Showing papers in "Bulletin of the American Physical Society in 1993"

Young`s interference experiment with light scattered from two atoms

Abstract: We report the first observation of interference in the light scattered from two trapped atoms ({sup 198}Hg{sup +} ions localized in a linear Paul trap). The visibility of the interference fringes can be explained in the frame-work of Bragg scattering by a harmonic crystal, but with important differences compared to the case of a large crystal. Comparison of the experimental data with theory shows that the interference pattern offers another method to determine ion temperatures and separations. Furthermore, by exploiting the atom`s internal structure we have found a way to obtain {open_quotes}which path{close_quotes} information without invoking the position-momentum uncertainty relation. If the light scattered by the atoms is detected in a polarization-sensitive way, then it is possible to selectively demonstrate either the particle-nature or the wave-nature of the scattered photons.

Relativistic configuration interaction calculations of the ground state and n=2 singlet states of heliumlike ions

Abstract: The term energies based on the relativistic no-pair Hamiltonian including the Coulomb interaction and the retarded Breit interaction are determined for the ground state and n=2 singlet states of heliumlike ions with charges 4{<=}Z{<=}92. The eigenfunctions are expanded in a B-spline basis constructed from Dirac-Coulomb orbitals restricted to a finite cavity. The Hamiltonian matrix is evaluated and Davidson`s method is then employed to determine the lowest few eigenfunctions and eigenvalues. These calculations corrected for QED and mass polarization effects using values from Drake`s unified method are compared with other theoretical predictions and with experiment. For low Z ions, our results agree well with the unified method. For the ground state of He-like uranium, the present calculation differs from the unified method by 6.2 eV. Possible systematic discrepencies in K{alpha} x-ray energies between theory and experiment are discussed.

Generalized pseudospectral methods with mappings for bound and resonance state problems

Abstract: Several extensions of the pseudospectral method are made and applied to the solution of bound and resonance state problems. First, an algebraic mapping is introduced to remove the singularity and the domain truncation error common to Coulomb problems. In addition, the conventional procedure is modified, leading to a more desirable symmetric eigenvalue problem instead of an unsymmetric or generalized one. The simplicity, efficiency, and accuracy of the procedures are illustrated by solving the Dirac equation eigenvalue problem. Finally a new complex-scaling pseudospectral method is introduced for resonance state problems and applied to the determination of complex energies of H{sub 3}{sup +} resonances.

Photonic Band Structure

Abstract: We employ the concepts of band theory to describe the behavior of electromagnetic waves in three dimensionally periodic face-centered-cubic (fcc) dielectric structures. This can produce a “photonic band gap” in which optical modes, spontaneous emission, and zero point fluctuations are all absent. In the course of a broad experimental survey, we have found that most fcc dielectric structures have “semi-metallic” band structure. Nevertheless, we have identified one particular dielectric “crystal” which actually has a “photonic band gap”. This dielectric structure, consisting of 86% empty space, requires a refractive index contrast greater than 3 to 1, which happens to be readily obtainable in semiconductor materials.

New measurement of the relativistic Doppler shift in neon

Abstract: The Doppler free two photon transition from the metastable 1S{sub 5} to 4S{sub 1}{prime}{double_prime} in neon was measured for both a fast beam ({approx}120 keV) and a slow thermal beam The transition frequencies for each beam were measured independently relative to a hyperfine component of a nearby I{sub 2} reference line The absolute frequency shift between the two beams was obtained This measurement of the relativistic Doppler shift verifies the time dilation effect to an accuracy of 23 ppm which represents a more than 10 fold improvement over previous measurements

High-order harmonic generation in atomic hydrogen at 248 nm: Dipole-moment versus acceleration spectrum

Abstract: We present a study of the high-order harmonic-generation (KG) spectra of atomic hydrogen at 248 nm based on the Fourier transform of the expectation values of the induced dipole moment and acceleration. The calculations were performed by extending a fast-Fourier-transformation split-operator technique (in spherical coordinates) to the solution of the time-dependent wave functions in intense laser fields. It is seen that the acceleration form provides a more satisfactory and accurate framework for the study of the photoemission HG spectrum at very intense fields, particularly when ionization becomes appreciable.

