Project of an internal target for the antiproton ring at FAIR

The case of the internal target for the hyper-nuclear experiment of the PANDA (antiproton Annihilation at Darmstadt) Collaboration at the High Energy Storage Ring of Facility for Antiproton and Ion Research is illustrated. After a discussion of the problems arising from the interaction of a solid internal target with an antiproton beam, the design of material, shape and sizes of a target satisfying the experimental requirements is presented. The techniques used to produce a prototype of this target are illustrated. Then the results of the tests performed on the prototype for investigating the properties (purity, radiation hardness, structure modifications after shaping) are reported and the plan of the future activity is pointed out.     

Ultrasound-assisted pullulan/montmorillonite bionanocomposite coating with high oxygen barrier properties

In this paper, the preparation and characterization of oxygen barrier pullulan sodium montmorillonite (Na(+)-MMT) nanocomposite coatings are presented for the first time. Full exfoliation of platelets during preparation of the coating water dispersions was mediated by ultrasonic treatment, which turned out to be a pivotal factor in the oxygen barrier performance of the final material even at high relative humidity (RH) conditions [oxygen permeability coefficients ~1.43 ± 0.39 and 258.05 ± 13.78 mL·μm·m(-2)·(24 h)(-1)·atm(-1) at 23 °C and 0% RH and 70% RH, respectively]. At the micro- and nanoscale, the reasons are discussed. The final morphology of the coatings revealed that clay lamellae were stacked on top of one another, probably due to the forced confinement of the platelets within the coating thickness after solvent evaporation. This was also confirmed by modeling the experimental oxygen permeability data with the well-known Nielsen and Cussler permeation theoretical models, which suggested a reasonable aspect ratio (α) of ~100. Electron microscopic analyses also disclosed a peculiar cell-like arrangement of the platelets. The stacking of the clay lamellae and the cell-like arrangement create the excellent oxygen barrier properties. Finally, we demonstrated that the slight haze increase in the bionanocomposite coating materials arising from the addition of the clays depends on the clay concentration but not so much on the sonication time, due to the balance of opposite effects after sonication (an increase in the number of scattering centers but a reduction in their size).     

Electric field redistribution under IR radiation in quantum well infrared photodetectors as deduced from current noise measurements at low temperature and bias

Current noise has been investigated in AlGaAs/GaAs quantum well infrared photodetectors (QWIPs), having nominally the same design except the number of wells N. The experiments have been carried out in the dark and under infrared (IR) radiation in a wide range of currents and temperatures. We have found that the current noise scales as the inverse of the number of wells N in the dark condition. In the presence of IR radiation, the noise exhibits strong deviations from the simple 1/N behavior. These effects are still more evident when the photocurrent noise is measured at low biases and temperatures. Nonlinear effects in the QWIPs operation at high IR power, related to the potential redistribution in the interelectrodic region, are probably responsible for such anomalies. This conclusion is consistent with results of the steady-state responsivity obtained in the QWIPs in the same experimental conditions.