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Establishment of M1 multipolarity of a 6.5 (micro)2n resonance in 172Yb at E(gamma) = 3.3 MeV

Description: Two-step-cascade spectra in {sup 172}Yb have been measured after thermal neutron capture. they are compared to calculations based on experimental values of the level density and radiative strength function (RSF) obtained from the {sup 173}Yb(3{sup 3}He,{alpha}{gamma}){sup 172}Yb reaction. The multipolarity of a 6.5(15) {mu}{sub N}{sup 2} resonance at E{sub {gamma}} = 3.3(1) MeV in the RSF is determined to be M1 by this comparison.
Date: February 4, 2004
Creator: Schiller, A; Voinov, A; Algin, E; Becker, J A; Bernstein, L A; Garrett, P E et al.
Partner: UNT Libraries Government Documents Department

Bulk Properties of Iron Isotopes

Description: Nuclear level densities and radiative strength functions (RSF) in {sup 56}Fe and {sup 57}Fe were measured using the {sup 57}Fe({sup 3}He,{alpha}{gamma}) and {sup 57}Fe({sup 3}He, {sup 3}He{prime}{gamma}) reactions, respectively, at Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4 MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the {sup 56}Fe(n,2{gamma}) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSF. In a third experiment, the neutron evaporation spectrum from the {sup 55}Mn(dn,N){sup 56}Fe reaction was measured at 7-MeV deuteron energy at John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of {sup 56}Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft {gamma} rays is supported by the last experiment.
Date: July 27, 2006
Creator: Algin, E; Schiller, A; Voinov, A; Agvannluvsan, U; Belgya, T; Bernstein, L et al.
Partner: UNT Libraries Government Documents Department

Combinatorial nuclear level-density model

Description: A microscopic nuclear level-density model is presented. The model is a completely combinatorial (micro-canonical) model based on the folded-Yukawa single-particle potential and includes explicit treatment of pairing, rotational and vibrational states. The microscopic character of all states enables extraction of level distribution functions with respect to pairing gaps, parity and angular momentum. The results of the model are compared to available experimental data: neutron separation energy level spacings, data on total level-density functions from the Oslo method and data on parity ratios.
Date: January 1, 2008
Creator: Moller, Peter; Aberg, Sven; Uhrenhoit, Henrik & Ickhikawa, Takatoshi
Partner: UNT Libraries Government Documents Department

Chaos and structure of level densities

Description: The energy region of the first few MeV above the ground state shows interesting features of the nucleus. Beyond an ordered energy region just above the ground-state the dynamics changes, and chaotic features are observed in the neutron resonance region. The statistical properties of energies and wave-functions are common to all chaotic nuclei. However, if instead a global property, like the local level-density function is studied, strong structure effects emerge. In this contribution we discuss these two different facets of warm nuclei. In section 2 the onset of chaos with increasing excitation energy is discussed, with both experimental observations and proposed theoretical mechanisms as starting points. The structure of level densities in the same excitation energy region based on the two different starting points, is treated in section 3, where we give a short presentation of a newly developed combinatorial level-density modell. Some results from the model are presented and discussed. Two coexisting facets of warm nuclei, quantum chaos and structure of the level density, are considered. A newly developed combinatorial level-density model is presented, and the role of collective enhancements discussed. An example of extreme parity enhancement is shown.
Date: January 1, 2008
Creator: Moller, Peter; Aberg, Sven; Uhrenholt, Henrik & Ickhikawa, Takatoshi
Partner: UNT Libraries Government Documents Department

Missing and Spurious Level Corrections for Nuclear Resonances

Description: Neutron and proton resonances provide detailed level density information. However, due to experimental limitations, some levels are missed and some are assigned incorrect quantum numbers. The standard method to correct for missing levels uses the experimental widths and the Porter-Thomas distribution. Analysis of the spacing distribution provides an independent determination of the fraction of missing levels. We have derived a general expression for such an imperfect spacing distribution using the maximum entropy principle and applied it to a variety of nuclear resonance data. The problem of spurious levels has not been extensively addressed.
Date: June 23, 2005
Creator: Mitchell, G E; Agvaanluvsan, U; Pato, M P & Shriner, J F
Partner: UNT Libraries Government Documents Department

Level densities of iron isotopes and lower-energy enhancement of y-strength function

