Excitation of autoionizing states of helium-like ions by scattering of high-energy particles

The cross sections for two-electron excitations of helium-like atomic systems into the autoionizing 2s ² (¹ S)- and 2p ² (¹ S)-states by collisions with high-energy electrons and photons are deduced. The evaluations are performed to the leading order of non-relativistic perturbation theory. The analytical formulas for cross sections are obtained in the form of universal scalings. A comparison of our theoretical predictions with available theoretical and experimental results for the helium atom is made.     

Energy loss of heavy ions in carbon foils

The energy loss of Ar, Ti, Kr, Xe, Pb and U ions in the energy range from 0.2 to 1.4 MeV/amu in carbon foils was measured. The results are compared with theoretical and semiempirical estimations.     

Energy distributions of ions produced by electron-stimulated desorption

We have measured the initial kinetic energy distributions of ions produced by electron bombardment of various oxides and halides. The instrument used allows ions directly ejected from the sample surface to be distinguished from ions formed by electron impact in the gas phase. Singly and multiply charged positive ions of species present in the matrix as anions and cations were desorbed by high energy ( 11 keV) electron impact. Directly desorbed positive halogen ions show a narrow, low energy peak, consistent with conventional models of electron stimulated desorption (ESD). In addition, some of the cation species exhibited similar narrow energy spectra. Charge states up to +6 were observed for the halides; with the exception of F²⁺ and Cl²⁺, multiple charge states were due to electron impact ionization of desorbed neutrals. Charge states up to +4 were seen for silicon from electron-bombarded SiO₂; energy distributions of Si⁺, Si²⁺ and Si³⁺ showed that these species were desorbed directly from the surface. The energy distributions of O⁺ and O²⁺ ions ejected from SiO₂ are relatively wide, compared to the energy distribution of Si⁺ ions. In contrast, O⁺ ions ejected from TiO₂ have a much narrower energy distribution, like those observed for the halogen ions.     

Angular momentum transfer in nucleon exchange scattering of heavy ions

The elastic scattering of ¹⁶O on ¹⁷O has been measured at E_lab = 24, 28 and 32 MeV and θ_c.m. = 90° ?150°. At large energy the cross section exhibits a structureless rise at backward angles which can be described consistently with the DWBA approach for the elastic transfer.     

Angular momentum transport produced by shear flow driven drift waves in a collisional magnetoplasma

A shear flow instability in a nonuniform partially ionized magnetoplasma has been investigated and the angular momentum transport of charged particles caused by drift waves has been estimated. The angular momentum transport of the electrons and ions is not equal because the system is not conservative. The present investigation should help to understand the origin of fluctuations and associated parallel momentum transport of charged particles in nonuniform laboratory and astrophysical plasmas with sheared ion flow.     

Angular distributions in the photoelectron spectroscopy of carbon monoxide

The angular distributions of the photoelectron intensity for CO have been investigated using a photoelectron spectrometer that has a rotatable detector and an HeI light source. The asymmetry parameter β was carefully measured for 24 vibrational transitions spanning three ionization bands. Its variation with final-state vibrational quantum number was found to have an unusual behavior. It is concluded that an autoionizing state of CO should exist at 584 Å in order to account for this behavior, and that the value of β is very sensitive to the presence of such a state.     

Rapidity and transverse momentum distributions of heavy quarks produced by double pomeron exchange

Zeitschrift für Physik C Particles and Fields - Rapidity and transverse momentum distributions of heavy quarks produced by double exchange of Donnachie-Landshoff pomeron are presented and...     

Angular distributions of muon pairs produced by negative pions on deuterium and tungsten

We present the angular distributions of high-mass muon pairs produced in a high-statistics experiment by 140 and 194 GeV/c π^? beams impinging on a tungsten target, and by 286 GeV/c π^? beam on deuterium and tungsten targets. We find no evidence for a center-of-mass energy dependence or a nuclear dependence of the angular distribution parameters. The two parameters λ and μ are found to be essentially independent of any kinematical variable. In contrast, the parameterv increase with the dimuon transverse momentumP _T , at variance with recent perturbative QCD predictions. Our statistics at largex ₁ are insufficient to substantiate the highertwist prediction.     

Angular distributions of muon pairs produced by 194 GeV/c negative pions

We present the angular distributions of muon pairs obtained in a high-statistics experiment using a 194-GeV/c π^- impinging on a tungsten target. Our results are based on the analysis of 145,000 events with positive Feynmanx and mass above 4.07 GeV/c², excluding the ? region. Simple first-order QCD relations allow us to determine the ratio of annihilation with hard-gluon emission to the sum of annihilation with hard-gluon emission and hard-gluon Compton scattering, which is found to be about 58% to 75%. We determine the parton square intrinsic transverse momenta to be of the order of 0.6 (GeV/c)², and about 30% larger in the pion than in the nucleon. At largex ₁, our data agree with the higher-twist hypothesis, and support the interpretation of the relevant scale parameter as the dimuon square transverse momentum.     

