The binding of alkali atoms to the surfaces of liquid helium and hydrogen

Alkali atoms have been shown previously to have only unstable binding states inside liquid⁴He. We calculate the equilibrium configurations and binding energies of single alkali atoms near the liquid-vapor interface of⁴He and³He. A simple interface model is used to predict the surface deformation due to the presence of the atoms. A more realistic density functional model yields somewhat higher energies in the case of⁴He. For all alkali atoms, we find the surface binding energies to be around 10 to 20 K. A similar analysis with atom-H₂ interactions finds that alkali atoms tend to submerge into liquid H₂, with the exception of Li.     

Basic connection between superconductivity and superfluidity

A basic and inherently simple connection is shown to exist between superconductivity and superfluidity. It is shown that the author's previously derived general equation, which agrees well with the superconducting transition temperatures for the heavy-electron superconductors, metallic superconductors, oxide superconductors, metallic hydrogen, and neutron stars, also works well for the superfluid transition temperature of 2.6 mK for liquid³He. Reasonable estimates are made from 10^–3 to 10⁹ K — a range of 12 orders of magnitude. The same paradigm applies to the superfluid transition temperature of liquid⁴He, but results in a slightly different equation. The superfluid transition temperature for dilute solutions of³He in superfluid⁴He is estimated to be l–10K. This paradigm works well in detail for metallic, cuprate, and organic superconductors.     

Paired-phonon analysis of impurities in bose fluids

Summary The paired-phonon analysis for boson mixtures is employed in conjunction with the hypernetted-chain approximation to study the ground-state properties of an impurity embedded in liquid⁴He. Chemical potentials, volume coefficients and other thermodynamic quantities as well as some of the most interesting optimal correlation functions are calculated for various impurities interacting with the⁴He background atoms via Lennard-Jones potentials of differing strength. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Observation of the spin polarization of Cs atoms during optical orientation of metastable helium atoms in alkali-helium plasma

We are the first to experimentally observe a magnetic-resonance signal of 6² S _1/2 Cs atoms by absorption of light from a helium lamp that was used to optically orient metastable 2³ S ₁ He atoms. The amplitude of the cesium signal proved to be almost three orders of magnitude lower than the amplitude of the magnetic resonance of 2³ S ₁ He atoms. Particular features of the creation and observation of the collisional polarization of cesium under conditions of alkali-helium plasma have been discussed.     

Self-consistent quantum structure of diffuse helium atom clusters

Diffuse clusters of arbitrary numbers of helium atoms are treated in a mean-field theory of the many-body system. The nonlinear Hartree self-consistent-field equations are solved numerically to give their energy eigenvalues and eigenfunctions. Both isotopes ⁴He and ³He are treated according to their bosonic and fermionic statistics and symmetry requirements. Clusters of all sizes of ⁴He atoms are stable, but there is a minimum threshold of ～70 atoms for the formation of ³He clusters. All the excited states in addition to the ground state were found. The wave functions are seen to have interesting differences from electronic wave functions in atoms.     

High nuclear polarization in3He and3He-4He gas mixtures by optical pumping with a laser diode

New diode lasers delivering 50 mW output power at 1083 nm are shown to be efficient sources for optical pumping of helium. They can polarize nuclei in a³He gas up toM = 50% over the pressure range 0.4–1.6 torr. Larger nuclear polarizationsM of³He nuclei, of order 80%, can be obtained in³He-⁴He mixtures when the laser frequency is tuned to a⁴He line. A standard optical measurement of nuclear polarizationM has been extended to the case of³He-⁴He mixtures. The effect of various parameters on the steady-state polarizationM and on the pumping timeT _p is discussed.Laboratoire associé au Centre National de la Recherche Scientifique et à l'Université P. M. Curie     

Neutron star matter superfluidity and superconductivity

The possibility of superfluidity or superconductivity in neutron or proton subsystems in the nuclear-matter region in neutron stars is investigated. The energy gap and corresponding critical temperature and critical magnetic field is calculated or estimated as function of density or Fermi momentum. In the calculations are used reaction matrix elements calculated earlier by means of Brueckner theory by the author. The final results indicate that neutron superfluidity, corresponding specifically toS-state pairing, may exist in a low-density shell in the nuclear-matter region of a neutron star. There is probably anisotropic neutron superfluidity, corresponding to the³ P ₂ or the singletD state, for higher densities. Superfluidity or superconductivity, corresponding toS-state pairing for the proton subsystem, is quite likely in most of the nuclear-matter region. The expected temperatures and magnetic fields in neutron stars seem to be well below the estimated critical temperatures or critical magnetic fields corresponding to the calculated values of the energy gap. However, similar methods have earlier predicted a much too high critical temperature for liquid³He.     