Studies of Electron-Molecule Collisions on Massively Parallel Computers

Abstract: Electron-molecule collisions, particularly those leading to dissociation of molecules and hence to production of chemically reactive fragments, play an important role in the modelling of plasmas used in materials processing. The available data base of the cross sections needed in modelling such plasmas is quite fragmentary. In fact, the lack of an adequate data base of relevant cross sections for calculating plasma properties is one of the major obstacles to improved modelling and simulation of plasma processes. In this presentation we review the progress we have made in exploiting the high-performance computing provided by the Intel Delta System to obtain quantitatively useful estimates of these electron impact cross sections.

Orbital M1 versus E2 strength in deformed nuclei: A new energy weighted sum rule

Abstract: Within the unified model of Bohr and Mottelson we derive the following linear energy weighted sum rule for low energy orbital 1{sup +} excitations in even-even deformed nuclei S{sup lew}{sub LE}(M{sup orb}{sub 1}) {congruent} (6/5){epsilon}(B(E2; 0{sup +}{sub 1} {r_arrow} 2{sup +}{sub 1}K = 0)/Ze{sup 2} {sup 2}){mu}{sup 2}{sub N} with B(E2) the E2 strength for the trimsition from the ground state to the first excited state in the ground state rotational band, the charge nin.s. radius squared and e the binding energy per nucleon in the nuclear ground state. It is shown that this energy weighted sum rule is in good agreement with available experimental data. The. sum rule is derived Using a simple ansatz for the intrinsic ground state wave function that predicts also high energy 1{sup +} strength at 2h{omega} carrying 50% of the total m{sub 1} moment of the orbital M{sub 1} operator.

Oscillator strengths of selected resonance transitions in neutral sulfur

Abstract: As part of our continuing program of measuring f-values which are of astrophysical interest, meanlives and branching ratios for the 4s {sup 3}S{sup o} level was determined using beam foil techniques with the Toledo Heavy Ion Accelerator, THIA. The value 1.875{plus_minus}0.094 ns was obtained for the meanlife from multiexponential fitting to decay curves, a procedure which is reliable when all significant cascades are from levels with much longer meanlives. Oscillator strengths for the transitions 3p{sup 4} {sup 3}P{sub 0,1,2} - 4s {sup 3}S{sup o}{sub 1} were determined from this value together with the measured branching ratios. The preliminary result for the multiplet oscillator strength, 0.088{plus_minus}0.015, is slightly below other experimental measurements but is of improved accuracy. The mean of previous experimental measurements and theoretical calculations for this multiplet are in good agreement with our result. The 3p{sup 4} {sup 3}P{sub 2}- 4s {sup 3}S{sup o}{sub 1} transition of this multiplet at 1807.34{Angstrom}, is of particular interest to the study of interstellar matter since it involves a ground state transition. An investigation of the 3p{sup 4} {sup 3}P{sub 0,1,2} - 4s{double_prime} {sup 3}P{sup o}{sub 2,1,0} transitions in neutral sulfur is in progress and its results will also be reported.

Microwave-driven He Rydberg atoms: Floquet-state degeneracy lifted by a second frequency, Stueckelberg oscillations, and their destruction by added noise

Abstract: We investigate excitation of He 28{sup 3}S atoms and find that a 2nd microwave field lifts the degeneracy of certain Floquet states describing the [atom + single microwave field] system. As a result a microwave pulse produces two patterns of Stueckelberg oscillations. They depend sensitively on the frequencies and amplitudes of both microwave fields and are influenced differently by added by added noise. We present two-frequency (2-f) Floquet maps showing the origin of the intererferences. We are able theoretically to reproduce reasonably well our observed 2-f Stueckelberg oscillations for (stronger) 30 GHz and (much weaker) 36 GHz 2-field. The case of both fields strong is much more complicated. It still remains theoretically to explain why the noise influences the two patterns of Stueckelberg oscillations differently.

