90 research outputs found
Radioluminescence of synthetic and natural quartz
The effect of X-ray irradiation and thermal treatments on the radio-luminescence emission spectrum of both a natural pegmatitic quartz and a synthetic one was investigated. All the emission spectra could be deconvolved into the same set of five Gaussian components. Among the identified RL bands, a blue emission at 2.53 eV (480 nm) is enhanced under X-ray irradiation. A strong correlation with the sensitization of the so called "110 degrees C" TSL peak (in our measurements seen at lower temperature due to the lower heating rate) was proved, suggesting that the recombination centers associated with the 2.53 eV band are produced under X-ray irradiation and are involved in both RL and TSL luminescence mechanisms. When each irradiation was followed by heating up to 500 degrees C a strong sensitization of the RL band emitting at 3.44 eV and of the 110 degrees C TSL peak were observed. A perfect correlation between the RL and TSL emissions suggests that the recombination centers involved in the RL and TSL emissions are the sam
Les sables de Fontainebleau: a natural quartz reference sample and its characterisation
Fundamental studies on luminescence production
in natural quartz require samples
which can be studied by groups of laboratories
using complementary methods. In the framework
of a European collaboration studying
quartz luminescence, a sample originating
from the Fontainebleau Sandstone Formation
in France was selected for characterisation
and distribution to establish a starting point
for interlaboratory work. Here we report on
the preparation and characterisation work
undertaken before distribution with the aim
of ensuring that each laboratory received
comparable material. Material was purified to
enrich the quartz concentration, followed by
mineralogical screening by SEM and ICP-MS
analyses. Luminescence screening measurements
were undertaken at a single laboratory
(SUERC) to verify the suitability of the sample
for use within the study, and to establish the
level of homogeneity of subsamples prepared
for distribution. The sample underwent minimal
non-chemical pre-treatment by multiple
cycles of magnetic separation and annealing.
SEM analysis showed that the sample
consists mainly of SiO2. The luminescence
characterisation confirmed a dose sensitivity
of ca. 22,000â160,000 cts Kâ1 Gyâ1 per 260â
290 grains for the 110âŠC UV TL peak, well
developed low (here: 100â300âŠC) temperature
(pre-dose) TL signals and high OSL sensitivities.
The grain to grain OSL response varies by
more than one order of magnitude. No significant
IRSL signal was observed. In summary,
the results from luminescence characterisation
confirm the suitability of the sample for the
luminescence experiments envisaged and have
established a basis for comparability in studies
conducted by a network of laboratories
SILICATE NANOPARTICLES PRODUCED BY LABORATORY SIMULATED SPACE WEATHERING OF OLIVINE SINGLE CRYSTALS
Silicate nanoparticles, otherwise
referred to as very small grains (VSGs) [1], occur in
the interstellar medium. These grains experience a
strong structural modification during their lifetime in
the diffuse interstellar medium, due to events such as
grain-grain collisions and irradiation. Grain
amorphization is one of the major effects, transforming
crystalline dust concentrated in star envelopes into
amorphous silicate grains populating the interstellar
medium [2]. Moreover, several studies have pointed
out that the main building blocks of these silicates are
O, Si, Fe, Mg, Al and Ca, all elements that are among
the principal constituents of the Earthâs surface [3],
thus leading to the name âastronomical silicatesâ.
However, the structure and chemical evolution
together with the origin of these grains are still poorly
understood and intensively debated [4,5].
The aim of this study is the simulation of space
weathering processes by liquid phase pulsed laser
ablation (LP-PLA) on olivine single crystals. We adopt
a multiple technique characterization, taking advantage
of optical spectroscopy analyses and high- resolution
transmission electron microscopy (HR-TEM), to shed
light on the structure and chemical evolution of the
ablated material
Astronomical silicate nanoparticle analogues produced by pulsed laser ablation on olivine single crystals
Silicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in various
astrophysical environments. These grains experience substantial processing (e.g., amorphization)
during their lifetime in the diffuse interstellar medium due to events such as grain-grain collisions
and irradiation [2]. Moreover, several studies have pointed out that the main building blocks of
these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of
the Earthâs surface [3], thus leading to the name âastronomical silicatesâ. However, the structure
and chemical evolution together with the origin of these grains are still poorly understood and
intensively debated [4,5].
