Ne(I) spectral lines from a Ne-O2 d.c. glow discharge

Measurements have been made of intensities of the spectral lines emitted from an Ne-O₂ d.c. discharge with small discharge current (1–4 mA) under the following conditions: gas pressures of 2 and 3 torr and oxygen partial pressures (P₀₂) up to 0.1 torr. All of the Ne(I) line intensities observed decrease when O₂ is added. The Ne(I) λ5852 line (1s₂-2p₁) has been studied in detail as a representative example. The population density of the 2p₁ level of neon has been obtained from the intensity measurements as a function of P₀₂. The energy-distribution function of electrons has been determined using Druyvesteyn's method in order to calculate the population density for a corona model. The high-energy tail of the measured distribution function is markedly reduced when O₂ is added. It is shown that inelastic collisions of electrons with O₂ produce large energy losses for the electrons. These cause a decrease in population density of the 2p₁ level when O₂ is added. The population density of the 2p₁ level at a gas pressure of 2 torr is 1.2×10⁴ cm^-3 in pure neon and 5.2×10² cm^-3 in an Ne-O₂ mixture (P₀₂ = 0.01 torr). The electron densities and average electron energies are 3.5×10⁸ cm^-3 and 8.7 eV and 1.7×10⁸ cm^-3 and 5.3 eV, respectively, for the specified two cases.     

Nature of the stable oxide layer formed on an aluminum surface by work function measurements

The interaction of oxygen with clean aluminum results in formation of a stable oxide layer on the surface of the metal. This stable layer has a lower work function than that of clean aluminum. The nature of this stable layer is studied by measurement of work function changes. Heating of the stable layer, formed at room temperature and low oxygen pressures' (~10^?8 torr), in ultra-high vacuum resulted in a further decrease in the work function. The extent of this additional decrease was a function of temperature and the changes in work function caused by heating were irreversible in nature. At high oxygen pressures (p_O2 > 10^?2 torr) the effect of growth of incorporated oxide on the net limiting work function change appears to be small and the reversible changes in the work function are mainly a result of the variation in the amount of surface oxide. At 250°C, the contribution of incorporated oxide to net limiting work function change was dependent on oxygen pressure when it was formed at low oxygen pressures (P < 10^?7 torr). However, when the incorporated oxide was formed at oxygen pressures above 10^?7 torr, its contribution to the limiting work function change and, perhaps, the structure of the incorporated oxide itself were nearly independent of oxygen pressure. The difference in limiting work function change at various oxygen pressures was mainly because of the difference in the limiting amounts of surface oxide. Similar behavior is expected at room temperature.     

Influence of collisions and pulse intensity on multiple photon absorption in SF6

Using a pyroelectric detector, the multiple photon absorption (MPA) of the SF₆ molecule in a wide range of pressures (10^-3 -1 torr) has been studied. The significant role of collisions in MPA has been shown. The fraction of molecules excited under essentially collisionless conditions has been defined. It is shown that under collisionless excitation of SF₆ (p < 10^-2 torr) at energy fluences E < 10^-1 J/cm² the intensity of the laser pulse plays the essential role, while in presence of collisions MPA is determined mainly by the energy fluence in the pulse.     

Eine Modellvorstellung für das „Auroral Afterglow“ und das „Pink Afterglow“

Based on own measurements of the decay of light intensity and electron density, a simple model for the auroral afterglow and the pink afterglow is proposed. To a certain extent the model can account for the influence of pressure and tube diameter on the behaviour of the afterglow. The first decay of the electron density towards the first minimum seems not to be influenced by creation processes for electrons during 3 to 15 ms. Therefore, the first decay can be used to measure the neutralization processes of electrons and positive ions. At pressures lower than 3 torr the electrons are removed by ambipolar diffusion with a rate given byD _a ·p≈2100 torr·cm²·s^?1. From this value an electron temperature of about 7200 °K could be derived. Assuming that ambipolar diffusion will remain the dominant loss process the time dependence of the electron creation rate has been evaluated. At a pressure of 1,75 torr the maximum electron creation rate was 4·10¹² s^?1·cm^?3. At the same time the emission density rate of the first negative bands was found to be 2.7·10¹³ cm^?3 s^?1. During one decay process about five times more electrons are created than the initial number. To explain the proportionality found between the electron density and the emission of the first negative bands, it is assumed that the ions, presumable N ₂ ⁺ -ions, are repeatedly excited to theB ² Σ _u ⁺ -state by metastables.     

