Isotropic CO2 Research Articles

A very personal, 35 years long journey in ESR dating

This paper describes a personal journey in ESR dating and gives some insights of the progress made over 35 years in ESR dating of tooth enamel. When I started, samples were irradiated with four additive dose steps of 5, 10, 15 and 20 krad and the linear extrapolation yielded the dose value. An assumed dose rate of 100 mrad/a yielded the age of the sample. Since then I learned that one actually has to measure the dose rate. I also learned that the dose response can be described by a single saturating function, or perhaps two, and that errors can be appropriately calculated. Rather than having a single anisotropic CO2− radical, tooth enamel consists of two anisotropic CO2− radicals and two isotropic CO2− radicals, one stable, one unstable. Also, the dose response shows spatial differences in the production of these different radicals in response to beta and gamma rays. Then there is the problem of uranium uptake over time. We solved this by combining ESR and U-series analyses. We can even measure appropriate beta attenuation factors including sequential laser ablation U-series analyses. Even better, all analyses can be carried out on small enamel fragments, which can be glued back into their original position with little to no visible damage. Still, when using the most sophisticated dose rate calculations, they're often close to 1000 μGy a−1.

ESR dating of stalagmite from Keloğlan cave in the southwestern part of Turkey

The determination of the geological age of two stalagmites (designated as A and B) found in Keloğlan cave (Denizli, Acıpayam, Turkey) was investigated using an electron spin resonance (ESR) technique. The natural ESR spectra had the signals of Mn2+ in addition to the signal at g=2.0006. In the ESR spectra of the γ-irradiated samples, three additional signals appear at g=2.0030, g=20016 and g=1.9972. The radicals produced by irradiation in stalagmites were attributed to orthorhombic and isotropic CO ion radicals. The signal intensity of the CO was used as a dating signal. Stalagmites were irradiated with a 60Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve, and fitted with the sum of two single exponential saturation functions. Based on this model, accumulated geological dose (DE) values for dating are obtained by using an additive dose method. The DE values of A and B stalagmites for each section range from 15±1 to 83±4 and 25±1 to 100±6 Gy, respectively. As the 238U, 232Th and 40K concentrations of the stalagmites are very low, the measured in situ value of the external gamma dose rate was used for dating calculations. Because some parts of the stalagmites show secondary calcite recrystallization in the pore spaces, the calculated age values of these parts do not agree with the model of stalagmite growth. Except these porous parts, the ESR ages of other sections between A.5–A.8 and B.3–B.6 range from 14±2 to 86±18 and 24±5 to 92±19 kyr, respectively, which is consistent with the model of stalagmite growth.

Isotropic radical [formula omitted] in biological apatites

The isotropic CO 2 - EPR spectrum at g ∼ 2.0006 for γ -irradiated powders of dental enamel annealed at different temperatures up to 320 ∘ C is studied. The signal intensity is found to increase with the growth of annealing temperature up to 240 ∘ C . This finding contradicts to the existing model of isotropic CO 2 - radical in apatites. The possible models of the radical in biological apatite are analyzed and discussed. On the basis of the results obtained it is suggested that in tooth enamel apatite the isotropic CO 2 - radical is the bulk radical localized in structural voids of hydroxyapatite lattice, which occur in the vicinity of a carbon radical in position B.

Polarization selection by optical feedback

We present experimental and numerical evidence of polarization selection in an isotropic CO 2 laser achieved by means of an unpolarized optical feedback. This mechanism can be applied in situations where the direction of polarization plays a crucial role, including polarization coding.

Manipulating the activation barrier for H2(D2) desorption from potassium-modified palladium surfaces

In this work the permeation and desorption of hydrogen (deuterium) from potassium-modified Pd(111) and polycrystalline palladium surfaces have been studied in the temperature range from 350 to 523 K. Time-of-flight spectroscopy has been used to determine the translational energy distributions of associatively desorbing H(2)(D(2)) molecules as a function of the potassium coverage and additional isotropic O(2) and CO background pressures. It turned out that the energy distribution of the hydrogen desorption flux is thermalized for the clean Pd surfaces but hyperthermal for the potassium-covered surfaces. The activation barrier for adsorption was found to increase with the potassium coverage but to decrease again in the presence of coadsorbates such as O(2) or CO. Especially by choosing different isotropic CO pressures, the effective desorption barrier for hydrogen could be reversibly decreased and increased, which resulted in the equivalent changes of the mean kinetic energies of the desorbing H(2) molecules.

