Abstract
Lead fluoride (PbF
2
) crystals represent an excellent and
relatively innovative choice for high resolution electromagnetic
calorimeters with high granularity and fast timing for high
...intensity environments. For this reason two PbF
2
crystals, sized
5× 5 × 40 mm
3
, were irradiated with
60
Co
photons up to ∼ 4 Mrad and with 14 MeV neutrons up to a
10
13
n/cm
2
total fluence. Their loss in transmittance was
evaluated at different steps of the photon and neutron irradiation
campaign, resulting in a total of 30% loss above 350 nm. With
crystals always kept in dark conditions, natural and thermal
annealing, as well as optical bleaching with 400 nm light, were
performed on the irradiated specimens, resulting in a partial
recovery of their original optical characteristics.
Abstract
Cerium-doped Lutetium-Yttrium Oxyorthosilicate (LYSO:Ce) is
one of the most widely used Cerium-doped Lutetium based
scintillation crystals. Initially developed for medical detectors it
...rapidly became attractive for High Energy Particle Physics (HEP)
applications, especially in the frame of high luminosity particle
colliders.
In this paper, a comprehensive and systematic study of LYSO:Ce
(Lu
(1-
x
)
Y
x
2
SiO
5
:Ce) crystals
is presented. It involves for the first time a large number of
crystal samples (180) of the same size from a dozen of producers.
The study consists of a comparative characterization of LYSO:Ce
crystal products available on the market by mechanical, optical and
scintillation measurements and aims specifically, to investigate key
parameters of timing applications for HEP.
Development of technologies which utilize hydrogen as energy vector requires the realization of efficient gas storage systems. Materials suitable for hydrogen storage at the solid state have to ...fulfill some specific requirements in order to be used inside the reactors. First of all it is necessary to have a material which could be cycled without observing reduction of performances in terms of kinetics and total hydrogen capacity. The reaction of the material with hydrogen must be reversible even after long time cycling, i.e. repeated absorption and desorption runs. For what concerns the efficiency of the reactors, one of the main parameters to be taken into account is the thermal conductivity of the bed of hydride. The use of powder is detrimental for thermal conductivity and also for gas permeability and particle entrainment by the gas flow in the reactor. Moreover powders after long term cycling tend to pack and sinter evidencing the problems reported before. For this reason powders of hydrides are compacted, generally in cylindrical shape, after mixing with agents for enhancing thermal conductivity and mechanical stability (for example Al, Cu, carbon-based materials). It has been reported that compacted systems during cycling tend to disaggregate returning to the form of powder in the loose form. This swelling mechanism causes rapid slowdown of the kinetics and all the problems correlated to the use of the powders. For this reason many efforts have been spent in order to extend the life of the compacted systems. In this work it is reported the study performed to improve the preparation of compacted powder systems by a procedure which includes the deposition of a thin layer of a metal on the surface of the pellet. The pellets prepared with this procedure demonstrated, after 50 cycles, variations of dimension eight time lower in comparison to those obtained on pellets prepared without coating. The quantity of metal deposited is less than 0.1% of the weight of the pellet and it doesn't affect hydrogen capacity and kinetics of reaction. Kinetics of reaction and microstructure have been studied with a volumetric Sievert's type apparatus and with Optical and Scanning Electron Microscopy respectively.
•Compacted powders were prepared by ball milling MgH2 with Nb2O5 and ENG.•A thin metal coating has been deposited on the pellet surface.•Pellet prepared following this procedure presented increased stability to cycling.•The coating remained continuous and intimately attached to the pellet surface.•Kinetics and total hydrogen capacity has not been affected by the coating.
Heat management in hydrogen storage tanks is a mandatory issue in order to ensure high level performances both in terms of hydrogen release/uptake kinetics and storage capacity. Previous research has ...ascertained that powders tend to pack and sinter during charge/discharge cycling giving rise to non-reacting material. Moreover powders, with intrinsically low thermal conductivity, can show problems related to hydrogen permeability, and suffer from hydraulic losses and particle entrainment by gas flow. To overtake these problems and to keep high performances, hydride powders mixed with high thermal conductivity additives are compacted in pellets. Some materials, like Expanded Natural Graphite (ENG), besides improving the pellet mechanical stability during cycling, can impart a thermal conductivity higher by order of magnitudes with respect to a simple powdered bed. On the basis of these considerations, pelleting can be very effective in improving tank performances. However pellets tend to swell and lose compactness during long term operation, returning back to the powder form with a detrimental effect on tank performances. In this work the swelling process caused by cycling of pellets simulating tank exercise has been studied. The pellets, which are constituted by ball milled magnesium hydride (MgH2) with the addition of niobium oxide (Nb2O5) and ENG, have been deeply studied by different microscopic methods including Scanning Electron Microscopy (SEM), Helium Ion Microscopy (HeIM) and high resolution Computed Tomography (CT) with the purpose of ascertaining microstructural modification and degradation mechanism in order to define strategies for material preparation able to reduce the entity of the swelling process.
