Kiyotaka Ninagawa

Investigation of TLD Phosphors by Optical Excitation ?Luminescence of Eu2+ Centers in MgSO4, CaSO4, SrSO4, BaSO4?

The photoluminescence (PL) and excitation spectra of various thermoluminescence dosimetry (TLD) phosphors were measured at temperatures of 6, 17, 80 and 300 K. Their PL spectra at 300 K consist of a single band in the vicinity of 380 nm. The emission bands and their excitation bands are ascribed to the electronic 4f6 5d ↔4f7 transitions in the Eu2+ ions. In the PL spectra of MgSO4:Eu2+, SrSO4:Eu2+ and BaSO4:Eu2+, the emission lines due to the electronic 4f7 →4f7 transition in the Eu2+ ion were also observed near 360 nm, in addition to the broad band. No line emission due to the Eu3+ center was observed in any of the phosphors prepared in the present work. In CaSO4:Eu2+ cooled to low temperatures, phonon structures are observed on the emission band and the low-energy excitation band. The TL emission spectra of BaSO4:Eu2+ at various temperatures were also measured.

Thermoluminescence and compositional zoning in the mesostasis of a Semarkona group A1 chondrule and new insights into the chondrule-forming process

A large, group A1, porphyritic olivine chondrule in the Semarkona (LL3.0) chondrite with induced thermoluminescence (TL) and compositional zoning in its mesostasis has been discovered. The chondrule has Ca-rich and Fe-poor olivine (CaO, 0.36–0.40 wt%, Fa0.3–0.5) and its mesostasis is highly anorthite-normative (~52.5 wt%). The chondrule shows an intense induced TL peak at ~300°C with a half-width of ~180°C. The induced TL in the 40–440°C range increases monotonically by a factor of ~6 from center to rim, while SiO2, Na2O, and MnO increase by factors of ~1.1, ~3.6, and ~6, respectively. The spectrum of the induced TL over the 200–350°C range (i.e., a dominant peak at ~570 nm with a half-width of about 100 nm) and the Mn-TL correlation suggest Mn-activated plagioclase is an important constituent of the refractory mesostases in group A1 chondrules. The zoning may reflect fractional crystallization, Soret diffusion, transport of volatiles into the chondrule by aqueous alteration, a zoned precursor, reduction of precursor dust aggregate, or recondensation of volatiles lost during chondrule formation. The first four possibilities seem unlikely explanations for the zoning of the mesostasis, but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning. Reducing conditions at high temperatures are suggested to have prevailed during the formation of group A1 chondrules.

Experimental investigation into the effects of meteoritic impacts on the spectral properties of phyllosilicates on Mars

[1] Phyllosilicates have been identified in some of the most highly cratered Noachian terrains on Mars. To study the effects of such impacts on the properties of phyllosilicates, we experimentally shocked six phyllosilicate minerals relevant to the Martian surface: montmorillonite, nontronite, kaolinite, prehnite, chlorite, and serpentine. The shock-treated samples were analyzed with X-ray diffraction (XRD), near- and mid-infrared (NIR and MIR) spectroscopy, Raman spectroscopy, cathodoluminescence (CL), and the shock pressures and temperatures in some were modeled using Autodyn modeling software. XRD data show that the structure of each mineral, except prehnite, underwent partial structural deformation or amorphization. We also found that while the NIR spectra of shocked samples were very similar to that of the original sample, the MIR spectra changed significantly. This may explain some of the discrepancies between CRISM/OMEGA data (NIR) and TES/THEMIS (MIR) observations of phyllosilicates on Mars. Quartz was identified as a secondary phase in the XRD of shocked chlorite.

Thermoluminescence measurements of a calcite shell for dating

Abstract For thermoluminescence (TL)-dating of fossil calcite shells of Pecten, a new procedure is introduced. A supralinear function fitted to the ‘first-glow growth’ of the fossil shell makes it possible to evaluate the natural dose. From the natural doses obtained, we can estimate TL ages of fossil shells from about 5 × 105 years ago to more recently.

