Elastic scattering of 40Ar on 40Ca at Elab = 191, 236 and 272 MeV

Cross sections for elastic scattering of ⁴⁰Ar on ⁴⁰Ca have been measured at energies E_lab = 191, 236 and 272 MeV employing position-sensitive detectors and the method of kinematical coincidences. The experimental data are first compared with the ordinary and the generalized Fresnel models. Only the generalized Fresnel model describes the experimental data well. An optical model analysis with a Woods-Saxon potential yields an energy independent set of parameters (V_R = ?21.76 MeV, r_OR = 1.37 fm, a_R = 0.45 fm; W₁ = ?13.69 MeV, r₀₁ = 1.40 fm, a₁ = 0.36 fm) very similar to the one found in ⁴⁰Ca-⁴⁰Ca scattering at corresponding energies. Values deduced for the total reaction cross sections for the three energies are in good agreement with those predicted by the generalized Fresnel model. The data are also compared with optical model calculations with the real part of the potential replaced by various microscopically determined potentials. The proximity, Fleckner-Mosel and the Krappe-Nix-Sierk potentials like the phenomenological optical model potential reproduce the measured data fairly well over several orders of magnitude.     

Laser spectroscopic properties of Nd3+ -doped tellurite glasses

The stimulated emission cross-section σ and fluorescence lifetime for the 1.06 μm emission (⁴F_3/2 →⁴I_1/12) have been measured for a number of Nd-doped tellurite glasses. The measured value of σ ? 9 × 10^-20 cm ² for the tellurite glasses is to be compared with the value of 3.5 × 10^-20 cm ² for the ED-2 glass. Based on the measured spectroscopic parameters, an LED-pumped tellurite glass fiber laser is predicted to perform better than ED-2 glass, both in the longitudinal and transverse pumping configuration. The threshold for side-pumped tellurite glass laser can be comparable or even lower than that in Nd:YAG.     

Permeability of heterogeneous gels

Gels made by radical copolymerization of monofunctional and difunctional monomer units in the presence of swelling medium will tend to be heterogeneous. A case in point is acrylamide co-polymerized with N,N′-methylene bis-acrylamide in water. Such gels can be assumed to be two-phasic with both phases gels, but of different average concentration and average degree of cross-linking. As Weiss and Silberberg have shown, permeability can be used to characterize the distribution in space. In this paper, their earlier model is expanded and improved by considering specifically the permeability of each of the two phases and taking into account that each of these phases separately must have come into swelling equilibrium with the swelling medium, water. It can be shown that only the length of the Kuhn statistical element remains as a free parameter in this model. Essentially the same value of this parameter, however, accurately accounts for the measured permeability. It is found that at an overall volume fraction of about 0.16, the two-phase structure tends to disappear. For higher degrees of crosslinking, this occurs because the more dilute phase takes over the entire space; for more lightly crosslinked systems, the more concentrated phase takes over. The heterogeneity of the distribution lies in the nanometer range and reasonable agreement between the results obtainable from permeability and from viscoelasticity can be demonstrated. These results are consistent with the model for the polymerization process.     

Probabilistic quark-model approach to proton fragmentation

A probabilistic approach is formulated to study the behaviour of the incident hadron quark flavours in the fragmentation process of high energy protons in lowp _T reactions. Analysis of available data onpp collisions, mainly on hyperon and antibaryon multiplicities, leads to estimates of the probabilities for the different ways in which the incident valence quarks recombine into final hadrons. We find that all three incident quarks emerge in one and the same outgoing nucleon (or nucleon resonance) with probabilityA ₃=0.35–0.4, that two of them emerge in one baryon and the third in another hadron (mostly a meson or meson resonance) with probabilityA ₂=0.6–0.5, and that they emerge in three distinct hadrons (mostly mesons or meson resonances) with probabilityA ₁=0.05–0.1. We find good support for a very simple probabilistic picture of the fragmentation process.     

Redistribution of population among the higher levels of Na atoms in an H2-O2-Ar flame

A substantial fraction of the population of Na-atoms in an H₂-O₂-Ar flame is found to be distributed among the higher levels as a result of two-photon laser excitation, spontaneous emission and collisions with flame gas atoms and molecules. Several population inversions are observed. From the laser-excited level upwards, a partial Boltzmann equilibrium, corresponding to the flame temperature, has been found in some cases. Estimates of weighted average rate-constants for collisional energy transfer from groups of higher levels to the 3P-level are given. Some level-pairs appear to be strongly coupled to each other.     

Base-induced cycloaddition of N-(tosylmethyl)imino compounds to michael acceptors. Synthesis of 2,3,4-trisubstituted pyrroles

A series of N-(tosylmethyl)imino compounds [TosCH₂N?C(L)A] has been prepared, and applied to a new, base-induced, one-operational synthesis of otherwise more difficultly accessible 2,3,4-trisubstituted pyrroles from electron deficient olefins. This regiospecific process probably is an 1,3-anionic cycloaddition, combined with the elimination of sulfinic acid and a leaving group L. The group A is retained as the 2-substituent of the resulting pyrroles.     

A monitor for the specific determination of nickel carbonyl based on the chemiluminescence reaction with ozone and carbon monoxide

The chemiluminescence, measured at 500 nm, allows nickel carbonyl to be measured in the range 1 ppb to several ppm in combustion gases. Interferences from iron pentacarbonyl and nitrogen monoxide are eliminated by optical and spatial discrimination and by choice of the pressure in the reaction chamber.