Axial vector coupling constant of the constituent quark

Abstract: We analyze the axial vector coupling of a constituent quark in the large-N{sub c} limit. We point out that the {pi} - A{sub 1} mixing mechanism produces a contribution to 1 - 9{sub A} at the level N{sup 0}{sub c}. Following Weinberg, we use the Adler-Weisberger sum rule and demonstrate that the reggeized p-meson exchange in the t-channel generates the leading N{sub e}-contribution to g{sub A}.

High order collective flow correlation in heavy-ion collision

Abstract: Using newly-measured data from the EOS TPC, the authors study azimuthal and {vert_bar}P{sub t}{vert_bar} correlations among triplets and higher-order multiplets, and explore the extent to which all fragments contribute to the flow. Results for Au + Au from 250 to 1200 A MeV and other data will be presented.

Ab initio method for calculating total cross sections

Abstract: A method for calculating total cross sections, without formally including non-elastic channels, is presented. The idea is to use a one channel T-matrix variational principle with a complex correlation function. The derived T-matrix is therefore not unitary: elastic scattering is calculated from {vert_bar}T{vert_bar}{sup 2}, but total scattering is derived from the imaginary part of T using the optical theorem. The method is applied to the spherically symmetric model of electron-hydrogen scattering. No spurious structure arises; results for {sigma}{sub el} and {sigma}{sub total} are in excellent agreement with calculations of Callaway and Oza. The method has wide potential applicability.

Semiclassical approximation for the average level density of a system of identical interacting particles

Abstract: We derive the analogue of the Weyl formula for the average level density, in the case of a system of identical particles (taking fermions as an example). This is accomplished by introducing the projection operator onto states in Hilbert space which have the symmetry imposed by particle identity. The semiclassical result is obtained by using the Wigner representation for this operator and by letting h {r_arrow} 0. Numerical examples for few degrees of freedom show in general good agreement with exact diagonalization even near the ground state of the system.

Perception of risk and the future of nuclear power

Abstract: Public support for nuclear power has declined greatly, driven by a number of powerful forces and events. Numerous studies have demonstrated the public`s extreme perceptions of risk and negative attitudes regarding nuclear power. This negativity is remarkable in light of the confidence most technical analysts have regarding the safety of this technology. Public fears and opposition to nuclear power can be seen as a crisis in confidence, a profound breakdown in trust in the scientific, governmental, and industrial managers of nuclear technologies. The problem is not due to public ignorance or irrationality, but is deeply rooted in individual psychology and the adversarial nature of our social, institutional, legal, and political systems of risk management. In the absence of revolutionary changes in the ways that risks are managed in our society, it is unlikely that public trust, confidence, and acceptance of nuclear power can be regained.

Energy dependence of double giant resonances in pion double charge exchange

Abstract: The energy dependence of the giant dipole resonance built on the isobaric analog state was measured in pion-induced double charge exchange on {sup 13}C at incident pion energies of 140-295 MeV. The cross-section increases with energy. The excitation function has a typical non-spin-flip signature, expected from simple considerations and verified by sequential model calculation. The results indicate that the pion DCX reaction excites this resonance predominantly via a two-step sequential process. Three narrower low-lying states in {sup 13}O (E{sub x}=2.9, 4.3 and 5.9 MeV) exhibit a clear spin=flip signature and most likely correspond to the giant Gamow-Teller strength built on the isobaric analog state. The authors will discuss the new results from LAMPF and the general features of these exotic nuclear states.