Zur O2-Dissoziation in der Gleichstromglimmentladung. Teil I Bestimmung des Dissoziationsgrades mittels der O3-Bildung an gekühlten Oberflächen

The synthesis of ozone on the surface S cooled with liquid nitrogen O + O₂·S→O₃·S[1] was used to measure the concentration of atoms in a flow tube downstream of a d.c. discharge. The flow tube was constructed in the form of a U-tube. The ozone was deposited as a blue liquid film in the neighbourhood of the surface of the liquid nitrogen on the walls of the part of the U-tube, which was connected with the discharge tube. The oxygen atom decay in the U-tube was observed by measuring the production of ozone as the distance between the discharge tube (diameter: 5,2 cm) and the surface of the liquid nitrogen was varied. The decay is first order in atom concentration for the pressures p > 1 torr. But for the pressures below p = 1 torr near by the discharge tube we observed deviations from the law of decay In [O]₀/[O] = k·t for the currents of about i = 100 mA. This effect was attributed to the process From the extrapolation of an ozone production curve atom concentrations in the discharge have been obtained. The transition from the ?H”? form to the ?T”? form (striated, low average electric field) of the discharge [2] caused the dissociation to decrease rapidly. The highest dissociation (10%) was obtained in the ?H”? form at high currents (i = 120 mA) and low pressures (p = 0,60 torr). The yield of atomic oxygen per kilowatt hour of energy was measured as functions of pressure and gas flow rate for i = 100 mA and i = 50 mA.     

Origin of threshold electrons produced in decay of the Xe 4d−1 np resonance

Coincidence spectra of energetic electrons with threshold electrons were measured following photo-excitation of the Xe 4d_3/2, 5/2 → np resonances, in order to investigate the origin of threshold electrons, and the mechanism leading to formation of the Xe²⁺ 5p⁻² and 5s⁻¹5p⁻¹ final states. A two-step decay process was observed in the production of Xe²⁺ 5p⁻²(¹D) following decay of the 7p resonance, where the intermediate state is Xe^+* 5p⁻²(¹S)8p that autoionizes emitting a pseudo-threshold electron. This process was confirmed in a time-of-flight analysis of the coincidence spectra of the energetic electrons with the threshold photoelectrons. It is suggested that a similar two-step process also contributes to the population of excited Xe²⁺ states and is the main origin for the production of threshold electrons in decay of the 4d⁻¹ np resonances.     

Alpha decay of the new isotope172Au

The first observation of the extremely neutrondeficient nucleus¹⁷²Au is reported, produced using the fusion evaporation reaction⁷⁰Ge+¹⁰⁶Cd→¹⁷⁶Hg^* (E_x?64 MeV). Mass separated evaporation residues were implanted into a double-sided silicon strip detector, and the energy and time of subsequent decay events were recorded. The alpha decay of¹⁷²Au was measured with an energy =6860±10 KeV, corresponding to =7020±10 Kev, and a half-life of 4±1 ms. No evidence was seen for a proton decay branch, implying a limit ofb _p ≤ 2 %.     

Study of the 8Be first T = 2 state with 4He + α and 7Li + p initiated excitation functions

In a high resolution study of the ⁴He + α initiated excitation functions in the region of the ⁸Be first T = 2 state, weak resonance excursions have been observed in some reaction channels yielding the total width Γ = 14.7 ± 4.0 keV. No resonance excursion has been observed in the ⁴He + α elastic scattering yielding the branching ratio Γ_α/Γ ≦ 0.003 for the decay of the ⁸Be first T = 2 state into two α-particles. For the decay to the low-lying states of ⁶Li and ⁷Li lower limits of the branching ratio are given. The reinvestigation of the ⁷Li+p initiated excitation functions revealed no resonance anomaly in the region of the ⁸Be first T = 2 state. The upper limit Γ_p/Γ ≦ 0.023 has been derived for the proton decay to the ⁷Li_g.s.. The results are compared with previous measurements and with shell-model calculations.     