The aim of this study is the simulation of space weathering processes on olivine single
crystals by liquid phase pulsed laser ablation (LP-PLA). The study of the resulting structure of both
the target and the ablated material together with their chemical evolution has been carried out by a
multiple technique characterization. In particular, spectroscopy and dynamic light scattering
measurements, analyses of the electrostatic properties and reactivity to acids and bases on the
obtained colloidal solutions of the ablated nanoproducts have been performed and coupled with highresolution transmission electron microscopy (HR-TEM).
Selected olivine target crystals (Fo87) from the SĂŁo Miguel island (Azores) were analyzed
by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). LP-PLA
experiments were performed with a Nd:YAG laser focused via a singlet lens onto the surface of the
target, which was fixed at the bottom of a polystyrene box filled with 4 ml of deionized water (type
1) to immerge it completely. Laser pulses of 5 ns and 100 mJ simulate the timeframe and energy
exchange occurring during grain-grain interstellar collisions [6] and they generate a plasma plume
at the crystal/liquid interface. The rapid cooling induced by the confining liquid layer brings about
the condensation of the chemical vapor it contains with production of a colloidal solution of
nanoparticles. These solutions were analyzed by dynamic light scattering techniques and optical
absorption spectroscopy in the range from 200 nm to 1100 nm (6.20 eV - 1.13 eV). Absorption
measurements on the colloidal solutions have been compared against reference colloidal solutions
dispersed in deionized water (i.e. mesoporous silica [SiO2] nanoparticles, brucite [Mg(OH)2]
nanoparticles, aluminum hydroxide [Al(OH)3] nanoparticles, chrysotile [Mg3Si2O5(OH)4] nanotubes,
and synthetic forsterite [Mg2SiO4] nanoparticles). Moreover, additional absorption analyses have
been carried out as a function of the addition of known aliquots of sulfuric acid and sodium
hydroxide solutions. TEM/EDS analyses were then performed on the ablated nanoparticles deposited
via electrophoresis on C-coated Cu grids and compositional variations of the ablated target were
determined by X-ray photo-emission spectroscopy analyses.
The size distribution of LP-PLA synthesized nanoparticles is typically multimodal due to
aggregation phenomena. Aggregation is consistent with the measured ζ-potential, which is negative
with a relatively low absolute value, within the range 30-50 mV. Nonetheless, a recurrent mode is
centered at about 2 nm (hydrodynamic diameter) and it is consistent with the measured size
distribution obtained by transmission electron microscopy analysis (average nanoparticles diameter
around 3-5 nm). Optical absorption measurements on the ejected material show a main band
around 215 nm. This feature is very similar to the âB2 bandâ reported in several studies on silica
glass [7] and ascribed to oxygen vacancies, but its nature is still far to be fully understood. We also
found that this feature at 215 nm is very common among both Si and Mg compounds (e.g., Sioxide, Mg-hydroxide, chrysotile). Moreover, additional absorption bands in the range 240-350nm are
observed suggesting the formation of new space weathering products as result of the ablation
process.
