Configuration of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mi mathvariant="normal">−</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math>radicals in γ-irradiated<i>A</i>-type carbonated apatites:  Theory and experimental EPR and ENDOR studies

Schramm, D.U.; Terra, Joice; Rossi, Alexandre M.; Ellis, Donald E

doi:10.1103/physrevb.63.024107

Cited by 29 publications

(15 citation statements)

References 28 publications

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“…Previously, a number of groups performed first-principles calculations for HAp. [12][13][14][15] For example, Calderín et al employed a pseudopotential method to investigate the electronic structures of a series of stoichiometric apatites ͓Ca 5 ͑PO 4 ͒ 3 X , X =F,Cl,OH,O 0.5 ͔ and discussed the relative stability between monoclinic and hexagonal structures in the cases of X = OH and Cl based on their total energies. 12 Rulis et al used the orthogonalized linear combination of the atomic orbital method for the apatites and showed their chemical bonding states and theoretical optical spectra.…”

Section: Introductionmentioning

confidence: 99%

First-principles study of vacancy formation in hydroxyapatite

2007

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First-principles plane-wave calculations were performed for hydroxyapatite ͑HAp͒ in order to investigate the electronic structure and vacancy formation mechanisms. The HAp unit cell contains PO 4 tetrahedra and OH groups formed by covalent P-O and H-O bonds. Ca ions play a role for connecting the PO 4 tetrahedra and OH groups in an ionic character of bonding. It is found that OH − vacancies with accompanying H + vacancies are dominantly formed and that their spontaneous formation takes place at temperatures above 1000 K. This corresponds to the nonstoichiometry of HAp due to OH deficiency that is experimentally observed near 1073 K.

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Section: Introductionmentioning

confidence: 99%

First-principles study of vacancy formation in hydroxyapatite

2007

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“…A number of first-principles studies on substitutional defects in HAp have been reported so far. [11][12][13][14][15][16][17] However, most of the previous studies investigated atomic and electronic structures around substitutional defects and did not systematically reveal the trend in stability of foreign cations substituting for Ca 2+ in HAp by ion exchange. The results obtained by thermodynamic treatments of first-principles total energies are compared with available experimental data, and the origin of the ion exchange ability of HAp will be discussed in terms of atomic and electronic structures localized around the exchanged divalent cations.…”

Section: Introductionmentioning

confidence: 99%

Theoretical trend of ion exchange ability with divalent cations in hydroxyapatite

2008

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First-principles calculations are performed for hydroxyapatite ͑Hap͒ in order to investigate the relative ion exchange ability with divalent cations such as Mg 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Sr 2+ , Cd 2+ , Ba 2+ , and Pb 2+. Their ionic substitutional energies are calculated from total energies of supercells and chemical potentials for Ca 2+ and the foreign cations determined under chemical equilibrium between HAp and its saturated solution. It is found that, in most cases, the ion exchange ability is basically dependent on the ionic sizes and the larger or smaller-sized cations than Ca 2+ tend to exhibit more difficulty of substitution for Ca 2+ in HAp. However, Pb 2+ exhibits the extremely small substitutional energy, which originates from covalent bonds with the adjacent oxygen atoms. In particular, Pb 2+ at the Ca-1 site of HAp has covalency with the second-nearest-neighboring oxygen atoms as well as the first nearest-neighboring ones. The covalent bond formation plays an important role for the distinct ion exchange ability for Pb 2+ by HAp observed experimentally.

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“…Finally, we will mention an ENDOR study of A-type carbonated apatites where CO 2 -on an A-site could be detected (Schramm et al, 2001). As only matrix 1 H ENDOR was measured, the conclusion is essentially based on the interaction with a single 31 P nucleus.…”

Section: Endor Of Co 2 -mentioning

confidence: 99%

EPR dosimetry with tooth enamel: A review

Fattibene

Callens

2010

Applied Radiation and Isotopes

212

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When tooth enamel is exposed to ionizing radiation, radicals are formed that can be detected using Electron Paramagnetic Resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method.The first part of the paper is quite fundamental and deals with the main properties of tooth enamel and several of its model systems (e.g., synthetic apatites). Considerable attention is also devoted to the numerous radiation-induced and native EPR signals, and the radicals responsible for them. The relevant EPR detection, identification and spectrum analysing methods are reviewed from a general point of view. Finally, the need for solid state modelling and the linearity of the dose response are investigated.The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns the preparation of samples, specific irradiation problems, spectrum acquisition and it is described how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with.In the final chapter the future of EPR dosimetry with tooth enamel is analysed.

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Configuration ofCO2−radicals in γ-irradiatedA-type carbonated apatites: Theory and experimental EPR and ENDOR studies

Cited by 29 publications

References 28 publications

First-principles study of vacancy formation in hydroxyapatite

First-principles study of vacancy formation in hydroxyapatite

Theoretical trend of ion exchange ability with divalent cations in hydroxyapatite

EPR dosimetry with tooth enamel: A review

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