Rotational bands in 167Hf

High-spin states in ¹⁶⁷Hf, populated in the ¹⁴¹Pr(³⁰Si, p3n)¹⁶⁷Hf reaction, have been studied using the nordball Ge detector array. Three rotational cascades have been observed for the first time and the previously-known level scheme has been extended to significantly higher spin. Band-crossing effects are discussed within the framework of Woods-Saxon cranking calculations and are found to be in good agreement. Received: 9 April 1999 / Revised version: 13 May 1999     

Synthesis and Structure of Ba7F12Cl2

Crystals of ordered and disordered Ba₇F₁₂Cl₂ were prepared by flux growth and solid state reactions. These new structures were characterized by single crystal and powder X‐ray diffraction. The disordered variant which shows disorder on one of the cation sites was obtained from a BaF₂ + BaCl₂ + NaCl/NaF flux. It has hexagonal space group P6₃/m (176) with one formula unit per unit cell. The lattice constants are a = b = 1059.55(5) pm and c = 420.10(4) pm (at 21 °C). The structure was refined to R(R_w) = 0.026(0.030) for 346 independent reflections and 26 parameters. Slow cooling of a mixture of BaF₂ and LiCl yields the ordered variant. This one crystallizes in the hexagonal space group P6 (174) with one formula per unit cell. Lattice constants at 21 °C are a = b = 1063.46(2) pm and c = 417.52(1) pm. The structure was refined to R(R_w) = 0.017 (0.017) for 638 independent reflections and 45 parameters. The structural arrangement and the interatomic distances of the two variants are mutually similar. The barium atoms have coordination number nine. Propeller‐type arrangements with a chloride ion on the axis and the fluoride ions as blades are observed. These latter ones are interconnected into ‘channels' of tricapped fluoride prisms. Occupation disorder of the barium sites in the channels of the disordered variant makes the main difference between the two. An unexpectedly high X‐ray density obtained for both variants of Ba₇F₁₂Cl₂ can be correlated to the density of other barium fluorohalides having a coordination number of nine for the barium ion.     

Subhertz-linewidth infrared frequency source with a long-term instability below 5 × 10−15

Distributing a stable, absolute optical reference frequency via fiber network would serve research and development in academia and industry. Lasers stabilized to high-finesse Fabry–Pérot cavities can achieve fractional frequency instabilities of less than 10^?15 for periods up to several seconds. Their instabilities increase for longer averaging times due to a variable frequency drift, with a linear drift component of the order of 10…100 mHz/s. Hydrogen masers, on the other hand, yield an instability floor of a few parts in 10^?15, but suffer from poor stabilities on short timescales. We demonstrate an infrared optical frequency source that combines a cavity-stabilized laser with a hydrogen maser to achieve a residual fractional frequency instability better than 5 × 10^?15 for all averaging times from 0.4 up to 10,000 s. The frequency drift of the system over a period of 40,000 s is less than 30 µHz/s. For obtaining absolute frequency accuracy, the hydrogen maser is referenced to a primary frequency standard.     

First triaxial superdeformed band in 170Hf

First evidence is presented for triaxial superdeformation in ¹⁷⁰Hf. High-spin states in this nucleus have been investigated in a γ-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima. Received: 11 September 2002 / Accepted: 15 October 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: neusser@iskp.uni-bonn.de Communicated by D. Schwalm     

Investigations into beam monitors at the AEg ̄ IS experiment

Detailed diagnostic of antiproton beams at low energies is required for essentially all experiments at the Antiproton Decelerator (AD), but will be particularly important for the future Extra Low ENergy Antiproton ring (ELENA) and its keV beam lines to the different experiments. Many monitors have been successfully developed and operated at the AD, but in particular beam profile monitoring remains a challenge. A dedicated beam instrumentation and detector test stand has recently been setup at the AE \(\bar {g}\) IS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Located behind the actual experiment, it allows for parasitic use of the antiproton beam at different energies for testing and calibration. With the aim to explore and validate different candidate technologies for future low energy beam lines, as well as the downstream antihydrogen detector in AE \(\bar {g}\) IS, measurements have been carried out using Silicon strip and pixel detectors, a purpose-built secondary emission monitor and emulsions. Here, results from measurements and characterization of the different detector types with regard to their future use at the AD complex are presented.     

Das Reziprokentheorem in beliebigen linearen Koordinatenräumen

Ohne ZusammenfassungDiese Arbeit ist von der philosophischen Fakultät der Universität Bonn als Dissertation angenommen worden. Den Herren O. Toeplitz und G. Köthe bin ich für mannigfache Anregungen und Ratschläge zu größtem Dank verpflichtet.     

An Environmentally Benign Process for the Hydrogenation of Ketones with Homogeneous Iron Catalysts

Iron complexes generated in situ catalyze homogeneously the transfer hydrogenation of aliphatic and aromatic ketones by utilizing 2‐propanol as a hydrogen donor in the presence of base. The influence of different reaction parameters on the catalytic activity is investigated in detail by applying a three‐component catalyst system composed of an iron salt, 2,2′:6′,2′′‐terpyridine, and PPh₃. The scope and limitations of the described catalyst is shown in the reduction of 11 different ketones. In most cases, high conversion and excellent chemoselectivity are obtained. Mechanistic studies indicate a monohydride reaction pathway for the homogeneous iron catalyst.     

Lifetimes in the ground-state band and the structure of 118Te

Lifetimes of excited states in ¹¹⁸Te have been measured using the Doppler Shift Attenuation (DSA) and Recoil Distance (RD) methods in the ¹⁰⁹Ag(¹³C, p3n) reaction at a beam energy of 54 MeV. Lifetime values of the ground-state band levels with spins I ^π = 2⁺-16⁺ have been obtained. The excitation energies and B(E2) values are interpreted in the framework of a version of IBFM ( IBM + 2qp) with the maximum boson number exceeding its standard value. A satisfactory agreement with experimental level scheme and B(E2) values for the ground-state band is achieved. Received: 7 June 2001 / Accepted: 7 February 2002     

Collective excitations in the 123, 125I nuclei

The odd-proton nuclei ¹²³I and ¹²⁵I have been studied in the reactions ¹²¹Sb(α, 2n)¹²³I and ¹²³Sb(α, 2n)¹²⁵I, respectively. The level schemes, spin and parity assignments are based on results obtained from singles γ-ray spectra (E_α = 27 MeV) and excitation functions, from measurements of delayed γ-rays, γ-γ coincidences, internal conversion electrons and γ-ray angular distributions. High-spin positive- and negative-parity bands with energies up to 2948 keV and spins up to $\text{23}\text{2}$ in ¹²³I and with energies up to 3775 keV and spins up to $\text{27}\text{2}\text{in}{}^{125}\text{I}$ have been established. In the decay schemes of both nuclei two separated structures of levels have been observed. One group of levels shows a strong ΔJ = 2 quasirotational pattern predicted by the particle-vibration coupling model. The ΔJ = 1 sequence on a $\text{9}\text{2}$⁺ state is assigned as a rotational structure built on the axially symmetric deformed state $\text{9}\text{2}{}^{\mathrm{+}}\text{[404]}$. In ¹²³I a 28 ns isomer at 2660.0 keV has been found.