Description: The neutron spectrum from the {sup 55}Mn(d,n){sup 56}Fe reaction has been measured at E{sub d} = 7 MeV. The level density of {sup 56}Fe obtained from neutron evaporation spectrum has been compared to the level density from Oslo-type {sup 57}Fe({sup 3}He, a{gamma}){sup 56}Fe experiment [1]. The good agreement supports the recent results [1, 8] including an availability of a low-energy enhancement in the {gamma}-strength function for iron isotopes. The new level density function allowed us to investigate an excitation energy dependence of this enhancement, which is shown to increase with increasing excitation energy.
Date: August 30, 2005
Creator: Voinov, A V; Grimes, S M; Agvaanluvsan, U; Algin, E; Belgya, T; Brune, C R et al.
Partner: UNT Libraries Government Documents Department

Soft radiative strength in warm nuclei

Description: We present data on the soft (E{sub {gamma}} < 3-4 MeV) radiative strength function (RSF) for electromagnetic transitions between warm states (i.e. states several MeV above the yrast line) from two different types of experiments. The Oslo method provides data on the total level density and the sum (over all multipolarities) of all RSFs by sequential extraction from primary-{gamma} spectra. Measurements of two-step-decay spectra following neutron capture yields two-step-cascade (TSC) intensities which are roughly proportional to the product of two RSFs. Investigations on {sup 172}Yb and {sup 57}Fe have produced unexpected results. In the first case, a strong (B(M1 {up_arrow}) = 6.5 {mu}{sub N}{sup 2}) resonance at E = 3.3 MeV was identified. In the second case, a large (more than a factor of 10) enhancement compared to theoretical estimates of the very soft (E{sub {gamma}} {le} 3 MeV), summed RSF for transitions between warm states was observed. A somewhat weaker (factor {approx} 3) enhancement of the RSF in Mo isotopes observed within the Oslo method still awaits confirmation from TSC experiments.
Date: September 29, 2005
Creator: Schiller, A; Voinov, A; Agvaanluvsan, U; Algin, E; Becker, J; Belgya, T et al.
Partner: UNT Libraries Government Documents Department

FIGARO : measuring neutron emission spectra with a white neutron source /.

Description: Neutron emission spectra from reactions induced by fast neutrons are of importance in basic physics and applications. Very few data are available in the literature over a wide range of incident neutron energies such as produced with a white neutron source. The FIGARO facility at the WNR/LANSCE neutron source has been established to measure such neutron emission over a range of incident neutron energies from 1 to over 100 MeV. Using the time-of-flight technique twice (once to determine the incident neutron energy and again to determine the outgoing neutron energy), we are measuring neutron emission spectra for several reactions such as (n,n') and (n,f). Neutron emission from inelastic scattering gives information on the level density of excited states of the target nucleus. Our first measurements are on structural materials such as iron.
Date: January 1, 2002
Creator: Haight, Robert C.; O'Donnell, J. M.; Zanini, L.; Devlin, M. & Rochman, D. (Dimitri)
Partner: UNT Libraries Government Documents Department

Feeding of the 1 1/2- isomers in stable Ir and Au isotopes

Description: Excited states were studied and absolute partial {gamma}-ray cross sections were measured using the ({eta}, {eta}'{gamma}) reaction in {sup 191}Ir, {sup 193}Ir and {sup 197}Au. A Compton-suppressed germanium-detector array (GEANIE) for {gamma}-ray spectroscopy and the broad-spectrum pulsed neutron source of the Los Alamos Neutron Science Center's WNR facility were used for the measurement. The energy of the incident neutrons was determined using the time-of-flight technique. Absolute partial {gamma}-ray cross sections were measured up to incident neutron energy of 20 MeV for several transitions feeding directly the 1 1/2- isomers and ground states in {sup 191}Ir, {sup 193}Ir and {sup 197}Au. The feeding of the 1 1/2- isomers, which originate from the odd proton occupying the h{sub 1 1/2} orbital, was found for the three targets to be very similar and increasing relative to the feeding of the corresponding ground state with increasing neutron energy up to E{sub n} {approx} 10 MeV. Above this neutron energy the opening of the (n, 2{sub n}) reaction channel strongly affects the population of the isomers and leads to a decrease of their relative population compared to the population of the ground states. The experimental results are compared with theoretical predictions from the GNASH reaction model calculation implementing a version of the spin distribution for the pre-equilibrium reaction piece with either a compound nucleus spin distribution (CN-GNASH) or a Feshbach-Kerman-Koonin (FKK-GNASH) quantum mechanical spin distribution. The effects of the spin cutoff parameter values on the population of states are examined. Evidence is presented that FKK-GNASH provides a description of the experimental data that mitigates the need for adjustment of the level density parameter to fit the data.
Date: January 1, 2008
Creator: Fotiadis, Nikolaos; Nelson, Ronald O; Devlin, Matthew; Holloway, Shannon T; Kawano, Toshihiko; Talou, Patrick et al.
Partner: UNT Libraries Government Documents Department

Recent developments of the CEM2K and LAQGSM codes.

