Characterization of luminescence centres in neodymium implanted zinc sulphide

Analysis of the cathodoluminescence emission spectra of neodymium implanted cubic single crystal ZnS as a function of post-implantation annealing temperature has enabled groups of emission lines to be identified as originating from transitions within particular luminescence centres. For each group of lines the wavelength separations yield energy splittings characteristic of the crystal field at the luminescence centre. Comparison of these splittings with values calculated by crystal field theory on the basis of a point charge model, with due regard to possible sites of cubic symmetry in ZnS, has allowed two luminescence centres (A and B) to be identified.Centre A, which exists at low annealing temperatures, consists of a Nd³⁺ ion situated interstitially with 4 tetrahedrally disposed nearest neighbour S^2? ions. At higher annealing temperatures the emissions from centre A were found to decline giving way to those of centre B, which analysis shows to be a Nd³⁺ ion situated on a zinc substitutional site.     

Neutron spectra at 0° from (p,n) reactions on 9Be, 12C,and 27Al at 647 and 800 MeV

The measured cross sections show a narrow high-energy peak (20–30 MeV/cFWHM) and a broad bump at lower momenta associated with pion production. Comparison is made to an intranuclear cascade calculation.     

THE NATURE OF ULTRAVIOLET LIGHT-INDUCED STRAND BREAKAGE IN DNA CONTAINING BROMOURACIL

Abstract— Single-strand breaks are produced in the phosphodiester backbone of ultraviolet-light-irradiated 5–bromodeoxyuridine-containing DNA (BU-DNA) after treatment with alkali. No radiation dependent breakage is observed in thymine-containing DNA (thy-DNA). The relative yields of breaks terminated by 5'-hydroxyl and 5'-phosphate groups was determined by measuring the rate of phosphorylation achieved with polynucleotide kinase in BU-DNA single strands before and after treatment with alkaline phosphatase. The ratio of 5'-phosphate to 5' hydroxyl groups ranged from 2.3 to 2.9 in different experiments. When cysteamine was present during irradiation no new end groups were produced.
In order to identify the nucleoside(s) at the 5'-termini, phosphate groups were removed with alkaline phosphatase and the 5'-hydroxyl groups were phosphorylated with polynucleotide kinase. Electrophoresis of enzymatic digests showed a single ³²P-labeled component migrating more rapidly than any of the four usual 5'-mononucleotides. Upon column chromatography this component resolved into a major peak coincident with 5'-dUMP and a lesser unidentified constituent. No 5'-dBUM³²P was observed among these nucleotides.     

Infrared spectral changes with crystallization in poly(vinylchloride): Correlations with X-ray and density data

The influence of crystallinity and stereoregularity on the infrared (IR) spectrum of atactic PVC in the solid state has been studied by many researchers [1-12]. Although the molecules in commercial PVC consist of both syndiotactic and isotactic sequences, the bulk polymer is not highly stereoregular, having approximately 50% syndiotacticity. Its infrared spectrum is different from that of highly syndiotactic PVC [3,5,7,9,10-12], particularly in the carbon-to-chlorine stretching region where there are three bands located at 610(615), 635, and 690 cm^?1. These three bands are known to be of complex origin, since each band consists of more than one absorption frequency and its relative intensity depends on the physical state or history of the specimen [3,5,7,9,10-12]. The spectrum in this region is most rigorously interpreted in terms of chain conformational structure, the spatial arrangement of the atoms around the C-C1 bond. Thus, while changes in absorbance intensities for the bands with history do not necessarily reflect changes in crystallinity, their history dependence renders these bands potentially useful as crystallinity indicators.     

Raman Scattering Tensors in Biological Molecules and Their Assemblies

INTRODUCTION

The tensor associated with a Raman band plays an important role in determining the band intensity and its structural significance. Each Raman tensor interrelates two electric vectors, that of the exciting radiation (i.e. laser photon) and that of the Raman scattered radiation (i.e. the inelastically scattered photon which results from the exchange of a vibrational quantum between the exciting photon and the molecule). The Raman tensor is obtained formally as the first derivative of the molecular polarizability tensor, the derivative being taken with respect to the vibrational normal coordinate. In other words, the Raman tensor associated with a vibrational Raman band is an indicator of how the polarizability of the molecule oscillates with the molecular normal mode of vibration.     

Implantation of ytterbium ions into group II-VI compounds

50 keV ytterbium ions have been implanted into ZnS, CdS, ZnSe, CdTe, CdSe and ZnTe and, after subsequent annealing treatments of varying degree, the cathodoluminescence emission spectra produced by 10 keV or 100 keV electron excitation have been studied.     

On the Hamilton‐Waterloo Problem for Bipartite 2‐Factors

Given two 2‐regular graphs F₁ and F₂, both of order n, the Hamilton‐Waterloo Problem for F₁ and F₂ asks for a factorization of the complete graph into α₁ copies of F₁, α₂ copies of F₂, and a 1‐factor if n is even, for all nonnegative integers α₁ and α₂ satisfying . We settle the Hamilton‐Waterloo Problem for all bipartite 2‐regular graphs F₁ and F₂ where F₁ can be obtained from F₂ by replacing each cycle with a bipartite 2‐regular graph of the same order.     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.