Optical properties of impurity atoms in pressurized superfluid helium

We report on the optical properties of alkali atoms (Cs and Rb) in the pressurized superfluid helium. We observed excitation and emission spectra at various pressures from the saturated vapor pressure to about 25 atm. The theoretical calculations on the basis of the atomic bubble model have also been worked out. The qualitative agreement between the theoretical and experimental results with respect to the peak shift, the linewidth, and their pressure dependence is achieved in the framework of the spherical atomic bubble model. TheD ₂ excitation spectra with the double peaks are interpreted qualitatively in terms of the Jahn-Teller effect, indicating the existence of the nontotally symmetrical density distribution of the surrounding helium atoms.     

Kaon absorption from kaonic atoms and formation spectra of kaonic nuclei

We considered the kaon absorption from atomic states into the nucleus. We found that the nuclear density probed by the atomic kaon significantly depends on the kaon orbit. Then, we re-examined the meanings of the observed strengths of one-body and two-body kaon absorption, and investigated the effects to the formation spectra of kaon bound states by in-flight (K ^-, p) reactions. As a natural consequence, if the atomic kaon probes a smaller nuclear density, the ratio of the two-body absorption at nuclear center is larger than the observed value in kaonic atoms, and the depth of the imaginary potential is deeper even at smaller kaon energies as in kaonic nuclear states because of the large phase space for the two-body processes. This deeper imaginary potential makes the signals of kaonic nucleus formation more unclear in the (K ^-, p) spectra.     

Isotope shift measurements in titanium I

The use of an effusive beam of titanium atoms crossed with a CW single-mode tunable dye laser has allowed the high-resolution, Doppler-free study of the isotope shifts between⁵⁰Ti,⁴⁸Ti and⁴⁶Ti, for seven 3d ² 4s ² a³ F _J 3d ² 4s 4p z ⁵ D _J , visible transitions of Ti I. The measurements show without ambiguity the existence of a non-negligible field shift. Using the values of the nuclear radii of titanium (coming from muonic X-ray measurements), it is possible to determine the respective values of the field and mass shifts.     

Resonant state expansions of the continuum

It is shown that the set of bound states and single-pa tide esonances consisting of the outgoing solutions of the Schödinge equation can be used as a ep esentation to describe p ocesses taking place in the continuum part of nuclear spectra. This is the first thoough investigation of completeness properties using realistic nuclear wave functions.This work was supported in part by the OTKA Foundation Hungary (contract number 3010) and by the Swedish Natural Science Research Council.     

Investigation of gain and hyperfine splitting in the niobium X-ray laser

Neon-like niobium X-ray lasers have been studied using both slab and thin-foil target geometries. Niobium foils of various lengths were irradiated from both sides with two beams of the frequency-doubled Nova laser system using a line focus. We looked for gain by measuring spectrally integrated line intensities at different plasma lengths. Gain was observed in four neon-like niobium lines corresponding to 3s–3p transitions. The line profile of theJ = 0–1 line ( = 145.9 ) shows splitting due to the hyperfine effect. Improved contrast in the hyperfine structure is observed as the plasma length is increased. Hyperfine splitting may be relevant to other 3s–3p transitions in neon-like niobium as well as other neon-like X-ray laser systems.     

The spin-orbit field in superdeformed nuclei: a relativistic investigation

Relativistic Mean Field (RMF) theory is used to investigate the behavior of the spin orbit potential,V _ls, in nuclear states of very large deformation and high angular velocity. As a by-product we present a set of parameters for an approximation of the relativistic scalar- and vector-potentialsS andV in the Dirac equation in terms of Saxon-Woods shapes. These reproduce more or less the same single particle specta as a full selfconsistent relativistic mean field calculation.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

Hard form factors for meson-baryon strong couplings as derived from deep inelastic lepton scattering

As stimulated by earlier attempts for obtaining theNN andN form factors from the deep inelastic lepton scattering data, we extend the analysis by taking into account effects of additional mesons including, , ,K, andK ^*, with the coupling constants fixed by the lowenergy nucleon-nucleon and hyperon-nucleon scattering data. Contrary to an earlier claim that the NN andN form factor must be very soft (e.g., with the cutoff mass less than 500 MeV in the monopole form), we find, for example, that with all form factors parametrized in the dipole form, a universal cutoff mass of 1150 MeV in the/N sector and 1400 MeV in the/ sector yields predictions in excellent agreement with recently published neutrino data on the momentum fractions carried by thes, , and¯d quarks, as well as consistent with the sea-to-valence ratio extracted from the CDHS data and the Femilab E615 experiment. Similar results can also be obtained by using exponential cutoffs for all couplings, or by using monopole forms for some vertices while retaining dipole forms for the rest. The success of the mesonexchange picture in generating the strangeness content in a proton suggests an alternative understanding of the origin of sea quarks in the proton.We wish to thank G. Garvey, K. Holinde, L.-C. Liu, M. B. Johnson, M. Strikman, A. W. Thomas and Jochen Wambach for helpful conversations. W-Y. P. Hwang wishes to acknowledge the Alexander von Humboldt Foundation for a fellowship to visit Jülich for conducting research. His research works was also supported in part by the National Science Council of the Republic of China. The work of G. E. Brown is supported in part by a Humboldt award, in part by NATO Grant RG85/0093, and in part by the U.S. Department of Energy.     

Bloch-Messiah theorem at finite temperature

The Bloch-Messiah theorem is extended to the thermal Hartree-Fock-Bogoliubov (THFB) theory by making use of the thermo field dynamics. This enables us to define the correct order parameter describing the superconducting phase at finite temperature, and demonstrates consistency of the THFB formalism.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

The relativistic Hartree-Fock-Approximation for finite temperatures and its semiclassical expansion

A derivation of the relativistic Hartree-Fock-Approximation for finite temperatures is given by utilizing a thermodynamic extremum principle for the construction of an approximate (thermal HF-) hamiltonian of single-particle structure. By use of the Wigner transform one can obtain the so-called quasi-classical expansion of the theory; i.e. the thermal Thomas-Fermi theory plus quantum corrections. The details are illustrated for the Walecka Lagrangian density.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

Laser-induced-fluorescence characteristics of a helium arcjet flow

Laser-induced fluorescence is used to characterize the axial velocity and temperature field at the exit plane of a low-power helium arcjet. Two cases were examined, one in which the mass-flow rate was changed at a constant current, and the other where the current was changed at a constant mass-flow rate. At constant mass-flow rate, the velocity scales with the increase in power. At constant current, a higher specific energy results in an unexpected lower mean exit velocity. The temperature profiles show that the nozzle-wall temperature is greater than the mean exit temperature. Along the axis of the arcjet, these measurements indicate the presence of a shock less than one nozzle diameter downstream of the exit. Received: 10 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +1-650-723-1748, E-mail: qwalker@stanford.edu