Description: Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions are briefly described. The improved cascade-exciton model as implemented in the code CEM97 [l] differs from the CEM95 version [4] by incorporating new approximations for the elementary cross sections used in the cascade, using more precise {approx} values for nuclear masses and pairing energies, using corrected systematics for the I level-density parameters, and several other refinements. Algorithms used in many i subroutines have been improved, decreasing the computing time by up to a factor of 6 for heavy targets. A number of further recent improvements and changes to CEM97, motivated by new data on isotope production measured at GSI will be presented. This leads us to CEM2k [2], a new version of the CEM code. CEM2k has a longer cascade stage, less preequilibrium emission, and evaporation from more highly excited compound nuclei compared to earlier versions. CEM2k also has other improvements and allows us to better model neutron, radionuclide, and gas production in Accelerator Transmutation of nuclear Wastes (ATW) spallation targets. The improved CEM97 code was recently used both to study fundamental nuclear physics problems like the role of nuclear medium effects in transport of 7r mesons in nuclei [5] and fission processes at intermediate energies [6], and was incorporated in the well known transport code MCNPX (LANL) to solve applied problems. The CEM95 version [4] of the CEM was incorporated in the MARS (FNAL) and CALOR95 (ORNL) transport codes, and its preequilibrium part was incorporated in many other transport codes like GEANT4 (CERN, see, e.g., [7]), HETC-3STEP (JAERI), HADRON (IHEP, Protvino), CASCADE (JINR, Dubna), SONET (RPCPI, Minsk), etc. The latest version of the CEM code, CEM2k, is still under development. The increased accuracy and predictive power of the code CEM2k will be shown by several examples. Further necessary work ...
Date: January 1, 2002
Creator: Mashnik, S. G. (Stepan G.); Gudima, K. K. (Konstantin K.) & Sierk, A. J. (Arnold J.)
Partner: UNT Libraries Government Documents Department

Polynomial approximations for materials simulations

Description: Chebyshev polynomial approximations are an efficient and numerically stable way to calculate properties of the very large Hamiltonians important in computational materials science. The authors describe kernel polynomial methods (KPM) producing estimates for densities-of-states (DOS) which are strictly positive and simple convolutions of known broadening functions, or kernels, with true DOS. The methods are demonstrated for tight binding electronic structure calculations of Si, yielding rapid convergence of cohesive and vacancy formation energies. KPM are also applicable to dynamical spectral functions, statistical mechanics, and density matrices.
Date: February 1, 1995
Creator: Silver, R.N.; Voter, A.F.; Kress, J.D. & Roeder, H.
Partner: UNT Libraries Government Documents Department

[Coherent control of photoabsorption processes and calculation of nonlinear optical processes]. Final technical report

Description: The work on the grant for the entire period of its duration concentrated on two different but related areas, namely coherent control of photoabsorption processes and the calculation of non linear optical processes with short wavelength radiation. On the first topic, the work dealt with the problem of controlling the population transfer from one to another bound state of a system in a route that passes through a continuum. This question is most important in the context of transferring populations between vibrational states of a molecule through a sequence of two pulses taking the system via the dissociation continuum. On the second topic, their work was motivated by the availability of XUV and soft X-ray coherent radiation sources obtained through high order harmonic generation. In addition, a few other techniques based on schemes of photo-pumped X-ray lasers promise to provide in the near-future similarly coherent sources. It is thus important to have an assessment of the possibility of extending non-linear optical processes to this range of wavelengths. This means assessing the relevant magnitude of the susceptibilities for third harmonic generation, stimulated Raman scattering, two-photon absorption, etc.
Date: July 1, 1998
Creator: Lambropoulos, P.
Partner: UNT Libraries Government Documents Department

