We report accurate measurements of excess electron mobility in high-density Ar gas at a temperature T 163 K in the density range (4 & N & 70) x 10 cm as a function of the electric-field strength. The positive-density efFect shown by the zero-field density-normalized mobility p, oN can be explained within the same theoretical framework recently used for neon gas, where p,oN shows a negative-density effect. Thus the analysis of our present measurements indicates that there is no need for two separate theories for both negative-and positive-scattering-length gases.PACS number(s): 51.50+v, 52.25 Fi

In liquid helium, an electron is surrounded by a cavity called an electron bubble of 20 Ångstroms in diameter. A positive helium ion is solvated by an electrostriction induced solid helium-ice shell called a snowball of 7 Ångstroms in diameter. By studying their transport properties, these objects are well suited for the testing of the microscopic properties of superfluidity. At low temperatures and with small electric fields, the drift velocity of the charges depends on their interaction with the elementary excitations of the superfluid: phonons, rotons, and 3He atomic impurities. At higher fields, ions produce quantized vortex rings and vortex lines and studying these sheds light on quantum hydrodynamics. In the fermionic liquid, the 3He isotope ion transport properties display important pieces of information on the coupling of a charge to a Fermi liquid and on the richer topological structure of the superfluid phases appearing at ultralow temperatures. In the normal liquid phases of both isotopes, ions and electrons are used to probe classical hydrodynamics at the λ-transition and at the liquid-vapor transition at which long-range critical fluctuations of the appropriate order parameter occur. Several experiments have investigated the structure of electron bubbles. Electron drift velocity measurements in dense helium gas have elucidated the dynamics of electron bubble formation. This book provides a review of the more than forty-year-long experimental and theoretical research on the transport properties of electrons and ions in liquid and gaseous helium.

No abstract

The electron drift mobility has been measured in a wide range of temperatures and densities in neon gas and saturated vapor. The "zero-Geld" density-normalized mobility poS exhibits a strong density dependence, which cannot be accounted for by the existing multiple-scattering theories. The data, however, can be well 6tted by assuming a density dependence in the e-Ne scattering cross section.

We report experimental results of proton- and electron-beam-induced near-infrared fluorescence in high-pressure Xe gas and in a 90% Ar–10% Xe gaseous mixture at room temperature. The investigated wavelength band spans the range 0.7⩽λ⩽1.8 μm. In the previously unexplored range for λ⩾1.05 μm we have detected a broad continuum near-infrared fluorescence centered at λ≈1.3 μm. The continuum shifts towards longer wavelengths as pressure is increased up to 1.5 MPa. The shift is quantitatively different in pure Xe or in the mixture, but qualitatively similar. We believe that this continuum is produced by a bound-free Xe2 excimer transition in a way similar to the well-known first and second vacuum ultraviolet continua of noble gas excimers. The pressure-dependent shift can then be explained by the interaction of the outer electron in the excimer with the atoms of the host gas