Nuclear charge radii from muonic X-ray transitions in F,Na, Al,Si, P,S and K

Energies of muonic X-rays of the Lyman series of seven light natural elements (F, Na, Al, Si, P, S and K) have been determined with an accuracy of between 15 and 30 eV. Equivalent charge radii have been deduced. For μ^?-K, transitions to the 2s state allowed an additional constraint on the Fermi c-t diagram. The results are in good agreement with, and generally of an order of magnitude higher precision than, comparable electron scattering data.     

Quantitative Spurenbestimmung von Quecksilber im Harn nach elektrolytischer Anreicherung

A flameless atomicabsorption method (Brandenberger and Bader [1]) was taken up to determine the amounts of mercury in urine. The procedure was extended to special problems of occupational medicine. The mercury is collected on a copper wire by electrolysis. The wire is heated electrically in the light path of an atomic absorption spectrophotometer, the evaporating mercury diminishing the beam of a hollow cathode lamp. The change of intensity is recorded in an analogous way. After 60 min of electrolysis (15 mA, 3 V) 97.4% of mercury have been recovered. The relative detection limit, referred to 1% absorption, is 1 µg of mercury/l. An accuracy of 10% is obtained when measuring in urine. An average of 4.31 ± 2.33 µg of mercury was found when the urines of 26 non-exposed men were analyzed.     

Gas-chromatographic elemental analysis via di(trifluoroethyl)dithiocarbamato-chelates

Summary The capillary gas chromatographic determination of Cr[VI] besides Cr[III] and of Co in Rhine water is described. The previously reported [9] optimized arrangement is used. Detection is performed with an ECD, extraction of the chelates from aqueous solution, pH 3, is carried out with a solid phase extraction system. The detection limits of Cr[VI] and Co are 0.05 ppb and 0.2 ppb, respectively.

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Gas-Chromatographische Elementanalyse mit Hilfe von Di(trifluorethyl)dithiocarbamat-ChelatenX. Capillar-Gas-Chromatographie im pg-Bereich — Bestimmung von Co und Cr[VI] neben Cr[III] in Flußwasser

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1 Part IX see [9]     

The Calf Intestinal Alkaline Phosphatase. II. Reaction between the metal content and the enzyme activity

Pure alkaline phosphatase (EC 3.1.3.1; 1500 U/mg) was dialyzed at 4° during 168 h against water, 10^?4M EDTA or 10^?4M o-phenanthroline. During the dialysis, samples were periodically removed and analyzed for metal content and activity. The results indicate that 1 mol of native calf intestinal alkaline phosphatase contains 4 g-atom of zinc and 4 g-atom of magnesium tightly bound, and that both metal ions are necessary for full enzyme activity. The dialyzed, partially demetallized enzyme could be reactivated by the addition of zinc and/or magnesium salts.     

Gas-chromatographischer Nachweis von Methylquecksilber im Vollblut im Nanogrammbereich

Ohne Zusammenfassung

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Detection of methylmercury in blood at the nanogram level by gas chromatography

     

X-ray absorption spectroscopy of liquid methanol microjets: bulk electronic structure and hydrogen bonding network

We have measured the X-ray absorption (XA) spectrum of liquid (298 K) methanol at the oxygen and carbon K edges. The 4a(1) orbital at the O K edge exhibits a pronounced sensitivity to the formation of intermolecular hydrogen bonds, with significant differences observed between the vapor and bulk spectra, whereas the C K edge reveals only subtle corresponding spectral changes. Comparison with DFT computed spectra of model methanol clusters indicates that the bulk liquid comprises long chains (n > 6) and rings of hydrogen-bonded monomers.     

Direct observation of the ionization step in solvolysis reactions: electrophilicity versus electrofugality of carbocations

Rates and equilibria of the reactions of highly stabilized amino-substituted benzhydrylium ions (Ar2CH+) with carboxylate ions have been determined photometrically in acetone and acetonitrile solutions. Treatment of covalent benzhydryl carboxylates (Ar2CH-O2CR) with aqueous acetone or acetonitrile leads to the regeneration of the colored amino-substituted benzhydrylium ions Ar2CH+, which do not undergo subsequent reactions with the solvent. One can, therefore, directly measure the first step of S(N)1 reactions. The electrofugality order, i.e., the relative ionization rates of benzhydryl esters Ar2CH-O2CR with the same anionic leaving group, does not correlate with the corresponding electrophilicity order, i.e., the relative reactivities of the corresponding benzhydrylium ions Ar2CH+ toward a common nucleophile. Thus, benzhydrylium ions which are produced with equal rates by ionization of the corresponding covalent esters may differ by more than 2 orders of magnitude in their reactivities toward nucleophiles, e.g., carboxylate ions. Variable intrinsic barriers account for the breakdown of the rate-equilibrium relationships. Complete free-energy profiles for the ionization of benzhydryl carboxylates Ar2CH-O2CR are constructed, which demonstrate that the transition states of these ionizations are not carbocation-like. As a consequence, variation of the solvent-ionizing power Y has only a small effect on the ionization rate constant (m = 0.35 to 0.55) indicating that small values of m in the Winstein-Grunwald equation do not necessarily imply an S(N)2 type mechanism.     

Experimental evidence for muonicX-rays from fission fragments

In the spectrum of muonic X-rays of²³⁸U measured in coincidence with prompt fission events a structure has been found which is attributed to 2p1s transitions of the muon attached to heavy fragments. The intensityI _s of this structure relative to the strengthI _pf observed for prompt fission has been determined to beI _s/I _pf=(6.0± 2.1) %. Although the experimental significance for the appeareance of this phenomenon is weak, this is the first experimental indication for its occuxence.We are indebted to the following institutes or organizations for financial support: Bundesministerium für Forschung und Technologie der Bundesrepublik Deutschland contract number 06BN271 (CR,PD,HH,FR,WS), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK,CTAMdL,AT), the Swiss National Foundation (SNF) (LAS,LS), and the Heinrich-Hertz-Foundation (HH) (FFK,BS).     

Counting statistics of collective photon transmissions

We theoretically study cooperative effects in the steady-state transmission of photons through a medium of N radiators. Using methods from quantum transport, we find a cross-over in scaling from N to N² in the current and to even higher powers of N in the higher cumulants of the photon counting statistics as a function of the tunable source occupation. The effect should be observable for atoms confined within a nano-cell with a pumped optical cavity as photon source.