Thickness and uniformity characterization of thin targets for intense ion beam experiments

The NUMEN Experiment aims to get information on the Nuclear Matrix Elements of the Neutrinoless Double Beta Decay, by measuring heavyion induced Double Charge Exchange (DCE) reactions cross sections. A good energy resolution is needed to clearly distinguish energy states of DCE products. To measure the energy of reaction products with the required resolution, the target must be thin and uniform to minimise dispersion and straggling effects on the ejectile energy. Few hundreds of nanometers of the target isotope are deposited on a Highly Oriented Pyrolytic Graphite substrate a few micrometers thick. The results of the characterisation of the first target prototypes of tin and tellurium are presented. The Scanning Electron Microscopy was used to qualitatively analyse the samples surface. A setup to study Alpha Particle Transmission has been assembled to measure thickness and uniformity of the targets; the thickness results have been verified by the Rutherford Backscattering measurements. To evaluate the effects of the thickness on the resolution of the DCE products energy, a Monte Carlo code has been implemented, using the measured thickness and uniformity as input data for the simulation

Evaluation of target non-uniformity and dispersion effects on energy measurement resolution in NUMEN experiment

In the NUMEN Experiment, Double Charge Exchange (DCE) reactions will be studied to get very precise measurements of their cross sections and final state levels. The interest for these reactions lies in the possibility for some nuclides to have DCE with initial and final states identical to those of the Neutrinoless Double β-Decay. To reach a good precision in the energy measurements, high statistics is needed and severe constraints about the target thickness must be satisfied. A 50 μA intense ion beam will provide the desired statistics, while posing the problem of dissipating the massive heat generated in the target. It is therefore necessary to design a suitable cooling system, which must affect the particles' energy as little as possible. Said energy is already influenced by the current setup. The Superconducting Cyclotron (SC) and the MAGNEX Spectrometer introduce an error on the particles' energy by 1/1000th (FWHM value) of its average energy. In the target, the main sources of error are straggling of projectiles and reaction products, and the dispersion effect. Both closely depend on the target thickness, which must be of the order of few hundred nanometres. In addition, the two effects are worsened if the target thickness is not uniform. The solution to these problems has been found by backing the target isotope with relatively thin substrate of Highly Oriented Pyrolytic Graphite (HOPG). Its thermodynamic properties fit the cooling requirements and can be as thin as 450 μg cm-2. The further straggling suffered by the ejectiles is tolerable, falling within the resolution requirements. Samples are deposited by using Electron Beam Evaporation: results obtained for Sn and Te are checked by Scanning Electron Microscopy (SEM). A quantitative evaluation of the samples' thickness has been performed by Alpha-Particle Transmission (APT) and Rutherford Backscattering Spectrometry (RBS) measurements. A Monte Carlo code has been implemented to estimate the ejectiles energy distribution using the experimental measurements as input. Results from characterization and simulations help in optimizing the target thickness and the energy resolution of reaction products

Curvature driven diffusion, Rayleigh-Plateau, and Gregory-Laflamme

It can be expected that the respective endpoints of the Gregory-Laflamme black brane instability and the Rayleigh-Plateau membrane instability are related because the bifurcation diagrams of the black hole-black string system and the liquid drop-liquid bridge system display many similarities. In this paper, we investigate the non-linear dynamics of the Rayleigh-Plateau instability in a range of dimensions, including the critical dimension at which the phase structure changes. We show that near the critical dimension and above, depending on a parameter in initial conditions an unstable cylinder will either pinch off or converge to an equilibrium state. The equilibrium state is apparently non-uniform but has a constant mean curvature everywhere. The results suggest that in the gravity side, near the critical dimension and above, the final state of an unstable black string (which is not too long) is a non-uniform black string. The equation of motion adopted to describe the dynamics is the surface diffusion equation, which was originally proposed to describe a grooving process of heated metal surfaces. An interesting correspondence between the diffusion dynamics and black hole (thermo)dynamics is discussed.Comment: 14 pages, 5 figures; v2: references added, typos fixe

Tests of a cooling system for thin targets submitted to intense ion beams for the numen experiment

The NUMEN experiment, hosted at LNS (Catania, Italy), aims to determine the Nuclear Matrix Elements (NMEs) involved in 0β β decay via heavy-ion induced Double Charge Exchange (DCE) reactions. High intensity beams of about 50 μA and of energies ranging from 15 to 60 MeV/u are necessary, due to the low DCE cross sections and the use of very thin targets (several hundreds of nm) needed to reach the required energy resolution. These intense beams produce a considerable amount of heat inside the target, which can be dissipated by depositing the targets on a highly thermally conductive substrate, HOPG (Highly Oriented Pyrolytic Graphite), and coupling it with a suitable designed target-cooler system. The heat transfer from the beam spot to the cold region has been studied by solving numerically the heat equation to determine the evolution in space and time of the temperature inside the target. According to calculations, the temperatures of most of the target isotopes remain under the melting points. Experimental tests with a laser were initiated to validate the whole cooling system and the calculations

