AP-Seminars

AP-Sonderseminar

Mi., 5. September 2001, 10:15 h, Vorraum Atomphysik

H. Rothard, CIRIL-Ganil, Caen, France

"Auger-, Binary Encounter and ‘Fermi shuttle’ electron Ejection in Heavy Ion-Solid Collisions"

The application of a large detector array (ARGOS), initially designed for nuclear physics studies, to atomic collision experiments at GANIL/Caen and CS of LNS/Catania made the determination of absolute electron emission cross sections possible. Binary encounter electron ejection in forward direction from solid foils can be well described by relativistic ionisation and transport theory. Evidence was found for multiple collision sequences of electrons between target and projectile nuclei often referred to as "Fermi-shuttle". Heavy ion induced Auger electron spectra show hypersatellite lines from double K shell ionisation, and a broadening is observed with increasing ion charge. One interpretation of this latter effect is a possible "electronic temperature" increase.

Atomphysik-Sonderseminar

Mi., 01. August 2001, 10:15 h, Vorraum Atomphysik

Xiaohong Cai, Inst. of Modern Physics, Lanzhou

The Cooler Storage Ring Facility for Atomic Physics in Lanzhou

A new heavy ion storage ring system, HIRFL-CSR, is presently in construction at the National Laboratory of Heavy Ion Research Facility in Lanzhou, China. A report on the layout and the present status is given.

Atomphysik-Seminar

Mi., 11. Juli 2001, 10:15 h, Vorraum Atomphysik

Davor Protić, FZ Jülich

Aktuelle Entwicklungen auf dem Gebiet ortsempfindlicher Germanium- und Si(Li)-Detektoren

In dem Labor für Halbleiterdetektoren des Instituts für Kernphysik werden seit Jahren ortsempfindliche Detektoren aus hochreinem Germanium und durch Lithium-Drift kompensiertem Silizium entwickelt und für COSY-Experimente (z.B. GEM) wie auch für spezielle Anwendungen (z.B. GSI) gebaut.

Planare ortsempfindliche Germaniumdetektoren werden aus beidseitig implantierten p⁺-i-n⁺-Dioden durch Teilung der p⁺- und n⁺-Kontakte in mehrere, über Photolithographie definierte, Detektorelemente realisiert. Einige bereits laufende Detektorsysteme werden vorgestellt.

Si(Li)-Detektoren wurden bisher nur auf dem Bor-implantierten p⁺-Kontakt strukturiert. Zweidimensionale Mikrostreifen-Detektoren wurden nicht hergestellt, da die feinen Strukturen auf dem ~500 mm dicken Li-diffundierten Kontakt schwer zu realisieren sind.

Die in letzter Zeit intensiv diskutierte dreidimensionale Ortsbestimmung mit Hilfe von dickeren Detektoren, die auf beiden Kontakten orthogonal zueinander angeordnete Streifenstrukturen haben, führte zu der Entwicklung von beidseitig strukturierten Si(Li)-Detektoren. Wichtige Punkte dabei sind die Entwicklung von dünnen Li-diffundierten Kontakten und deren Strukturierung.

Atomphysik-Seminar

Mi., 04. Juli 2001, 10:15 h, Vorraum Atomphysik

Frank Rathmann, FZ Jülich

„Experiments with Polarized Gas Targets in Storage Rings“

The talk will give an overview about experiments involving polarized internal targets. Much experience has been gained in operating these targets in electron and ion storage rings. The physics results cover a wide range of topics from deep inelastic electron-proton scattering over measurements of spin-spin observables in elastic and inelastic proton-proton collisions. Atomic physics experiments have been carried out to study polarization effects in recombined hydrogen and deuterium molecules. The experiments greatly benefit from the high purity of the target material and the high degree of polarization. Fast polarization reversal and the alignment along different axes eliminates systematic asymmetries to a very high degree. Polarized targets internal to a storage ring can thus be regarded as an ideal tool for high precision experiments. They have just begun to open a new door to hadronic interaction studies and will continue to play a major role in years to come.

