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.     

Cluster radioactivity in xenon isotopes

Half-life time and branching ratio for cluster decay from various xenon isotopes are studied taking Coulomb and proximity potentials as interacting barrier. Inclusion of proximity potential reduces the height of potential barrier, which closely agrees with the experiments. It is found that⁴He,⁸Be,¹²C and¹⁶O emissions are well within the present upper limit for measurements (T _1/2 10³⁰ s). Our predicted half-life time values lie close to those values reported by Gupta and collaborators based on preformed cluster model (PCM) and also with those values reported by Poenaruet al based on ASAFM. The calculated half-life time shows that⁸Be from¹⁰⁸Xe and¹¹⁰Xe are most favourable for emission (T _1/2 ≈ 10⁸ s). LowestT ^1/2 value for⁸Be emission from¹⁰⁸Xe stress the role of doubly magic¹⁰⁰Sn daughter in cluster decay process. The logarithm of half-life time calculated for⁴He emission from¹¹⁰Xe is −0.39 s which is in good agreement with experimental value which is −0.40 s. Geiger-Nuttall plots for all clusters are studied and are found to be linear. Nuclear structure effect and shell effect are evident from the observed variation in slope and intercept of Geiger—Nuttall plots. It is found that neutron excess in the parent will slow down the cluster decay process.     

Signature inversion in the yrare band of <Superscript>119</Superscript>Xe

Excited states of the ¹¹⁹Xe nucleus have been studied by using in-beam γ-ray spectroscopy with the ¹⁰⁷Ag ( ¹⁶O, p3n) ¹¹⁹Xe fusion-evaporation reaction at a beam energy of 85 MeV. The level scheme of ¹¹⁹Xe has been derived from γ-γ coincidence and γ-γ angular correlation analyses. We have, for the first time, established the second negative-parity favored and unfavored states built on the 11/2^- state, namely the yrare rotational bands in ¹¹⁹Xe. In contrast to the behavior of the yrast bands where the favored states are lying lower in energy, the yrare favored states were observed to lie above the unfavored band. Such a signature inversion in ¹¹⁹Xe is changed to be normal at I = 12?. Received: 8 January 2002 / Accepted: 18 April 2002     

High spin states and evidence for octupole correlations in 117Xe

High-spin states of ¹¹⁷Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of ²⁸Si bombarding a ⁹²Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in ¹¹⁷Xe. The B(E1) values increase with spin. The νd_5/2 band was firmly established up to 27/2⁺ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh_11/2 and νg_7/2 [413]5/2⁺α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and 0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In a γ–γ–t measurement, the 11/2⁻ and 7/2⁻ levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively. Received: 17 June 1997 / Revised version: 29 September 1997     

High resolution spectroscopy of stable xenon isotopes

In this paper we investigate the hyperfine structure and isotope shift of four near infrared xenon transitions by means of a semiconductor diode laser. Doppler free spectra were obtained by using either a saturation spectroscopy technique in cell or a laser induced fluorescence technique on a collimated atomic metastable beam. The hyperfine coupling constants of ¹²⁹Xe and ¹³¹Xe were determined for the levels 1s₅, 1s₄, 1s₄2, 2p₂, 2p₄ and 2p₆ (Paschen notation). Moreover, a systematic study of the isotope shift was performed for the 1s₃ → 2p₄ and 1s₅ → 2p₆ transitions for which all the stable isotopes ^128–131Xe , ¹³²Xe, ¹³⁴Xe, and ¹³⁶Xe were fully resolved. This revised version was published online in August 2006 with corrections to the Cover Date.     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Determination of the cluster spectroscopic factor of the 10.3 MeV state in 12Be

From an inelastic excitation and breakup experiment with a ¹²Be beam at 29 MeV/u, a large ⁴He+⁸He cluster decay width of 1.1(2) MeV is determined for a state at an excitation energy of 10.3 MeV and with a spin parity of 0+. By using the R-matrix analysis, a cluster spectroscopic factor of 0.53(10) is extracted from the cluster partial width, providing a strong support for the clustering structure in ¹²Be. A specially designed zero-degree telescope played an essential role in the present experiment and has been demonstrated to be a promising tool in future studies of the molecular-like resonances near the cluster separation threshold.     