Effect of cascading of higher-lying states on a delayed 1s-2p transition after beam-foil excitation of 56 MeV hydrogen-like oxygen and fluorine

The delayed fluorescence of the soft X-ray (1s-2p) transition was observed for H-like ions (O⁷⁺ and F⁸⁺) between 1.3 ns and 20 ns decay time after beam-foil excitation. The delayed X-ray fluorescence was found to decay with at ^Δ power law time dependence. The non-exponential decay is attributed to cascading through higher lying states. We found thatΔ ₀=1.40±0.08 andΔ _F =1.44±0.02 for H-like oxygen and fluorine, respectively. Present results are in fair agreement with the previously reported exponent,Δ ₀=1.5, measured over 3 ns after excitation.     

Identification of Cu(I) and Cu(II) oxides by electron spectroscopic methods: AES,ELS and UPS investigations

The externally prepared black-coloured copper oxide (T? 700 K, P_O2 ? 100 torr) on a Cu(100) surface is identified by electron spectroscopy as CuO. Compared to the red-coloured Cu(I) oxide (in situ oxidation at T ? 400 K, P_O2 ? 0.5 torr, ～ 10⁹ L), the He(I)- excited photoemisson from CuO reveals characteristic shake-up satellites 10–12 eV below E_F and a broadened emission from overlapping oxygen-induced 2p and Cu 3d states. From the AES and ELS results, in correlation with the data from core electron spectroscopy, chemical shifts of Cu 2p, Cu 3s and Cu 3p in CuO to higher binding energy and decreases in binding energy of the oxygen-induced states were deduced. The unoccupied electron states of Cu at 5 and 7.5 eV above E_F — postulated from the ELS results — are preserved in Cu₂O and CuO compounds. Annealing of the Cu(II) oxide at 670 K is accompanied by decomposition into Cu₂O due to the solid-state reaction following the scheme: 2CuO → 1/2 O₂ + Cu₂O.     

Pressure broadening of the NO2 hyperfine multiplet at 93 GHz

Line shapes of the hyperfine NO₂ 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δF=δJ=δN=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10^-5 cm^-1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10^-4 cm^-1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ?10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line.     

Decay rate constants of sputtered vanadium oxide clusters

Results from studying the emission and fragmentation of V _n O _m ^± clusters sputtered from a vanadium surface by Xe⁺ ions at O₂ pressures of P = 4–5 × 10^?3 Pa are presented. The average decay rate constants of V _n O _m ^± clusters for major fragmentation channels are determined. It is shown that the decay rate constants for clusters of similar stoichiometry do not depend on their charge states.     

Spontaneous Raman scattering in atomic thallium vapor

Using a cw argon-ion laser, we have measured the spontaneous Raman scattering cross section, σ_R, and linewidth in atomic thallium vapor. For 4880-Å excitation, σ_R = 1.6 × 10^?27 cm². We observe no pressure broadening of the Raman line at vapor pressures to 100 torr.     

Muon transfer in dµ + H2 collisions

The impact of excited state muon transfer in dμ + H₂ collisions has been investigated. The formation of metastable pdμ^* molecules and their subsequent decay into the pμ (1s) + d channel opens a transfer channel that is otherwise closed at the n=2 level. This mechanism enlarges the fraction of muons arriving to the ground state of the lighter isotope. The resulting ground state population P _1s ^pμ as function of deuterium concentration appears to be in qualitative agreement with recent measurements of the K _α X-ray yield in H₂/D₂ mixtures. This revised version was published online in August 2006 with corrections to the Cover Date.     

