16 Matching Results

Search Results

Advanced search parameters have been applied.

Atomic collisions with 33-TeV lead ions

Description: Recent availability of relativistic and ultrarelativistic beams of heavy ions has permitted the first controlled studies of atomic collisions at energies sufficient to measure effects of several new basic phenomena. These include measurements substantiating recently predicted finite nuclear size effects resulting in a reduction in the total electronic energy loss of heavy ions in matter, and measurements of Coulomb collisions in which electrons are excited from the Dirac negative energy continuum. Measurements of total energy loss, free electron-positron pair production, and electron capture from pair production have been recently performed using 33-TeV Pb{sup 82+} ions from the CERN SPS accelerator in Geneva. Results of these studies are presented, along with comparisons with relevant theory.
Date: October 1, 1996
Creator: Vane, C.R.; Datz, S. & Krause, H.F.
Partner: UNT Libraries Government Documents Department

Strong forward-backward asymmetries in electron emission from overlapping resonance states in fast C/sup 3 +/ on He collisions

Description: Autoionizing electrons from the configuration 1s/sup 2/2pnl produced by transfer and excitation were measured for 2.5 to 5.0 MeV C/sup 3 +/ + He-gas collision employing the method of zero-degree Auger spectroscopy. The elctron analyzer was operated with an energy resolution of 300 MeV (FWHM), which corresponds to the projectile rest frame energy resolution (approx.40 MeV). (WRF)
Date: January 1, 1986
Creator: Yamazaki, Y.; Miller, P.D.; Krause, H.F.; Pepmiller, P.L.; Datz, S. & Sellin, I.A.
Partner: UNT Libraries Government Documents Department

Measurement of inelasticities for charge correlated multiple ionization of Ne by fast C/sup 6 +/ ions

Description: A description of measurements of inelasticities for multiple ionization in fast-single collisions is given for the example of 10 MeV C/sup 6 +/ ions with Ne atoms. The degree of multiple ionization was determined by time-of-flight of the recoil ions, extracted by an electric field in coincidence with the projectiles. Their energy loss for a given degree of multiple ionization was measured with a position-sensitive silicon detector in the focal plane of an Elbek magnetic spectrograph with an energy resolution of about 10/sup -4/.
Date: January 1, 1987
Creator: Schuch, R.; Datz, S.; Dittner, P.F.; Krause, H.F. & Miller, P.D.
Partner: UNT Libraries Government Documents Department

Heavy-ion-induced x-ray satellite emission as a chemical probe

Description: Advances in energy technology often require correspondidng advances in materials fabrication and characterization. Among the new techniques being developed for the improved characterization of materials is an x-ray fluorescence method which uses heavy ions for excitation. High resolution measurements of heavy-ion excited x-ray spectra have revealed a series of prominent satellite lines in addition to the normal emission lines. It has been shown that these satellites display intensity variations indicative of the chemical state or environment of the emitting target atom and the projectile velocity. In order to evaluate heavy-ion induced x-ray satellite emission (HIXSE) as a chemical probe, we have examined a series of sulfur compounds and titanium, vanadium and molybdenum alloys and compounds. Results will be presented which demonstrate the chemical sensitivity of this technique, the range of elements which can be analyzed and the potential for applications to real chemical and materials problems.
Date: January 1, 1983
Creator: Rosseel, T.M.; Dale, J.M.; Hulett, L.D.; Krause, H.F.; Raman, S.; Vane, C.R. et al.
Partner: UNT Libraries Government Documents Department

Non-statistically populated autoionizing levels of Li-like carbon: Hidden-crossings

Description: The intensities of the Auger-electron lines from autoionizing (AI) states of Li-like (1s2s2l) configurations excited in ion-atom collisions vary as functions of the collision parameters such as, for example, the collision velocity. A statistical population of the three-electron levels is at best incomplete and underscores the intricate dynamical development of the electronic states. The authors compare several experimental studies to calculations using ``hidden-crossing`` techniques to explore some of the details of these Auger-electron intensity variation phenomena. The investigations show promising results suggesting that Auger-electron intensity variations can be used to probe collision dynamics.
Date: December 31, 1995
Creator: Deveney, E. F.; Krause, H. F. & Jones, N. L.
Partner: UNT Libraries Government Documents Department

