Emission of cadmium excited ions upon α particle bombardment

Ion emission due to the sputtering of metallic cadmium by α particles from ²³⁸Pu is studied. Experiments are carried out in helium at different cadmium foil temperatures (from 20 to 280°C) and gas pressures (from 75 to 2200 torr). The sputtering of the metallic cadmium causes the emission of Cd(II) excited ions in the 4d ⁹5s ²² D _{3/2, 5/2} and 4d ¹⁰6s ² S _1/2 states. Above 160°C, the population of these stares grows exponentially. At a temperature of 240°C and a helium pressure in the chamber of 600 torr, the sputtering ratio of metallic cadmium is found to be 6.26×10⁻¹⁴ g per α particle; i.e., one α particle knocks out about 10⁸ cadmium atoms from the foil. From spectroscopy and microphotography examinations of the metallic sample surface, a two-step model of ion emission is suggested. The model involves (1) the formation of a high-temperature wedge, which ejects a cadmium droplet, and (2) self-diffusion of displaced cadmium atoms in the droplet toward the surface.     

Influence of Ar, Ne, Xe, and CCl4 impurities on luminescence kinetics of Cd II ions (5s22D5/2-5p2P3/2 transition, λ = 441.6 nm) in He-Cd mixture

The luminescence kinetics of the Cd II ion at a wavelength of 441.6 nm has been studied experi-mentally in a high-pressure He-Cd mixture in the presence of Ar, Ne, Xe, and CCl₄ impurities. Cadmium ions were excited through the bombardment of a cadmium foil heated up to 240°C by a pulsed electron beam with an electron energy of 150 keV, a pulse duration of 3 ns, and a current of 500 A. The constants of collisional quenching of the Cd II 5s ^{2 2} D _5/2 level by Ar, Ne, and Xe atoms and CCl₄ molecules and the integral luminescence quenching constants of this level in the helium medium by these impurity gases have been determined. The constants of collisional quenching appeared to be 8.1 × 10⁻¹² (Ar), 1.2 × 10⁻¹² (Xe), 1.5 × 10⁻¹³ (Ne), and 1.8 × 10⁻¹⁰ cm³/s (CCl₄, for λ = 325 nm), while the integral constants were found to be, respectively, 4.1 × 10⁻¹¹, 3.4 × 10⁻¹¹, 9.5 × 10⁻¹², 1.4 × 10⁻⁹ cm³/s for Ar, Ne, Xe, and CCl₄ at a buffer gas pressure of 1 atm. Original Russian Text ? A.I. Miskevich, Liu Tao, 2009, published in Optika i Spektroskopiya, 2009, Vol. 107, No. 1, pp. 45–49.     

Optical properties of laser-produced plasmas from Cd and layered crystalline CdAl2Se4 targets

An experimental investigation into emission by plasmas from Cd and crystalline CdAl₂Se₄ targets irradiated with a pulse-periodic YAG: Nd³⁺ laser is presented. The laser operates at a pulse width of 20 ns and provides 1−2×10⁹ W/cm² at the focus. The spectral and time characteristics of the emission are examined. The main findings are as follows: (1) The strongest lines correspond to the transitions from the 6³ S ₁ and 5³ D ₂ levels of Cd I. (2) With the Cd target, the recombination bottlenecks are 5² D _5/2 of Cd II (E _up=20.11 eV) and 8³ D _{1, 3} of Cd I (E _up=8.60–8.65 eV). (3) The average electron temperature outside the core of the plume is 0.64 eV. (4) For the 508.6-nm line of Cd I, the high filling rate of the 6³ S ₁ upper energy level may be related to the rapid recombination of cadmium ions with electrons via the intermediate levels of Cd⁻ at 6.82 and 7.24 eV.     

