Excitation spectrum of helium II: A series representation

A series representation is described which has pressure dependent phonon dispersion, and which is consistent with neutron scattering and calorimetric data.     

On the Cd III spectrum in a pulsed helium discharge

On the basis of the spectral line intensity relaxation during the plasma decay, fifty six spectral lines between 219 nm and 330 nm in the cadmium (Cd) spectrum were identified as Cd III (doubly ionized) or Cd IV (triply ionized) lines. The measured Stark widths of twelve, the most intense spectral lines around 315±15 nm with well defined profiles, are presented. Investigated spectral lines originate from the high lying energy levels, not classified up to now. A linear low-pressure pulsed arc was used as an optically thin plasma source. A pulsed discharge was produced in a pyrex discharge tube. Helium was chosen as the carrier gas. The cadmium atoms were sputtered from the thin cadmium cylindrical plates located in the homogeneous axial part of the discharge tube. The helium plasma was operated at electron temperatures up to 19 000 K and 1.1 × 10²³ m^-3 electron density. The stepwise ionization processes via the high lying singly ionized (Cd II) energy levels, populated well due to the Penning and charge exchange effects, provide high density of the Cd III (and Cd IV) ions in our helium plasma. The temporal evolutions of the spectral line intensities were monitored using a spectrograph and an ICCD camera as a highly sensitive detection system.     

On the correlation energy in an adsorbed helium monolayer

The correlation energies in helium monolayers absorbed on argon surfaces are calculated variationally. They are very different from the -15°K implied by experimental data discounting the importance of surface inhomogeneities.     

On the energy spectrum of cosmogenic neutrons

The processes of the generation of cosmogenic neutrons (cg-neutrons) underground are considered. The neutrons produced by cosmic-ray muons in their interactions with matter are called cosmogenic. Deep-inelastic πA-collisions of pions in muon-induced hadronic showers are mainly their source at energies above 30 MeV. The characteristics of the energy spectrum for the generation of cg-neutrons have been determined by invoking the additive quark model of deep-inelastic soft processes and the mechanism for the interactions of high-energy nucleons in a nucleus. The three-component shape of the spectrum is explained, and the energy of the “knee” in the spectrum has been found to depend on the mass number A. The peculiarities of deep-inelastic πA-scattering lead to the conclusion that the spectrum of cg-neutrons steepens sharply at energies above 1 GeV. The calculated quantitative characteristics of the spectrum are compared with those obtained in measurements.     

On the spectrum of the rayleigh piston II

Building on results of an earlier paper we study the discrete spectrum of the Rayleigh piston. We first prove the absence of discrete spectrum on the subspace of odd functions everywhere in the Lorentz regime. Then we give upper bounds on the number of discrete eigenvectors as a function of the mass ratio using a variety of methods which to some degree complement each other. We also investigate the precise degree of divergence of these bounds as the mass ratio goes to infinity respectively zero.     

On the energy spectrum of excitations in type-II superconductors

The quasi-classical approximation has been applied in order to study the energy spectrum of the bound excitations with the radial quantum number n≠0 in the isolated vortex line core in a pure type-II superconductor. The qualitative estimations of the number of levels and the numeric calculations of the spectrum for the special form of potentials A_θ(r) and Δ(r) have been made.     

Expected energy spectrum of cosmic ray protons and helium below4 PeV measured by LHAASO

The Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array(KM2 A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array(WCDA) and wide field-of-view Cherenkov telescope array(WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from 10~(14) eV to 10~(18) eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium(HHe) samples are 900 m~2 Sr and1800 m~2 Sr, respectively. Prospect of obtaining proton and HHe spectra from 100 TeV to 4 PeV is discussed.     

Ab initio potential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. II. Thermophysical standard values for low-density helium

A helium–helium interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation considering relativistic retardation effects (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. (in press)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body and three-body interactions. The second pressure virial coefficient as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for ³He and ⁴He from 1 to 10 000 K and the third pressure virial coefficient for ⁴He from 20 to 10 000 K. The transport property values can be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of ±0.02% for temperatures above 15 K. This uncertainty is superior to the best experimental measurements at ambient temperature.     

On the valence shell binding energy spectrum of carbonyl sulphide

The valence shell binding energy spectrum of carbonyl sulphide (10–45 eV) has been measured using both binary (e,2e) and dipole (e,2e) electron impact spectroscopy and calculated by the 2ph-TDA many body Green's function technique. The spectrum shows extensive structure above 20 eV, indicating a major breakdown of the quasi-particle picture for ionization of COS. The calculation is in good agreement with the present experimental and literature ESCA binding energy spectra. Binary (e,2e) spectra at two azimuthal angles support the theoretical prediction that this extensive final ion state structure arises primarily from ionization of the COS 6σ and 7σ inner valence electrons.     

