Electron capture to the continuum from atomic hydrogen

The first known measurement of the differential cross section for electron capture to the continuum(ECC) from atomic hydrogen is presented. A 12 MeV beam of C/sup 6 +/ ions traversed a static target of atomic hydrogen produced by an electron impact heated dissociation oven. The resulting ECC spectrum was obtained with a channel electron multiplier detector mounted at the exit of a 160/sup 0/ spherical sector electrostatic spectrometer with an angular acceptance of 2/sup 0/. The ECC spectrum clearly shows the asymmetry generally associated with ECC spectra from gaseous targets. The ratio of the singly differential cross section of H to that of H/sub 2/ was found to be 0.80. 16 references, 3 figures

Production and transport of convoy electrons in amorphous carbon foils

The production of free convoy electrons, emitted with velocities near the ion velocity in ion-solid collisions, is not well understood. Experiments concerning thickness-dependent yields have suggested the dominant mechanism for convoy production is electron loss to the continuum (ELC) in the bulk of the solid. Free electrons created in the bulk are subject to multiple elastic and inelastic scattering during transport through remaining layers of the solid. We discuss doubly-differential measurements of convoy measurements of convoy electrons as a function of target thickness for fast O/sup 5 +/ ion projectiles incident on carbon foils of varied thicknesses. Angular distributions confirm the ELC model for convoy production. From the radial broadening of the convoy cusps we have determined energy and angular spreading parameters due to post-collisional multiple scattering. 8 refs., 2 figs., 1 tab

Molecular effects in beam-foil collision-induced alignment of He I

We have measured the alignment of beam-foil collision-excited states of He I produced by bombarding carbon foils of various (1.3-110 μg/cm2) areal densities with beams of He+ and HeH+. In addition, we have measured the total light yield of several transitions in He I, He II, and H as a function of foil thickness using beams of HeH+ ions. Experiments were done with He-foil exit energies of 125, 500, 550, and 650 keV. He I alignment decreases in all cases for the thinnest foils when molecular projectiles are used. Total light intensities generally increase with thin foils (small proton-He emergent internuclear separation), but a few decrease or are independent of foil thickness. We are able to explain several features of the alignment and intensity data in terms of the formation of quasimolecular HeH+ states at or near the foil surface. Alignment reduction results from incoherent Stark mixing of the He I excited states in the field of the close proton. A calculation of the rms emergent H-He internuclear separation as a function of foil thickness and beam energy is presented

Comparisons between theory and experiment in two-electron systems

Recent measurements of the wavelengths of the 1s2s /sup 3/S/sub 1/ - 1s2p /sup 3/P/sub 0/ /sub 2/ transitions in helium-like ions of nuclear charge Z = 8 to 26 at several laboratories, including Argonne, Notre Dame, Oxford, Lyon, Berkeley, and Lund are reported. The precision of some of these measurements is sufficient to test the QED contributions to these transition energies to a few parts per thousand

LAMB SHIFT AND FINE STRUCTURE OF n = 2 IN 35Cl XVI

Nous avons mesuré les longueurs d'onde des transitions 2s 3S1 - 2p 3P2 et 2s 3S1 - 2p 3P0 dans Cl XVI à 613.825 ± 0.012 Å et 705.975 ± 0.064 Å. Ces résultats donnent une mesure du Lamb shift 2s - 2p pour Z = 17 avec un précision de ±0.3%.We have measured the wavelengths of the 2s 3S1 - 2p 3P2 and 2s 3S1 - 2p 3P0 transitions in Cl XVI to be 613.825 ± 0.012 Å and 705.975 ± 0.064 Å. Our precision is sufficient to provide measurements of the 2s1/2 - 2P1/2 and 2s1/2 - 2P3/2 Lamb shifts to an accuracy of ±0.3% and to test Q.E.D. theory in the strong field region

Orientation and alignment of the 3\u3ci\u3ep\u3c/i\u3e \u3csup\u3e1\u3c/sup\u3e\u3ci\u3eP\u3c/i\u3e and 4\u3ci\u3ed\u3c/i\u3e \u3csup\u3e1\u3c/sup\u3e\u3ci\u3eD\u3c/i\u3e levels of neutral helium

The alignment and orientation produced by the tilted-foil excitation of He was studied for a wide range of foil tilt angles and outgoing-atom velocities. In particular, two quantum states of different orbital angular momentum (3p 1P and 4d 1D) were investigated and the results were compared with a number of previously proposed models

Energy dependence of alignment in foil collision-excited \u3ci\u3en\u3c/i\u3e=3 states of He I

We have measured the beam-foil collision-induced alignment of the 3p 1P, 3p 3P, 3d 1D, and 3d 3D states of He I for He+ beam energies between 30 and 1300 keV. The alignment of all four states is found to vary with beam-current density as well as energy. The number of secondary electrons emitted per incident ion, γ, has also been measured as a function of foil temperature and beam energy between 400 and 1400 keV. The rate of change of both alignment and γ with foil temperature exhibits a general correlation. The energy dependence of alignment may be understood in terms of simple impact-excitation collisions. We also discuss our results in terms of the Kupfer-Winter surface electric-field model. The interaction between atoms emerging from the foil and slow secondary electrons is considered

Observation of rapid evolution of convoy electron angular distributions

International audienc

Angular distributions of very low energy recoil ions

We present the first measurements of the angular distribution of recoil ions near 90/sup 0/ with respect to the incident projectile direction. Beams of 22.5 and 33 MeV chlorine ions (incident charge states q =4,5,8) have been used as ''hammer'' beams incident on Ne atoms. We confirm the long standing assumption that these recoil ions are ejected preferentially at angles near 90/sup 0/ with respect to the primary beam direction and with energies typically less than 5 eV. Recoil ions ejected around 90/sup 0/ have an energy distribution appreciably wider than those ejected at either larger or smaller angles. 9 refs., 6 figs