Identification and valuation of paramagnetic radicals in natural dolomites as an indicator of geological events

Geological sedimentary dolomite samples from the Superior Proterozoic are studied using electron paramagnetic resonance (EPR) spectroscopy. The complex spectra in the g=2.0 region is composed of Mn2+ lines and signals due to crystallization and radiation-induced defects. Measurements in microwave frequencies of 9.5 GHz (X-band) and 35 GHz (Q-band), and thermal and/or radiation treatments allowed identification of seven paramagnetic radicals in the g=2.0 region: (1) isotropic organic radical; (2) axial SO2 −; (3) axial PO2 0 or PO2 2−; (4) isotropic CO2 −; (5) axial CO2 −; (6) axial CO3 3−; (7) isotropic unknown line. The use of these paramagnetic centres as indicators of geological events is discussed.

Electron spin resonance (ESR), electron nuclear double resonance (ENDOR) and general triple resonance of irradiated biocarbonates

Several irradiated biocarbonates were studied by magnetic resonance techniques. Seven paramagnetic species, attributed to CO 2 −, SO 2 − and SO 3 − were identified. Comparison between radiation induced defects in bioaragonites and aragonite single-crystals shows that isotropic and orhorhombic CO 2 − centers with broad line spectra are not produced in the latter samples. Vibrational and rotational properties of isotropic CO 2 − centers were studied from low temperature Q-band spectra. Vibrational frequency is determined from the 13CO 2 − hyperfine spectrum and yielded v=1.54 × 10 13 s −1. The correlation time for isotropic CO 2 −, τ c=1.2 × 10 −11s ( T=300 K), is typical of radicals rotating in liquids. ENDOR and General Triple spectroscopy show that orthorhombic CO 2 − centers are surrounded by water molecules located in the second nearest CO 3 2− sites at 5.14, 5.35 and 6.02 Å. Water molecules replacing carbonates or as liquid inclusion of growth solution in local crystal imperfections may be responsible for the variety of orthorhombic and isotropic CO 2 − species, respectively.

An ESR study of defects in irradiated hydroxyapatite

Radiation-induced defects in synthetic hydroxyapatite (HAp) of six different origins have been investigated by electron spin resonance (ESR), X-ray diffraction (XRD), Raman scattering and IR measurements. The orthorhombic CO 2 − radicals were detected in almost of all the samples examined, but the isotropic CO 2 − was produced only in water-containing HAp with low crystallinity. The doublet signal due to H 0 was clearly detected in HAp with extreme calcium deficiency as compared to the stoichiometry. The results of ESR and FTIR suggest that water molecules in low crystalline HAp are not on the surface but embedded in the HAp crystalline lattice.

An Electron Nuclear Double Resonance and Electron Spin Resonance Study of Isotropic CO2- and SO2- Radicals in Natural Carbonates

Natural samples often exhibit isotropic electron spin resonance (ESR) signals at g=2.0006 ( CO2-) and g=2.0057 ( SO2-). Electron nuclear double resonance (ENDOR) data were collected for various calcitic or aragonitic samples of marine origin. The small and isotropic 1H hyperfine ENDOR splitting (250–350 kHz) is explained by a locally disordered water environment for these species. As for the isotropic CO2- and CO3- radicals in synthetic monohydrocalcite and apatite, the radicals are most probably located in the occluded water embedded in these samples, and not in the crystal matrix.

Pulsed and cw-ESR Studies of CO2- in CaCO3 Irradiated by He+ and γ-Rays for ESR Dating

Orthorhombic CO2- produced by γ- and He+-irradiation in aragonite has been measured by electron spin resonance (ESR). An α/γ effectiveness ratio in producing defects, k-value, of 0.0027±0.0011 was obtained from the growth curve. Pulsed ESR provided the spin-spin relaxation times, T2=1.25±0.04 µ s for orthorhombic CO2- in γ-irradiated modern coral and T2=1.58±0.02 µ s in nonirradiated fossil shell. The signal of the isotropic CO2- is found to be almost removed in the field sweep electron spin echo (ESE) spectrum, and the selective detection of orthorhombic CO2- becomes possible. ESR dating and dosimetry can be performed for impurity-included carbonates whose spectra are superposed using the ESE technique.