Equation of state of fluid helium at high temperatures and densities

Helium, hydrogen, and their isotopes are the simplest monoatomic and diatomic molecules. It is relatively easy to describe their properties using the basic principles of quantum mechanics. In condensed matter physics, hydrogen and helium serve as the models for the condensed matter properties at extreme conditions so that both experi- mental and theoretical physicists pay much attention to the study of their properties[1], especially the insulator-metal transition of hydrogen[2]. The aim to st…     

Equation of state of fluid helium at high temperatures and densities

Hugoniot curves and shock temperatures of gas helium with initial temperature 293 K and three initial pressures 0.6, 1.2, and 5.0 MPa were measured up to 15000 K using a two-stage light-gas gun and transient radiation pyrometer. It was found that the calculated Hugoniot EOS of gas helium at the same initial pressure using Saha equation with Debye-Hückel correction was in good agreement with the experimental data. The curve of the calculated shock wave velocity with the particle velocity of gas helium which is shocked from the initial pressure 5 MPa and temperature 293 K, i.e., theD ≈u relation,D=C ₀+λu (u<10 km/s, λ=1.32) in a low pressure region, is approximately parallel with the fittedD ≈u (λ=1.36) of liquid helium from the experimental data of Nellis et al. Our calculations show that the Hugoniot parameter λ is independent of the initial density p{in0}. TheD≈u curves of gas helium will transfer to another one and approach a limiting value of compression when their temperature elevates to about 18000 K and the ionization degree of the shocked gas helium reaches 10⁻³.     

Measurement of electric field strengths in a waveguide by means of the dynamic Stark effect in hydrogen and neutral helium spectral lines

The dynamic Stark effect of the spectral lines H_β and of the neutral helium lines λ=402.6 nm (2³ P ⁰−5³ D) and λ=438.8 nm (2¹ P ⁰−5¹ D) emitted from a discharge tube was used for probing rf electric fields in a transverse waveguide. Calculations accounting for the pertubation of the atomic states by strong unidirectional fields prove to be suitable in order to interprete the main experimental results. If the waveguide is terminated with a metallic reflector and the plasma in the discharge tube becomes overdense—then representing a slightly permeable mirror—a resonant enhancement of the electric field strength may be achieved by tuning. This enhancement is well recognizable in the spectral line contours.     

Mass-spectrometric analysis of diffusion and solubility of helium in cerium-gadolinium ceramics with a submicrocrystalline structure

Diffusion and solubility of helium in Ce_0.8Gd_0.2O_{1.9 − δ} ceramics (δ = 0, 0.015) with a submicrocrystal structure are studied by thermodesorption of helium from preliminarily saturated (in the gas phase) crystals at temperatures of 613 and 673 K in the saturated pressure range 0–21 MPa. It is shown that, in this ceramics (δ = 0), the defect-trap diffusion mechanism operates. The main positions for dissolution are neutral anion vacancies formed as a result of thermal dissociation of impurity-vacancy complexes and saturated up to ∼1 × 10¹⁹ cm⁻³ at P = 6 MPa and T = 673 K. The dissociation energy of the complex and the energy of helium dissolution in the neutral anion vacancy are estimated at ∼2 eV and below −0.3 eV, respectively.     

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.     

Decay rate measurements of upper laser level in He-Cd+ laser

The decay rate of² D _5/2 level of Cd II has been measured by the magnetic-field power-dip method. The decay rate at the zero-pressure limit is found to be 2.4·10⁶s⁻¹. The calculated collision cross section for excited Cd ions with He atoms equals 0.91·10⁻¹⁵ cm². This work was supported by the Institute of Quantum Electronics. WAT Warszawa, within the project 06.2.3.     

Monitoring of all hydrogen isotopologues at tritium laboratory Karlsruhe using Raman spectroscopy

