I.Y. Al-Qaradawi

Antihydrogen Physics: gravitation and spectroscopy in AEgIS

AEgIS (Antimatter experiment: gravity, interferometry, spectroscopy) is an experiment approved by CERN with the goal of studying antihydrogen physics. In AEgIS, antihydrogen will be produced by charge exchange reactions of cold antiprotons with positronium atoms excited in a Rydberg state (n > 20). In the first phase of the experiment, controlled acceleration by an electric field gradient (Stark effect) and subsequent measurement of free fall in a Moire deflectometer will allow a test of the weak equivalence principle. In a second phase, the antihydrogen will be slowed, confined, and laser-cooled to perform CPT studies and detailed spectroscopy. In the present work, after a general description of the experiment, the present status of advancement will be reviewed, with special attention to the production and excitation of positronium atoms.

Formation Of A Cold Antihydrogen Beam in AEGIS For Gravity Measurements

The formation of the antihydrogen beam in the AEGIS experiment through the use of inhomogeneous electric fields is discussed and simulation results including the geometry of the apparatus and realistic hypothesis about the antihydrogen initial conditions are shown. The resulting velocity distribution matches the requirements of the gravity experiment. In particular it is shown that the inhomogeneous electric fields provide radial cooling of the beam during the acceleration.

Thermalization times of positrons in molecular gases

The time taken for positrons to reach thermal equilibrium in a number of simple molecular gases has been estimated using the gas mixture technique devised by Paul and Leung (Paul D A L and Leung C Y Can. J. Phys. 46 2779-88). Times below 100 ps Amagat have been found for a number of species, suggesting their use as efficient coolers for rapid-cycle positron traps and accumulators.

Electron irradiated low-density polyethylene studied by positron annihilation lifetime spectroscopy

Abstract A study of the degree and rate of cross-linking of low-density polyethylene (LDPE) as a result of irradiation by high-energy electron beam has been performed using positron annihilation lifetime (PAL) technique. The PAL measurements were carried out at room temperature with a conventional fast–fast coincidence system. The lifetime spectra were analysed into four components using the PATFIT program to extract the positron parameters such as lifetime, mean lifetime, intensities, free volume radius, and fractional free volume. Almost all parameters exhibited differences between the unirradiated and irradiated LDPE. It can be concluded that the effect of irradiation on polyethylene results in intensive network formation, which is intensified as the electron energy is increased. The results manifest another proof of the usefulness of positron techniques in the study of the microstructure of polymers.

Aqueous electrolyte system for porous silicon using electrochemical anodization

Electrochemical anodization on n-type silicon was performed with silicon as anode and platinum as cathode in a weak-acid aqueous electrolyte containing orthophosphoric acid and ammonium fluoride. Anodization was carried out in two different modes, i.e., potentiostatic and galvanostatic with the voltage and current density of 5-80 V and 10-50 mA/cm2 respectively. Anodization time was varied from 5 min to 10 hours. Morphology of the anodized samples was studied using scanning electron microscopy (SEM), revealing the formation of pores with uniform distribution throughout the silicon substrate. The pore size and density were controllable by varying the anodization voltage and current. Results showed that, in a broad spectrum range of 400-1100 nm, the total reflectance (sum of diffused and specular reflectance) of the porous silicon was about 10% compared to >30% of the as-received silicon wafer. The porous silicon is promising for solar cell applications due to the low reflection loss.

The Aegis Experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy)

A.S. BELOV , G. BONOMI, I. BOSCOLO, N. BRAMBILLA, J. BREMER, R. S. BRUSA, V.M. BYAKOV, G. B URGHART, L. CABARET, C. CARRARO, F. CASTELLI, S. CIALDI, D. COMPARAT, G. CONSOLATI, L. DASSA, N. DJOURELOV, M. DOSER, G. DROBYCHEV, A. DUDAREV, A. DUPASQUIER, T. EISEL, D. FABRIS, R. FERRAGUT, G. FERRARI, A. FISCHER, A. FONTANA, P. FORGET, M. LUNARDON, A. GERVASINI, M. G. GIAMMARCHI, S. N. GNINENKO, G. GRIBAKIN, F. HAUG, S.D. HOGAN, L. V. JOERGENSEN, A. KELLERBAUER, T. KOETTIG, D. KRASNICKY, V. LAGOMARSINO, G. MANUZIO, S. MARIAZZI, V. A. MATVEEV, F. MERKT, S. MORETTO, G. NEBBIA, P. NEDELEC, M. K. OBERTHALER, D. PERINI, V. PETRACEK, M. PREVEDELLI, I. Y. AL-QARADAWI , F. QUASSO, C. RICCARDI, O. ROHNE, S. PESENTE, A. ROTONDI, S. STAPNES, D. SILLOU, S.V. STEPANOV, H. H. STROKE, D. TREZZI, A. VAIRO, G. VIESTI , F. VILLA, H. WALTERS, U. WARRING, S. ZAVATARELLI , A. ZENONI, D. S. ZVEZHINSKIJ (AEGIS COLLABORATION)

Positron Annihilation Lifetime Study of Helium Ions Implanted Polyethylene Blends

The structural defects of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) blends implanted with helium ions were investigated using positron annihilation lifetime (PAL) technique. The positron annihilation lifetime measurements were carried out at room temperature with a conventional fast-fast coincidence system. The lifetime spectra were analyzed into four components using the PATFIT program to extract the positron parameters such as lifetime components, and their corresponding intensities. Almost all parameters exhibited a correlation with microstructure changes resulting from implantation. The results were further discussed by comparison with modifications in the morphology of implanted samples using Scanning Electron Microscope (SEM) and Differential Scanning Calorimeter (DSC). Virgin Samples of Polyethylene blends are shown to be miscible by singlet DSC melting temperatures. After ion implantation the thermal properties of blends exhibit different behaviors depending on ion fluence and blending ratio i.e. polymer structure.