Atomphysik-Seminar

Mi., 27. Juni 2001, 10:15 h, Vorraum Atomphysik

S.P. Møller, ISA, University of Aarhus

„The Development of the Electrostatic Storage Ring ELISA;
New Possibilities within Atomic Physics and Biology?“

The considerations, which partly came from experiments at the storage ring ASTRID, which led to the development of the electrostatic storage ring ELISA, will be outlined. Operational experience with ELISA will be described, and some initial and planned experiments at ELISA will be presented.

Atomphysik-Seminar

Mi., 20. Juni 2001, 14:15 h, Vorraum Atomphysik

Reinhard Dörner, Universität Freiburg

„Von tanzenden Elektronen und zitternden Kernen“

Moderne atomphysikalische Imaging Systeme erlauben es, korrelierte Bewegung der Teilchen in Quantensytemen aus Elektronen und Kernen sichtbar zu machen. Wir zeigen, wie in unterschiedlichsten Streuexperimenten einfache atomare und molekulare Systeme zum Aufbruch gebracht werden und sich die Bewegungsstruktur der Teilchen sichtbar machen läßt. Als Beispiele diskutieren wir die Elektronenemission aus raumfesten Molekülen, den Aufbruch von Helium Atoms nach Absorption eines Photons oder im Lichtblitz eines Kurzzeitlasers

Atomphysik-Seminar

Mi., 13. Juni 2001, 10:15 h, Vorraum Atomphysik

Ullrich Schramm, LMU München

„Dichte kristalline Ionenstrahlen – der RFQ Speicherring PALLAS“

Wir berichten über die aktuelle experimentelle Realisierung dichter kristalliner Ionenstrahlen in dem RFQ Speicherring Pallas. Bei Strahlenergien im eV-Bereich wurden sowohl kontinuierliche, als auch gebunchte Mg-Ionenstrahlen mit Hilfe von Laserlicht gekühlt und der Phasenübergang zur linearen Kette detailliert untersucht Eigenschaften wie die außerordentliche Stabilität der Strahlkristalle bei abgeschalteter Kühlung und die Übertragbarkeit der Modellergebnisse auf Schwerionenspeicherringe werden diskutiert.

Atomphysik-Seminar

Mi., 06. Juni 2001, 10:15 h, Vorraum Atomphysik

Jörg Schmiedmayer, Univ. Heidelberg

„Towards Mesoscopic Physics with Cold Atoms“

In mesoscopic quantum electronics, electrons move inside semiconductor structures and are manipulated using potentials where at least one dimension is comparable to the de-Broglie wavelength of the electrons. Similar potentials can be created for neutral atoms moving microns above surfaces using nano-fabricated charged and current carrying structures nanofabricated on a surface. These two interactions may be combined or used independently.

We describe the experimental realisation of such traps and guides for neutral atoms for thin wires and their miniaturization on a nano-fabricated Chip. The chip we have used in this work is made of a mm thick gold layer placed on a GaAs substrate, the patterns are created by standard nanofabrication processes. We have loaded atom traps 10 mm above a surface and realized realize different trap geometries, atom guides and a beam splitter for guided atoms. Trap parameters with a transverse ground state size below 100 nm and frequencies of above 100 kHz (as required by the QIP proposals) have been achieved. Furthermore we could trap and guide atoms exclusively with the fields created on the chip. All these can be built using standard nano-fabrication techniques and materials. This will allow us to use much thinner wires and reach traps with ground state sizes of 10 nm and trap frequencies in the MHz range. A final integrated Atom Chip, should have a reliable source of cold atoms with an efficient loading mechanism, single mode guides for coherent transportation of atoms, nano-scale traps, movable potentials allowing controlled collisions for the creation of entanglement between atoms, extremely high resolution light fields for the manipulation of individual atoms, and internal state sensitive detection of atoms. All of these, including the bias fields and probably even the light sources, could be on-board a self-contained chip. This would involve sophisticated 3D nano-fabrication and the integration of a diversity of electronic and optical elements, as well as extensive research into fundamental issues such as decoherence near a surface. Such a robust and easy to use device, would make possible advances in many different fields of quantum optics: from applications such as clocks and sensors to implementations of quantum information processing and communication.

