Alpha-decay studies of the new isotopes 191At and 193At

Detailed alpha-decay studies have been performed for the neutron-deficient isotopes ¹⁹¹At and ¹⁹³At. The nuclei were produced in fusion-evaporation reactions of ⁵⁴Fe and ⁵⁶Fe ions with a ¹⁴¹Pr target. The fusion products were separated in-flight using a gas-filled recoil separator and implanted into a position-sensitive silicon detector. The isotopes were identified using position, time and energy correlations between the implants and subsequent alpha-decays. Three alpha-decaying states were identified for ¹⁹³At and two for ¹⁹¹At. The spin and parity of the initial states in the astatine isotopes were deduced based on unhindered alpha-decays to states in the bismuth daughter nuclei. In both astatine isotopes the 1/2⁺ intruder state was determined to be the ground state and a 7/2^- state to be the first-excited state. In ¹⁹³At the alpha-decay of the 13/2⁺ state was observed in coincidence with a previously known gamma-ray transition from the 13/2⁺ state in the corresponding daughter nucleus ¹⁸⁹Bi. In ¹⁸⁷Bi and ¹⁸⁹Bi low-lying 7/2^- states were observed for the first time via alpha-decay of the mother nuclei.Received: 16 December 2002, Revised: 26 March 2003, Published online: 4 August 2003PACS: 23.60.+e Alpha decay - 27.80.+w - 23.20.Lv transitions and level energies - 21.10.Dr Binding energies and masses     

Recoil-fission tagging of the transfermium nucleus 252No

An in-beam study of the transfermium nucleus ²⁵²No has been performed using the JUROSPHERE II array of germanium detectors coupled to the gas-filled recoil separator RITU. A new technique of recoil-fission tagging was used to extract tagged γ-ray data. Having significant spontaneous fission and α-decay branches, ²⁵²No is an ideal candidate for a comparative study. In a similar manner to α-decay tagging the fission events can be used to obtain γ-ray data. The recoil-fission tagged γ-ray spectrum showed a similar structure to the α-decay tagged γ-ray spectrum. By comparing the α-tagged and fission-tagged spectra and decay curves, it was shown that the spontaneous fission originates from the same initial state as the α decay. This extension of the tagging method allows in-beam spectroscopic data to be obtained from heavy nuclei with significant spontaneous-fission branches.     

Degradation of viscose fibers during acidic treatment

Novel developments in the fiber sector require additional investigation of their behaviour during the production process. In the core step of the viscose process, cellulose fibres are regenerated in an acidic spinning bath. To investigate the influence of hemicellulose content and temperature on the kinetics of fiber degradation, standard and hemicellose-enriched fibers were treated in the acidic standard spinning bath for time periods up to 292 h. Viscose samples of different hemicellulose content were prepared under standardized conditions and the never dried fibres were subjected to long term degradation in the standard spinning bath at 40, 50 and 60 °C. The changes in the degree of polymerization (DP), molar mass distribution, hemicellulose and the generation of the total organic carbon in the spinning bath were monitored. Further, the changes in crystallinity and the level-off-DP of the fibers were determined to improve the accuracy of the existing degradation model. Changes in morphology of the fibers were monitored by optical microscopy and scanning electron microscopy.     

Interpretation of the 13C NMR spectrum of physostigmine

The 25.1 MHz ¹³C nmr spectrum of physostigmine in deuteriochloroform has been reanalysed with the aid of high resolution proton coupled spectrum and selective proton irradiation experiments. In addition to unambiguous assignment the analysis yielded values for carbon-proton coupling constants.     

Towards a Molecular Understanding of Asymmetric Heterogeneous Catalysis: Hydrogenation of 1-Phenyl-1,2-Propanedione1

The present work comprises a detailed investigation of a complex reaction system, revealing features of reaction mechanisms that are general for asymmetric heterogeneous catalysis. Heterogeneous enantioselective hydrogenation of 1-phenyl-1,2-propanedione was studied over cinchonidine modified Pt catalysts producing (R)-1-hydroxy-1-phenylpropanone as the main product with an enantiomeric excess (ee) of 65% at maximum yield, which could be further increased above 90% due to kinetic resolution. The results of kinetic studies in batch and continuous reactors, catalyst screening and characterization results, as well as quantum chemical calculations, are summarized, and pertinent mechanistic aspects are discussed.     

On the decrease in charge radii of multi-quasi particle isomers

We report changes in mean-square charge radii, δ〈r²〉$\delta 〈r^2〉$, magnetic moments and quadrupole moments for three multi-quasi particle isomers; ^97m2Y, ^176mYb and ^178m1Hf. All the isomers are observed to display a decrease in 〈r²〉$〈r^2〉$ compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈r²〉$〈r^2〉$ occur despite the isomers showing increases in quadrupole moment. Possible mechanisms for the effect, which is now seen for six multi-quasi particle isomers, are discussed.     

A combined NMR, DFT, and X-ray investigation of some cinchona alkaloid O-ethers

Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction.