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Response of cathodoluminescence of alkali feldspar to He+ ion implantation and electron irradiation

Kayama M., Nishido H., Toyoda S., Komuro K., Finch A. A., Lee M. R., Ninagawa K.

Geochronometria

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2013

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Vol. 40, no. 4

244--249

EN

Cathodoluminescence (CL) of minerals such as quartz and zircon has been extensively studied to be used as an indicator for geodosimetry and geochronometry. There are, however, very few investigations on CL of other rock-forming minerals such as feldspars, regardless of their great scientific interest. This study has sought to clarify the effect of He+ ion implantation and electron irra-diation on luminescent emissions by acquiring CL spectra from various types of feldspars including anorthoclase, amazonite and adularia. CL intensities of UV and blue emissions, assigned to Pb2+ and Ti4+ impurity centers respectively, decrease with an increase in radiation dose of He+ ion implantation and electron irradiation time. This may be due to decrease in the luminescence efficiencies by a change of the activation energy or a conversion of the emission center to a non-luminescent center due to an alteration of the energy state. Also, CL spectroscopy of the alkali feldspar revealed an in-crease in the blue and yellow emission intensity assigned to Al-O−-Al/Ti defect and radiation-induced defect centers with the radiation dose and the electron irradiation time. Taken together these results indicate that CL signal should be used for estimation of the α and β radiation doses from natural radi-onuclides that alkali feldspars have experienced.

2

Investigation of the temporal change of the sources of Aeolian dust delivered to East Asia using electron spin resonance signals in quartz

Yamamoto Y., Toyoda S., Nagasima K., Igarashi Y., Tada R.

Geochronometria

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2013

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Vol. 40, no. 4

355--359

EN

The temporal change in the number of oxygen vacancies in quartz was investigated by observing the E1’ center in the atmospheric depositions collected at two cities in Japan in the recent past. The depositions collected at Fukuoka in March show the ESR intensities being correlated with the sum of the number of the days, in the month, on which Kosa was observed while no such correlation was found in the deposition those collected at Akita but a trend of decrease with time. The present results suggest that the number of oxygen vacancies in quartz might be useful to estimate quantitatively the contribution of the dust originated from China to the atmospheric deposition in Japan.

3

Characteristics of ESR signals and TLCLs of quartz included in various source rocks and sediments in Japan: A clue to sediment provenance

Shimada A., Takada M., Toyoda S.

Geochronometria

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2013

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Vol. 40, no. 4

334--340

EN

The variation of electron spin resonance (ESR) signal intensities and thermoluminescence colour images (TLCIs) of quartz was investigated in the present study for various rocks and sediments in Japan, to discuss the possibilities of identifying the sediment provenance. The ESR signal intensity of the E1' centre in the same grain size in granitic quartz varies from sample to sample, except for that in Quaternary samples of volcanic sediment, which is very low, close to the noise level. It was found that the diagram, ESR intensities of Al versus Ti-Li centre signal intensities, distinguish volcanic from the same grain size in granitic quartz as well as distinguish individual tephra from another. The TLCIs from volcanic quartz and some granitic quartz samples is almost red and that from the rest of granitic and metamudstone quartz is blue as results of TLCIs although the emission intensities are dif-ferent. Our results suggest that examining the multiple-centre signal intensities of ESR and the TLCIs are ef-fective to identify the source of quartz and to estimate the sediment provenance.

4

The E1' center in natural quartz: its formation and applications to dating and provenance researches

Toyoda S.