Radiation effects on cathodoluminescence of albite

Abstract He+ ion implantation on albite (Minas Gerais, Brazil) at 4.0 MeV, corresponding to the energy of α particle from 238U fission, has been conducted to clarify the radiation effects of α particles from radioactive minerals on cathodoluminescence (CL) of albite. CL of albite results in various emission bands at ~380, ~560, and ~740 nm, and in the UV range. Red emission at 700-750 nm is detected in the CL spectra of the implanted samples. Total CL intensities of these UV, blue, yellow, red, and IR emissions vary among the samples. High-resolution CL imaging of the cross-section samples shows a CL halo on the implanted surface of approximately 14 μm thickness, which is consistent with a theoretical range of α particles of 4.0 MeV. It was first confirmed experimentally that the CL halo is created by α particles. The deconvolution of CL spectra in the red emission range by Gaussian fitting provides the component at 1.861 eV that is attributed to a radiation-induced defect center produced by He+ ion implantation. The intensity of the component at 1.861 eV linearly correlates with the dose density of He+ implantation on albite as a function of the population of the radiation-induced defect center, regardless of other factors such as concentration and distribution of other emission centers, existence of microstructures and textures, and crystallographic orientation. The CL spectral deconvolution has a high potential for quantitative evaluation of the radiation dose of α particles from natural radionuclides on albite for a geodosimetry.

Thermoluminescence dating of calcite shells in the pectinidae family

Abstract Previously we investigated the thermoluminescence (TL) of a calcite shell, Pectinidae Pecten (Notovola) albicans (Schroter) (abbreviated to albicans), and we found that TL dating was possible for fossil calcite shells of albicans from 5 × 10 5 years ago to the present. In the present work, we investigate the TL emission spectra and the first glow-growth of 5 other species in the Pectinidae family, and it is found that the TL characteristics of these species are the same as those of the albicans. This means that the application of TL dating can be extended to these species. Furthermore, we tried to date fossil calcite shells older than 5 × 10 5 years ago, and we found that the upper limit for TL dating of fossil calcite shells is about 6 × 10 5 years.

Cathodoluminescence and Raman Spectroscopic Characterization of Experimentally Shocked Plagioclase

Cathodoluminescence (CL) spectrum of plagioclase shows four emission bands at around 350, 420, 570 and 750 nm, which can be assigned to Ce3+, Al[Single Bond]O−[Single Bond]Al or Ti4+, Mn2+ and Fe3+ centers, respectively. Their CL intensities decrease with an increase in experimentally shock pressure. The peak wavelength of the emission band related to Mn2+ shifts from 570 nm for unshocked plagioclase to 630 nm for plagioclase shocked above 20 GPa. The Raman spectrum of unshocked plagioclase has pronounced peaks at around 170, 280, 480 and 510 cm−1, whereas Raman intensities of all peaks decrease with an increase in shock pressure. This result suggests that shock pressure causes destruction of the framework structure in various extents depending on the pressure applied to plagioclase. This destruction is responsible for a decrease in CL intensity and a peak shift of yellow emission related to Mn2+. An emission band at around 380 nm in the UV-blue region is observed in only plagioclase shocked above 30 GPa, whereas it has not been recognized in the unshocked plagioclase. Raman spectroscopy reveals that shock pressure above 30 GPa converts plagioclase into maskelynite. It implies that an emission band at around 380 nm is regarded as a characteristic CL signal for maskelynite. CL images of plagioclase shocked above 30 GPa show a dark linear stripe pattern superimposed on bright background, suggesting planer deformation features (PDFs) observed under an optical microscope. Similar pattern can be identified in Raman spectral maps. CL and Raman spectroscopy can be expected as a useful tool to evaluate shock pressure induced on the plagioclase in terrestrial and meteoritic samples.

Cathodoluminescence characterization of tridymite and cristobalite: Effects of electron irradiation and sample temperature