Location and Motion of Isotropic Paramagnetic Centres in Synthetic Monohydrocalcite

The isotropic CO-2 and CO-3 centres in CaCO3·H2O were examined with electron spin resonance (ESR), electron-nuclear double resonance (ENDOR) and thermogravimetric analysis (TGA). From the absence of anisotropy and the small value of the 1H ENDOR splitting ( ∼0.3 MHz), the effect of crushing and/or thermal annealing on the ESR and TGA spectra, it is concluded that both isotropic centres are located in the occluded water, surrounding the constituent crystallites of the spherulites. ESR line width and 13C hyperfine coupling parameter measurements yield approximate values for the rotation activation energy (ΔE( CO3-<ΔE( CO2-) with ΔE∼ 0.2 eV) and for the vibrational frequency ( ∼2.1012 Hz for CO2-).

An ESR study of radicals in CaCO3 produced by 1.6 MeV He+- and γ-irradiation

The effects of charged-particle irradiation on the formation of defects in CaCO3 have been studied using electron spin resonance (ESR). An orthorhombic CO2− was dominant in powdered synthetic aragonite irradiated by 1.6 MeV He+, while both orthorhombic and isotropic CO2− were observed in α-irradiated aragonite powder. G-values (number of defects per 100 eV) for α-and γ-rays were obtained to be Gα = 0.0041 and Gγ = 0.27 for aragonite leading to a k-value (γ-ray efficiency) of 0.015.

Effects of trivalent metal impurities on radiation-induced radicals in calcite

Effects of Al 3+, Sc +3, Y 3+ and Fe 3+ on radiation-induced radicals in calcite are investigated by ESR. Doping with Al 3+, Sc 3+ and Y 3+ ions increases the formation yield of isotropic CO 2 − centers ( g = 2.0007). The increase was considered to be related to abundant water molecules incorporated together with the M 3+ ions. Radicals associated with Al 3+ and Sc 3+ were not observed, while Y 3+-stabilized CO 3 3− ions were confirmed. Iron suppressed the yield of the isotropic CO 2 − radicals and sulfite-associated radicals ( g ⊥ = 2.0038 and g ∥ = 2.0024). The suppression effect was explained by the valence change of iron in the vicinity of the radicals.

Hydration effects on CO 2− radicals in calcium carbonates and hydroxyapatite

The effect of water on radiation-induced CO 2 − radicals in calcitic and aragonitic calcium carbonate (CaCO 2) and in hydroxyapatite (HAP) has been studied by electron spin resonance (ESR) and near-infrared (NIR) reflectance measurements. Hydration suppresses the formation of orthorhombic CO 2 − ions, but induces rotating or tumbling CO 2 − ions (isotropic CO 2 −) in aragonite and in HAP. On the other hand, the isotropic CO 2 − radical has hardly been detected in calcite. The amount of the rotating CO 2 − ions correlates with the intensity change of the H 2O reflectance peak.

Paramagnetic centers in γ-irradiated synthetic monohydrocalcite

When spherulitic grains of Ca 12,13CO 3·H 2O are γ-irradiated at room temperature, only three isotropic paramagnetic species are produced: 1) the tumbling CO 3 − radical with g = 2.0115 and A 13c = 11.4 gauss; 2) the tumbling CO 2 − radical with g = 2.0006 and A 13c = 148 gauss; and 3) a non-carbon-centered species (SO 3 −?) with g = 2.0032 exhibiting an hyperfine coupling interaction of 21.2 gauss with two equivalent I = 1 2 nuclei (H). If these rotating species do substitute for the carbonate ion, they are surrounded by a sphere of water molecules. The isotropic CO 2 − (dating signal) observed in natural carbonates and the CO 2 − radical in monohydrocalcite have very similar characteristics, suggesting that the first one is also surrounded by water molecules incorporated in the lattice in some “parasitic” manner, for example together with Mg 2+ or Zn 2+ ions.

