Systematics of back angle 12C scattering — the 12C + 20Ne and 12C + 24Mg systems

The back angle scattering of ²⁰Ne and ²⁴Mg ions from ¹²C display structured excitation functions and oscillatory angular distributions. These measurements bridge the gap between the previously studied ¹²C + ¹⁶O and ¹²C + ²⁸Si systems.     

Three photon virtual annihilation contributions to positronium hyperfine structure

Three photon virtual annihilation contributions to the positronium hyperfine interval are calculated to order α⁶m(α⁴R_∞). The result is obtained in analytic form and leads to the small value of -0.91 MHz for the contribution to the ground state energy difference from this source.     

Investigation of 91Zr by high resolution (d,p), (p,p′) and (p,d) reactions

Energy spectra and angular distributions of light particles (Z = 3–8) produced in the reactions ¹³C+^{58, 60, 64}Ni have been measured at 105 MeV. Coincidence events between light outgoing particles Li, Be, B and α, p have been observed for the first time in the ¹³C+⁵⁸Ni and ¹³C+⁶⁴Ni reactions. The results show that at least part of the ‘deep-inelastic’ events are due to many-particle reactions.     

Energy levels and level ordering in the WKB approximation

Energy levels and level orderings for a particle in a non-relativistic potential are examined in the WKB approximation. In particular, power-law potentials (V(r) = ar^γ, ?2 < γ < ∞) are discussed in some detail. The energy levels are shown to be determined in terms of a single function G(η, γ) of a variable η. Expansions of this function, valid for small (large) angular momentum quantum numbers (l) and large (small) radial quantum numbers (n), approximate the energy levels well. The ordering of the levels follows from the monotonic behavior of (?/?η)G(η, γ). The values γ = 2 (harmonic oscillator potential) and γ = ?1 (Coulomb potential) for which the WKB approximation gives the exact (i.e. Schrödinger) results lead to degenerate levels. It is about these values of γ that the monotonic behavior of (?/?η)G(η, γ) changes sign (as a function of γ). We also find an ordering theorem for arbitrary central potentials which is valid for large l and small n and is possibly correct for smaller l. The ordering depends on various sums of derivatives of the potential. Similar theorems, which follow from the Schrödinger equation, have been obtained recently for low-lying levels and are compared to our results.     

Reevaluation of the 22Na(p,gamma) reaction rate: implications for the detection of 22Na gamma rays from novae

Understanding the processes which create and destroy 22Na is important for diagnosing classical nova outbursts. Conventional 22Na(p,gamma) studies are complicated by the need to employ radioactive targets. In contrast, we have formed the particle-unbound states of interest through the heavy-ion fusion reaction, 12C(12C,n)23Mg and used the Gammasphere array to investigate their radiative decay branches. Detailed spectroscopy was possible and the 22Na(p,gamma) reaction rate has been reevaluated. New hydrodynamical calculations incorporating the upper and lower limits on the new rate suggest a reduction in the yield of 22Na with respect to previous estimates, implying a reduction in the maximum detectability distance for 22Na gamma rays from novae.     

Optical stark decelerator for molecules

We demonstrate a single stage optical Stark decelerator for neutral molecules which is capable of reducing the translational energy of benzene molecules within a molecular beam by 15% in a single pulsed Gaussian optical field of 15 ns duration. The change in velocity induced by the optical potential is measured by the change in the time of flight of benzene molecules ionized by a second optical field after the slowing field is turned off. A maximum reduction in the velocity of 25 m/s was measured using a single Gaussian beam with a peak intensity of 1.6 x 10(12) W/cm(2) corresponding to a maximum well depth of 253 K.     

State of Supported Nickel Nanoparticles during Catalysis in Aqueous Media

The state of Ni supported on HZSM‐5 zeolite, silica, and sulfonated carbon was studied during aqueous‐phase catalysis of phenol hydrodeoxygenation using in situ extended X‐ray absorption fine structure spectroscopy. On sulfonated carbon and HZSM‐5 supports, NiO and Ni(OH)₂ were readily reduced to Ni⁰ under reaction conditions (≈35 bar H₂ in aqueous phenol solutions containing up to 0.5 wt. % phosphoric acid at 473 K). In contrast, Ni supported on SiO₂ was not stable in a fully reduced Ni⁰ state. Water enables the formation of Ni^II phyllosilicate, which is more stable, that is, difficult to reduce, than either α‐Ni(OH)₂ or NiO. Leaching of Ni from the supports was not observed over a broad range of reaction conditions. Ni⁰ particles on HZSM‐5 were stable even in presence of 15 wt. % acetic acid at 473 K and 35 bar H₂.     

The synthesis of monomeric terminal lead aryloxides: dependence on reagents and conditions

The successful synthesis of terminal lead aryloxides is shown to be dependent upon reaction conditions, including choice of solvent and alkali metal aryloxide precursor.     

Colour development and luminescence phenomena in epoxy glasses

The process of colour development in aromatic-amine cured epoxy resin glasses following exposure to oxygen has been studied using electron spin resonance (ESR) and thermoluminescence (TL). Even short duration exposure to oxygen was found to produce species in glassy epoxy resins which gave rise to TL when heated from room temperature to a temperature just below the cure temperature. In some epoxy samples, oxygen exposure over longer periods was found to produce sample colouration. UV-visible spectrophotometry revealed chromophores which were believed to arise from the diaminodiphenylmethane structural unit found in epoxy systems containing the resin, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) or the curing agent, 4,4′-diaminodiphenylmethane (DDM). The chromophore produced in TGDDM-based resins appeared to be simlar to the "Wurster's salt'-type structure produced by photo-ionization of these systems. A distinctive ESR spectrum was also noted for samples exposed to oxygen. These results are indicative of both peroxide group formation on the methylene groups as well as the formation of amine centred radical cations, and are consistent with the oxidative sensitivity of these epoxy resins. The TL is believed to result from the thermally induced recombination of the 'Wurster's salt'-like cations with peroxy anions leading to the production of an electronically excited diaminobenzophenone structure © 1998 John Wiley & Sons, Ltd.