Abstract Cathodoluminescence (CL) spectra of tridymite and cristobalite have broad peaks around 430 and 400 nm, respectively, both of which can be assigned to the [AlO4/M+]0 defect. The CL intensities of these spectral peaks in the blue region decrease with prolonged exposure to electron irradiation, similar to the short-lived luminescence observed in quartz, although quartz shows a lower decrease in CL intensity compared to these minerals. Cristobalite has a higher CL intensity reduction rate during irradiation than does tridymite. Irradiation of these minerals at low temperatures results in a more rapid decay of CL emission, whereas that of quartz shows no apparent change in the rate of CL emission at similar temperatures. Confocal micro-Raman spectroscopy of the electron irradiated surface of these minerals reveals the amorphization caused by the interaction of the electron beam with the surface layer to a depth of several micrometers. This suggests that such structural destruction diminishes the activity of CL emission centers related to the [AlO4/M+]0 defects by migration of monovalent cations associated with exchanged Al in the tetrahedral sites. Both samples present a considerable reduction of their CL intensities at higher temperature, suggesting a temperature quenching phenomenon. The activation energy in the quenching process was evaluated by a least-squares fitting of the Arrhenius plots, assuming the Mott-Seitz model. The result implies that the energy of non-radiative transition in this process might be transferred to lattice vibrations as phonons in two different manners. This might be related to different irradiation responses of the CL with a change in sample temperature.

Red thermoluminescence of volcanic glass fractions from tephras

Abstract The thermoluminescence (TL) spectra of the volcanic glass fractions from tephras collected in Japan were investigated by a TL time-resolving spectroscopy system. As a result, a broad, intense and red emission band at 620 nm with a glow peak at 330°C was obtained from the glass fractions and it was found to be grown by γ irradiation. Based on the correspondence between the TL emission spectra of the glass fractions and those of quartz and plagioclase crystals, we have attributed the high TL intensity of the glass fractions to quartz and plagioclase microcrystals included in the glass shards. In particular, the red TL of quartz is so strong that even a small content of quartz microcrystals in glass shards can be detected. Therefore the red TL of volcanic glass fractions will be applied to the dating.

Cathodoluminescence of alkali feldspars and radiation effects on the luminescent properties

Abstract Cathodoluminescence (CL) spectroscopy provides useful information about the existence of radiation-induced defect centers with a few micrometer resolutions and therefore has great potential to estimate the accumulated dose of natural radiation in micrometer-ordered mineral grains from radioactive decay. Although great scientific interest exists concerning the CL of various types of minerals, very few investigation have been conducted on the luminescence properties of radiation-induced alkali feldspars. This study, therefore, has sought a clarification of radiation effects on emission centers detected by CL analysis of alkali feldspar implanted with He+ ions at 4.0 MeV, which corresponds to the energy of an α particle derived from radioactive decay of 238U and 232Th. Panchromatic CL images of cross sections of sanidine, orthoclase, and microcline show a dark line with ~1 μm width on the bright luminescent background at 12-15 μm beneath the implanted surface, of which behavior may be corresponding to the electronic energy loss process of 4.0 MeV He+ ion. CL and Raman spectroscopy revealed that He+ ion implantation may leads to a partial destruction of the feldspar framework and Na+ migration, resulting in a quenching of CL emission from alkali feldspar, proportional to the radiation dose. CL spectra of unimplanted and He+-ion-implanted sanidine, orthoclase and microcline have emission bands at ~400-410 nm and at ~730 nm. Deconvolution of the CL spectra can successfully separate these emission bands into emission components at 3.05, 2.81, 2.09, 1.73, and 1.68 eV. These components are assigned to the Ti4+ impurity, Al-O--Al/Ti defect, a radiation-induced defect center, and Fe3+ impurities on the T1 and T2 sites, respectively. The intensity at 3.05 eV negatively correlates with radiation dose owing to decreases in the luminescence efficiency. A slight Na+ diffusion and breaking of the linkage between Ti4+ and oxygen as a ligand might reduce the activation energy, which decreases the availability of radiative energy in the luminescence process of Ti4+ impurity centers. Furthermore, He+ ion implantation causes electron holes to be trapped at and released from Löwenstein bridges as a consequence of Na+ migration and leads to a partial destruction of Al-O bonds, which might be responsible for an increase and decrease in the intensity of emission component at 2.81 eV. With an enhanced radiation dose, there is a decrease in intensity at 1.73 eV and an increase in intensity at 1.68 eV. Deconvoluted CL spectra of the alkali feldspars reveal a positive correlation between intensity at 2.09 eV and the radiation dose, which may be due to the formation of a radiation-induced defect center. These correlations can be fitted by an exponential curve, where the gradients differ between the alkali feldspars studied, and are largest for the microcline, followed by the orthoclase and then the sanidine. The intensity at 2.09 eV has the potential to be used in geodosimetry and geochronometry.