Die Szintillations-Anisotropie von Anthrazen bei tiefen Temperaturen. II

Continuing previous work the scintillation anisotropy of anthracene bombarded with α particles has been measured as a function of temperature between 1.9 and about 80° K. With all crystal specimens investigated a pronounced minimum has been found between 20 and 30° K. The anisotropy is constant below about 9° K, whereas the light yield still increases with decreasing temperature down to 1.9° K. The light yield has been found to be a nonlinear function of the temperature.     

Verzweigungsverhältnisse von Ag110(T 1/2=24,4 sec)

The branching ratios of 24 sec Ag¹¹⁰ have been measured with scintillation spectrometers. A new upper limit of 0.9% is given for decay byK-electron capture.     

Ionenstrahlspektroskopie mit Wasserstoffionen als Primärteilchen

Relative initial populations of foil-excited hydrogen atoms in the2p, 3s, 3p, and3d states are determined by measuring the Balmer-α and Lyman-α emissions simultaneously. The data are analyzed by a computer program which takes into account the correlation of both emissions. The results show a dependence on the kind of incident ions: molecular ions give more light and lead to more pronounced excitation of higher angular momentum states than do atomic ions. A possible mechanism to explain this “molecule effect” is discussed qualitatively.     

Observation of transitions between quartet levels of doubly excited Al10+

The line multiplet Al XI 1s2s2p 4P^o-1s2p^{2 4}P has been observed using beam-foil spectroscopy. The mean transition wavelength λ=(53.283±0.01) nm and three out of four finestructure intervals have been determined. The results are compared to recent theoretical calculations.     

Beam-foil lifetimes of O VII in the 10–100 ps-range

Measured lifetimes of foil-excited O VII are found to be in good agreement with theoretical predictions. Experimental and evaluational problems are discussed. Examination of the lineλ=20.48 nm shows a blending of the second orderλ=10.24 nm transition in O VIII with 3d?7p,f transitions in O VII.     

Beam-foil spectrum of silicon in the extreme UV

UV-spectra of foil-excited Si ions accelerated to 20 MeV show 120 known lines of Si VIII-XIV and about 150 additional lines in the region 8–61 nm. 28 new classifications are proposed. Then=2 level scheme of Si X is revised. Two transitions are reassigned.     

Supramolecular Structure of Precipitated Nanosize β-Carotene Particles

A combination of analytical methods and molecular modeling calculations has provided a detailed picture of the supramolecular and microscopic structure of precipitated lipophilic carotenoids. The nanoparticles have a core/shell structure (see schematic representation) in which the particle core (120 nm) consists of a variety of molecular aggregates of different sizes, and the shell (40 nm) consists of an adsorbed gelatin layer.     

Structure-Property Relationships in Rubber-Modified Styrenic Polymers

Styrenic polymers and copolymers are often impact modified with rubber particles. The efficiency of rubber toughening depends mainly on the size of the rubber particles and the degree of cross-linking. The deformation rate, the temperature, the orientation of the polymer molecules and the efficiency of rubber grafting also influence rubber toughening. It is thought that on impact, cavitation inside the rubber particles occurs which reduces the detrimental dilatational stress in the bulk polymer without forming cracks in the brittle matrix or at the rubber-matrix interface. Crazing and shearing are facilitated if the rubber particles can easily cavitate. This can be achieved by either avoiding too much cross-linking or by adding oil (silicone oil in the case of ABS) into the rubber particles, which acts as nuclei for void formation. An electron spectroscopic imaging method is described which allows visualizing the location of the oil. Already after cooling silicone oil modified ABS samples down to liquid nitrogen temperature rubber cavitation is observed. This cavitation is caused by the thermal stress developing due to the differences in thermal expansion coefficient between the rubber phase and the SAN-matrix and is facilitated by silicone oil. Voiding also leads to an increase of light scattering, which can be detected by an optical microscope using dark field illumination.     

Determination of particle size in multiphase blends by different methods

Different methods for characterizing the morphology of multiphase blends were applied to a blend of thermoplastic polyurethane with 20 wt% polypropylene as the dispersed phase. Optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and light scattering were compared. The microscopy methods were evaluated with respect to their suitability for quantitative image analysis for determination of the particle size distribution. Comparison of the particle size distributions revealed that the dependence of the measured particle size on the method of preparation and technique was not very pronounced. The main difference resulted from cutting the particles outside their maximum diameter. The measured particle sizes determined with methods that analyze the whole particles, such as SEM on separated particles and laser light scattering, are larger than those measured on cut specimens. The factor 4/π valid in monodisperse systems for the ratio between the real particle size and that measured on sections was found also to be applicable to this polydisperse blend system. Although light micros-copy requires the least preparation efforts, it is a reliable method for this blend system.