Paramagnetic holelike defect in irradiated calcium hydroxyapatite single crystals

Abstract

Electron-spin-resonance studies have been conducted at 9.2 and 23.1 GHz on synthetic calcium hydroxyapatite single crystals after exposure to ionizing radiation. The major paramagnetic defect is a spin-1/2 holelike center which is observable at 92 K but not at room temperature. It exhibits hyperfine interaction with a hydrogen nucleus as proved by deuterium substitution. The center is believed to be an 0 ion which results from removal of hydrogen from an OH ion. The hyper6ne interaction is w1th the hydI'ogen of an adjacent OH Ion. In first approximation the defect 1s axially symmetric with respect to the pseudohexagonal c axis; the spin-Hamiltonian parameters are g~I --2.0018~0.0002, g~= 2.0683~0.0002, A~~---5.6~0.2 G, and A j = +5.9~0.2 G. "Forbidden" transitions -+ -+ EM, =~1 cause complex unresolved spectra for orientations intermediate between H j[c nnd H i c. To Gt computer-simulated spectra to the experimental spectra, it was necessary to postulate that the hypefflne interaction is with an OH ion tilted 6 or 7 relative to c in six geometrically inequivalent directions. The isotropic hyperfine interaction was calculated using an approximate wave function constructed by a linear combination of orbitals from the 0 and OH ions. This establishes that the hole is strongly localized on the 0 and gives the absolute signs of the hyperfine components. the investigations of Shcherbakova et aE ' and of Gilinskaya et aE. ' on mineral fluorapatite crystals. The latter study is of particular interest since it reports the presence of the CO, and COS centers substituted for PO& in the apatite structure. This substitution is of interest because of its relation to carbonate impurity in biological crystals. Some similar studies on synthetic single crystals of chlorapatite, Ca, (POt), C1, have been reported. Banks et aE. '7 have studied by ESR the substitution of CrO~for PO', in chlorapatite single crystals. ESR investigations of Mna' substituted at the calcium sites were done by Piper' and Piper and I rener. " Knotterus et aE. 19 described an optical and ESR study of several electx'on-excess and bole-excess centex'8 1Q 1x'1Rd1Rtedchlorapatite. Hovrever, the models that these authors ploposed fox' two of the holellke centex'8 where disputed by Roufosse, Stapelbroek, Bartram, and Gilliam, " whose computer-simulated fit of the spectrum and agxeement between observed and calculated hyperfine parameters for one of the defects

EPR dosimetry with tooth enamel: A review

“…Furthermore, superhyperfine interaction with a proton of a neighboring hydroxyl group has been reported (Mengeot et al, 1973(Mengeot et al, , 1974. As mentioned in the theoretical part, a reliable identification of such centers in non-model systems is not easy because of the absence of hyperfine structure and possible confusion with other oxygen radicals.…”

“…Therefore, we will start our review with these two anions. (Mengeot et al, 1974), these results should be considered as highly reliable. ENDOR of CO 3 3-has also been reported in the g-range 2.0045 -2.0018 in the same type of samples (Sadlo et al, 1998b).…”

“…The most relevant work was carried out on HAp single crystals by Mengeot et al (1974). This work was very unique because sufficiently large hydroxyapatite single crystals of good quality were scarce (Mengeot et al, 1973(Mengeot et al, , 1974.…”

“…The most relevant work was carried out on HAp single crystals by Mengeot et al (1974). This work was very unique because sufficiently large hydroxyapatite single crystals of good quality were scarce (Mengeot et al, 1973(Mengeot et al, , 1974. Although this radical is unobservable in such crystals at room temperature (after irradiation either at room temperature or at 77 K), its g-tensor of g // = 2.0018 and g ⊥ = 2.0683 (axial with respect to the pseudohexagonal c-axis) indicates potential significance of this species for EPR dosimetry.…”

Multifrequency Epr Study of Radiation-Induced Defects in Chlorapatite

“…Similarly, defect centers in the anion columns of hydroxylapatite and chlorapatite have been investigated by EPR studies (Knottnerus et al 1972, Roufosse et al 1974, Mengeot et al 1975, Pan & Fleet 2002, and references herein). For example, Mengeot et al (1975) reported a spin-½ hole-like center exhibiting hyperfi ne interaction with a hydrogen nucleus (confirmed by deuteration) in X-irradiated hydroxylapatite.…”