Measurement of Electromagnetic Cross Sections in Heavy Ion Interations and Its Consequences for Luminosity Lifetimes in Ion Colliders

Description: The limitation of the luminosity lifetime in high energy heavy ion colliders like RHIC or LHC operating in ion mode is set by the very large cross section of beam - beam interactions. One of the dominant processes at relativistic energies is electron capture from pair production in the strong electromagnetic field provided by the high Z of the ions. The capture cross sections for Pb<sup>82+</sup> interacting with a number targets have been measured using one of the high energy resolution 158 GeV/nucleon beams at CERN. The results, together with results on electromagnetic dissociation, are discussed in terms of beam lifetimes for RHIC and LHC using extrapolations of the measurements to the corresponding collider energies.
Date: March 29, 1999
Creator: Datz, S.; Grafstroem, P.; Knudsen, H.; Krause, H.F.; Mikkelsen, U.; Scheidenberger, C. et al.
Partner: UNT Libraries Government Documents Department

Production of autoionizing Rydberg states by transfer excitation in high energy ion atom collisions

Description: The method of zero-degree Auger spectroscopy was used to study the production of autoionizing Rydberg states in collisions of carbon and oxygen projectiles incident at several MeV on He gas and carbon foils. The autoionization electrons were measured with high resolution so that the quantum defect corresponding to the angular momenta of the Rydberg electrons could be observed. The main purpose of the present experiment is to gain information about the n and l distribution of the Rydberg electron captured in the collision. The well-known n/sup -3/ law is confirmed. For the He gas target it is found that the angular momenta p and d are predominantly produced. For the foil target the higher angular momenta are clearly enhanced. 15 refs., 6 figs.
Date: January 1, 1986
Creator: Stolterfoht, N.; Miller, P.D.; Krause, H.F.; Yamazaki, Y.; Dittner, P.F.; Pepmiller, P.L. et al.
Partner: UNT Libraries Government Documents Department

Electron ion interactions in crystal channels: Collisions in ultra-dense electron media

Description: Dielectronic excitation of H-like S, Ca and Ti is shown to occur in the dense electron gas of a crystal channel. Cross sections for collisional ionization of the short lived excited states can then be determined. Ionic excitation can also be achieved by resonant coherent excitation in which case specific m states can be excited for further study. 12 refs., 8 figs.
Date: January 1, 1990
Creator: Datz, S.; Dittner, P.F.; Gomez del Campo, J.; Krause, H.F.; Rosseel, T.M. & Vane, C.R.
Partner: UNT Libraries Government Documents Department

Charge and angular correlated inelasticities in MeV/nucleon ion-atom collisions

Description: Using an Elbek high-resolution magnetic spectrograph, we measured energy loss an angular distributions of MeV/nucleon projectile ions in coincidence with target recoil-ion charge state. We investigated collisions of 10 and 20 MeV C/sup 6 +/ on He, Ne, Ar, and Kr where the target atom is multiply ionized and the projectile emerges in charge state q or q-1. The amount of energy transferred to the continuum electrons exceeds, by far, the sum of the values of the ionization potentials and shows a strong target Z dependence. Both an n-body classical-trajectory Monte Carlo method (nCTMC) and an energy deposition model are used for comparison with the experimental data. 12 refs., 3 figs.
Date: January 1, 1988
Creator: Schoene, H.; Schuch, R.; Datz, S.; Dittner, P.F.; Giese, J.P.; Krause, H.F. et al.
Partner: UNT Libraries Government Documents Department

