Abstract
In this work, a simple numerical model is presented in order to evaluate the energetic release of short fiber composite PA66GF35 under static tensile tests. The micro-mechanical behavior of ...the fiber-matrix system was taken into account, as well as the fiber distribution and orientation. Numerical simulation at macro scale level were carried out to predict the temperature evolution of the material under monotonic load. Experimental validation was performed on dog-bone specimens monitoring the surface temperature with an infrared camera. A deviation from the linearity of the thermoelastic effect has been noticed for a stress level below the yielding strength of the material. The analysis of the temperature trend evolution may be a useful aid in order to identify damage initiation within the material that would lead to failure, especially under fatigue load, even adopting a simple and rapid static tensile test.
Abstract We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for ...accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The 134 Cs, 176 Lu, and 48 Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the γ activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall γ -detection system’s efficiency using GEANT4, including the poisoning γ -signal from the walls of the trap, relevant for the γ -tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.
Abstract Metals can be injected into electron cyclotron resonance ion sources (ECRIS) via different techniques, among which resistive ovens are used to vaporize neutral materials, later captured by ...the energetic plasma that will step-wise ionize them, hence giving multiply charged ion beams for accelerators. Recently, PANDORA, a novel ECR plasma trap, has been conceived to perform interdisciplinary research spanning from nuclear physics to astrophysics, where in-plasma high charge states of metallic species are demanded. However, a full knowledge on the vaporization method and on the coupling of neutral atoms with plasma and its overall dynamics is still not available. Simulations, hence, are of fundamental relevance to improve the overall efficiency, reduce consumption of rare expensive isotopes, and to improve the ion source performance. We present a numerical study about metallic species suitable for oven injection in ECRIS, focusing on metals diffusion, transport, and wall deposition under molecular flow regime. We studied the metal dynamics with and without plasma. Results underline the plasma role on a space-dependent conversion yield, reflecting the strongly inhomogeneous ECR plasma. The plasma and its parameters have been modelled using an established self-consistent particle-in-cell model. The numerical tool is conceived for the PANDORA plasma trap but can be extended to other ECR plasmas and traps. As test cases we studied the 134 Cs and 48 Ca radioisotopes, as metals of interest for the modern nuclear physics. A focus is given on the β -decaying 134 Cs, as an application case for PANDORA, providing quantitative estimates of the γ-detection signal-poisoning effect by neutral metals deposition at the chamber wall.
Abstract An innovative ECR ion trap facility, called PANDORA (Plasma for Astrophysics, Nuclear Decay Observation and Radiation for Archaeometry), was designed for fundamental plasma processes and ...nuclear physics investigations. The overall structure consists of three subsystems: a) a large (70 cm in length, 28 cm in inner diameter) ECR plasma trap with a fully superconducting B-minimum magnetic system (B max = 3.0 T) and an innovative design to host detectors and diagnostic tools; b) an advanced non-invasive plasma multidiagnostics system to locally characterize the plasma thermodynamic properties; c) an array of 14 HPGe detectors. The PANDORA facility is conceived to measure, for the first time, in-plasma β -decaying isotope rates under stellar-like conditions. The experimental approach consists in a direct correlation of plasma parameters and nuclear activity by disentangling - by means of the multidiagnostic system that will work in synergy with the γ-ray array - the photons emitted by the plasma (from microwave to hard X-ray) and γ-rays emitted after the isotope β -decay. In addition to nuclear physics research, fundamental plasma physics studies can be conducted in this unconventional ion source equipped with tens of detection and diagnostic devices (RF polarimeter, optical emission spectroscopy (OES), X-ray imaging, space and time-resolved spectroscopy, RF probes, scope), with relevant implications for R&D of ion sources for accelerator physics and technology. Several studies have already been performed in downsized nowadays operating ECRIS. Stable and turbulent plasma regimes have been described quantitatively, studying the change of plasma morphology, confinement, and dynamics of losses using space resolved X-ray spectroscopy.
Abstract
Static Thermographic Method is a rapid test procedure able to predict the fatigue limit of the material evaluating the end of the thermoelastic phase during a static tensile test. In order ...to investigate the energetic release of the material, experimental tests have been carried out on double edge steel notched specimens. During the test, the surface temperature was monitored with an infrared camera and the true stress-strain curve of the material was retrieved. Numerical simulations have been carried out to predict the temperature evolution of the material under monotonic load. The relationship between the elasto-plastic behavior and the energetic release has been investigated comparing numerical and experimental data. The rise of irreversible plastic deformation severally affects the temperature trend introducing an additional heat amount that leads to a deviation from the linearity of the thermoelastic effect. The analysis of the temperature evolution during a static tensile test may be adopted as a novel approach to relate the local stress state with a macroscopic stress value that introduce in the material the first micro plasticization.