Geochronometria

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2011

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Vol. 38, no. 3

242-248

EN

Quartz is one of the minerals useful for electron spin resonance (ESR) dating. The E1' center is one of well-known paramagnetic defects in crystalline quartz. This center has a unique feature; its intensity increases on heating. An electronic process to explain this increase was found to be con-trolled not only by the number of oxygen vacancies, which are the precursors, but also by the number of Al hole centers, which depend on the previous radiation dose and on the Al concentration. The maximum intensity on heating is called the heat treated E1' center, which has been posited to correspond to the number of oxygen vacancies in quartz and was found to be correlated with the ages of the host granites (Toyoda and Hattori, 2000). The experimental results on spin-spin relaxation times of the E1' center indicate that external beta and gamma rays create oxygen vacancies in natural quartz rather than alpha or alpha recoil particles (Toyoda et al., 2005). The correlation between the numbers of the oxygen vacancies in quartz and the ages of the host granite made it possible to distinguish the quartz of a sedimentary reservoir from another with different age of crystallization (Toyoda and Naruse, 2002). Quartz fractions extracted from leoss and atmospheric deposition in Japan and from sediments in Japan sea were analyzed by ESR. The temporal change of the contributions from two dust sources in China were discussed in the context of climate change.

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The grain size influence on the E1'centre observed in quartz of atmospheric deposition at two Japanese cities : a preliminary study

Yamamoto Y., Toyoda S., Nagasima K., Igarashi Y., Tada R.

Geochronometria

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2010

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Vol. 37

9-12

EN

The grain size influence on the number of oxygen vacancies in quartz was investigated by ESR in atmospheric deposition collected at two Japanese cities, Fukuoka and Akita, in 1969 and 1971. The finer grain size fraction shows the highest value of concentration of oxygen vacancies, most closely resembling dust originating in the Taklamakan desert. Month to month and year to year variation of the dependence was also observed which could possibly be attributed to the variation of the mixture ratio of at least two dust sources in China, A conclusive statement can not be made at this stage.

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ESR dating of marine barite in chimneys deposited from hydrothermal vents

Okumura T., Toyoda S., Sato F., Uchida A., Ishibashi J., Nakai S.

Geochronometria

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2010

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Vol. 37

57-61

EN

Electron Spin Resonance (ESR) dating of marine barite in chimneys deposited from hydrothermal vents was attempted to determine the time since hydrothermal activity occurred. In this study, we used Barite (BaSO4) precipitated in icroenvironments in the chimneys deposited from the hydrothermal vents at the Archaean site in South Mariana spreading centre (12°56.4'N, 143°37.9'E) and at Hakurei site in the Izena caldron (27°15‘N, 127°04‘E) for ESR measurements. ESR spectrum of marine barite is characterized by an electron-type centre with g values of 2.0034, 2.0022 and 1.9995 attributed to SO3 –. The signal intensity increased with gamma ray dose. The dose rates of hydrothermal chimneys from the Archaean site and from the Hakurei site were calculated using a model that assumed a grain size and that incorporation of radionuclides after 226Ra in U series into the chimney, and assuming the efficiency of the defect formation by alpha particles to be the same as that for OSL. The ESR ages were estimated to be 470 years old for barite from the Archaean site and 5670 years old for one from the Hakurei site, although there is a considerable difference between the present ESR ages and the 210Pb/226Ra disequilibrium ages previously reported.

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ESR dating of sedimentary quartz from two pleistocene deposits using Al and Ti-centers

Tissoux H., Toyoda S., Falgueres C., Voinchet P., Takada M., Bahain J-J., Despriée J.

Geochronometria

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2008

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Vol. 30

23-31

EN

One sample from a fluvial terrace of Loir river (France) deposited during isotopic stages 7-8 and two samples from isotopic stage 5 marine sediments of Echizen Coast (Japan) were dated by ESR of quartz grains. Both additive and regenerative techniques were used on Ti-Li and Ti-H centers of quartz. No change of sensitivity of the centers was observed during regeneration which significantly reduced the errors on the equivalent doses. Bleaching experiments indicated that the Ti-Li center is less sensitive to UV(ultra-violet)-A (365-412 nm) than to the full sun spectrum whereas UVA alone is sufficient to reset the bleachable component of the Al-center. This effect could be the origin of the strong overestimation of the ages determined using the Ti-Li center in this study. The comparison of the equivalent doses determined by the two Ti-centers indicated that bleaching before deposition of the fluvial sediment was apparently better than for the marine sample.