Specific features of the excitation spectrum of helium II in a plasma initiated by an electron beam

The emission of a low-pressure helium plasma (P≤2 Torr) initiated by a monochromatic electron beam is investigated. It is found that an increase in the current leads to a drastic increase in the rate of charge exchange of doubly charged helium ions. The assumption is made that inelastic collisions of He⁺⁺ ions with metastable helium atoms provide the main channel of charge exchange of these ions due to the reaction He⁺⁺+Hem→ He⁺*+He ₀ ⁺ .     

Neutron-scattering investigation of the excitation spectrum of liquid helium

The results of the investigation of the temperature evolution of the scattering law S(Q, ω) of superfluid helium measured in the wave-vector range 0.3 < Q < 0.8 Å^?1 and helium temperatures from 1.0 to 2.2 K are reported. The investigations have been performed on the high-flux reactor at the Institut Laue-Langevin (France) with the IN6 neutron inelastic-scattering spectrometer. The deviation of the experimental scattering law of liquid helium from the damping harmonic oscillator model, which was previously observed independently in the experiments with the IN6 spectrometer [1] and with the DIN-2PI spectrometer (at the IBR-2 reactor, Dubna, Russia) [2, 3] and were more recently called extrapeak, has been corroborated. The temperature dependence of the extrapeak parameters has been determined. This dependence makes it possible to propose hypotheses on the nature of the extrapeak.     

On the discontinuities in the energy spectrum of a model Hamiltonian

The occurrence of discontinuities in the energy spectrum of thes-wave Hamiltonian in three dimensionsH(μ, λ) =p ²/2 − 1/r + 2μr + 2λ ² r ² has been reported by us. In this communication we develop a unified understanding, based principally on the topography of the energy surfaces, of the different discontinuities we reported earlier. These discontinuities do not in general occur wherever the corresponding classical system would display catastrophic behaviour.     

On the low energy tail of the electron-hole drop recombination spectrum

The luminescence line shape of electron-hole drops in germanium is calculated assuming that the final state of the radiative transition is lifetime broadened due to Auger processes in the degenerate bands. This level broadening can account for the existence of the experimentally observed low energy tail in the recombination spectrum. The theoretical line shape is in good agreement with experimental results.     

On the electron energy spectrum in heavily doped non-parabolic semiconductors

An attempt is made to present a simple theoretical analysis of the energy-wave vector dispersion relation of the conduction electrons in heavily doped non-parabolic semiconductors forming band tails. We observe that the complex energy spectrum in doped small-gap materials whose unperturbed conduction band is described by the three band model of Kane is due to the interaction of the impurity atoms in the tail with the spin-orbit splitting constant of the valence band (Δ), For band-gap (E_g)<Δ the imaginary part predominates which tails in to the conduction band. For the opposite inequality the real part comes in to play which tails in to the split-off band. In the absence of the band tailing effect, the imaginary part of the complex energy spectrum vanishes and the same is also true for doped two-band Kane-type and parabolic energy bands respectively. The present formulation helps us in investigating the Boltzmann transport equation dependent transport properties of degenerate semiconductors and are expected to agree better with experiments. The well-known results of unperturbed three and two band models of Kane together with wide-gap parabolic energy bands have been obtained as special cases of our generalized analysis under certain limiting conditions.     

On the multipole structure of exchange dispersion energy in the interaction of two helium atoms

The exchange dispersion energy for the interaction of two helium atoms is expressed as a sum of multipole components. In contrast to the analogous expansion for the dispersion energy the derived series converges very slowly and the rate of convergence does not improve with an increasing interatomic distance. Numerical calculations show that at the van der Waals minimum the first term of the series, referred to as dipole-dipole exchange energy, represents merely 17 per cent of the exchange dispersion energy. Moreover, even the inclusion of dipole-quadrupole and quadrupole-quadrupole terms can account for only half of the total exchange dispersion interaction. The above difficulty can be avoided by expanding the dispersion pair function in terms of ionic type or explicitly correlated functions.     

The contribution of the central region of the electron energy spectrum to the total double photoionization cross section of helium in the asymptotic nonrelativistic energy region

The double photoionization of helium at high photon energies is considered using a nonrelativistic approach. The central region of the energy spectrum and its contribution to the total process cross section and to the ratio between the double and single ionization cross sections are studied. Interelectronic interaction in the initial state is included exactly, whereas the interaction between the fast outgoing electrons is calculated by perturbation theory. A detailed derivation of the expression for the cross section ratio between double and single ionizations is given. The corresponding results obtained by other authors are analyzed and corrected.     

On the electronic energy spectrum of linear models for disordered systems

In this paper the basic relations for describing the electronic structure of linear models for monatomic and diatomic disordered systems are derived using a F.E.N. theoretical approach. Elegant three terms recurrence formulae between the wavefunctions at three successive atomic sites are established and their relation is discussed with recurrence formulae obtained previously by means of Green's function techniques.