Surgery of fast, highly charged ions studied by zero-degree Auger spectroscopy

Description: Zero-degree Auger spectra were measured in collisions of oxygen and carbon on He with incident charge states of q = 2 to 5 and for energies from 5 to 30 MeV. Since the light target particle He acts selectively on the projectile ion, we refer to the present method as ion surgery. Apart from the one-electron processes single excitation and single loss, two-electron processes such as transfer excitation and transfer loss are studied. 17 refs., 4 figs., 1 tab.
Date: January 1, 1986
Creator: Stolterfoht, N.; Miller, P.D.; Krause, H.F.; Yamazaki, Y.; Swenson, J.K.; Bruch, R. et al.
Partner: UNT Libraries Government Documents Department

Electron transfer processes in collisions of highly charged energetic (0. 1 to 1. 0 MeV/nucleon) ions with helium atoms

Description: We have investigated charge transfer in collisions of energetic (0.1 - 1 MeV/nucleon) highly charged ions with helium atoms with the principal aim clarifying the nature of two-electron processes. The sensitivity of partial charge-changing cross sections (i.e., single- and double-charge transfer, transfer ionization (TI), and single and double ionization) to core configuration and scaling rules for one- and two-electron processes were investigated with iodine ions (q = 5+ ..-->.. 26+) and uranium ions (q = 17+ ..-->.. 44+) using an ion-charge state, recoil-ion coincidence method. Using zero-degree electron spectroscopy in coincidence with charge transfer, we found that at the higher energies, as in the case of 0.1 MeV/nucleon ions previously reported, TI involves the transfer of two electrons to a higher correlated state followed by loss of one electron to the continuum. In addition, we observe very high Rydberg electrons in coincidence with TI, implying a possible up-down correlation in the pair transfer. In addition, we made measurements of VUV photons emitted at the collision in coincidence with He/sup +/ and He/sup 2 +/ recoils. The results show that TI leads to capture into lower n states than single-charge transfer. 15 refs., 10 figs.
Date: January 1, 1987
Creator: Datz, S.; Hippler, R.; Andersen, L.H.; Dittner, P.F.; Knudsen, H.; Krause, H.F. et al.
Partner: UNT Libraries Government Documents Department

L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions

Description: Article discussing research on L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions.
Date: October 15, 1987
Creator: Andrews, M. C.; McDaniel, Floyd Del. (Floyd Delbert), 1942-; Duggan, Jerome L.; Miller, P. D.; Pepmiller, P. L.; Krause, H. F. et al.
Partner: UNT College of Arts and Sciences

Electrons Emitted from 33-TeV Pb Ions During Penetratiaon of Solids

Description: At ultrarelativistic energies, ionization cross sections exceed electron capture cross sections by several orders of magnitude (1,2). Effectively, all electrons transferred to a highly relativistic heavy ion moving in a solid or gaseous target medium are stripped in a relatively short distance. Above ~20 GeV/nucleon, the principal mechanism for electron capture is from pair production (ECPP) (2). The total cross sections for ECPP are te&nically important for making reliable predictions of operating limitations for relativistic heavy-ion colliders, e.g., RHIC and LHC (3). In ECPP, it is expected that ~30% of capture proceeds to excited states of the capturing ion. Some of these relatively weakly bound electrons are radiatively long-lived and easily lost in secondary collisions in solid targets, making measurements of their contributions to total capture experimentally difficult. Electrons lost from high-energy ions in collisions with target atoms form a cusp-shaped spectral peak in the forward direction in the laboratory frame centered at the velocity of the moving ion (4-5). The shape of this electron loss to projectile continuum (ELC) peak has been shown (5,6) to depend on the initial atomic bound state from which the electron is ionized. We have measured and compared ELC electrons from direct ionization of hydrogenlike 33-TeV Pb<sup>81+</sup>(ls) ions (Lorentz factory <font face="symbol">g</font> = 168) in Al with similar data for electrons created by ECPP for bare Pb<sup>82+</sup> ions in Au - followed by ionization. Both measured ELC peaks are narrow in momentum and angle and very similar in shape.
Date: July 22, 1999
Creator: Datz, S.; Grafstroem, P.; Knudsen, H.; Krause, H.F.; Mikkelsen, U.; Moeller, S. et al.
Partner: UNT Libraries Government Documents Department

