Chemical structural effects on γ-ray spectra of positron annihilation in fluorobenzenes

Spectra of ?-ray Doppler shifts for positron annihilation in benzene and its fluoro-derivatives are simulated using low energy plane wave positron (LEPWP) approximation. The results are compared with available measurements. It is found that the Doppler shifts in these larger aromatic compounds are dominated by the contributions of the valence electrons and that the LEPWP model overestimates the measurements by approximately 30%, in agreement with previous findings in noble gases and small molecules. It is further revealed that the halogen atoms not only switch the sign of the charges on carbon atoms that they bond to, but that they also polarize other C-H bonds in the molecule leading to a redistribution of the molecular electrostatic potentials. As a result, it is likely that the halogen atoms contribute more significantly to the annihilation process. The present study also suggests that, while the Doppler shifts are sensitive to the number of valence electrons in the molecules, they are less sensitive to the chemical structures of isomers that have the same numbers and type of atoms and, hence, the same numbers of electrons. Further investigation of this effect is warranted. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.

Acceleration of ions up to 20MeV/nucleon in the ultrashort, high-intensity regime

The measurements reported here provide scaling laws for the ion acceleration process in the regime of ultrashort (50 fs), ultrahigh contrast (10) and ultrahigh intensity (> 10W/cm ), never investigated previously. The scaling of the accelerated ion energies was studied by varying a number of parameters such as target thickness (down to 10nm), target material (C and Al) and laser light polar- ization (circular and linear) at 35° and normal laser incidence. A twofold increase in proton energy and an order of magnitude enhancement in ion flux have been observed over the investigated thickness range at 35° angle of incidence. Further- more, at normal laser incidence, measured peak proton energies of about 20 MeV are observed almost independently of the target thickness over a wide range (50nm- 10 µm). 1. © 2012 by Società Italiana di Fisica.

Laser-driven acceleration of ions:State of the art, perspectives and applications

The acceleration of ions with high-power lasers has been a very active field of research during the past 10 years. This paper summarizes the main results obtained in the field, detailing the mechanisms of the acceleration process and the main observed beam characteristics. Perspectives for future development of the field and current and future applications are also discussed. © 2012 by Società Italiana di Fisica.

Coal Combustion Residuals valorisation through the production of compressed masonry brick

The Niger Coal Society (Societé Nigérienne de Charbon – SONICHAR) produces electricity for local consumption in Tefereyre, 75 km north-west from Agadez, Niger. The coal combustion residuals production is about 150,000 tons per year. In order to reduce this environmental burden and to valorize these by-products, a study focusing on their physical and chemical features as well as on the mechanical resistance of compressed brick has been undertaken. Physical characterization of coal slag, chemical and lixiviation tests have been carried out, assessing the material main parameters, verifying the presence of hazardous composites and elements and comparing the obtained results with the findings of an in-deep literary review. Cement powder has been chosen as stabilizing agent as a preliminary option. Four different dosages have been tested and bricks have been produced with a hand-operated press. Compressive strength has been tested at different days of curing. Results show remarkable uniaxial compressive strengths (UCS) for all the mixes after cure, ranging from 4MPa up to more than 20MPa for the highest stabilization ratio. UCS higher than 5MPa have been observed for 20% and 30% cement stabilization ratios after only 7 days of cure, reaching respectively about 11MPa and 13MPa after 45 days. In conclusion obtained bricks show good mechanical resistance and low weight. No health threat has been detected from the obtained sample. Study developments are oriented towards the feasibility of the utilization of low-cost, locally available stabilization means, notably clay and cohesive soils, and on thermal properties assessment.