Multielement analysis of minor components using a 14 MeV neutron generator

14-MeV neutron activation has been used for the determination of F, Al, Si, P, K, Mn, Mo and W in minerals and steel. Most of these elements have been estimated simultaneously through gamma-ray spectrometry. The evaluation of the effects of interferences is discussed and the sensitivities are given. The main features of the neutron generator fabricated in this Centre and used in this work are briefly described.     

Determination of the stoichiometry of vanadium nitride films by proton back-scattering

Vanadium nitride films were grown on stainless steel and silicon, with different nitrogen concentrations by varying the partial pressures of nitrogen in a DC magnetron sputtering set up. These films were characterized for their composition by proton back-scattering and their micro hardness values were correlated with their N/V ratio.     

Feature extraction from spectral and other data by the principal components and discriminant function techniques

Principal component analysis is applied to the interpretation of ¹³C-n.m.r. spectra and to the resolution of mass spectral data. A procedure is given for determining the relative amounts of pure components, with and without the use of pure mass lines, in mass spectra of mixtures. The use of the Fisher discriminant method in combination with the principal components technique is demonstrated in the treatment of trace element data on hair for environmental purposes. The importance of feature generation and selection is emphasized.     

Elemental characterisation through instrumental neutron activation

Neutron activation has been used to characterise the elemental composition of geological and biological materials. Both reactor neutrons and 14 MeV neutrons have been used. Instrumental approach has been followed incorporating coincidence measurements. The system and the methodology have been discussed. The results for the 3 Canadian rock standards (SY-2, SY-3, MRG-1), a trachyte, 2 NBS SRMS (1571 Orchard leaves, 1577 Bovine liver) and an IAEA intercomparison sample, Animal Muscle H.4 have been given for 15–25 elements.     

Determination of Cd, Co, Cu, Fe and Ni at parts per billion level in high-purity gallium by graphite furnace atomic absorption spectrometry (GFAAS)

Summary The determination of Cd, Co, Cu, Fe and Ni in 6N gallium by GFAAS is reported. The analytes are extracted as pyrrolidine dithiocarbamates into methyl-iso-butyl-ketone (MIBK) in the presence of tartrate. The conditions of extraction, quantity of reagents required and the matrix interference aspects are discussed. The method offers one-step matrix removal and preconcentration, leading to low experimental blanks.     

Determination of stoichiometry of cadmium telluride by XPS

Summary The stoichiometry of cadmium telluride has been determined by the non-destructive technique of XPS. The determination has been based on differential photoionisation cross-sections, electron mean free paths and areas due to M₅ electrons of Cd and Te. The stoichiometry of Cd and Te determined by XPS has been found to be in good agreement with that obtained by analysing Cd and Te independently by chemical methods.     

High temperature superconductivity in bismuth-alkaline earth-copper-oxygen system

Electrical resistivity measurements of a series of compounds in the bismuth-alkaline earth-copper-oxygen system have been carried out. Several compositions (BiSrCaCu₂O _x , BiSrCaCu₃O _x , Bi₂Sr₂CaCu₄O _x and Bi₄Sr₃Ca₃Cu₈O _x ) showed superconducting onset temperatures in the range 90–130 K, though none of them showedT _cf(R=0) above 77 K. ExtrapolatedT _cf of three compounds are in the range 72–75 K. All compounds are multiphasic.     

Triple coincidence measurement of annihilation radiation — chemical application

Three photon yields and $\text{2γ}\text{3γ}$ ratios have been measured for several copper containing substances. The different extents of positronium formation have been substantiated through Doppler broadening, angular correlation and magnetic quenching in angular correlation and in peak-to-valley ratios of singles spectra at different fields. Application to chemical characterisation is indicated.