The energy levels of79Br and81Br

The low-lying energy level and decay schemes of the stable bromine isotopes were studied by observing the γ-rays from the (n, n′γ) reactions in a natural bromine sample with the aid of a Ge (Li) detector. A pulsed neutron source and time-of-flight methods were used to reduce background due to neutron events in the detector. Most of the γ-rays observed could be assigned to transitions in either⁷⁹Br or⁸¹Br. In addition to those levels previously known from γ-decay or Coulomb excitation experiments, several new levels were excited in each isotope.     

Energy transfer in unimolecular reactions at high temperatures

The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant–reactant and reactant–inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock-tube measurements, may be greater than has been believed hitherto. The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock-tube conditions the apparent first-order rate coefficient may be at least ten times less than the high-pressure limiting value.     

An investigation of 73As energy levels by means of (p,n) and (p,nγ) reactions

The energy levels of ⁷³As were studied by means of the ⁷³Ge(p, n)⁷³As reaction at proton energies between 2.1 and 3.3 MeV. Neutron energies were measured by time of flight, and γ-ray energies with Ge(Li) detectors. The γ-decay of levels was studied by means of γ-n coincidences. Angular distributions were measured for the strongest de-excitation γ-rays, and relative excitation strengths of levels were derived from the neutron spectra. These are compared with predictions of the statistical theory to derive spins for a number of levels. A level and decay scheme for ⁷³As up to 1.98 MeV excitation is presented.     

Experimental study of stark broadening of nitrogen ion lines in a theta pinch plasma

We have studied the Stark broadening of the 3s-3p, 3p-3d and 3d-4f emission lines of the nitrogen II, III, and IV ions emitted from a hot plasma. The plasma was created by a 60 kJ, 60 kV single turn coil theta pinch, where the fill gas was 3 torr of (49%He+51%N₂). The plasma was diagnosed by measuring the Stark-broadened profile of the He(II) 4686 Å line and by taking shadowgrams of the plasma development. It was found that the ionization stage distribution and thus the electron density departed from that predicted by Saha-Boltzmann equilibrium relations. The analysis of the plasma parameters gave an electron density of 1.4 x 10¹⁸ cm^-3. The electron temperature was measured from the relative intensities of emission lines as well as from the line-to-continuum ratio and was found to be 5.0 eV. The line profiles have been fitted to Lorentzian profiles and the thus measure line widths are compared with earlier experimental data as well as with simple theoretical calculations. We find that our line widths are broader than earlier data taken at lower densities if we assume a linear scaling of the half width with the density. A simple Lorentzian profile fits in most cases quite well to the observed line profile. The simple calculations can predict the linewidths within 20% for the low lying levels of both the singly and doubly ionized nitrogen while the predictions are far too narrow for the higher lying levels from the multiply ionized atoms.     

Preparative and spectroscopic features of ferricenium tetrachloroferrate(III). Interconversion to diferricenium μ-oxo-bis[trichloroferrate(III)]

Summary Ferricenium tetrachloroferrate(III)(1), one of the more frequently cited ferricenium salts, has recently attracted biomedical interest because of its pronounced antineoplastic activity against Ehrlich ascites murine tumor. In this paper, synthetic methods are reinvestigated in an effort to prepare pure(1) free from a common contaminant, diferricenium-oxo-bis(trichloroferrate)(3). The oxodiferrate, or mixtures of this salt with(1), can readily be converted into pure(1) under acidic conditions. Conversely, dimerization of(1) with participation of water to give the oxodiferrate(3) is brought about by recrystallization of the former from moist acetonitrile/methanol in the presence of base; this reaction thus represents a simple procedure for the preparation of pure(3) from crude(1) readily obtainable by the long known interaction of ferrocene and iron(III) chloride in indifferent media. The i.r. and electronic absorption spectra of(1) are presented, as are the Mössbauer and x-ray photoelectron spectra. The room-temperature effective magnetic moment, 6.40 _B, of the salt is lower than would be expected on the basis of typical ferricenium cation (2.4 _B) and tetrachloroferrate(III) anion (5.9 _B) moments determined for related salts. This suggests the possibility of weak inter- or intra-molecular antiferromagnetic interaction in the crystal.     

End point of the rp process on accreting neutron stars

We calculate the rapid proton ( rp) capture process of hydrogen burning on the surface of an accreting neutron star with an updated reaction network that extends up to Xe, far beyond previous work. In both steady-state nuclear burning appropriate for rapidly accreting neutron stars (such as the magnetic polar caps of accreting x-ray pulsars) and unstable burning of type I x-ray bursts, we find that the rp process ends in a closed SnSbTe cycle. This prevents the synthesis of elements heavier than Te and has important consequences for x-ray burst profiles, the composition of accreting neutron stars, and potentially galactic nucleosynthesis of light p nuclei.     

Nondestructive evaluation of helicopter rotor blades using guided Lamb modes

This paper presents an application for turning and direct modes in a complex composite laminate structure. The propagation and interaction of turning modes and fundamental Lamb modes are investigated in the skin, spar and web sections of a helicopter rotor blade. Finite element models were used to understand the various mode conversions at geometric discontinuities such as web-spar joints. Experimental investigation was carried out with the help of air coupled ultrasonic transducers. The turning and direct modes were confirmed with the help of particle displacements and velocities. Experimental B-Scans were performed on damaged and undamaged samples for qualitative and quantitative assessment of the structure. A strong correlation between the numerical and experimental results was observed and reported.     

The first Raman spectroscopic study of San rock art in the Ukhahlamba Drakensberg Park,South Africa

San rock art sites are found throughout southern Africa; unfortunately this unique heritage is rapidly being lost through natural weathering processes, which have been the focus of various studies conducted in the uKhahlamba Drakensberg Park since 1992. It has recently been shown that the ability of Raman spectroscopy to identify salts on rock faces on a micro, as well as nano scale, can make a contribution to these projects. In order to test the feasibility of undertaking on‐site analyses, a small rock fragment with red and white pigments still attached, which had weathered off the rock face, was analysed with Raman spectroscopy under laboratory conditions, using a Dilor XY Raman instrument and a DeltaNu Inspector Raman portable instrument. A small sample of black pigment (<1 mm²), collected from a badly deteriorated painting and a few relevant samples collected on site, were analysed as well. It was possible to identify most of the inorganic pigments and minerals detected with previous XRD and EDX measurements including whewellite and weddellite coatings, which could be a tool for carbon dating purposes. Two carotenoid pigments were detected for the first time in San rock art pigments. Animal fat was also observed for the first time on both red and white pigments, on the rock face adjacent to the paintings and in highest concentrations on the back of the rock fragment. The spectra quality makes successful on‐site measurements a good prospect. Copyright © 2008 John Wiley & Sons, Ltd.