Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography

Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies in predictions for the electron–positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10⁻⁴, with an over threefold improvement on the previous measurement.

CPT violation could manifest itself in annihilating positronium events, but searching for this effect would require to know the spin of the annihilating system. Here, the authors do this using a positron-emission tomography scanner, finding no violation with a statistical precision of 10⁻⁴.

Adsorption of Alcohols from Multicomponent Solutions onto Silica Gel

Adsorption equilibria of the binary and ternary solutions of alcohols in benzene and n-heptane on silica gel have been studied in order to clarify their mechanisms of adsorption. Excess adsorption isotherms have been measured for hydrocarbon solutions of methanol, ethanol, butanol and pentanol. Interpretation of the experimental data was performed in terms of material balance between bulk and surface phase. In n-heptane solutions the multilayer surface structure is formed and the surface phase contains the alcohol only. For benzene and ternary (alcohol + benzene + n-heptane) solutions a mixed surface phase is observed whose composition is determined by competition of liquid components for silica surface as well as its tendency to complex. Moreover, the extent of adsorption in methanol systems is connected with the miscibility of liquid components.

The Porosity of Carbon Materials as Estimated by Thermogravimetric Analysis

The thermal desorption of benzene has been measured using a thermal analyzer. Pore size distributions of active carbons and carbon blacks have been determined on the basis of thermogravimetric curves using the Kelvin equation. Calculated distributions and total pore volumes have been compared with those derived from adsorption/desorption isotherms of nitrogen and benzene vapour.

Effect of silica precursor transformation on diclofenac sodium release

The present paper describes the preparation of a new type of ternary composites where pure silica gel or polysilsesquioxane was deposited on a polymer carrier loaded with a high dose of diclofenac sodium.

Nanostructured polymer-titanium composites and titanium oxide through polymer swelling in titania precursor

Polymer (XAD7HP)/Ti⁴⁺ nanocomposites were prepared through the swelling of polymer in titanium (IV) ethoxide as a titanium dioxide precursor. The nanocomposite beads exhibit relatively high porosity different than the porosity of the initial polymer. Thermal treatment of composite particles up to 200 °C in vacuum causes the change of their internal structure. At higher temperature, the components of composite become more tightly packed. Calcination at 600 °C and total removal of polymer produce spherically shaped TiO₂ condensed phase as determined by XRD. Thermally treated composites show the substantial change of pore dimensions within micro- and mesopores. The presence of micropores and their transformation during thermal processing was studied successfully by positron annihilation lifetime spectroscopy (PALS). The results derived from PALS experiment were compared with those obtaining from low-temperature nitrogen adsorption data.

Vacuum removal of the template in MCM-41 silica studied by the positron annihilation method

Positron annihilation lifetime spectra were measured for ordered silica before template (octadecyltrimethyl ammonium) removal. An intermediate lifetime component, well pronounced in the spectra, indicates the presence of structural defects in the template being the size of a surfactant molecule. At the temperature near 420 K a radical change of template structure occurs, consisting in appearance of disorder and the degradation of template; evaporation of the fragments begins. It seems that moderate heating (up to about 500 K only) in vacuum for several hours is an effective and simple method of template removal, leaving no pure carbon residue in the pore structure. The results are compared with the data from the liquid nitrogen adsorption/desorption method and elemental analysis, confirming the positron annihilation results.

Study of Adsorption Equilibria in the Systems Ternary Liquid Mixtures-Modified Activated Carbons

The adsorption abilities of commercial activated carbon after thermal and chemical treatment were investigated. The chemical character of carbon surfaces was determined by applying the thermogravimetric method, measurement of adsorption isotherms of water vapor, and the process of neutralization of surface functional groups. Total amounts of oxygen and nitrogen in all carbon samples were estimated by elemental analysis. Adsorption-desorption isotherms of benzene vapor were used to determine the parameters of the Dubinin-Radushkevich equation characterizing the porous structure of investigated carbons. These analyses show that chemical modification of carbon samples leads to strong differentiation of the chemical character of adsorbent surfaces; however, the porous structures show distinct similarity. In order to study the adsorption equilibria from liquid phase, the adsorption isotherms were measured for ternary mixtures of benzene, diethyl ketone, and n-heptane on all carbons. A strong effect of the chemical character of the carbon surface on liquid adsorption was found and discussed for all systems. Copyright 1999 Academic Press.

Effects of Surface Heterogeneity in Adsorption from Binary Solutions on Modified Silica Gels

The adsorption of benzene from cyclohexane solutions on modified silica gels is analysed using expressions derived from the model of adsorption of binary solutions on heterogeneous solid surfaces. The adsorption equation is found to represent the data for several systems and leads to a method for estimating the energetical heterogeneity of the adsorbent surface. The energy distribution functions for investigated systems are calculated. The same adsorption data are analysed using the simple form of isotherm equation for adsorption of binary liquid mixtures on heterogeneous solid surfaces. The results obtained by using two different methods for the same adsorption systems are discussed.