Transfer and excitation processes studied in H-like S and Li-like and H-like F colliding with H/sub 2/

Description: We have studied transfer and simultaneous excitation by three different experimental techniques. Coincidences between two K x rays were measured for S/sup 15 +/, coincidences between one K x ray and the charge exchanged projectile for Li-like F and projectile Auger electrons for H-like F in each case colliding with H/sub 2/. For all three collision systems, the measured cross sections are dominated by Resonant Transfer and Excitation (RTE). Also, for the F projectiles, strong contributions from Two Electron Transfer and Excitation (2eTE) were found. 9 refs., 3 figs.
Date: January 1, 1988
Creator: Schulz, M.; Datz, S.; Dittner, P.F.; Giese, J.P.; Krause, H.F.; Miller, P.D. et al.
Partner: UNT Libraries Government Documents Department

Resonant coherent excitation of Mg sup 11+ : Electronic collisions of state specified short-lived excited states in a crystal channel

Description: Hydrogenic ions passing through axial and planar channels can be excited from n = 1 to n = 2 when the frequency of perturbation by the atoms in the crystal spaced a distance d apart comes into resonance with the spacing between eigenstates i and j {Delta}E{sub ij} = hK(v{sub i}/d) where K is a harmonic 1,2,3{hor ellipsis} of the (v{sub i}/d) frequency. The degeneracy in the n = 2 levels is removed; first by the assymetry in the crystal field and second by Stark mixing of 2s with 2p{sub x} which is caused by the wake field. Thus, the resonant frequency, and hence velocity, for excitation to 2p{sub x,y} is different than that for 2p{sub x} and they can be excited selectively. In the present work we used Mg{sup 11+}, where the n = 2 ionization cross section is small enough to permit escape of some of the excited ions from the crystal without being ionized by subsequent collisions and with the subsequent emission of radiation. Since we can excite different orientations of the ion selectively by varying the velocity we can measure the separate ionization cross sections for these states by determining the yields of totally stripped ions compared to those which emit a Ly {alpha} x-ray. A comparison of the two channels shows that the probability of escape from the crystal without ionizations is greater for ions in the 2p{sub x} state than those in the 2p{sub x,y} state. These RCE data and are presented as proof of principal for experiments which measure electron bombardment ionization cross sections for short lived excited states with specific polarization.
Date: January 1, 1990
Creator: Datz, S.; Dittner, P.F.; Gomez del Campo, J.; Krause, H.F.; Rosseel, T.M.; Vane, C.R. (Oak Ridge National Lab., TN (USA)) et al.
Partner: UNT Libraries Government Documents Department

Excitation curve for auger decay of the (1S2S2P sup 2 ) sup 3 D state of C sup 4+ formed through RTE (Resonant Transfer and Excitation)

Description: The ORNL EN tandem supplied beams of 3.5--9 MeV C{sup 3+} ions which were incident on a differentially pumped He target. Auger electrons emitted by fast C{sup 4+} ions emerged at 10 deg(lab)w.r.t. the incident ion beam. They were detected using a two stage spectrometer with kinematic refocusing. An excitation curve was obtained for the (1s2s2p){sup 3}D state Auger decay to the ground state of C{sup 3+}. The excitation curve peaks at {approximately}6 MeV, which strongly supports the notion that the state is formed through Resonant Transfer and Excitation. 10 refs., 2 figs.
Date: January 1, 1990
Creator: Shafroth, S.M.; McDonald, F.; Benhenni, M. (North Carolina Univ., Chapel Hill, NC (USA)); Kessel, Q.; Deveney, E. (Connecticut Univ., Storrs, CT (USA)); Swenson, J.K. et al.
Partner: UNT Libraries Government Documents Department