Étude comparative et validation de modèles prédictifs de résistance thermique de contact dans le cas solide-liquide avec prise en compte de la tension superficielle

La plupart des modèles prédictifs de résistance thermique de contact portent sur les contacts solides-solides. La nature des contacts (glissant ou statique), la complexité de la description des rugosités de surface ou les niveaux de pressions de contact mises en jeu, ont conduit au développement d'un nombre important de modèles prédictifs. Cependant, ceux portant sur l’étude des contacts solides-liquides sont très rares bien que l’étude des transferts thermiques dans ce type de contacts soit d’un intérêt majeur dans de nombreuses applications: contact polymère fondu et surface métallique au cours de la mise en forme de composites, contact bitume liquide et granulat au cours de la fabrication d'enrobé bitumineux, contact solide-solide avec matériau d'interface en microélectronique. Toutefois, ces modèles nécessitent la prise en compte de propriétés adhésives des liquides sur les surfaces solides contribuant à modifier les résistances de contacts. La validation de ces modèles prédictifs nécessite des tests sur un grand nombre de matériaux de textures et de caractéristiques chimiques de surface différentes (tension superficielle, angle de contact). Dans cette étude nous présentons et comparons deux modèles prédictifs de résistance thermique de contact récemment mis au point pour les contacts solides-liquides et mettant en évidence l'influence des caractéristiques chimiques de surface ainsi que la structure topographique de l'interface solide-liquide. Ces modèles ont été confrontés à des résultats expérimentaux obtenus par mesure de résistance de contact entre un granulat très rugueux et du bitume liquide pour différentes températures de contact et pour une pression de contact modérée correspondant aux conditions d’élaboration de nouveaux procédés d'enrobés bitumineux économes en énergie. Les résultats obtenus montrent un bon accord entre les prédictions et les résultats expérimentaux obtenus

A Novel Intraoperative Ultrasound Probe for Transsphenoidal Surgery: First-in-human study.

Background. Ultrasound has been explored as an alternative, less bulky, less time-consuming and less expensive means of intraoperative imaging in pituitary surgery. However, its use has been limited by the size of its probes relative to the transsphenoidal corridor. We developed a novel prototype that is more slender than previously reported forward-viewing probes and, in this report, we assess its feasibility and safety in an initial patient cohort. Method. The probe was integrated into the transsphenoidal approach in patients with pituitary adenoma, following a single-centre prospective proof of concept study design, as defined by the Innovation, Development, Exploration, Assessment and Long-Term Study (IDEAL) guidelines for assessing innovation in surgery (IDEAL stage 1 - Idea phase). Results. The probe was employed in 5 cases, and its ability to be used alongside the standard surgical equipment was demonstrated in each case. No adverse events were encountered. The average surgical time was 20 minutes longer than that of 30 contemporaneous cases operated without intraoperative ultrasound. Conclusion. We demonstrate the safety and feasibility of our novel ultrasound probe during transsphenoidal procedures to the pituitary fossa, and, as a next step, plan to integrate the device into a surgical navigation system (IDEAL Stage 2a - Development phase)

Predictions from Heavy New Physics Interpretation of the Top Forward-Backward Asymmetry

We derive generic predictions at hadron colliders from the large forward-backward asymmetry observed at the Tevatron, assuming the latter arises from heavy new physics beyond the Standard Model. We use an effective field theory approach to characterize the associated unknown dynamics. By fitting the Tevatron t \bar t data we derive constraints on the form of the new physics. Furthermore, we show that heavy new physics explaining the Tevatron data generically enhances at high invariant masses both the top pair production cross section and the charge asymmetry at the LHC. This enhancement can be within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be able to exclude a large class of models of heavy new physics or provide hints for its presence. The same new physics implies a contribution to the forward-backward asymmetry in bottom pair production at low invariant masses of order a permil at most.Comment: 11 pages, 6 figures. v2: added remarks on EFT validity range, dijet bounds and UV completions; matches published versio

Extrapolation of neutron-rich isotope cross-sections from projectile fragmentation

Using the measured fragmentation cross sections produced from the 48Ca and 64Ni beams at 140 MeV per nucleon on 9Be and 181Ta targets, we find that the cross sections of unmeasured neutron rich nuclei can be extrapolated using a systematic trend involving the average binding energy. The extrapolated cross-sections will be very useful in planning experiments with neutron rich isotopes produced from projectile fragmentation. The proposed method is general and could be applied to other fragmentation systems including those used in other radioactive ion beam facilities.Comment: accepted for publication in Europhysics Letter