Sn-vacancy defects in GaP

Complex¹¹⁹Sn-vacancy defects in GaP have been studied by Mössbauer-emission spectroscopy on the 24-keV γ radiation of¹¹⁹Sn. The defects were created by ion implantations of radioactive¹¹⁹In⁺ and¹¹⁹Sb⁺, which in their decays both populate the Mössbauer state of¹¹⁹Sn. The radiogenic¹¹⁹Sn-vacancy defects are proposed to consist of substitutional¹¹⁹Sn on Ga or P sites, respectively, associated with (P or Ga) vacancies.     

Geometrical description of binary reactions and large p⊥ phenomena

We study consequences of defining the impact parameter as being the variable conjugate to transverse relative c.m. momentum, p_⊥. This coincides with a proposal originally made by Chang and Raman. The dynamical information carried by these are intimately connected to the behaviour of 90° scattering. In particular, impact parameter dynamics is a priori qualitatively different from direct channel angular momentum dynamics. A phenomenological study of elastic π^±p and pp data at fixed values of longitudinal momentum, p₆, leads to a generalized geometrical scaling hypothesis. In contrast with the power behaviour predicted by parton models, the data suggest exponential behaviour of the scaling amplitudes at fixed p₆ of the type e^Rp⊥ with R ? 1 fm. Correspondingly these amplitudes are described by a pair of complex conjugate singularities on the imaginary axis in the impact parameter plane.     

A simple multifunctional valve for flow injection analysis

A simple and versatile pneumatically-operated two-layer rotary valve is described for simultaneous introduction of sample and diversion of analytical streams in flow injection analysis. Examples of application include valve configuration with time-controlled sample volume and with loop-controlled sample volumes in one or two loops; both configurations are useful in routine analyses of samples of highly varying analyte concentrations. The usefulness of the valve for ion-exchange preconcentration procedure is also demostrated.     

The (3He,n) reaction in the lower 2s1d shell

The two-proton transfer reaction (³He, n) has been measured on four gas targets, ¹⁶O, ¹⁸O, ²⁰Ne, and ²²Ne, with an incident ³He energy of 18.3 MeV. The data were taken with a neutron time-of-flight spectrometer in the angular range 0° to 40° c.m. The results for selected transitions are compared to DWBA predictions using shell-model spectroscopic amplitudes. In addition, the data for the ¹⁸O(³He, n)²⁰Ne reaction are compared to predictions of the SU(3) strong coupling model.     

STM investigations of PTCDA and PTCDI on graphite and MoS2. A systematic study of epitaxy and STM image contrast

Monolayers of the organic molecules perylene-3,4,9,10-tetra-carboxylic-dianhydride (PTCDA) and diimide (PTCDI) on graphite and MoS₂ have been imaged with scanning tunneling microscopy. The epitaxial growth of the two molecules is determined by the intermolecular interaction but nearly independent of the substrate. On both substrates the STM image contrast in the submolecularly resolved images is dominated by the aromatic perylene system whereas the polar oxygen and nitrogen groups are invisible. The correlation of the observed inner structure of the molecules to their molecular structure allows us to compare our results with theoretical considerations.     

Isolation and analysis of N-oxide metabolites of tertiary amines: quantitation of nicotine-1'-N-oxide formation in mice

To investigate the formation and elimination of nicotine-1'-N-oxide (NNO) in mice treated with a single injection of nicotine, sensitive and selective methods were developed to quantitate this polar and heat-labile metabolite. The compound was isolated from tissue homogenates as a dodecyl sulfate ion pair with C18 extraction cartridges and analyzed on an amino bonded-phase high-performance liquid chromatographic column with a mobile phase consisting of isopropanol-water. Overall recoveries of NNO were 64-76% from biological media. Several methods of detection were evaluated; radiolabeling was necessary to achieve the sensitivity required for pharmacokinetic studies in mice. The cis and trans isomers of NNO were separated on a Partisil PAC column and enzymatic selectivity was evaluated for the formation of these isomers in mice.     

Positron annihilation study of voids in a neutron irradiated aluminum single crystal

We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·10²¹ n/cm² (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·10¹⁴ voids/cm³ with a mean diameter of 330 ?, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT ^1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum. Research sponsored in part by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation.