Colour centres in plasma-sprayed hydroxyapatite.
Very pure hydroxyapatite is diamagnetic and shows no electron paramagnetic resonance (EPR) spectrum. Plasma-sprayed coatings made with such a pure hydroxyapatite contain paramagnetic point-defects. Irradiated deposits show a strong EPR absorption assigned to an O2- anion adjacent to a calcium vacancy, with anisotropic parameters, g1 = 2.004, g2 = 2.013 and g3 = 2.038. The EPR spectra and colour fade away following thermal annealing. These features are discussed in terms of point-defects in the hydroxyapatite crystal structure.
ESR identification of radiation damage in synthetic apatites: a study of the 13C-hyperfine coupling.
Although radiogenic free radicals are widely used as molecular probes in biological calcified tissues, their nature and their location remain controversial. In the present study we have synthesized and irradiated apatites in which 13CO3(2-) ions substitute hydroxyl or phosphate ions in hydroxyapatite. The 13C-couplings show that the carbon-centered radicals are CO2- --rather than CO3(3-)--the locations of which depend on the type of carbonate and the treatment of the sample.
Dislocation loop growth in an electron irradiated thin foil
Abstract Large faulted dislocation loops are grown in thin foils of nickel at 450°c by electron irradiation in the beam of a high voltage electron microscope. Loop size is directly proportional to time, implying that surfaces are the dominant sinks for interstitials. A model of loop growth under these conditions is developed and predicts a growth rate in agreement with that observed. This paper is published by permission of the Central Electricity Generating Board.