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.     

Modelling wave dynamics of compressible elastic materials

An Eulerian conservative hyperbolic model of isotropic elastic materials subjected to finite deformation is addressed. It was developed by Godunov [S.K. Godunov, Elements of continuum mechanics, Nauka, Moscow, 1978 (in Russian) and G.H. Miller, P. Colella, A high-order Eulerian Godunov method for elastic–plastic flow in solids, J. Comput. Phys. 167 (2001) 131–176]. Some modifications are made concerning a more suitable form of governing equations. They form a set of evolution equations for a local cobasis which is naturally related to the Almansi deformation tensor. Another novelty is that the equation of state is given in terms of invariants of the Almansi tensor in a form which separates hydrodynamic and shear effects. This model is compared with another hyperbolic non-conservative model which is widely used in engineering sciences. For this model we develop a Riemann solver and determine some reference solutions which are compared with the conservative model. The numerical results for different tests show good agreement of both models for waves of very small and very large amplitude. However, for waves of intermediate amplitude important discrepancies between results are clearly visible.     

A technique for searching for the 2K capture in 124Xe with a copper proportional counter

Physics of Atomic Nuclei - An experimental technique for searching for the 2K capture in 124Xe with a large low-background copper proportional counter is described. Such an experiment is conducted...     

Effect of high pressures on exchange and hyperfine interactions in rare-earth orthoferrites

The effect of high pressures P on the Néel temperature T _N , the crystal lattice parameters, and the magnitude of the hyperfine magnetic field H ^Sn at a nucleus of a diamagnetic tin atom was studied in pure and tin-doped orthoferrites RFeO₃ (R = Nd, Lu). The dependence of these quantities on the geometry of the exchange bonds, specifically, the angle and length of the chemical bond Fe-O-Fe(Sn), was analyzed. It was established that under pressure the angular contribution decreases and the radial contribution increases T _N and H ^Sn, the radial contribution being greater than the angular contribution in absolute magnitude. Numerical estimates were obtained for the angular and radial contributions to T _N and H ^Sn. In lutecium orthoferrite, at P > 30 GPa anomalies indicating a possible phase transition were observed in the behavior of the lattice parameters and the value of H ^Sn.     

Measurement of the <Superscript>14</Superscript>C Content in Liquid Scintillators by Means of a Small-Volume Detector in the Low-Background Chamber of the Baksan Neutrino Observatory

A setup for measuring natural-radioactivity backgrounds and ultralow concentrations of the isotope ¹⁴C in samples of a liquid organic scintillator was created at the low-background laboratory of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) at a depth of 4900 mwe. The concentration of the radiocarbon ^14C in a sample of a scintillator based on domestically produced linear alkylbenzene was measured, and it was found that ¹⁴C/¹²C (3.3 ± 0.5) × 10^?17.     

Observation of daily and annular variations in the <Superscript>214</Superscript>Po half-life

Results of the analysis of a time series of values of the half-life (τ) of the ²¹⁴Po nucleus with a different time step obtained from the TAU-1 (354 days) and TAU-2 (973 days) installations are presented. The annual variation with an amplitude of (9.8 ± 0.6) × 10^?4 and daily variations in the solar, lunar, and sidereal times with amplitudes of (5.3 ± 0.3) × 10^?4, (6.9 ± 2.0) × 10^?4, and (7.2 ± 1.2) × 10^?4, respectively, are found in the series of τ values. It is shown that variations in microclimatic parameters cannot be a cause of τ variations.     

Search for <Emphasis Type="Italic">2K</Emphasis>(2ν)-capture of <Superscript>124</Superscript>Xe

The results of a search for two neutrino mode of double K-capture of ¹²⁴Xe using a large copper low-background proportional counter are presented. Data collected during 3220 hours of measurements with 58.6 g of ¹²⁴Xe provides us to a new limit on the half-life of ¹²⁴Xe regarding 2K-capture at the level: T _1/2 ≥ 2.0 × 10²¹ years at a 90% confidence level.     

The origin of the background radioactive isotope <Superscript>127</Superscript>Xe in the sample of Xe enriched in <Superscript>124</Superscript>Xe

The results of investigation of ¹²⁷Xe radioactive isotope production in the xenon sample enriched in ¹²⁴Xe, ¹²⁶Xe, ¹²⁸Xe are presented. The isotope is supposed to be the source of the background events in the low-background experiment on search for 2K-capture of ¹²⁴Xe. In this work we consider two channels of ¹²⁷Xe production: the neutron knock-out from ¹²⁸Xe nucleus by cosmogenic muons and the neutron capture by ¹²⁶Xe nucleus. For the first channel the upper limit of the cross section of ¹²⁷Xe production was found to be σ ≤ 0.007 × 10^?24 cm² at 95% C.L. For the second channel the value obtained for the cross section was found to be equal to σ = (2.74 ± 0.4) × 10^?24 cm², which coincides well, within the statistical error, with reference value.