Kosei Komuro

Changes in osmotic and ionic concentrations in the hemolymph of Macrobrachium rosenbergii exposed to varying salinities and correlation to ionic and crystalline composition of the cuticle

Abstract Osmotic and ionic regulatory ability were examined in the giant freshwater prawn, Macrobrachium rosenbergii in response to varying salinities. In freshwater, and under conditions of low salinity, hemolymph osmolality was maintained around 450 mOsm. Under high salinity, osmolality values increased in a time-wise manner until reaching levels of the surrounding rearing water. Changes in sodium concentration generally paralleled osmotic change, and potassium and magnesium concentrations increased upon exposure to extremely high salinity. In contrast, total calcium concentration was maintained at high levels regardless of salinity treatment. Examination of crystalline structure and ionic composition of the cuticle revealed that it was comprised principally of an α -chitin-like material, and calcite (calcium carbonate). Calcite accounted for 25% of total bulk weight in freshwater, while sodium, potassium and magnesium constituents combined comprised less than 2.5% of this total. Although sodium, potassium and magnesium contents increased nearly 2-fold in response to changing salinity, calcium levels remained relatively constant.

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.

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.

Combined Cathodoluminescence and Micro-Raman Study of Helium-Ion-Implanted Albite

ABSTRACT Cathodoluminescence (CL) spectra of experimentally radiated albite at 4.0 MeV energy of He+ ion implantation have red emissions at 700−750 nm, of which the intensities increase with an increase in the radiation dose. These emissions are assigned to a radiation-induced defect center. Pseudocolor CL images of the implanted samples show red CL halo on the implanted surface, of which thickness is approximately 14 µm corresponding to a theoretical range of He+ ion implantation of 4.0 MeV. 2D Raman mapping of the peak at 508 cm−1 for CL halo area indicates minimum intensity and maximum full width at half maximum at ∼14 µm from the implanted surface, suggesting production of radiation-induced defect center due to a partial breaking of the framework structure. CL spectral deconvolution of the red emission reveals a Gaussian component at 1.861 eV attributed to the defect center. The integral intensity of this component closely correlates with the radiation dose as a function of radiation-induced defect center, but does not depend on the density and distribution of other emission centers related to CL of albite, the presence of microstructures or texture, and crystallographic orientation. CL spectral deconvolution is expected to be used for quantitative estimation of alpha radiation dose from natural radionuclides on Na-rich feldspar as an indicator for geodosimetry.

RESPONSE OF CATHODOLUMINESCENCE OF ALKALI FELDSPAR TO He + ION IMPLANTATION AND ELECTRON IRRADIATION

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 irradiation 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 radionuclides that alkali feldspars have experienced.

The Bilimoia gold deposit, Kainantu, Papua New Guinea: A fault-controlled, lode-type, synorogenic tellurium-rich quartz-gold vein system

The Bilimoia gold deposit (1.77 Moz), Papua New Guinea (PNG), is a fault-hosted quartz-gold vein system hosted by 290–221 Ma years old basement that was regionally metamorphosed to greenschist facies at ∼45 Ma. Mineralisation occurred during S3-S4 ductile events in a S1-S4 deformation sequence, rapid uplift, crustal thickening and when the plate motions changed from oblique-transpressional to orthogonal convergence. It is spatially and temporally related to I-type, intermediate-felsic 9–7 Ma year-old porphyries. Distal quartz-specularite-calcite veins with chlorite-epidote selvage is the earliest hydrothermal event. Wallrock has been altered to quartz-illite-pyrite and quartz-sericite-mariposite/fuchsitepyrite, respectively. Infilling stages are divided into quartz±ferberite ±adularia, hematite, pyrite, quartz-sphalerite-galena-chalcopyrite, quartz-Cu±Sn sulphides-gold-tellurides-Te-Ag-Sb-Bi±Cu phases and carbonates-clays, respectively. Hypogene gold occurs as native gold, electrum, calaverite, kostovite, petzite and sylvanite; calaverite hosts 90–95% of the total gold. Gold distribution in the supergene zone (<200 m) primarily mirrors the primary mineralisation. Fluid inclusions from stage 4 quartz define low salinity (0.9–5.4 wt% NaCl) mixed aqueous-carbonic fluids at 210–330 °C. Inclusions that homogenised at 300–330 °C host coexisting liquid and vapour-rich (including CO2-bearing) phases, implicating phase separation. Ferberite was deposited from low salinity (0.9–1.1 wt% NaCl) mixed aqueous-carbonic fluids at 240–260 °C. Gold deposition occurred after phase separation due to decreasing temperature and sulphur activity, fluctuating pressure and change in the fluid oxidation state between 260 and 100 °C. Bisulphides and gold-telluride complexes transported gold. Bilimoia is similar to many gold deposits classified by many workers as epizonal orogenic and intrusion-related. Ore-forming fluids were derived from metamorphic devolatilisation at sites located above rising magma melts, crystallising intrusions associated with magma that was contaminated by reduced basement/subducted sediments, or a mixture of these sites.