Atomphysik-Seminar

Mi., 30. Mai 2001, 10:15 h, Vorraum Atomphysik

Uwe Becker

Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

„Kohärenz in der Photoelektronenemission homonuklearer Moleküle“

Die Frage, ob die Emission von Rumpfelektronen zweiatomiger homonuklearer Moleküle kohärent oder inkohärent von beiden atomaren Rümpfen erfolgt, ist Gegenstand langjähriger Diskussionen gewesen, die auch unter dem Schlagwort der Rumpfloch-Lokalisation Eingang in die Literatur gefunden hat. Das Problem der Eindeutigkeit derartiger Messungen soll anhand neuerer Untersuchungen mittels winkelaufgelöster Elektron-Ion-Koinzidenz-messungen neu erörtert werden. Besonderes Gewicht wird auf die Rolle des nachfolgenden Augerzerfalls und der damit verbundenen Fragmentierung des Moleküls gelegt.

Atomphysik-Seminar

Mi., 23. Mai 2001, 10:15 h, Vorraum Atomphysik

E. Weigold, Canberra, Australien, z.Zt. Univ. Frankfurt

„Orbital and spin polarization transfer in ionizing electron atom collisions“

The first measurements of (e,2e) ionization cross sections for oriented and polarized atomic targets by spin polarized electrons are discussed. An outline will be given of the experimental techniques used to obtain the measurements. The differential cross section will be expressed in terms of tensors with spherical components. This general expression has the advantage of separating the geometrical effects from the dynamical ones, and the orbital angular effects from the spin ones. The data are expressed in terms of these irreducible tensors, both for the excited oriented and spin polarized 3p state of sodium and the spin polarized 3s ground state of sodium. The data are compared with the results of calculations in the first Born and distorted wave Born approximations and the dynamically screened Coulomb wave approximation. The study provides insight into mechanisms by which angular momentum and spin are transferred from the incident channel to the two final-state continuum electrons.

Atomphysik-Seminar

Mi., 28. März 2001, 11:15 h, Vorraum Atomphysik

Z.-T. Lu, Argonne Nat. Lab., USA

"Ultrasensitive Trace-Isotope Analysis with a Magneto-Optical Trap"

We have developed a new method of ultrasensitive trace-isotope analysis based upon the technique of laser manipulation of neutral atoms [C.Y. Chen et. al., Science 286, 1139 (1999)]. This new method allows us to count individual ⁸⁵Kr and ⁸¹Kr atoms present in a natural krypton sample with isotopic abundances in the range of 10^-11 and 10^-13, respectively. Isotope analysis of ⁸¹Kr can be used to date polar ice; and ⁸⁵Kr is a tracer used in monitoring nuclear wastes. In this experiment metastable Kr atoms were produced in a discharge, decelerated via the Zeeman slowing technique, and captured by a magneto-optical trap where the atoms were counted by measuring their fluorescence. At present our system is capable of counting, in average, one ⁸¹Kr atom for about 12 minutes with a total efficiency of 2x10^-7. We are currently working to improve our system efficiency by re-circulating the gas in the vacuum system. This method can be used to analyze many other isotope tracers for a wide range of applications.

Atomphysik-Seminar

Mi., 21. März 2001, 10:15 h, Vorraum Atomphysik

V.M. Shabaev, St. Petersburg State University

"Towards Tests of QED in Heavy Ions"

The present status of the QED calculations of heavy ions is reviewed. The currently available theoretical results for the Lamb shift, the hyperfine splitting, and the bound-electron g factor are compared with recent experiments. A special attention is focused on testing QED in a strong Coulomb field induced by a heavy nucleus. In particular, a possibilty for investigations of QED in experiments on the hyperfine splitting in heavy ions is examined. It is found that QED effects can be probed on the level of about a few percent in a specific difference of the hyperfine splitting values in hydrogenlike and lithiumlike bismuth. This could provide a test of QED in the strongest electric field available at present for experimental study.

Atomphysik-Seminar

Mi., 28. Februar 2001, 10:15 h, Vorraum Atomphysik

A.V. Nefiodov, Petersburg Nuclear Physics Institute

"Experiments on parity-violation effects at ion storage rings"

There are two sources of parity nonconservation (PNC) in atoms: the electron-nucleus weak interaction and the contact magnetic interaction of electrons with the nuclear anapole moment. A recent experiment with atomic caesium has provided the first measurement of a nuclear anapole moment. The extracted weak charge differs from the prediction of the Standard Model. The main uncertainty in the value of the Cs weak charge results from the theoretical evaluation of PNC matrix elements that require the inclusion of electron-electron correlation effects. The most natural way to resolve the discrepancy is to turn to simpler electronic systems, in particular, to few-electron highly charged ions. We shall discuss feasibilities of PNC experiments at ion storage rings, with emphasis on a test of the Standard Model in strong fields and measurements of nuclear anapole moments.