Charged-particle decay of 28Si induced by quasi-monochromatic annihilation photons in the GDR

Spectra of protons and alpha-particles, emitted from the giant electric dipole resonance of ²⁸Si excited by quasi-monochromatic photons from in-flight annihilation of accelerated positrons, were measured. Cross sections for six charged-particle decay channels were extracted in the energy region from 16.8 to 25.7 MeV. While the (γ, α₀) cross section is completely statistical in nature, the (γ, p) process was found to have a 65% semidirect component, mainly in the (γ, p₀) and (γ, p₁₊₂) channels.     

On behaviour of the form factor of decay of the 63-1k63-1k63-1kinto the dalitz pair in a region of small invariant masses

Dependence of the decay form factor \(F_{\pi ^0 \to e^ + e^ - \gamma } (s)\) on the invariant mass squared of the Dalitz pairs=(p ₊+p _?)² at smalls is calculated with the use of bound-state wave functions-solutions of a covariant single-time equation for a system of two spinor quarks. A quasipotential of one-gluon exchange and an oscillator potential are chosen as quasipotential.     

Study of the excited states of119Sn by the decay of119g+m In

The decay of^119g+m In to the excited states of¹¹⁹Sn was investigated.¹¹⁹In was produced by the¹²⁰Sn(γ,p)¹¹⁹In reaction on an enriched SnO₂ target. The isomeric transition of 311.25 keV to the¹¹⁹In ground state was observed. In the beta decay of^119m In excited states at 23.9, 920.5, 921.4, 1089.0, 1187.9 and 1249.6keV in¹¹⁹Sn withJ ^π values of 3/2⁺, 3/2⁺, 5/2⁺, 5/2⁺, 3/2⁺ and 1/2⁺ respectively, are fed. In the decay of the¹¹⁹In ground state only the 7/2⁺ level in¹¹⁹Sn at 787.0 keV is fed.     

Pressure broadening of UF6 by argon

Pressure broadening of the R(6) manifold in ν₃ of UF₆ at 628.32 cm^?1 has been measured at pressures of 0–30 torr of Ar in a long-path cell at 199 ± 1 K. We obtain a pressure-broadening coefficient of 9.0 ± 1.5 MHz/torr (FWHM), which corresponds to 7.3 ± 1.2 MHz/torr at 300 K. The UF₆-Ar optical collision diameter is 7.4 ± 0.6 Å; this is larger than the hard-sphere kinetic theory collision diameter of 5.2 Å obtained from the diffusion coefficient and implies rapid rotational relaxation.     

CEMS study on diluted magneto titanium oxide films prepared by pulsed laser deposition

6% ⁵⁷Fe doped titanium oxide films, prepared by pulsed laser deposition (PLD) on sapphire substrate at 650°C under various vacuum conditions, were characterized mainly by conversion electron Mössbauer spectrometry (CEMS). Two magnetic sextets with hyperfine fields 33 and 29 T, and one doublet were observed in the CEMS spectra of TiO₂ films prepared under PO₂ = 10^?6 and 10^?8 torr, which showed ferromagnetism at room temperature, whereas only the doublet of paramagnetic Fe³⁺ species was observed for the film prepared under PO₂ = 10^?1 torr.     

The impact parameter dependence of the K MO X-ray emission in208Pb +208Pb collisions

The emission probabilities for quasimolecular K-x-radiation (K-MOR) have been measured in²⁰⁸Pb +²⁰⁸Pb collisions at 4.3 MeV/u and 4.8 MeV/u as a function of the scattering angle using the particle-photon-coincidence technique. The probabilities exhibit a superposition of two exponential slopes with different fall-off constants. We identify the sharp fall off at very small impact parameters (<60 fm) with the K-MOR contribution from the decay of 1sσ-vacancies. The flatter slope for impact parameters larger than 60 fm is attributed to the radiative decay of holes in 2p _1/2 σ molecular states. In this way, experimental “1sσ-MOR-emission probabilities” could be extracted and compared with theory. For 4.3 MeV/u the1sσ- and 2p _1/2 σ-excitation probabilities could also be determined and have been compared to coupled-channel calculations and to a scaling law for 1sσ excitation.