We have recorded Raman spectra for all hydrogen isotopologues, using a CW Nd:YVO₄ laser (5 W output power at 532 nm) and a high-throughput (f/1.8) spectrograph coupled to a Peltier-cooled (200 K) CCD-array detector (512 × 2048 pixels). A (static) gas cell was used in all measurements. We investigated (i) “pure” fillings of the homonuclear isotopologues H₂, D₂, and T₂; (ii) equilibrated binary fillings of H₂ + D₂, H₂ + T₂, and D₂ + T₂, thus providing the heteronuclear isotopologues HD, HT, and DT in a controlled manner; and (iii) general mixtures containing all isotopologues at varying concentration levels. Cell fillings within the total pressure range 13–985 mbar were studied, in order to determine the dynamic range of the Raman system and the detection limits for all isotopologues. Spectra were recorded for an accumulation period of 1000 s. The preliminary data evaluation was based on simple peak-height analysis of the ro-vibrational Q₁-branches, yielding 3σ measurement sensitivities of 5 × 10⁻³, 7 × 10⁻³, and 25 × 10⁻³ mbar for the tritium-containing isotopologues T₂, DT, and HT, respectively. These three isotopologues are the relevant ones for the KATRIN experiment and in the ITER fusion fuel cycle. While the measurement reported here were carried out with static-gas fillings, the cells are also ready for use with flowing-gas samples.     

Fast electron energy deposition in aluminium foils: Resistive vs. drag heating

The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 10¹⁹ Wcm^-2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (T _h ^tail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (T _h ^bulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2ω₀ emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under 10¹² Acm^-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 μm depth.     

Quenching of photoconductivity by a strong electric field in tin δ-doped GaAs structures

The conductivity of GaAs structures δ-doped with tin on the vicinal and singular faces was investigated in strong electric fields up to E=10⁴ V/cm and temperatures in the range 4.2 K <T<300 K. The measurements were performed in the dark and under illumination with visible light. Long-time photoconductivity of 2D electrons with threshold T _c ≈240 K was observed in samples which were δ-doped with tin on the vicinal face. A strong electric field not only quenches photoconductivity, but also increases the resistance of the structures at temperatures T<T _c by several orders of magnitude with respect to the dark resistance. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 326–330 (10 March 1996)     

Pressure dependence of the superconducting state parameters of metallic glass superconductor Mg70Zn30

Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ^*) considering the variation of Fermi momentum (κ _F) and Debye temperature (θ _D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (T _C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N ₀ V) for metallic glass superconductor Mg₇₀Zn₃₀. It has been observed that T _C of the metallic glass Mg₇₀Zn₃₀ decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ^* curve shows a minimum and an elbow is formed in the Φ graph.     

Mass-spectroscopic study of the diffusion and solubility of helium in submicrocrystalline palladium

By the method of helium thermal desorption from submicrocrystalline palladium presaturated in the gaseous phase, the diffusion coefficient D _eff and solubility coefficient C _eff of helium are measured in the range P=0–3 MPa and T=293–508 K. The pressure dependence of C _eff flattens at high pressures. At low saturation pressures, the temperature dependences of the diffusion and solubility coefficients may be divided into (1) high-temperature (400–508 K) and (2) low-temperature (293–400 K) ranges described by the exponentials D _{1, 2}=D ₀exp (−E _{1, 2} ^D /kT) and C _{1, 2}=C ₀exp (−E _{1, 2} ^S /kT). The energies of diffusion activation are E ₂ ^D =0.0036±0.0015 eV and E ₁ ^D =0.33±0.03 eV, and the solution energies are E ₂ ^S =−0.025±0.008 eV and E ₁ ^S =0.086±0.008 eV in the low-and high-temperature ranges, respectively. Mechanisms behind the diffusion and solution of helium are discussed.     

Measurement of atomic parameters for the3 D 1 state of I–II

The decay rates of the³ D ₁ level of I–II and the 3s ₂ level of neon have been measured by the magnetic-field power dip method. The decay rate at the zero-pressure limit is found to be 7.1 MHz/2π for the³ D ₁ level. The collision cross-section for excited I ions with helium atoms equals 0.19×10⁻¹⁵ cm². This work was supported by project MR-1.5-1.05.     

Constants of quenching of 5s 22 D 5/2, 3/2 CdII levels by argon

Constants of quenching of the CdII ion Beutler levels by argon were experimentally determined. Excited cadmium ions in the 5s ^{2 2} D _{5/2, 3/2} states were produced by sputtering metal cadmium with alpha-particles at a temperature of 240°C. The quenching constants for the 5s ^{2 2} D _5/2 and 5s ^{2 2} D _3/2 CdII ion levels were found to be 1.3×10^?10 and 1.8×10^?10 cm³ s^?1, respectively.     