Atomphysik-Seminar

Mi., 21. Februar 2001, 10:15 h, Vorraum Atomphysik

Ken Taylor, Queen’s University Belfast

“Double Ionization of Helium with a Few Fat Photons”

A single `fat' photon (in the helium context) carries enough energy so that, when shared by the two helium electrons, both can escape the atom. The imminent availability of high intensity pulses of such fat photons via Free Electron Laser sources makes the absorption of several such fat photons by a helium atom a topical enquiry. Recent accurate, predictive calculations yielding interesting results for this phenomenon will be presented and contrast made with absorption of the `famished' photons typical of optical lasers.

Atomphysik-Seminar

Mi., 14. Februar 2001, 10:15 h, Vorraum Atomphysik

A. Saenz, Univ. Konstanz

“Molecules in strong fields: bond softening, enhanced ionisation and coherent control”

The behaviour of hydrogen molecules in strong electric or low-frequency laser fields is discussed. Based on the first fully correlated and three-dimensional ab initio calculation it will be shown that two truly molecular strong-field effects, bond softening and enhanced ionisation, cannot only occur for molecular ions, but also for neutral molecules. In the second part of the talk, coherent control of ionisation and dissociation by simultaneous one- and three-photon excitations of molecular hydrogen is discussed.

Atomphysik-Seminar

Mi., 31. Januar 2001, 10:15 h, Vorraum Atomphysik

José R. Crespo López-Urrutia, Univ. Freiburg

“Electron beam ion traps: current status and future developments"

Electron beam ion traps have been in use for more than a decade. With these instruments, highly charged ions up to naked U⁹²⁺ have been produced. Experimental studies have encompassed atomic spectroscopy in the x-ray, soft-x-ray, VUV, UV and visible regions for ions with ionization potentials below 40 keV. The Livermore SuperEBIT has also allowed routine studies of (among others) the ground state hfs of ¹⁶⁵Ho⁶⁶⁺, ^185,187Re⁷⁴⁺, and ^203,205Tl⁸⁰⁺, as well as the hfs of the x-ray 2s_1/2-2p_3/2 line of Li-like ²⁰⁹Bi⁸⁰⁺, and the Lyman-a transitions of Xe⁵³⁺, Pb⁸¹⁺, and U⁹¹⁺, thus complementing the storage-ring based methods applied at GSI. Ions extracted from the trap have also been used, mainly for ion-surface interaction research and for transfer in an external Penning-trap (RETRAP), where they have been sympathetically cooled by laser-cooled Be⁺ ions. However, the yield of naked ions of those heavy elements still lets room for improvement; electron beam energy and current upscaling could prove essential means. The Freiburg EBIT is currently undergoing a high-energy upgrade to achieve this purpose, after its performance in the lower energy region has been shown by the current experimental results.

Atomphysik-Seminar

Mi., 24. Januar 2001, 10:15 h, Vorraum Atomphysik

Clemens Schulze-Briese, PSI Villigen

“Curved Crystal Optics for Focussing and Imaging of Synchrotron Radiation”

Curved crystals optics offer a high degree of flexibility to adjust their reflection properties to the specific requirements of an experiment. They can be used in Bragg and Laue geometry or combination of them, in meridional or sagittal geometry and the asymmetry angle gives control over the rocking curve width. Moreover, their weak sensitivity to surface roughness make them ideally suited to conserve the brightness of 3rd generation synchrotron sources as well as for high energy X-rays where grazing-incidence-mirrors cannot be applied.

This presentation will review the properties of curved crystals. Their utility in the field of focussing of synchrotron radiation and in imaging techniques will be illustrated by showing some recent examples of their use.