Evaluation of carbon stripper foils produced by a nitrogen ion beam sputtering method

Carbon stripper foils having thicknesses in the range of 5–40 μg/cm² have been prepared by a nitrogen ion beam sputtering method and their lifetimes have been tested in the Van de Graaff accelerator facility with 3.2 MeV, Ne⁺ ions. The foils of 21 μg/cm² thickness had the longest mean lifetime of 1350.0 mC/cm² (irradiation dose of 8.4×10¹⁸ atoms/cm²) which was 50 times longer than that of commercial foils. However, foils with other thicknesses had extremely short lifetimes similar to commercial foils. The nitrogen content of the foils of both long and short lifetimes has been determined using elastic scattering of 3 MeV α-particles.     

Source-size measurements and charge distributions of ions accelerated from thin foils irradiated by high-intensity laser pulses

We report on measurements of source sizes and charge state distributions of ions accelerated from thin foils irradiated by ultrashort (100–300 fs) high-intensity (1-6×10¹⁹ W/cm²) laser pulses. The source sizes of proton and carbon ion beams originating from hydrocarbon contaminants on the surfaces of 5 m thick aluminum foils were investigated using the knife-edge method. For low-energy protons and low-carbon charge states, the source area was found to exceed the focal spot area by a factor of 10⁴. For the determination of charge state distributions, sandwich targets consisting of a 25 m thick tungsten layer, a 2-nm thin beryllium layer, and again a tungsten layer whose thickness was varied were used. These targets were resistively heated to remove the light surface contaminants. Peaked energy spectra of oxygen and argon ions corresponding to the equilibrium distribution after propagation through matter were observed. PACS 41.75.Jv; 52.38.Kd; 52.25.Jm; 52.50.Jm; 52.70.Nc; 41.75.Ak     

Angular distributions and forward recoil range distributions of residues created in the interaction of 12C and 16O ions with 103Rh

We have measured the angular distributions and the forward recoil range distributions of residues produced in the interaction of, respectively, 151, 228 and 402 MeV ¹²C ions with ¹⁰³Rh and the forward recoil range distributions of residues produced in the interaction of 303 MeV ¹⁶O ions with ¹⁰³Rh. These data have been successfully reproduced by a theory which assumes that the dominant mechanisms are complete and incomplete fusion of the projectile with the target and single nucleon transfers from the projectile to the target and predicts that, starting from an incident energy of about 250 MeV, a large fraction of the residues has a mass and charge very close to those of the target nucleus. This is because, at incident energies of a few hundred MeV, a large fraction of the kinetic energy of ¹²C and ¹⁶O is carried away by fast ejectiles which then leave behind the intermediate equilibrated nuclei with a rather small excitation energy and small forward linear momentum.     

Study on charge equilibration time of highly charged ions in carbon foils

Charge state distribution of 0.8MeV/u uranium ions after transmission through a thin carbon foil has been studied. It is observed that the charge state distribution is equilibrated after the uranium ions have passed through a 15μg/cm^2 carbon foil. The equilibrated average charge state is 33.72 and the charge equilibration time of uranium ions in carbon foil is less than 5.4fs.     

Study on charge equilibration time of highly charged ions in carbon foils

Charge state distribution of 0.8MeV/u uranium ions after transmission through a thin carbon foil has been studied. It is observed that the charge state distribution is equilibrated after the uranium ions have passed through a 15 $\mu $g/cm$^{2}$ carbon foil. The equilibrated average charge state is 33.72 and the charge equilibration time of uranium ions in carbon foil is less than 5.4fs.     

Angular momentum polarization of the molecules in the Li + HF reaction

A theoretical analysis of the orientation and alignment of the rotational angular momenta of the reactants and products of the Li + HF(v _r = 0, j _r = 3) → LiF(v, j) + H reaction at a collision energy of E _coll = 0.317 eV is performed. The polarization of the angular momentum of the molecules involved in the reaction is based on the technique of spherical tensor operators (state multipoles). Quantum-mechanical calculations of the S-matrix of the reaction are carried out using the wave packet method. In particular, the influence of the orientation of the angular momentum of the HF reactant on the differential cross section is examined. It is shown that the contribution to the differential cross section comes only from be reactants with an angular momentum perpendicular to the reaction plane. In addition, the angular dependence of the orientation and alignment of the angular momenta of the reaction products are examined. It is shown that, for an isotropic distribution of reactant molecules, the orientation of the angular momenta of the products differs from zero only in the direction perpendicular to the reaction plane. Different experimental geometries, based on radiation enhanced multiphoton ionization, are proposed to detect the predicted effects.     

Localization of carbon atoms and extended defects in silicon implanted separately with C+ and B+ ions and jointly with C+ and B+ ions

The possibility to control the localization of implanted carbon in sites and interstices in silicon immediately during the implantation has been demonstrated. The formation of residual extended defects in silicon implanted separately with C⁺ and B⁺ ions and jointly with C⁺ and B⁺ ions has been shown. It has been found that the formation of residual defects can be suppressed due to annihilation of point defects at C atoms (the Watkins effect). The positive effect is attained if implanted carbon is localized over lattice sites, which is provided by its implantation with the effective current density of the scanning ion beam no lower than 1.0 μA cm^?2.