Rotationally resolved flurorescence as a probe of molecular photoionization dynamics

Abstract: We present rotationally resolved data for N{sub 2}(2{sigma}{sub u}{sup -1}) photoionization in the excitation energy range 19 {<=} h{nu} {<=} 35 eV. These are the first rotationally resolved measurements on the photoion over an extended spectral range above the ionization threshold. The requisite resolution is obtained by measuring rotationally resolved fluorescence from electronically excited photoions created by synchrotron radiation. This technique is useful for studying dynamical features embedded deep in the ionization continua and should supplement laser-based methods that are limited to probing near-threshold phenomena. The present study shows that the outgoing photoelectron can alter the rotational motion of the more massive photoion by exchanging angular momentum and this partitioning of angular momentum depends on the ionization dynamics. Thus, our data directly probe electron-molecule interactions and are sensitive probes of scattering dynamics. We are currently investigating dynamical features such as shape resonances and Cooper minima with rotational resolution for deciphering microscopic aspects of molecular scattering and these efforts will be discussed.

Deep inelastic scattering at low x

Abstract: Measurements of the scattered electron energy spectrum and the differential cross sections d{sigma}/dlog(x) and d{sigma}/dQ{sup 2} for inclusive neutral current deep inelastic electron proton scattering are presented The data were obtained with the H1 detector at HERA in which 267 GeV electrons collided with 820 GeV protons The data allow the first studies of the structure of the proton at values of x down to 10{sup {minus}4} for Q{sup 2}>5GeV{sup 2}

The outlook for renewable energy

Abstract: Despite the relative inattention in public policy over the last 12 years to energy generally and to renewable energy in particular, major advances have been made on many fronts in the use of renewable energy sources for the production of fuels and electricity. These advances are likely to continue and may accelerate in the future, in response to growing concerns about the environment. If these emerging opportunities are seized it should be feasible to provide more than half of total world energy requirements with renewable energy sources by the middle of the next century at world energy prices that are not much higher than at present.

Coincidence summing in gamma-ray spectroscopy

Abstract: With a proliferation of highly efficient Ge detector the effect of coincidence summing deserves a new approach. The coincidence summing of {gamma} radiation occurs when two or more {gamma} rays are emitted in coincidence from the decay of the same nucleus, and are recorded as one pulse within the resolving time of a Ge detector. We present a new technique developed to calculate coincidence-summing corrections. The general coincidence-summing equations are derived in matrix notation, which allows extracting either the lst-order correction (combinations of only two coincident {gamma} rays) or a full correction (all possible combinations of emitted {gamma} rays). It is shown how the technique can be applied to the determination of source disintegration rate, {gamma}-ray emission rates (alternatively in-beam reaction rates), or peak efficiencies in the presence of coincidence summing. Our technique has been applied to the determination of peak efficiencies of a Ge detector. The above calculation showed that, in general, the full correction is necessary for complicated decay schemes such as that from {sup 154}Eu.

{Delta} excitations in nuclei and the coherent pion decay

Abstract: The (p,n) and ({sup 3}He, t) reactions at intermediate energies have shown that there is a substantial downward energy shift in the excitation spectra of the {Delta} resonance in nuclei compared with the corresponding spectra in the Proton target Part of this shift, is caused by a coherent medium effect on the spin-longitudinal response function The coherent, effect is produced by the attractive {pi} exchange interaction between {Delta}-hole states in the medium Evidence of such a coherent mode has recently been obtained in the {sup 12}C(p, n{pi}) and {sup 12}C({sup 3}He, {pi}) reaction In this paper, we report results of our calculations or the coherent pion production cross sections It is shown that the coherent pions provide a unique signature on the nuclear pionic mode; they have a peak energy of E{sub {pi}} = 250 MeV and a strongly forward peaks angular distribution It is now important that these results are confirmed and checked by other experiments, such as the {sup 12}C({tilde n}, {tilde n}{pi}{sup +}) spinflip transfer experiments at LANPF and {sup 12}C(e, e`{pi}{sup 0}) experiments at CEBAF