Numerical simulation of quantum many-body systems

Description: Results for the single-particle density of states and the conductivity were obtained for both the attractive-and repulsive-U Hubbard models. At half-filling the densities of states for both models are identical, but the gap for the attractive case arises from the formation of charge-density-wave and superconducting correlations, while for the repulsive-U Hubbard model the gap is the Mott-Hubbard gap and arises from the antiferromagnetic, Coulomb, correlations. Hubbard chains were studied by use of a generalization of Handscomb`s quantum Monte Carlo scheme. Monte Carlo calculations of the two-particle vertex of the 2D repulsive-U Hubbard model were carried out. Criteria for determining whether a system is insulating, metallic, or superconducting were investigated; it was found for lattice models (Hubbard, Holstein, etc.) that this is determined by the value of the current- function.
Date: December 31, 1992
Creator: Scalapino, D. J.
Partner: UNT Libraries Government Documents Department

The unusual properties of beryllium surfaces

Description: Be is a ``marginal metal.`` The stable phase, hcp-Be, has a low Fermi-level density of states and very anisotropic structural and elastic properties, similar to a semiconductor`s. At the Be(0001) surface, surface states drastically increase the Fermi-level density of states. The different nature of bonding in bulk-Be and at the Be(0001) surface explains the large outward relaxation. The presence of surface states causes large surface core-level shifts by inducing a higher electrostatic potential in the surface layers and by improving the screening at the surface. The authors experimental and theoretical investigations of atomic vibrations at the Be(0001) surface demonstrate clearly that Be screening of atomic motion by the surface states makes the surface phonon dispersion fundamentally different from that of the bulk. Properties of Be(0001) are so different from those of the bulk that the surface can be considered a new ``phase`` of beryllium with unique electronic and structural characteristics. For comparison they also study Be(11{bar 2}0), a very open surface without important surface states. Be(11{bar 2}0) is the only clean s-p metal surface known to reconstruct (1 {times} 3 missing row reconstruction).
Date: December 31, 1994
Creator: Stumpf, R.; Hannon, J. B. & Plummer, E. W.
Partner: UNT Libraries Government Documents Department

Final Report for DE-FG52-03NA00076

Description: Level densities and radiative strength functions are crucial for stewardship science, in particular for radiochemical studies. In addition, this information is key to undertanding nucleosynthesis and thus very important for astrophysics. We utilized a method derives simultaneously the nuclear level density and the radiative strength function for energy regions that are extremely difficult to study via other methods. In heavy nuclei there is evidence for the systematic appearance of a low energy resonance in the radiative strength function (the so-called pygmy resonance). We have studied the same final nuclide (171Yb) via different nuclear reactions and obtained the same energy and width for the pygmy resonance. We also extended the method to lighter nuclei, including 56,57Fe, 93-98Mo and 116,117Sn. For the iron and molybdenum isotopes an enhancement of the radiative strength function was observed at low energy. Subsequent measurements in iron appear to confirm this unusual effect. Our measurements in tin do not observe this enhancement, nor did any of the earlier measurements in heavy nuclei. The issue is still unsettled.
Date: October 16, 2006
Creator: Mitchell, G. E.
Partner: UNT Libraries Government Documents Department

Review of Livermore-Led Neutron Capture Studies Using DANCE

Description: We have made neutron capture cross-section measurements using the white neutron source at the Los Alamos Science Center, the DANCE detector array (Detector for Advanced Neutron Capture Experiments) and targets important for basic science and stockpile stewardship. In this paper, we review results from (n,{gamma}) reactions on {sup 94,95}Mo, {sup 152,154,157,160,nat}Gd, {sup 151,153}Eu and {sup 242m}Am for neutron energies from < 1eV up to {approx} 20 keV. We measured details of the {gamma}-ray cascade following neutron capture, for comparison with results of statistical model simulations. We determined the neutron energy dependent (n,{gamma}) cross section and gained information about statistical decay properties, including the nuclear level density and the photon strength function. Because of the high granularity of the detector array, it is possible to look at gamma cascades with a specified number of transitions (a specific multiplicity). We simulated {gamma}-ray cascades using a combination of the DICEBOX/GEANT computer codes. In the case of the deformed nuclei, we found evidence of a scissors-mode resonance. For the Eu, we also determined the (n,{gamma}) cross sections. For the {sup 94,95}Mo, we focused on the spin and parity assignments of the resonances and the determination of the photon strength functions for the compound nuclei {sup 95,96}Mo. Future plans include measurements on actinide targets; our immediate interest is in {sup 242m}Am.
Date: May 11, 2007
Creator: Parker, W; Sheets, S; Agvaanluvsan, U; Becker, J; Becvar, F; Bredeweg, T et al.
Partner: UNT Libraries Government Documents Department