Therefore, these results suggest that substantial chemical processing might be expected
during space weathering of âtypicalâ interstellar grains into VSGs. Moreover, coupling these
experimental results with remote sensing datasets will provide fundamental information about the
origin and evolution of these silicate grains
Temperature affects organic acid, terpene and stilbene metabolisms in wine grapes during postharvest dehydration
The partial dehydration of grapes after harvest is a traditional practice in several winegrowing regions that leads to the production of high quality wines. Postharvest dehydration (also known as withering) has a significant impact on the overall metabolism and physiology of the berry, yielding a final product that is richer in sugars, solutes, and aroma compounds. These changes are, at least in part, the result of a stress response, which is controlled at transcriptional level, and are highly dependent on the grape water loss kinetics and the environmental parameters of the facility where grapes are stored to wither. However, it is difficult to separate the effects driven by each single environmental factor from those of the dehydration rate, especially discerning the effect of temperature that greatly affects the water loss kinetics. To define the temperature influence on grape physiology and composition during postharvest dehydration, the withering of the red-skin grape cultivar Corvina (Vitis vinifera) was studied in two conditioned rooms set at distinct temperatures and at varying relative humidity to maintain an equal grape water loss rate. The effect of temperature was also studied by withering the grapes in two unconditioned facilities located in geographic areas with divergent climates. Technological, LC-MS and GC-MS analyses revealed higher levels of organic acids, flavonols, terpenes and cis- and trans-resveratrol in the grapes withered at lower temperature conditions, whereas higher concentrations of oligomeric stilbenes were found in the grapes stored at higher temperatures. Lower expression of the malate dehydrogenase and laccase, while higher expression of the phenylalanine ammonia-lyase, stilbene synthase and terpene synthase genes were detected in the grapes withered at lower temperatures. Our findings provide insights into the importance of the temperature in postharvest withering and its effect on the metabolism of the grapes and on the quality of the derived wines
Radiation hardness of Ce-doped sol-gel silica fibers for High Energy Physics applications
The results of irradiation tests on Ce-doped sol-gel
silica using X- and g-rays up to 10 kGy are reported,
in order to investigate the radiation hardness of this
material for high energy physics applications. Sol-gel
silica fibers with Ce concentrations of 0.0125 mol% and
0.05 mol% are characterized by means of optical absorption
and attenuation length measurements before
and after irradiation. The two different techniques
give comparable results, evidencing the formation of
a main broad radiation-induced absorption band, peaking
at about 2.2 eV, related to radiation-induced color
centers. The results are compared with those obtained
on bulk silica. This study reveals that an improvement
of the radiation hardness of Ce-doped silica fibers can
be achieved by reducing Ce content inside the fiber
core, paving the way for further material development
A systematic multi-technique comparison of luminescence characteristics of two reference quartz samples
MB did the experiments using the equipment belonging to the Centre for Modern Interdisciplinary Technologies, Nicolaus Copernicus University in Torun, ul. Wilenska 4, 87â100 Torun, Poland (e-mail: [email protected]) and has been financed by the grant of the National Science Centre, Poland, No. 2018/31/B/ST10/03917.International audienceFurther developments in luminescence dating, dosimetry and temperature-sensing require a deep understanding of luminescence processes and their driving parameters. Natural quartz is one of the most widely used minerals for these purposes. Still, poor reproducibility of results often hampers comparability and credibility of findings in the literature. We identified the lack of suitable natural reference samples as a pivotal problem impeding significant progression. Ideally, basic investigations involve several laboratories working on well-characterised reference quartz samples with different characteristics. Investigations should include multiple complementing methods to analyse luminescence properties and mineralogical and geochemical composition.Here, we present such a multi-technique luminescence comparison of two natural quartz samples. Next to the recently introduced Fontainebleau (FB) reference quartz, we propose another reference sample derived from the âSilver Sands of Morarâ (lab code âMRâ; Scotland, UK). Our experiments confirm that both quartz samples behave fundamentally different in terms of signal composition and sensitivity. The comparative characterisation of both samples targeted electron traps via thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques and luminescence centres via radioluminescence and time-resolved OSL spectrometry. In summary, we conclude that all observed differences are likely the results of divergent defect concentrations rather than variances in defects' composition (nature). The measurement data of our study are accessible open-access for inspection by others
On the dose rate dependence of radiofluorescence signals of natural quartz
International audienc
Ce doped SiO<sub>2</sub> optical fibers for remote radiation sensing and measurement
Scintillating materials, able to efficiently operate the conversion of energy absorbed in the form of ionizing radiation into light in the visible UV interval, are presently used in a wide class of applications as medical imaging, industrial inspection, security controls and high energy physics detector. In the last few years we studied and developed a new radiation sensor based on silica-glass fiber-optic technology. In its simplest configuration such device is composed by a short portion (about 10 mm) of scintillating fiber coupled to a photomultiplier by a suitably long passive silica fiber.At the early stage of its market introduction it is the smallest radiation sensor, also with respect to MOSFET and diode technology and it appears to be the ideal choice for in vivo measurements in medical field or remote sensing
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