Higher-order relativistic corrections to the polarization energies of helium Rydberg states

Abstract: Recent high precision helium n=10 fine-structure measurements are compared to the precise variational calculations of Drake and to predictions of long-range polarization calculations (which treat the system in terms of potentials between the He{sup +} core and a distant Rydberg electron). New calculations are presented for the {alpha}{sup 2} relativistic correction to the polarization energies. The results give simple formulas for these contributions which can be evaluated for any Rydberg state. With these new corrections, the variational and polarization energies show good agreement. Both, however, show significant disagreement with recent measurements, indicating the possible presence of physical effects not included in present calculations.

Coulomb excitation of {sup 189}Os

Abstract: The transitional nucleus {sup 189}Os has been studied by Coulomb excitation. Measurements with a Ge(HP) detector were made at 0{degrees}, 55{degrees}, 90{degrees} with beams of {sup 28}Si at 80 and 88 Me {sup 35}Cl at 80 MeV and {sup 16}O at 58 MeV. A total of gamma-ray transitions leading to 23 levels we used in the least-squares code GOSIA to determined reduced matrix elements. A theoretic understanding of this nucleus has been attempt from the point of view of current nuclear mode as they apply to systematics of the 1/2 {sup -}[510] 3/2 -[512], 1/2 [503] levels in this ma region.

Cooperative behavior in cavity-cooled, parametrically pumped electron oscillators

Abstract: Parametrically-pumped electron oscillators synchronize abruptly, when the pump power exceeds a threshold and the oscillators are radiatively cooled in a cylindrical Penning trap, with an instability which is approximated by a rigid model. The partially coherent, phase-bistable motion of the electron`s center-of-mass is observed to undergo self-organized, random transitions and other fluctuation phenomena. The precisely controlled environment within a cylindrical trap can be so simplified that better tests of QED can be made using one electron. Synchronized electrons are an ideal probe of the radiation field of a trap cavity, opening the way to a new generation of electron magnetic moment measurements, not limited by either cavity frequency shifts or damping widths, and to sideband cooling of an electron motion to mK temperatures.

Effects of critical fluctuations on the thermodynamic properties of fluids and fluid mixtures

Abstract: In fluids, critical fluctuations not only induce singular thermodynamic behavior asymptotically close to the critical point, but they also have a significant influence on the thermodynamic properties in a large region around the critical point. Based on an approximate solution of the renormalization-group equation, the authors present a procedure to obtain a renormalized Helmholtz free-energy density for one-component fluids that reproduces the universal singular behavior near the critical point, and crosses over to mean-field behavior far away from the critical point. This procedure is then extended to include binary fluid mixtures near the vapor-liquid critical line. A comparison with experimental data for carbon dioxide, ethane and their mixtures shows that the theory describes the thermodynamic properties of both one-component fluids and binary fluid mixtures in a very large range around the critical point.

Centrifugal rotational effects on the magnetic dipole strength distribution

Abstract: Even though various shell-model calculations of the M1 {open_quotes}scissor{close_quote} like state In deformed nuclei have been put forward, no simple Interpretation resulted. A rather Important fragmentation of 1{sup +} strength was obtained in almost all cases. Taking Into account, however, the centrifugal rotational effects that become Important when coupling two-quasi particle excitations to a deformed core, a much larger concentration of 1{sup +} strength near E{sub x} {approximately} 3 MeV results. The overlap of the strongest 1{sup +} state with a scissor state ({alpha} {cflx J}{sub {pi},{tau}}-{Beta} {cflx J}{sub v} +){vert_bar} {cflx 0} > increases dramatically to values of {approximately} 50%. Both schematic calculations and more detailed applications to the rare-earth region where besides the above centrifugal effects, residual interactions are taken into account are presented. We also suggest a new, geometrical interpretation as an orbital reorientation wobbling effect induced by the centrifugal motion.