PROPERTIES IMPORTANT TO MIXING FOR WTP LARGE SCALE INTEGRATED TESTING

Description: Large Scale Integrated Testing (LSIT) is being planned by Bechtel National, Inc. to address uncertainties in the full scale mixing performance of the Hanford Waste Treatment and Immobilization Plant (WTP). Testing will use simulated waste rather than actual Hanford waste. Therefore, the use of suitable simulants is critical to achieving the goals of the test program. External review boards have raised questions regarding the overall representativeness of simulants used in previous mixing tests. Accordingly, WTP requested the Savannah River National Laboratory (SRNL) to assist with development of simulants for use in LSIT. Among the first tasks assigned to SRNL was to develop a list of waste properties that matter to pulse-jet mixer (PJM) mixing of WTP tanks. This report satisfies Commitment 5.2.3.1 of the Department of Energy Implementation Plan for Defense Nuclear Facilities Safety Board Recommendation 2010-2: physical properties important to mixing and scaling. In support of waste simulant development, the following two objectives are the focus of this report: (1) Assess physical and chemical properties important to the testing and development of mixing scaling relationships; (2) Identify the governing properties and associated ranges for LSIT to achieve the Newtonian and non-Newtonian test objectives. This includes the properties to support testing of sampling and heel management systems. The test objectives for LSIT relate to transfer and pump out of solid particles, prototypic integrated operations, sparger operation, PJM controllability, vessel level/density measurement accuracy, sampling, heel management, PJM restart, design and safety margin, Computational Fluid Dynamics (CFD) Verification and Validation (V and V) and comparison, performance testing and scaling, and high temperature operation. The slurry properties that are most important to Performance Testing and Scaling depend on the test objective and rheological classification of the slurry (i.e., Newtonian or non-Newtonian). The most important properties for testing with Newtonian slurries are the Archimedes ...
Date: April 26, 2012
Creator: Koopman, D.; Martino, C. & Poirier, M.
Partner: UNT Libraries Government Documents Department

Photon Strength and the Low-Energy Enhancement

Description: The ability of atomic nuclei to emit and absorb photons with energy E{sub {gamma}} is known as the photon strength function f(E{sub {gamma}}). It has direct relevance to astrophysical element formation via neutron capture processes due to its central role in nuclear reactions. Studies of f(E{sub {gamma}}) have benefited from a wealth of data collected in neutron capture and direct reactions but also from newly commissioned inelastic photon scattering facilities. The majority of these experimental methods, however, rely on the use of models because measured {gamma}-ray spectra are simultaneously sensitive to both the nuclear level density and f(E{sub {gamma}}). As excitation energy increases towards the particle separation energies, the level density increases rapidly, creating the quasi-continuum. Nuclear properties in this excitation energy region are best characterized using statistical quantities, such as f(E{sub {gamma}}). A point of contention in studies of the quasi-continuum has been an unexpected and unexplained increase in f(E{sub {gamma}}) at low {gamma}-ray energies (i.e. below E{sub {gamma}} {approx}3 MeV) in a subset of light-to-medium mass nuclei. Ideally, a new model-independent experimental technique is required to address questions regarding the existence and origin of this low-energy enhancement in f(E{sub {gamma}}). Here such a model-independent approach is presented for determining the shape of f(E{sub {gamma}}) over a wide range of energies. The method involves the use of coupled high-resolution particle and {gamma}-ray spectroscopy to determine the emission of {gamma} rays from the quasi-continuum in a nucleus with defined excitation energy to individual discrete levels of known spins and parities. This method shares characteristics of two neutron capture-based techniques: the Average Resonance Capture (ARC) and the Two-Step Cascade analysis (TSC). The power of the new technique lies in the additional ability to positively identify primary {gamma}-ray decay from defined excitation energy regions to low-lying discrete states. This approach was used ...
Date: February 22, 2012
Creator: Wiedeking, M; Bernstein, L A; Krticka, M; Bleuel, D L; Allmond, J M; Basunia, M S et al.
Partner: UNT Libraries Government Documents Department

