First production of ultracold neutrons with a solid deuterium source at the pulsed reactor TRIGA Mainz⋆

The production rates of ultracold neutrons (UCN) with a solid deuterium converter have been measured at the pulsed reactor TRIGA Mainz. Exposed to a thermal neutron fluence of n·cm^-2·pulse^-1, the number of detected very cold and ultracold neutrons ranges up to 200 000 at 7mol of solid deuterium (sD₂) in combination with a pre-moderator (mesitylene). About 50% of the measured neutrons can be assigned to UCN with energies E of where V _F(sD ₂) = 105 neV and V _F(guide) = 190 neV are the Fermi potentials of the sD₂ converter and our stainless steel neutron guides, respectively. Thermal cycling of solid deuterium, which was frozen out from the gas phase, considerably improved the UCN yield, in particular at higher amounts of sD₂.     

Sensitivity improvement in laser ablation inductively coupled plasma mass spectrometry achieved using a methane/argon and methanol/water/argon mixed gas plasma

The influence of the addition of carbon using methane or methanol/water to an inductively coupled plasma (ICP) via the carrier gas flow on the sensitivity in laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was studied. During the ablation of SRM NIST 610 with simultaneous addition of CH(4) (0.6-1.4 ml min(-1)), a sensitivity enhancement of more than one order of magnitude for selected analytes (e.g. (75)As(+)) was observed. In addition to the sensitivity enhancement for As, Te, I and Se, also all other measured elements showed a significantly enhanced sensitivity (minimum by a factor of 2). Potential mechanisms for the observed intensity enhancement include charge transfer reactions, a change in the ICP shape and a temperature increase in the plasma. Furthermore, the aspiration of a methanol-water mixture into a cooled spray chamber and the simultaneous addition to the laser ablated aerosol was investigated. This type of mixing leads to a sensitivity enhancement up to a factor of 20. To prevent clogging of the sampler cone and skimmer cone by carbon deposition, a fast cleaning procedure for the interface is tested during running ICP, which allows the application of such a set-up for specific applications.     

Isometric groups,selection rules and irreducible tensors of semi-rigid molecules

A systematic treatment of multipole selection rules of non-rigid molecules is presented, based on the isomorphism of the isometric group to the symmetry group of the rotation-internal motion hamiltonian. A classification of isometric groups and relations among the representations of the isometric group on various substrates are discussed. A set of general transformation formulae for irreducible tensor operators of semi-rigid molecular models is derived. These formulae are used for the derivation of dipole and quadrupole selection rules of a considerable number of semi-rigid models. The relations among the representations of the isometric group give rise to some theorems which allow a compact presentation of selection rules of non-rigid molecules.     

Optimization of a peroxyoxalate chemiluminescence detection system for the liquid chromatographic determination of fluorescent compounds

Summary A peroxyoxalate chemiluminescence detection system for liquid chromatography is described. The excitation of fluorophores is generated by the reaction of bis-(2,4,6-trichlorophenyl)oxalate or bis(2,4-dinitrophenyl)oxalate and hydrogen peroxide, which are added to the column effluent. The influence of the solvents and the concentrations of the reagents have been investigated. The influence of the flow cell volume on sensitivity and on band broadening have also been studied and a chemical band narrowing effect has been observed. Different types of apparatus have been compared for detection of the emitted light. The system has been used for the detection of the dansyl derivative of a drug with a secondary amine functional group in serum samples. The detection limits are in the 1–10pg range.     

13C NMR of carbonyl compounds. 3. Structure and dynamics of protonated enones and dienones

The unsaturated ketones $\text{1}$1 – $\text{10}$10 were protonated at low temperatures and studied by dynamic ¹³C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond.     

Strangelet search and particle production studies in Pb+Pb collisions at 158 AGeV/c at CERN SPS

We searched for long-lived strange quark matter particles, so-calledstrangelets, and studied particle and antiparticle production in Pb+Pb collisions at 158 GeV/c per nucleon at zero degree production angle. We give upper limits for the production of strangelets covering a mass to charge ratio up to 120 GeV/c ² and lifetimest _lab>1.2 μs and plot invariant differential production cross sections as a function of rapidity for a variety of particles.