Motoji Ikeya

ESR dating of quartz phenocrysts in the El Cajete and Battleship Rock Members of Valles Rhyolite, Valles Caldera, New Mexico

Abstract The electron spin resonance (ESR) dating method was employed on quartz phenocrysts separated from pumice of the El Cajete and Battleship Rock Members of the Valles Rhyolite in the Valles caldera, New Mexico. The results of heating experiments indicate that Ti impurity centers have two components; a thermally stable one and a less stable, temperature sensitive one. ESR dates using the stable Ti center yield eruption ages of 59 ± 6 ka for the Battleship Rock Member and 53 ± 6 ka for the El Cajete Member while recent 14 C dates (S. Reneau and J. Gardner, unpub. data) from carbonized logs in the El Cajete pumice indicate that its age is older than 50 ka. Our results indicate that volcanism in the Valles caldera is much younger than previously thought (≥ 130 ka) and that recent revisions to the post-0.5 Ma stratigraphy of Valles caldera are probably in error. The results suggest that ESR dating of quartz may be a useful method for obtaining ages of units in other Quaternary volcanic areas.

ESR microscopy of fossil teeth

We have used thin sections of an archaeological tooth sample to obtain spatially resolved ESR spectra using a pin-hole cavity. This study presents the first ESR images of naturally generated radiation sensitive signals. The 3-D plots of the natural and irradiated samples show strong variations of the ESR intensities within the enamel layers. Owing to the relatively large scattering of the data points it has not been possible to produce 3-D dose plots.

ESR dating of pottery: a trial

Abstract An attempt of electron spin resonance (ESR) dating of pottery is described using natural radiation defects in quartz grains. Fragments of a neolithic ‘Trichterbecher’, previously dated by thermoluminescence (TL), were used. Although various radiation induced centres were identified, only the aluminium centre was useful for dating. The annual dose rate was calculated for a grain distribution from 0.1 to 1 mm, using external as well as internal components. The TL and ESR ages of (4720 ± 300)a and (4976 ± 800)a [(4589 ± 900)a], respectively, are in agreement; however, the uncertainty range in case of the ESR experiment is much larger.

Preliminary study for future ESR dating of solid SO2

Abstract Paramagnetic properties of irradiated solid SO2 have been studied for future ESR dating of icy materials on Io, the satellite of Jupiter. Radical species in solid SO2 formed by irradiation with γ-rays were measured with ESR at various temperatures to obtain the isothermal decay data, which gave their lifetimes at the ambient temperature on Io by the extrapolation in the Arrhenius plot. ESR parameters and speculative models for observed signals are presented.

Electron Spin Resonance Isochrone Dating of Fracture Age: Grain-Size Dependence of Dose Rates for Fault Gouge

A new isochrone method of electron spin resonance (ESR) dating has been proposed utilizing the different average dose rates of external radiation for different grain sizes due to the range of external α- and β-rays. The equivalent doses (ED s) obtained by the additive dose method were plotted as a function of the external dose rate (D ex) corrected for the grain sizes. The slope gives an ESR isochrone age since the fracture (T fra) or the surface formation; the coordinate abscissa gives the internal dose (D inT for) where D in is the internal dose rate and T for is the age of the mineral formation. The method has been applied to quartz ( SiO2) grains in geological fault gouge at outcrops of the Rokko Fault giving T fra=102,000 years and T for of nearly zero for grains less than 100 µ m.

ESR dating, dosimetry and microscopy A trip to interdisciplinary fields as a wanderer from physics of defects

Abstract A new field, Quantum Geophysics, is expected in the interdisciplinary field between geoscience and the physics of defects. An interdisciplinary research program of electron spin resonance (ESR) dating that detects cumulative radiation effects in natural minerals (CaCO3, SiO2 and CaSO4· H2O) and fossils has progressed considerably in these two decades. The principles and applications of ESR dating to various fields of earth sciences are described with models of defects produced by natural radiation in cave deposits, fossil shells and corals, bones, geological fault gouge (clays), volcanic ash and geothermal silica. The growth curve of defect formation in nature and in a laboratory by additive irradiation has been calculated and the age equation is given. The age can be determined directly without estimating the equivalent dose (ED).

PULSED ESR MEASUREMENTS OF OXYGEN DEFICIENT TYPE CENTERS IN VARIOUS QUARTZ

Abstract Phase-memory times T M for E′-centers in various quartz samples were measured by pulse-ESR. Manually ground quartz followed by γ-irradiation, α-irradiated quartz and that from a natural uranium deposit showed T M μ s indicating strong spin-spin interactions due to localized spins. Quartz glass and neutron-irradiated quartz showed longer T M of 15–18μs. Natural SiO 2 with dense spins, (∼ 3.96 Ga) and 12 sandstone from an impact crater were also examined.

Future ESR and optical dating of outer planet ICY materials

Abstract The possibility of future TL and ESR dating of icy materials in the outer planet world in our solar system is discussed. considering radiation effects by solar wind protons and cosmic rays as well as the long lifetime of radical species at extremely low ambient temperatures. A lightweight portable ESR and a gas combustion heating type TL using a photodetector are described for the in-situ observation, i.e. for the use on a landing craft with a -further suggestion to develop remote TL and OSL using laser beams. Both TL and ESR studies of ice (solid H 2 O doped with H 2 SO 3 were made to estimate the lifetimes of SO 3 − at the ambient temperature for comets from the Arrhenius plot of lifetimes. Molecular orbital calculation and g -factors of SO 3 − were made with MOPAC software. It is suggested that both ESR and optical dating of icy materials are useful for future dating in planetary science.

Is the quartet due to ·CH3 and ·C2H5 or ·NH3+ in alkali feldspars?

Abstract The intensity of broad quartet signal often identified as methyl radical (·CH 3 ) in alkali feldspars is enhanced by γ-irradiation. The average g factor and hyperfine A of the broad distorted signal are g = 2.0033 and A = 2.45 mT, respectively, and were previously identified as ·CH 3 or ·C 2 H 5 . The intensity of the quartet signal is enhanced by two orders of the magnitude by hydrothermal experiments of Na-feldspars in NH 3 atmosphere and therefore the signal was identified as ·NH 3 + where the anisotropic hyperfine due to N (I = 1) is not observed due to broadening in the powdered spectrum.

ESR IMAGING OF ALANINE DOSIMETER ANNEALED UNDER THERMAL GRADIENT

Abstract An ESR image has been measured for an irradiated alanine dosimeter annealed under a thermal gradient. An Arrhenius plot of the lifetime obtained from each pixel of the image gave apparent annealing parameters: the activation energy, E = 0.5 ± 0.3 eV and the preexponential frequency factor, νo = 4 × 102 Hz.