Atomphysik-Seminar

Mi., 17. Januar 2001, 10:15 h, Vorraum Atomphysik

Frank Herfurth, GSI / LMU München

“Masses of Short-Lived Nuclides for Fundamental Studies”

The atomic mass or nuclear binding energy incorporates all forces and interactions within the nucleus. Therefore, an accurate knowledge of this quantity is required when using the nucleus as laboratory for fundamental interactions as, for instance, the systematic investigation of super-allowed beta-decays or studies of the isospin formalism in nuclei. Mass measurements will be presented performed with the Penning trap mass spectrometer ISOLTRAP on light argon isotopes down to A=33, on A=73-78 krypton and on ⁷⁴Rb. While ⁷⁴Rb is the shortest-lived nuclide ever investigated in a Penning trap the mass of ⁷⁴Kr and ³⁴Ar could be determined with an unprecedented accuracy.

Atomphysik-Seminar

Mi., 20. Dezember 2000, 10:15 h, Vorraum Atomphysik

R. Morgenstern, KVI Groningen

Hot Recoils from Cold Atoms

For an investigation of atomic collision processes recoil spectroscopy is a powerful method which provides impact-parameter sensitive information. An essential requirement for this method is a "cold" target. So far this has mostly been realized by a supersonic expansion of rare gases such as He or Ne. We have developed a cold Na target by means of a magneto optical trap with primary energies of the target atoms in the neV range. First results, i.e. recoil momentum distributions of Na^q+ ions resulting from O⁶⁺ and C⁶⁺ impact will be discussed and compared with predictions from the classical over-the-barrier model and from CTMC calculations.

A review on the radiative electron capture (REC) studies performed at the ESR storage ring gas jet will be presented. The photon angular distribution of REC in ion-atom collisions is a sensitive tool to identify the spin-flip transitions. The photoionization process studied by its time-reversed process – REC - at high and low incident energies, proves that for high-Z systems higher-order multipole contributions and magnetic corrections persist even at energies close to the threshold. State-selective data of electron capture into high-Z projectiles are extracted from the well-resolved Balmer transitions. The first experimental results of the resonant transfer and excitation of H-like uranium projectiles will also be discussed briefly.

AP - Seminar im WS 2000/2001

10:15h im Vorraum der Atomphysik

The present status of theoretical calculations of the two-loop self-energy correction for hydrogen is discussed. An existing discrepancy between analytical methods based on a (Za) expansion and numerical non-perturbative (in Za) approaches is solved and analysed.

Atomphysik-Seminar

Mi., 22. November 2000, 10:15 h, Vorraum Atomphysik

Dietrich Beck, GSI

„The WITCH experiment“

The WITCH experiment is a retardation spectrometer coupled to a Penning trap and measures the beta-neutrino angular correlation via the shape of the recoil energy spectrum. The present form of the Standard Model describes weak processes in terms of vector and axial-vector type interactions, but the possible presence of scalar and tensor interactions is not yet ruled out. The main aim of this experiment is the search for possible scalar and tensor currents. The talk describes the experiment and a status report is given.

The mass is a fundamental nuclear property. For an improved understanding of the nuclear forces and hence for nuclear models as well as for astrophysical models of the synthesis of elements particularly the masses of unstable exotic nuclides are important. At the FRS/ESR two complementary methods for mass measurements of exotic nuclides have been developed: Schottky Mass Spectrometry (SMS) and Isochronous Mass Spectrometry (IMS). While SMS provides the higher resolving power and precision (» 5 · 10^-7) but is restricted to nuclides with half-lives greater than a few seconds, IMS has been developed particularly for rapidly decaying nuclei with half-lives down to a
few ms. A precision of about 10^-6 has been achieved. Both methods will be described, results of first experiments will be presented.

Im Rahmen einer internationalen Kollaboration der metrologischen Staatsinstitute soll der Artefakt der Masseneinheit - das Urkilogramm - durch einen hochreinen, perfekten Einkristall aus natürlichem Silicium ersetzt werden. Dazu müssen neben den Atommassen der beteiligten Silicium-Isotope mit den Massenzahlen A = 28, 29, 30 auch deren Isotopenhäufigkeiten und die im Kristall vorhandenen Verunreinigungen bekannt sein. Die einzige Methode, mit der all diese Fragestellungen zerstörungsfrei an massiven Proben gelöst werden können, ist die prompte (n,g)-Spektrometrie.