Role of atomic inelastic collisions in a Cs-He steady state discharge

The population of various excited states and the electron temperature in a mixture of cesium vapor and helium have been measured spectroscopically in a stationary electrical discharge where helium atoms remain in their ground state. An equilibrium between the populations of highly excited cesium levels was observed to be characterized by a Boltzmann temperature equal to the gas temperature. It is concluded that the populations of these high levels are more influenced by Cs¹+He inelastic collisions than by Cs¹+e collisions when [He]/[e]?10⁶. The influence of the helium atoms has also been observed on the relation between electron temperature and electron density.     

Excitation of vacuum UV transitions of alkali-metal atoms by charge-exchange reactions

We investigate the vacuum UV radiation spectra of atoms and ions of Rb, Cs, He, Ne, and Ar in a discharge plasma of their mixtures at different concentration of metal vapors in rare gases. The reactions leading to population and deactivation of resonant states of rare-gas atoms were studied. The observation of lines 109.1, 119.6, and 124.7 nm, corresponding to the radiation transitions from the 5p ⁵5d6s ⁴ P _5/2 quasi-metastable autoionizing level of cesium, allowed us to estimate experimentally the cross section σ=(9±3) · 10^?15 cm² of the charge-exchange reaction of the metastable cesium ion on the cesium atom, giving as a result the above-mentioned quasi-metastable state of cesium.     

Momentum distribution and one-body density matrix in liquid3He.

Summary The momentum distributionn(k) and the one-body density matrix ρ₁(r,r' have been calculated in normal liquid³He atT=0. A variational wave function containing two-, three-body and backflow correlations has been used. The Fermi hypernetted chain technique has been employed and the elementary diagrams have been evaluated by the scaling approximation. The present estimate ofn(k) is in good agreement with the Monte Carlo data obtained with similar wave functions.n(k) and the discontinuityZ ofn(k) at the Fermi surface have been computed at several values of the density. The density dependence of the effective massm ^* has been found to be mainly due to that ofZ.     

Measurement of helium-3 and deuterium stopping power ratio for negative muons

The measurement method and results measuring of the stopping power ratio of helium-3 and deuterium atoms for muons slowed down in the D/³He mixture are presented. Measurements were performed at four values of pure ³He gas target densities, ϕ_He = 0.0337, 0.0355, 0.0359, 0.0363 (normalized to the liquid hydrogen density) and at a density 0.0585 of the D/³He mixture. The experiment was carried out at PSI muon beam μE4 with the momentum Pμ= 34.0 MeV/c. The measured value of the mean stopping ratio S$_{3^He/D}$ is 1.66±0.04.     

Intrinsic point defects and light interstitials in metals

Clusters consisting of a radioactive probe atom and various point defects in metallic hosts were studied by means of NMR-ON and PAC. NMR resonance signals were observed for¹³¹IV₂ clusters in Fe and^114mInV₄ clusters in Ni. Decoration of¹¹¹InV₂ clusters by H atoms in W and Mo and by He atoms in W was monitored by PAC. The measurements yield the first reliable data on vacancy-hydrogen binding energies in these metals. The He-decoration results are in excellent agreement with the interpretation of He-desorption data and clearly show the existence of trap mutation.     

Quantum dynamics of molecules in 4He nano-droplets: Microscopic superfluidity

High resolution spectroscopy of doped molecules in ⁴He nano-droplets and clusters gives a signature of superfluidity in microscopic system, termed as microscopic superfluidity. Ro-vibrational spectrum of ⁴He_N-M clusters is studied with the help of some important observations, revealed from experiments (viz., localised and orderly arrangement of ⁴He atoms, although, being free to move in the order of their locations; individual ⁴He atoms can not be tagged as normal/ superfluid, etc.) and other factors (e.g., consideration that the ⁴He atoms which happen to fall in the plane of rotation of a molecule, render a equipotential ring and thus, do not take part in rotation; etc.) which effect the rotational and vibrational spectrum of the system. This helps us in successfully explaining the experimental findings which state that the rotational spectrum of clusters have sharp peaks (indicating that the molecule rotates like a free rotor) and moment of inertia and vibrational frequency shift have a non-trivial dependence on N.     