Light-emitting Si nanostructures formed in silica layers by irradiation with swift heavy ions

Thin SiO₂ layers were implanted with 140 keV Si ions to a dose of 10¹⁷ cm⁻². The samples were irradiated with 130 Mev Xe ions in the dose range of 3×10¹²–10¹⁴ cm⁻², either directly after implantation or after pre-annealing to form the embedded Si nanocrystals. In the as-implanted layers HREM revealed after Xe irradiations the 3–4 nm-size dark spots, whose number and size grew with increase in Xe dose. A photoluminescence band at 660–680 nm was observed in the layers with the intensity dependent on the Xe dose. It was found that passivation with hydrogen quenched that band and promoted emission at ∼780 nm, typical of Si nanocrystals. In spectra of pre-annealed layers strong ∼780 nm peak was observed initially. Under Xe bombardment its intensity fell, with subsequent appearance and growth of 660–680 nm band. The obtained results are interpreted as the emission at ∼660–680 nm belonging to the imperfect Si nanocrystals. It is concluded that electronic losses of Xe ions are mainly responsible for formation of new Si nanostructures in ion tracks, whereas elastic losses mainly introduce radiation defects, which quench the luminescence. Changes in the spectra with growth of Xe ion dose are accounted for by the difference in the diameters of Xe ion tracks and their displacement cascades.     

Exotic decay: Transition from cluster mode to fission mode

Exotic decay of some heavy nuclei with Z≥100 formed in heavy ion ‘cold fusion’ reaction were studied taking interacting barrier consisting of Coulomb and proximity potential. Calculated half-life time shows that some modes of decay are well within the present upper limit for measurements (T _1/2<10³⁰ s). Cluster formation probabilities are calculated for different clusters within fission model. It is found that transition from cluster mode to fission mode take place at mass of the cluster, A ₂=20 in exotic decay which is comparable with the value A ₂=16 of Shanmugam et al based on cubic plus Yukawa plus exponential model (CYEM).     

Electronic and geometric structure of doped rare-gas clusters: surface, site and size effects studied with luminescence spectroscopy

The electronic and geometric structure of rare gas clusters doped with rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation spectroscopy in the VUV spectral range. Several absorption bands are observed in the region of the first electronic excitations of the impurity atoms, which are related to the lowest spin-orbit split atomic ³P₁ and ¹P₁ states. Due to influence of surrounding atoms of the cluster, the atomic lines are shifted to the blue and broadened (“electronical cage effect”). From the known interaction potentials and the measured spectral shifts the coordination of the impurity atom in Ar_N, Kr_N, Ne_N and He_N could be studied in great detail. In the interior of Kr_N and Ar_N the Xe atoms are located in substitutional sites with 12 nearest neighbours and internuclear distances comparable to that of the host matrix. In Ne_N and He_N the cluster atoms (18 and 22, respectively) arrange themselves around the Xe impurity with a bondlength comparable to that of the heteronuclear dimer. The results confirm that He clusters are liquid while Ne clusters are solid for N≥ 300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is strong, small Rg_m-clusters (Rg = Xe, Kr, Ar, m≤10 ²) are formed in the interior sites of the host cluster made of Ne or He. Specific electronically excited states, assigned to interface excitons are observed. Their absorption bands appear and shift towards lower energy when the cluster size m increases, according to the Frenkel exciton model. The characteristic bulk excitons appear in the spectra, only when the cluster radius exceeds the penetration depth of the interface exciton, which can be considerably larger than that in free Rg_m clusters. This effect is sensitive to electron affinities of the guest and the host cluster.     

Ion beam induced atomic mixing in Fe/Al bilayered samples

Atomic mixing of Fe/Al bilayered samples induced by an energetic xenon beam has been studied by RBS-TEM and sheet resistivity measurements. Mixing is detected at 2.5 × 10¹⁵ Xe/cm² and then proceeds up to 2 × 10¹⁶ Xe/cm². A blocking effect of the mixing for larger doses is observed. Homogeneous concentration is not obtained across the sample. Instead a pronounced graded composition is reached. Several explanations of the mixing process and the subsequent blocking effect are suggested: — sharp gradients in the nuclear energy deposition profile which decrease with dose — grain growth phenomena — precipitation of crystalline xenon acting as efficient annihilation sinks for vacancies.     

Experimental evaluation of the gas-phase collision cross-section of effusive Au beam with noble gases: The effect of size and flux

We find that the effusive atomic beam of Au atoms is deflected away by collision with noble gas atoms crossing in a perpendicular geometry with a beam flux of >1 × 10¹⁶/cm²s. The ratio of defected Au atoms is found to increase proportional to the flux of noble gases. In addition, the effective cross-section for the collision between Au and noble gases (Ne, Ar, Xe) is measured to increase in an order of Ne < Ar < Xe. As a result of the increased collision probability, the deflection ratio of Au beam in the noble gases is measured to be enhanced for the Au flux in the range of 1 × 10¹¹–10¹³ Au/cm²s. Our results show that the gas-phase collision can be reliably determined by measuring the deflection ratio. The experimentally determined collision cross-section also explains the variation in the deflection ratio among various noble gases and the importance of a long-range van der Waals interaction between Au and noble gases in the deflection efficiency.     