The effect of carbonate content and drying temperature on the ESR-spectrum near g = 2 of carbonated calciumapatites synthesized from aqueous media.

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied as a function of their carbonate content and drying temperature. When the latter increases from 25 to 400 degrees C, the ESR spectrum is gradually modified and becomes similar to the spectrum of carbonated apatites, synthesized at high temperatures by solid state reactions. The latter ESR spectrum is dominated by CO3(3-)-contributions whereas the spectrum of precipitated samples dried at 25 degrees C can mainly be interpreted in terms of CO2-, CO3-, and O- ions. The behavior of these earlier-reported CO2-, CO3-, and O- centers is now studied as a function of drying temperature. In addition, the Spin Hamiltonian parameters of the CO3(3-) centers are determined and some other new paramagnetic radicals are discussed. It is shown that a CO3(2-) ion at a phosphate lattice site (B-type substitution) may give rise to either a CO2-, CO3-, or CO3(3-) radical on X-irradiation, depending on the sample preparation conditions. A surface CO3(2-) ion may cause a surface CO2-, CO3-, or O- radical. From the reported results it is not unambiguously clear whether the CO3(3-) ion detected in the samples with the relatively lowest carbonate content should be located on the surface or on a hydroxyl lattice site (A-type substitution). An important result is that the absolute concentration of the B-type CO3(3-) ion increases with increasing carbonate content as was also the case for the earlier reported B-type radicals (isotropic CO2- and CO3-). On the other hand, the absolute concentration of the surface radicals decreases with increasing carbonate content. The reported results show that similar deconvolution techniques can be applied in the future for the study of ESR spectra of calcified tissues. This will allow a more efficient phenomenological investigation of the latter.

Thermal Annealing of Radicals in Aragonitic CaCO3 and CaHPO4·2H2O

High-temperature annealing of radicals in aragonitic CaCO3 and in CaHPO4·2H2O has been studied by electron spin resonance (ESR), thermometric analyses (DTA and TGA) and thermally stimulated gas release (TSGR). An isotropic ESR signal at g=2.0007 is detected in coral and irradiated CaHPO4·2H2O. The signal in aragonitic coral is annealed out at 150-210°C, but the same signal in CaHPO4·2H2O fades out at 100-140°C. The signal annihilation is accompanied by water release from the specimens. The formation yield of the g=2.0007 signal by irradiation is reduced by sample preheating. The experimental results indicate that isotropic CO2- radicals responsible for the g=2.0007 signal are closely associated with the crystal water in aragonitic CaCO3 and in CaHPO4·2H2O. Some isotropic CO2- radicals may be associated with CO2- ions isolated by surrounding water molecules.

Generalized Langevin equation approach for the rotational relaxation of a molecule trapped in a 3D crystal. II. Application to CO and CH3F in argon

A numerical integration of the Langevin equations connected to the motions of a diatomic molecule trapped in a rare gas matrix is performed using a Runge–Kutta procedure and a Monte Carlo–Metropolis sampling for the initial configurations of the so-called primary system (cf. paper I). The rotational energy transfer from the molecule to the crystal is shown to strongly depend on the coupling between the molecule and the nearest-neighbor (NN) atoms and also on the ability for these NN atoms to dissipate their energy into the bath. Several cases are discussed according to the values of the viscous terms describing the damping of the molecule rotation and translation and of the NN atom vibrations. The prolate CH3F molecule trapped in an argon matrix seems to relax more quickly its rotational energy than the nearly isotropic CO molecule. Special trajectory calculations, when the molecule is rotationally excited or in thermal equilibrium, are considered in order to study the well jump and the librational motion of the CO molecule.

Assignment of IR transitions and FIR laser lines from torsionally excited CH 3OH

The R and P branches have been identified in high-resolution Fourier transform spectra of the C-O stretch band of CH 3OH for the (n τK) = (111) and (112) levels of the first excited torsional state. It has thereby been possible to assign the FIR laser lines and parent IR transitions optically pumped by the 13-9P16 and 13-9R12 isotropic CO 2 laser lines. The 13-9P16 line pumps the P(111, 11) transition of CH 3OH, and the 13-9R12 line pumps the Q(112, 7) transition.