The CDF level-3 trigger

Abstract: The Collider Detector at Fermilab (CDF) has been operating at the Tevatron and collecting data on proton-antiproton interactions with collision rates above 250,000 Hz Three levels of filtering select events for data logging at a rate of about 4 Hz The Level 3 trigger provides most of the capabilities of the offline production programs for event reconstruction and physics analysis The type of physics triggers, application of cuts, and combinations of logical requirements for event selection are controlled at run time by a trigger table using a syntax fully integrated with the Level 1 and Level 2 hardware triggers The level 3 software operates in 48 RISC/UNIX processors (over 1000 mips) served by four 20-MByte/sec data buses for input, output and control The system architecture, debugging, code validation, error reporting, analysis capabilities and performance will be described

Relativistic configuration interaction calculations of n=2 triplet states of heliumlike ions

Abstract: Eigenfunctions and eigenvalues of the relativistic no-pair Hamiltonian are determined for the n=2 triplet states of heliumlike ions with charges in the range Z=5-100. The eigenfunctions are expanded in a basis of two-electron wave functions constructed from Dirac-Coulomb orbitals restricted to a finite cavity. The Hamiltonian matrix is evaluated and Davidson`s method is then used to determine the lowest few eigenfunctions and eigenvalues. These calculations, which include the Coulomb interaction and the retarded Breit interaction, are corrected for QED and mass polarization effects using values from Drake`s unified method and are compared with other calculations and with experiment. For low Z ions, the present calculations agree well with MBPT and with the unified method, but disagree substantially with MCDF calculations corrected for correlations. Our energy intervals and fine structures are consistent with experiment throughout the entire range of Z.

Promoting energy efficiency in the utility sector through coordinated regulations and incentives

Abstract: Several recent studies have shown the realistic potential to reduce utility customers` energy use dramatically. One such effort projects reductions of thirty to fifty-five percent compared to a reference case (which already incorporates some efficiency improvements). These correspond to absolute reductions of about fifteen to twenty percent compared to current usage, even with projected growth of GDP by a factor of 2.4. Such a scenario covering all sectors of the economy can provide a seventy percent absolute reduction in US carbon dioxide emissions over the next forty years, at a net economic benefit of $2.3x10{sup 12}. In the past, the bulk of utility-sector energy savings have been obtained through state and federal efficiency standards for buildings, appliances, and other equipment. In recent years, the rapid growth of utility-run incentive programs allows the prediction that they will account for an increasing share of the savings. Incentives can promote increased efficiency among utility customers, and can interact synergistically with present and future standards. Retulation of utilities themselves can encourage or undermine such programs. Finally, the problem of promoting research, development, and commercialization of new energy efficiency technologies is described in the context of changing incentives at the utility customer level. Emerging mechanismsmore » and institutions may be able to address this problem, resulting in more effective and less costly options for energy efficiency.« less

Measurements of the radiative decay rates of 2s{sup 2}2p({sup 2}P{degrees})-2s2p{sup 2}({sup 4}P) intersystem transitions of C{sup +} ion

Abstract: The radiative decay rates of the 2s{sup 2}2p({sup 2}P{sup o})-2s2p{sup 2}({sup 4}p) intersystem transitions of C{sup +} ion have been measured by recording the time dependence of the {approximately}233 nm emission. A cylindrical radio frequency ion trap was used to store electron-impact-produced C{sup +} ions. The time dependent signals were analyzed by multi-exponential least-squares fit to the data. The measured radiative decay rates to the ground term are: 146.4(+8.3/-9.2) s{sup -1} for {sup 4}P{sub 1/2}, 11.6(+0.8/-1.7) s{sup -1} for {sup 4}P{sub 3/2}, and 51.2(+2.6/-3.5) s{sup -1} for {sup 4}P{sub 5/2}. Comparison of the measured values with theoretical values is presented.