Light Scattering by Cholesteric Skyrmions

We study the light scattering by localized quasi planar excitations of a Cholesteric Liquid Crystal known as spherulites. Due to the anisotropic optical properties of the medium and the peculiar shape of the excitations, we quantitatively evaluate the cross section of the axis-rotation of polarized light. Because of the complexity of the system under consideration, first we give a simplified, but analytical, description of the spherulite and we compare the Born approximation results in this setting with those obtained by resorting to a numerical exact solution. The effects of changing values of the driving external static electric (or magnetic) field is considered. Possible applications of the phenomenon are envisaged.Comment: 18 pages, 14 figure

Production and Extraction of Protons by Solid Hydrogenated Targets via UV Laser Ablation

In this work we present the preliminary investigations about the production of proton beams by pulsed laser ablation of solid disks produced by compressed Titanium dihydride powder. The laser we used was an excimer KrF, operating at low intensity and ns pulse duration. The ion emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector. We performed studies on the produced plasma for different laser fluence values and accelerating voltage. In free expansion mode we obtained protons and titanium ions having kinetic energy of some hundred of eV; by applying a postaccelerating voltage we obtained beams up to 15 keV

A Proton Source via Laser Ablation of Hydrogenated Targets

In this work we present results on the extraction of proton beams from a plasma generated by pulsed laser ablation of solid hydrogenated targets. The laser used was an excimer KrF operating at low irradiances (108–109 W/cm2) and nanosecond pulse duration. The ablated targets were disks obtained by compression of TiH2 powder. The ion emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector. In order to improve the ion yield, an electrostatic extraction system was applied. Studies on the produced plasma for different laser irradiances and accelerating voltages have been performed. The results obtained show that this setup is suitable for a high yield proton source

Bobina di Rogowski lineare

Oggigiorno, lo sviluppo e l'uso di impulsi sempre più veloci richiedono sistemi sofisticati per diagnosticarli. La bobina di Rogowski è un dispositivo ben conosciuto, sviluppato per la diagnostica di impulsi di corrente in sistemi a configurazione cilindrica, infatti è conosciuta anche come toro di Rogowski. Recentemente, stanno avendo sempre più successo esperimenti di radiofrequenza per stimolazioni biofisiche con l'uso di linee di trasmissione piane. Così, è stato necessario sviluppare bobine di Rogowski lineari per rilevare impulsi di corrente in conduttori piatti. Simili sistemi sono anche applicabili agli acceleratori di particelle di struttura lineare. In questo lavoro si analizza una bobina di rogowski lineare e si studia l'influenza della sua resistività come pure quella del nucleo magnetico. Il dispositivo sviluppato è in grado di registrare impulsi lunghi alcune centinaia di ns e con tempi di salita di circa 500 ps. Il coefficiente di attenuazione dipende principalmente dal numero di spire che compongono la bobina e dalle approssimazioni fatte sul campo magnetico, negli esperimenti condotti risulta pari a 1300 A/V

Ion beams delivered by two accelerating gaps for industrial and therapeutic applications

Laser ion sources offer the possibility to get ion beams utilizable to improve particle accelerators. Today many laboratories, as well as the LEAS, are involved to develop accelerators of very contained dimensions, easy to be installed in little laboratories and hospitals. Pulsed lasers at intensities of the order of 108 W/cm2 and of ns pulse duration, interacting with solid matter in vacuum, produce plasma of high temperature and density. The charge state distribution of the plasma generates high electric fields which accelerate ions along the normal to the target surface. The energy of emitted ions has a shifted Maxwell-Boltzmann distribution which depends on the ion charge state. To increase the ion energy, a post-acceleration system can be employed by means of high voltage power supplies of about 100 kV. The post acceleration system results a good method to obtain high ion currents using a not expensive system and the final ion beams find interesting applications in the field of the ion implantations, hadrontherapy, scientific applications and industrial use. In this work we study the electromagnetic and geometric proper-ties, like the emittance of the beams delivered by Cu target. Plasma‟s characterization was performed us-ing a Faraday cup for the electromagnetic characteris-tics, while for the geometric ones by adopting a pep-per pot system. Applying 60 kV of accelerating volt-age and a laser irradiance of 0.1 GW/cm2, we obtain 5.5 mA of output current and a normalized beam emittance of 0.2 π mm mrad. The brightness of the beams was 137 mA(p mm mrad)-2