Anisotropy of the transport properties of single-crystal Bi2 Te3 disordered by electron bombardment

Using single-crystal samples of Bi₂Te₃ bombarded by 5-MeV electrons at a temperature of 250 K, we study the electrical resistivity and the Hall effect in the temperature range 1.7–370 K and the Shubnikov-de Haas effect at T=4.2 K in magnetic fields up to 14 T. We find that electron bombardment of Bi₂Te₃ crystals results in a transition from the metallic p-type state to the metallic state with a Fermi surface. Annealing at 350 K eliminates the radiation defects and restores the p-type metallic conductance. Zh. éksp. Teor. Fiz. 113, 1787–1798 (May 1998)     

Effect of gas pressure on amplitude and duration of electron beam current in a gas-filled diode

The parameters of an electron beam generated in helium in the pressure range p = 10⁻⁴−12 atm are studied. Nanosecond high-voltage pulses are applied to a gap between a tubular cathode and planar anode, which is made of 45-μm-thick AlBe foil. Behind the anode, an electron beam is detected at a helium pressure of 12 atm. The pressure dependence of the beam current amplitude shows three peaks at p ≈ 0.01, ≈ 0.07, and ≈ 3 atm. The beam-induced glow of a luminescent film placed behind the foil and the discharge glow at different helium pressures in the gas-filled diode are photographed.     

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. II. HD,D2, T2–He mixtures

The comprehensive comparison between calculated bulk non-equilibrium properties of hydrogen–helium isotopomeric mixtures and experiment that has previously been carried out for H₂–helium mixtures [2004, Molec. Phys., submitted] has been extended to mixtures of HD, D₂ and T₂ with ³He and ⁴He. For HD–⁴He mixtures, comparison is also made, where possible, with previous calculations of Köhler and Schaefer [1983, Physica A, 120, 185]. The phenomena examined herein include low temperature interaction second virial coefficients, binary diffusion and thermal conductivity coefficients, rotational relaxation, transport property field effects and flow birefringence. Scattering calculations have been carried out for the HD–He PES of Schaefer and Köhler [1985, Physica A, 129, 469], and for both the Köhler–Schaefer and Tao [1994, J. chem. Phys., 100, 4947] potential surfaces for the D₂–He and T₂–He interactions. Comparisons between calculated and experimental results for HD, D₂, T₂–He mixtures confirm the conclusion, reached earlier from the H₂–He comparisons, that these potential surfaces are very close to the correct one for the hydrogen–helium interaction, and that the small differences between them cannot be distinguished readily by measurements of bulk gas phenomena unless the attendant experimental uncertainties are better than ±0.3%.     

First results for the measurement of double-electron capture of 106Cd in the experiment TGV II

Present status of the experiment TGV II which is devoted to the measurement of double-beta decay of ¹⁰⁶Cd is given. The low background spectrometer TGV II is installed in the Modane Underground Laboratory and has been running from February 2005 with approx 10 grams of ¹⁰⁶Cd enriched at 75%. After an analysis of 3736 hours of experimental data the new improved half-life limit for 2νEC/EC decay of ¹⁰⁶Cd (0 _g.s. ⁺ → 0 _g.s. ⁺ ) is given as T ₁ ^2/2ν > 4.8 × 10¹⁹ years (90% CL). The search for 2νEC/EC decay of ¹⁰⁶Cd to the excited states of ¹⁰⁶Pd allows to determine the limits of the half-lives T ₁ ^2/2ν (0 _g.s. ⁺ → 2 ₁ ⁺ ) > 3.9 × 10¹⁹ years (90% CL) and T ₁ ^2/2ν (0 _g.s. ⁺ → 0 ₁ ⁺ ) > 5.8 × 10¹⁹ years (90% CL). Presented by I. Štekl at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.