On the origin of negative target currents during laser ablation of polyethylene

The exposure of a target to a focused laser beam results in the occurrence of a time-varying current between the target itself and the grounded vacuum chamber. This current is composed by three distinct phases, namely the ignition phase, in which the laser pulse drives the electron emission, while electrons coming from the ground through the target holder balance the positive charge generated on the target. The active phase appears at post-pulse times and it is characterized by the presence of peaked structures in the time-resolved current, representing characteristics of the target composition. Lastly, the afterglow phase is determined by a current of electrons flowing from the target to the ground. During the active phase of the target current resulting from polymers ablation with an UV KrF laser, negative target current peaks are observed, whose origin is still unknown. We investigate the dependence of these current structures on the dimensions of the target, using ultra-high molecular weight polyethylene disks of different thickness

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

'Measuring' Electron Delocalization in π-Conjugated Systems

For the design of donor/acceptor functionalized π-conjugated compounds, electron delocalization is a widely used concept to make structure–property predictions. In this work we present a method based on the NBO analysis, which allows selected conjugation paths in these compounds to be studied. The method maps information obtained from complex quantum calculation onto simple concepts used by general chemists

Prevalence of contact urticaria in health care workers.

Abstract. Latex allergy is a major cause of IgE-mediated urticaria in occupational dermatology. Urticaria may be complicated by other pathological conditions, affecting the respiratory system: asthma and rhinitis. A cohort of 735 health workers examined at the Allergy Surgery of the Department of Environmental Medicine and Public health has been studied. All people (295 subjects, 40,1%) who experienced symptoms were examined. Latex exposure data were recorded, dividing the cases into three risk categories, high, medium and low, together with allergic symptoms and previous story of allergic diseases. In the group of 295 symptomatic patients, 130 workers (44.0%) reported symptoms of urticaria associated with occupational exposure. About half (46.1%) of these subjects were sensitized to natural latex. No correlation between risk exposure category and the latency to onset of symptoms was found, the prevalence of latex sensitization was similar in all groups. The likelihood of developing latex sensitization or allergy correlated only with the variable atopy