Kinetics of the sorption of <Superscript>3</Superscript>He by C<Subscript>60</Subscript> fullerite. The quantum diffusion of <Superscript>3</Superscript>He and <Superscript>4</Superscript>He in fullerite

The kinetics of the sorption and subsequent desorption of gaseous ³He in a C₆₀ fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of ³He and ⁴He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C₆₀ fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of ³He and ⁴He atoms at the same temperatures.     

Vacancy trapping and helium decoration in Sb ion-implanted tungsten studied by Mössbauer spectroscopy

Mössbauer effect measurements have been performed using sources of¹¹⁹Sb implanted in W without and with post-implanted helium. Each of the sources was subjected to an isochronal annealing sequence in order to study vacancy trapping, helium decoration and recovery of damage. Four sites have been identified for Sb implanted in tungsten; one of these corresponds with substitutional Sb atoms, two others are assigned to Sb atoms associated with vacancies, while the last one can be either vacancy or impurity associated. The development of site occupation as a function of annealing temperature is in accordance with the one-interstitial model. Injection of 2·10¹⁶ He/cm² leads to nucleation of helium bubbles. Helium atoms that are released from these bubbles at about 1300 K are retrapped by Sb atoms to form new bubbles.     

Nearly frictionless transport of solid helium-4 at higher temperature regime

Eyal et al. recently reported that there might be supersolidity of ⁴He around the temperature range: 1.3–1.9 K. By using the transition-state model together with the specific activation energy and activation volume, we found that the possible supersolidity of ⁴He might occur at the similar temperature range as Eyal et al. reported.     

Absolutmessung der Ionisierungsausbeute von Alkaliatomen an Metalloberflächen

Concluding the investigations of the positive surface ionization of alkali metals on incandescent clean polycristalline surfaces^1–3 the absolutely determined ionization coefficientsΒ of cesium on platinum are 1.00 between 1120 and 1700 ?K. A maximum ionization of cesium on tungsten is observed between 1000 and 1340 ?K withΒ very near 1.00. At higher temperatures there is a slight decrease ofΒ in the case of tungsten in agreement with the Saha-Langmuir-equation.     

Temperaturabhängigkeit von Knight-shift und Suszeptibilität von Vanadium und Niob

Knight-shiftK and susceptibility have been investigated on single-crystals of vanadium and niobium between 4 K and 290 K.In the case ofV the changes ofK and are found to be of opposite sign and proportional toT ² with good approximation. This can be explained by theT-dependence of spin-paramagnetism of 3d-electrons. The hyperfine field due to oned-electron spin is found to be — 90 kG. Small deviations from theT ²-law are explained by minor changes in the orbital susceptibility, which gives the main constituents toK and. In the case of Nb only is found to be proportional toT ². TheT-dependence ofK is very small and shows a maximum at 140 K. This can be explained by theT-dependence of spinparamagnetism of 4d-electrons as well as 5s-electrons.     

Helium wetting: Theme and variations on inhomogeneous helium

The surprising discovery, in 1991, that liquid helium does not wet a cesium surface at low temperature has triggered an important activity both theoretical and experimental: helium has become a model system for the study of wetting transitions. After summarizing the main theme of helium wetting, I will focus on more recent studies, such as the structure and excitations of helium interfaces, experiments on the capillary rise, the “surfactant effect” of helium-3 impurities on liquid helium-4 and the “quantum prewetting transition” of pure helium-3. Unexpected consequences on the phase separation of³He?⁴He mixtures in restricted geometry will be drawn.     

Electromagnetic contributions to proton- and neutron-4He scattering

A proper treatment of various electromagnetic contributions toN-⁴He scattering enables one to determinen(p)-⁴He observables fromp(n)-⁴He data. Several calculations ofn-⁴He observables considering different electromagnetic effects are presented. It is shown that the contribution of thep-⁴He Coulomb corrections ton-⁴He polarizations and differential cross sections dominates over other electromagnetic effects forθ _c.m.≧30°. For smaller scattering angles, neutron magnetic scattering is important and produces a divergingn-⁴He differential cross section atθ=0° and a large peak (Mott-Schwinger effect) in the polarization. The influence of thep- andn-⁴He vacuum polarizations on then-⁴He observables is found to be small.