.
Date: December 1998
Creator: Friar, J. L.
Partner: UNT Libraries Government Documents Department

Longitudinal and Transverse Quasi-Elastic Response Functions of Light Nuclei

Description: The {sup 3}He and {sup 4}He longitudinal and transverse response functions are determined from an analysis of the world data on quasi-elastic inclusive electron scattering. The corresponding Euclidean response functions are derived and compared to those calculated with Green's function Monte Carlo methods, using realistic interactions and currents. Large contributions associated with two-body currents are found, particularly in the {sup 4}He transverse response, in agreement with data. The contributions of two-body charge and current operators in the {sup 3}He, {sup 4}He, and {sup 6}Li response functions are also studied via sum-rule techniques. A semi-quantitative explanation for the observed systematics in the excess of transverse quasi-elastic strength, as function of mass number and momentum transfer, is provided. Finally, a number of model studies with simplified interactions, currents, and wave functions is carried out to elucidate the role played, in the full calculation, by tensor interactions and correlations.
Date: June 1, 2001
Creator: Carlson, J.; Jourdan, J.; Schiavilla, R. & Sick, I.
Partner: UNT Libraries Government Documents Department

Electroproduction of strangeness on light nuclei.

Description: The A(e,e{prime} K{sup +})YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at a beam energy of 3.245 GeV for {sup 1}H, {sup 2}H, {sup 3}He, {sup 4}He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of {Lambda} and {Sigma}{sup 0} hyperon production off the proton, and {Sigma}{sup -} off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for {Lambda}-hypernuclear bound states is seen for {sup 3,4}He targets.
Date: May 16, 2002
Creator: Dohrmann, F.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J. et al.
Partner: UNT Libraries Government Documents Department

Radiative effects in scattering of polarized leptons by polarized nucleons and light nuclei

Description: Recent developments in the field of radiative effects in polarized lepton-nuclear scattering are reviewed. The processes of inclusive, semi-inclusive, diffractive and elastic scattering are considered. The explicit formulae obtained within the covariant approach are discussed. FORTRAN codes POLRAD, RADGEN, HAPRAD, DIFFRAD and MASCARAD created on the basis of the formulae are briefly described. Applications for data analysis of the current experiments on lepton-nuclear scattering at CERN, DESY, SLAC and TJNAF are illustrated by numerical results.
Date: July 1, 2001
Creator: Akushevich, Igor; Ilyichev, A. & Shumeiko, N.
Partner: UNT Libraries Government Documents Department

Quantum Monte Carlo Calculations for Light Nuclei

Description: Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 are made using a realistic Hamiltonian that fits NN scattering data. Results for more than 30 different (j{sup {prime}}, T) states, plus isobaric analogs, are obtained and the known excitation spectra are reproduced reasonably well. Various density and momentum distributions and electromagnetic form factors and moments have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.
Date: August 1, 1998
Creator: Wiringa, R. B.
Partner: UNT Libraries Government Documents Department

Resolution of the classical Hyades lithium problem

Description: For the very first time, it has recently proved possible to make a well-motivated, physically plausible, and self-consistent prediction of the Hyades G- and K-dwarf (Li,T{sub eff}) relationship that matches the long-unexplained observations. The method employs the latest Iglesias &, Rogers (OPAL) interior opacities and Alexander surface opacities (whose respective values are now themselves close to empirical predictions or estimates made earlier in this Hyades project), King`s recently discovered [O/Fe] enhancement (another prediction!) and utterly conventional PMS (pre-main-sequence) evolution unaided by arbitrary and ad hoc adjustable parameters. Thus, the following assumptions form a self-consistent set explaining the Hyades G- and K-dwarf (Li,T{sub eff}) observations: (i) Pop. I interior opacities are now essentially correct; (ii) Pop. I surface opacities are now essentially correct; (iii) The Hyades distance is now essentially correct; (iv) The Hyades [Fe/H] and [O/Fe] are now essentially correct, and possible changes in [Ne, Mg., or Si/Fe] are likely to have only a small effect; (v) Convective envelope overshooting is negligible; (vi) Quarreling with the above means finding at least two compensating errors in assumptions (i) through (v).
Date: December 31, 1995
Creator: Faulkner, J. & Swenson, F. J.
Partner: UNT Libraries Government Documents Department

AFCI-2.0 Library of Neutron Cross Section Covariances

Description: Neutron cross section covariance library has been under development by BNL-LANL collaborative effort over the last three years. The primary purpose of the library is to provide covariances for the Advanced Fuel Cycle Initiative (AFCI) data adjustment project, which is focusing on the needs of fast advanced burner reactors. The covariances refer to central values given in the 2006 release of the U.S. neutron evaluated library ENDF/B-VII. The preliminary version (AFCI-2.0beta) has been completed in October 2010 and made available to the users for comments. In the final 2.0 release, covariances for a few materials were updated, in particular new LANL evaluations for {sup 238,240}Pu and {sup 241}Am were adopted. BNL was responsible for covariances for structural materials and fission products, management of the library and coordination of the work, while LANL was in charge of covariances for light nuclei and for actinides.
Date: June 26, 2011
Creator: Herman, M.; Herman,M.; Oblozinsky,P.; Mattoon,C.; Pigni,M.; Hoblit,S. et al.
Partner: UNT Libraries Government Documents Department