The abundance of 26Al carries a special role in astrophysics, since it probes active nucleosynthesis in the Milky Way and constrains the Galactic core-collapse supernovae rate. It is estimated ...through the detection of the 1809 keV γ-line and from the superabundance of 26Mg in comparison with the most abundant Mg isotope (A = 24) in meteorites. For this reason, high precision is necessary also in the investigation of the stable 27Al and 24Mg isotopes. Moreover, these nuclei enter the so-called MgAl cycle, playing an important role in the production of Al and Mg. Recently, high-resolution stellar surveys have shown that the Mg–Al anticorrelation in red-giant stars in globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not be correlated with Al. The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show large uncertainties owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84 keV resonance and to lower upper limits on the strength of nearby resonances. In intermediate-mass AGB stars experiencing hot bottom burning, a sizeable increase in surface aluminum abundance is observed at the lowest masses, while 24Mg is essentially unaffected by the change in the reaction rate.
Abstract
Resistive oven technique is used to inject vapours of metallic species in electron cyclotron resonance (ECR) plasma traps, where plasma provides step-wise ionization of neutral metals, ...producing charged ion beams for accelerators. We present a numerical survey of metallic species suitable for oven injection in ECR ion sources, studying neutrals diffusion and deposition under molecular flow regime. These aspects depend on geometry of the evaporation inlet, thermodynamics, and plasma parameters, which strongly impact on ionization and charge-exchange rate, thus on the fraction of reacting neutrals. We considered diffusion of metals with and without plasma. The plasma and its parameters have been modelled considering an established self-consistent particle-in-cell model. Numerical predictions might be relevant to reduce the metal consumption, to increase the overall efficiency, and to improve the plasma ion source performances. As test case, we studied the
134
Cs isotope, as one of the alkali metals of interest for the modern nuclear physics.
The FAZIA apparatus exploits Pulse Shape Analysis (PSA) to identify nuclear fragments stopped in the first layer of a Silicon-Silicon-CsI(Tl) detector telescope. In this work, for the first time, we ...show that the isotopes of fragments having atomic number as high as Z∼20 can be identified. Such a remarkable result has been obtained thanks to a careful construction of the Si detectors and to the use of low noise and high performance digitizing electronics. Moreover, optimized PSA algorithms are needed. This work deals with the choice of the best algorithm for PSA of current signals. A smoothing spline algorithm is demonstrated to give optimal results without requiring too much computational resources.
•A new indirect measurement of the 27Al(p,α)24Mg has been carried out down to astrophysical energies.•The strength of the 84.3 keV resonance has been measured, and more stringent upper limits of ...nearby resonances have been set.•A new recommended reaction rate has been established, leading to a factor of 3 lower 27Al destruction rate.•Preliminary nucleosynthesis calculations have shown ∼30% changes in 27Al and 24Mg abundances for intermediate mass stars.
The 26Al abundance holds a special role in present-day astrophysics, since it is a probe of active nucleosynthesis in the Galaxy and a valuable constraint of Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809-keV γ-line of the daughter 26Mg and from the superabundance of 26Mg in comparison with the most abundant 24Mg isotope in meteorites. Accurate knowledge of the reaction rates involving 26Al, its stable counterpart 27Al and 24Mg is then mandatory. Moreover, these nuclei enter the MgAl cycle playing an important role in the production of Al and Mg isotopes. Recently, high-resolution stellar surveys have shown that the Mg-Al anti-correlation in red giants of globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not show correlation with Al.
The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show an order of magnitude uncertainty owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84-keV resonance and to lower the upper limits on the strength of nearby resonances, with potential important impact for astrophysics. In particular, modifications in the 27Al and 24Mg abundances up to ∼30% are predicted for intermediate mass stars.
In the last 15 years the FRIBs@LNS facility has successfully produced Radioactive Ion Beams using the In-Flight technique. We report on the current status and future perspectives opened by FRAISE, a ...new fragment separator that will be build in connection with the upgrade of Superconducting Cyclotron of the INFN-LNS laboratories.
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