•Compacted powders were prepared by ball milling MgH2 with Nb2O5 and ENG.•Compacted powders have been cycled to study swelling mechanism.•Computed Tomography revealed the microstructure of the whole pellet before and after cycling.•SEM images highlighted different particles' morphology of cycled respect to as-milled ones.•High resolution Helium Ion Microscopy imaging showed recrystallization of MgH2.
Ultrathin stable transparent conductive nickel films were deposited on quartz substrates by radio frequency sputtering at room temperature. Such films showed visible transmittance up to 80% and ...conductivity up to 1.8×104S/cm, further increased to 2,3×105S/cm by incorporation of a micrometric silver grid. Atomic force microscopy and scanning electron microscopy revealed quite compact, smooth and low surface roughness films. Excellent film stability, ease, fast and low cost process fabrication make these films highly competitive compared to indium tin oxide alternative transparent conductors. Films were characterized regarding their morphological, optical and electrical properties.
•Indium-free transparent conductors are proposed.•Ultrathin Ni films are fabricated with a very fast process at room temperature.•Films have conductivity values up to 1.8×104S/cm.•Ni ultrathin films are good candidates for UV and NIR optoelectronic applications.
The global need for energy in the world is constantly increasing. Critical fission reactors have proved great efficiency in the energy production, but the fear of nuclear wastes and accidents due to ...an uncontrolled chain reaction makes these unpleasant to public. More safe fusion reactors, on the opposite, have low efficiency. Hybrid reactors capable of using the advantages of both are studied, but not yet developed. In this paper, a simple fusion–fission pilot experiment model has been developed. A Tokamak with the same characteristics of DTT (Divertor Tokamak Test facility) has been considered as a reference machine for the fusion component. The fusion system has been coupled with a relatively simple low-power fission blanket configured into three different modes by using different fuels and materials. This model could be useful in order to investigate the properties of the fusion–fission hybrid coupling from a neutronic point of view.
Optical components operating in radiation environments, like nuclear facilities, High Energy Physics and space experiments, are exposed to fluxes of energetic particles, which may deteriorate the ...image quality. In order to avoid undesired failure of such components that is due to changes produced in the material optical properties by the hostile conditions, it is useful to perform a preliminary investigation of the radiation induced damage on each material and on different types of optical components. In this work, coated optical components are investigated. A set of optical coatings were submitted to gamma irradiation at the Calliope super(60)Co radioisotope source (Research Centre ENEA-Casaccia, Rome) in order to simulate the hostile radiation environment in which they could be employed. The behavior of different substrates, single-layer materials and multilayer optical coatings was investigated by comparing both transmittance and reflectance measurements before and after the gamma -ray exposure.
The Radial Neutron Camera (RNC) of ITER (International Thermonuclear Experimental Reactor) is a multichannel detection system designed to measure the uncollided neutron flux from the fusion plasma, ...providing information on the neutron emissivity profiles and source strength. Fission chambers and diamond detectors are candidate detectors for the RNC In-port subsystem. This is a high radiation environment (up to ∼5 MGy gamma dose and ∼2×1016 n/cm2 neutron fluence) where about 500 baking cycles up to 240 °C are foreseen over the whole ITER lifetime. In order to assess the feasibility of using diamond detectors in such harsh conditions, and to study the best technological solutions, we are currently performing a set of tests to understand the behavior of diamond detectors under radiation and thermal stresses: (1) thermal stress tests at constant temperature of 240 °C and thermal cycling between 100 °C and 240 °C; (2) gamma-hardness test up to a total dose of 4.7 MGy; (3) neutron-hardness test (limited to 2 ×1014 n/cm2 in this work).
Lead fluoride (PbF\(_2\)) crystals represent an excellent and relatively innovative choice for high resolution electromagnetic calorimeters with high granularity and fast timing for high intensity ...environments. For this reason two PbF\(_2\) crystals, sized \(5\times 5 \times 40 \) mm\(^3\), were irradiated with \(^{60}\)Co photons up to \(\sim 4\) Mrad and with 14 MeV neutrons up to a \(10^{13}\) n/cm\(^2\) total fluence. Their loss in transmittance was evaluated at different steps of the photon and neutron irradiation campaign, resulting in a total of 30% loss above 350 nm. With crystals always kept in dark conditions, natural and thermal annealing, as well as optical bleaching with 400 nm light, were performed on the irradiated specimens, resulting in a partial recovery of their original optical characteristics.
Cerium-doped Lutetium-Yttrium Oxyorthosilicate (LYSO:Ce)is one of the most widely used Cerium-doped Lutetium based scintillation crystals. Initially developed for medical detectors it rapidly became ...attractive for High Energy Particle Physics (HEP) applications, especially in the frame of high luminosity particle colliders. In this paper, a comprehensive and systematic study of LYSO:Ce (\(Lu_{(1-x)}Y_x_2SiO_5\):\(Ce\)) crystals is presented. It involves for the first time a large number of crystal samples (180) of the same size from a dozen of producers.The study consists of a comparative characterization of LYSO:Ce crystal products available on the market by mechanical, optical and scintillation measurements and aims specifically, to investigate key parameters of timing applications for HEP.
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