Negative ions in liquid xenon

The structure and mobility of negative ions of oxygen in liquid Xe is investigated. It is shown that the strong exchange interaction of the outer, weakly bound electron of the negative ion with the surrounding liquid leads to a partial compensation of the electrostriction effect, and it prevents the formation of a solid cluster around the negative ion. A simple perturbative model describing the structure of the negative ion in the liquid matrix is developed. The mobility of O ₂ ⁻ ions in liquid Xe on the saturation line is estimated. The reasons for the difference in mobility of negative and positive ions are discussed. Zh. éksp. Teor. Fiz. 115, 584–592 (February 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Dynamics of an electron beam from a high-current picosecond accelerator

The dynamics of a high-current (10²–10⁴ A) electron beam with energies of 10⁵–10⁶ eV and picosecond duration (10⁻¹⁰ s) at the output of the accelerator tube is investigated. The slowing of electrons by the residual positive charge on the surface of the tube is found to have a significant influence in the case of short pulse durations. The distance of the electron beam from the surface of the tube in vacuum is estimated on the basis of a one-dimensional model. It is shown that the electron radiation can travel to a distance of several centimeters from the surface at current densities below 20 A/mm², whereas at high current densities the beam is trapped near the surface. Zh. Tekh. Fiz. 69, 111–115 (May 1999)     

Using frequency-narrowed,tunable laser diode arrays with integrated volume holographic gratings for spin-exchange optical pumping at high resonant fluxes and xenon densities

Next-generation laser diode arrays with integrated ‘on-chip’ volume holographic gratings can provide high power with spectrally narrowed output that can be tuned about the rubidium D₁ line—without causing significant changes to the laser’s flux or spectral profile. These properties were exploited to independently evaluate the effects of varying the laser centroid wavelength and power on batch-mode Rb/¹²⁹Xe spin-exchange optical pumping (SEOP) as functions of xenon partial pressure and cell temperature. Locally optimized SEOP was often achieved with the laser tuned to either the red or blue side of the Rb D₁ line; global optimization of SEOP was observed at lower cell temperatures and followed the D₁ absorption profile, which was asymmetrically broadened and red-shifted from the nominal wavelength. The complex dependence of the optimal wavelength for laser excitation on the cell temperature and Xe density appears to result from an interplay between cell illumination and the Rb/¹²⁹Xe spin-exchange rate, as well as [Xe]_cell-dependent changes to the Rb absorption lineshape that are in qualitative agreement with expectations based on previous work [Romalis et al., Phys. Rev. A, 56:4569–4578, (1997)], but significantly greater in magnitude. These next-generation lasers provide a ∼2–3-fold improvement in ¹²⁹Xe polarization compared to conventional broadband lasers.     

High-intensity and high-brightness source of moderated positrons using a brilliant γ beam

Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 10¹⁵ photons s⁻¹, as ultimately envisaged for an ERL-based γ-beam facility, narrow band width (10⁻³), and extremely low emittance (10⁻⁴ mm² mrad²) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×10¹³ (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive ²²Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×10¹¹ moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity would exceed that of present high-intensity positron sources by a factor of 100.     

Total rates of nuclear capture of negative muons in the isotopes 132Xe and 40Ar

The lifetimes of a negative muon in the isotopes ¹³²Xe and ⁴⁰Ar in the solid phase are measured. The lifetime of μ ⁻ in the 1s state of the isotope ¹³²Xe is τ(¹³²Xe)=101.7±1.7 ns, which corresponds to a total nuclear capture rate Λ_c(¹³²Xe)=9.4±0.2 μs⁻¹. The lifetime of μ ⁻ in the isotope ⁴⁰Ar, viz., τ (⁴⁰Ar)=568±6 ns, corresponding to a capture rate Λ_c(⁴⁰Ar)=1.31±0.01 μs⁻¹, is obtained to several times better accuracy as compared to previously published results. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 181–183 (10 February 1999)     

Production of relativistic antihydrogen atoms by pair production with positron capture and measurement of the Lamb shift

A beam of relativistic antihydrogen atoms — the bound state ( e⁺) — can be created by circulating the beam of an antiproton storage ring through an internal gas target. An antiproton which passes through the Coulomb field of a nucleus will create e⁺e⁻ pairs, and antihydrogen will form when a positron is created in a bound instead of continuum state about the antiproton. The cross section for this process is roughly 3Z ² pb for antiproton momenta about 6 GeV/c. A sample of 600 antihydrogen atoms in a low-emittance, neutral beam will be made in 1995 as an accidental byproduct of Fermilab experiment E760. We describe a simple experiment, Fermilab Proposal P862, which can detect this beam, and outline how a sample of a few-10⁴ atoms can be used to measure the antihydrogen Lamb shift to 1 %. Work supported in part by Department of Energy contract DE-AC03-76SF00515 (SLAC). Work supported by Fondo Nacional de Investigación Científica y Tecnológica, Chile.