Pairing correction for particle-hole state densities

Description: The pairing correction proposed by Ignatyuk and Sokolov for particle-hole state densities has been examined. It has been found that the accuracy of the correction is sufficient for practical applications only if the system is in its normal state (..delta.. = 0). In the superfluid state (..delta.. not equal to 0), a consistent pairing-Pauli correction is developed here for improved accuracy. Practical implementations of the pairing correction are given and further developments are outlined.
Date: January 1, 1983
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Sampling the Fermi-Dirac density

Description: A method is given for sampling the nonrelativistic Fermi-Dirac electron energy density for all values of the degeneracy parameter eta on the range - infinity < eta less than or equal to 50. The efficiency of the various rejection techniques employed is never less than 30%, and drops below 50% only for a short range of eta values around eta = 2. The range can certainly be extended beyond eta = 50, the efficiency there being 71%, and decreasing very slowly. 5 references.
Date: July 1, 1979
Creator: Cashwell, E.D. & Everett, C.J.
Partner: UNT Libraries Government Documents Department

Higgs phase in non-Abelian gauge theories

Description: A non-Abelian gauge theory involving scalar fields with non-tachyonic mass terms in the Lagrangian is considered, in order to construct a finite energy density trial vacuum for this theory. The usual scalar potential arguments suggest that the vacuum of such a theory would be in the perturbative phase. However, the obvious choices for a vacuum in this phase, the Axial gauge and the Coulomb gauge bare vacua, do not have finite energy densities even with an ultraviolet cutoff. Indeed, it is a non-trivial problem to construct finite energy density vacua for non-Abelian gauge theories and this is intimately connected with the gauge fixing degeneracies of these theories. Since the gauge fixing is achieved in the Unitary gauge, this suggests that the Unitary gauge bare vacuum might be a finite energy trial vacuum and, despite the form of the scalar potential, the vacuum of this theory might be in a Higgs phase rather than the perturbative phase.
Date: June 1, 1981
Creator: Kaymakcalan, O.S.
Partner: UNT Libraries Government Documents Department

Pairing correction of particle-hole state densities for two kinds of Fermions

Description: Pairing corrections in particle-hole (exciton) state-density formulas used in precompound nuclear reaction theories are, strictly speaking, dependent on the nuclear excitation energy U and the exciton number n. A general formula for (U,n)-dependent pairing corrections has been derived in an earlier paper for exciton state-density formulas for one kind of Fermion. In the present paper, a similar derivation is made for two kinds of Fermions. It is shown that the constant-pairing-energy correction used in standard level-density formulas, such as U/sub 0/ in Gilbert and Cameron, is a limiting case of the present general (U,n)-dependent results.
Date: January 1, 1985
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Numerical simulation of quantum many-body systems

Description: Results for the single-particle density of states and the conductivity were obtained for both the attractive-and repulsive-U Hubbard models. At half-filling the densities of states for both models are identical, but the gap for the attractive case arises from the formation of charge-density-wave and superconducting correlations, while for the repulsive-U Hubbard model the gap is the Mott-Hubbard gap and arises from the antiferromagnetic, Coulomb, correlations. Hubbard chains were studied by use of a generalization of Handscomb's quantum Monte Carlo scheme. Monte Carlo calculations of the two-particle vertex of the 2D repulsive-U Hubbard model were carried out. Criteria for determining whether a system is insulating, metallic, or superconducting were investigated; it was found for lattice models (Hubbard, Holstein, etc.) that this is determined by the value of the current- function.
Date: January 1, 1992
Creator: Scalapino, D.J.
Partner: UNT Libraries Government Documents Department

Unresolved dielectronic satellites of the resonance line of heliumlike iron (Fe XXV)

Description: (1s/sup 2/nl - 1s2pnl, n greater than or equal to 3) dielectronic satellites of the resonance line of Fe XXV at 1.85 A have been observed from PLT (Princeton Large Torus) tokamak discharges and are used for a detailed comparison with theory. The necessary corrections for Doppler broadening measurements are discussed, and accurate satellite to resonance line ratios allowing for a determination of the total dielectronic recombination rate of Fe XXV are derived.
Date: February 1, 1981
Creator: Bitter, M.; von Goeler, S.; Hill, K.W.; Horton, R.; Johnson, D.; Roney, W. et al.
Partner: UNT Libraries Government Documents Department