Measurement of the total active 8B solar neutrino flux at the Sudbury Neutrino Observatory with enhanced neutral current sensitivity

The Sudbury Neutrino Observatory has precisely determined the total active (nu(x)) 8B solar neutrino flux without assumptions about the energy dependence of the nu(e) survival probability. The measurements were made with dissolved NaCl in heavy water to enhance the sensitivity and signature for neutral-current interactions. The flux is found to be 5.21 +/- 0.27(stat)+/-0.38(syst) x 10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of these and other solar and reactor neutrino results yields Deltam(2)=7.1(+1.2)(-0.6) x 10(-5) eV(2) and theta=32.5(+2.4)(-2.3) degrees. Maximal mixing is rejected at the equivalent of 5.4 standard deviations.     

The effects of sample preparation methods on the variability of the electrospray ionization response for model drug compounds

A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd.     

Precision measurements of recoil-free fraction and interference with hundred Curie sources

We discuss our experiences with exceptionally intense Mössbauer sources (of order 100 Ci) and their use in making precision determinations of line shape parameters. We review our measurements of interference and recoilless fraction using conventional transmission geometry. Fitting simultaneous sets of data with known constraints greatly improves the efficiency of line-shape determination. Measurements of interference have been made using a two-absorber technique first introduced by Mössbauer and coworkers. Our results indicate that the method can be useful for determining interference, but that incorrect line shape parameters are obtained if powder samples are used which do not comply well with the assumption of thickness uniformity in the absorber.     

Independent measurement of the total active 8B solar neutrino flux using an array of 3He proportional counters at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results.     

Orientation dependence of the isoelectric point of TiO2 (rutile) surfaces

The electroosmotic behavior of the rutile polymorph of titanium dioxide was explored as a function of the crystallographic orientation. Atomic force microscopy (AFM) was employed to make high-resolution force spectroscopy measurements between a silica sphere attached to a traditional, contact-mode AFM cantilever and TiO2(110), TiO2(100), and TiO2(001) surfaces in aqueous solutions. Measurements were taken in multiple solution conditions across a broad range of pH values, and the resultant force-distance curves were used to deduce relative behaviors of each orientation of rutile, with particular interest in changes of the isoelectric point (iep). Differences in the iep as a function of orientation are explained in terms of differences in both the coordination number and density of acidic and basic sites on the surface. The results were supported by angle-resolved X-ray photoelectron spectroscopy (XPS) measurements of a nominal monolayer of palladium metal deposited on each of the three orientations studied. The palladium monolayer served as a means of probing the relative electron affinities of the three surfaces studied, which were exhibited in shifts of the palladium XPS peak that corresponded to differences in the binding energy as a function of the substrate orientation. The correlation between the rutile orientation and the shift in the palladium binding energy corresponded directly to the relationship between the isoelectric point and the orientation, with the surface of lowest isoelectric point exhibiting the highest Pd binding energy.     

Structural evolution of the MoO3(010) surface during lithium intercalation

Atomic force microscopy (AFM) has been used to characterize the structural evolution of the MoO₃(010) surface during the initial stage of Li⁺ intercalation. Lithiation was observed in situ using model cells comprised of a single crystal MoO₃ cathode, a dilute propylene carbonate (PC)-based electrolyte, and an Li metal anode. The insertion of Li⁺ into MoO₃ results in the topotactic nucleation and growth of acicular Li_xMoO₃ (x0.25) precipitates at the (010) surface. Because the interlayer spacing of Li_xMoO₃ (d=7.88 Å) is greater than that of MoO₃ (d=b/2=6.93 Å), the Li_xMoO₃ precipitates expand out of the (010) surface as they grow into the MoO₃ crystal along 010. The local strain associated with this expansion causes the Li_xMoO₃ precipitates to crack parallel to the MoO₃001 and 010 axes once their height exceeds approximately 20 nm. With continued Li⁺ intercalation, cracking becomes more prominent, and the (010) surface begins to fragment and disintegrate. Anisotropies in Li⁺ ion uptake and the influence of surface morphology on Li_xMoO₃ precipitation and crack propagation are described.     

Stability of voids formed in cavities at liquid-solid interfaces

A thermodynamic model is developed of the free energy of gas-filled voids formed within cavities on solid surfaces covered by a liquid. Capillary effects are assumed to be the only important contributions to the free energy, and expressions are derived for the free energy of the system as a function of the void size, the relative surface free energy densities involved, and the geometry of the cavity. The results of the model are (1) construction of a stability diagram that maps the most stable void configuration versus the wetting properties of the various solid surfaces involved, and (2) rough estimates of the work required to liberate a void of a given size and position. The model can give qualitative insight into the stability of coating defects on uneven surfaces, and also can be used to prescribe possible surface treatments for reducing the work required to remove voids from the system.