Quasi-monoenergetic proton beams by laser-plasma X-rays

We report the details of a technique for the production of proton beams with very low energy spread exploiting the short soft X-rays obtained by laser ablation. These beams have been generated by the dissociation and ionization of an hydrogen buffer gas induced by the laser-plasma X-rays and then accelerated by means of an electrostatic accelerator. Their properties have been analyzed through the time-of-flight method applying different accelerating voltages. The resulting energetic spread ranges between 6 and 11%, as a function of the applied voltage. Such a system could be extremely useful for producing quasi-monoenergetic proton beams

Study of Faraday cups for fast ion beams provided by a LIS source

Faraday cups are widely utilized to characterize ion and electrons beams. Owing to the secondary electron emission (SEE) induced by the collision of beams with collectors, wrong measurements could emerge from these detectors. To overcome this problem a polarized grid is utilized in front the cup collector at a negative voltage with respect to the collector. Unfortunately, the high voltage connection of the Faraday cups is hard to obtain. Then, in this work we want to study the secondary emission on different Al ion collector designs having tilted surfaces with respect to beam axis. Tests were performed using ion beams accelerated by a power supply up to 40 kV. The results by the modified collector surfaces were compared to the ones performed with a simple flat collector. The results we obtained point out that the secondary electron emission enhanced on incident beam energy and on the angle with respect to the normal direction of the surface. The ratio of the SEE to angle value results constant for the accelerating voltage and the possibility to design an ion collector able to reset the SEE seems not to be reached

The restoration of the Colosso di Barletta: EDXRF analysis

The Colosso di Barletta is an imposing outdoor bronze statue, dating back the V century, located near the Basilica of “Santo Sepolcro” in Barletta (Apulia, Southern Italy). The monument underwent a structural restoration in 1981, during which the Central Institute of Restoration in Rome performed cleaning treatments and consolidation of the patinas. Currently, the Laboratory of Archaeometry of the University of Salento is carrying on a campaign of non-destructive and in situ measurements by using energy dispersion X-ray fluorescence (EDXRF) in order to assess the chemical composition of the alloy and to study its patinas

Stress da radiazione RF a 900 MHz ed attivazione di elementi trasponibili in tessuti germinali di Drosophila melanogaster

Nel mondo naturale gli individui, le popolazioni e le specie si devono confrontare con variazioni delle condizioni ambientali. Gli organismi e le loro cellule mettono in atto un adattamento fisiologico attraverso risposte che sono immediate e reversibili. Condizioni di stress però, possono causare modificazioni a livello genomico che possono alterare processi biologici fondamentali conducendo a trasformazioni cellulari. È noto da tempo che fattori ambientali provocano condizioni di stress che possono indurre in vari organismi l’attivazione di elementi genetici mobili o elementi trasponibili (TEs) il cui movimento è tra le cause di instabilità genomica. In questo lavoro, individui di Drosophila melanogaster sono stati sottoposti a stress da radiazione RF a 900 MHz ed esaminati per l’attivazione di TEs nei tessuti germinali di entrambi i sessi. Tale stress ha causato un significativo incremento dell’attivazione di tali elementi, confermando che diversi stress ambientali possono avere come conseguenza l’instabilità dei genomi e la comparsa di mutazioni de novo dovute all’inserzione di elementi trasponibili in geni codificanti

Misure di radioattività naturale nel sito preistorico di Grotta dei Cervi in Porto Badisco (LE)

Nel presente lavoro sono riportati I risultati di una campagna di misure finalizzata alle determinazione della concentrazione di radon all’interno di Grotta dei Cervi di Porto Badisco (LE). Grotta dei Cervi è una cavità carsica caratterizzata da un complesso pittorico neolitico imponente