Exploring the WEP with a pulsed cold beam of antihydrogen View the table of contents for this issue, or go to the journal homepage for more 2012 Class. Quantum Grav. 29 184009

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Materials and components employed in the presence of intense neutron and gamma fields are expected to absorb high dose levels that may induce deep modifications of their physical and mechanical properties, possibly causing loss of their function. A protocol for irradiating elastomeric materials in reactor mixed neutron and gamma fields and for testing the evolution of their main mechanical and physical properties with absorbed dose has been developed. Four elastomeric compounds used for vacuum O-rings, one fluoroelastomer polymer (FPM) based and three ethylene propylene diene monomer rubber (EPDM) based, presently available on the market have been selected for the test. One EPDM is rated as radiation resistant in gamma fields, while the other elastomers are general purpose products. Particular care has been devoted to dosimetry calculations, since absorbed dose in neutron fields, unlike pure gamma fields, is strongly dependent on the material composition and, in particular, on the hydrogen content. The products have been tested up to about 2 MGy absorbed dose. The FPM based elastomer, in spite of its lower dose absorption in fast neutron fields, features the largest variations of properties, with a dramatic increase in stiffness and brittleness. Out of the three EPDM based compounds, one shows large and rapid changes in the main mechanical properties, whereas the other two feature more stable behaviors. The performance of the EPDM rated as radiation resistant in pure gamma fields does not appear significantly better than that of the standard product. The predictive capability of the accelerated irradiation tests performed as well as the applicable concepts of threshold of radiation damage is discussed in view of the use of the examined products in the selective production of exotic species facility, now under construction at the Legnaro National Laboratories of the Italian Istituto Nazionale di Fisica Nucleare. It results that a careful account of dose rate effects and oxygen penetration in the material, both during test irradiations and in operating conditions, is needed to obtain reliable predictions.

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We report stopping powers of hydrogen and helium for antiprotons of kinetic energies ranging from about 0.5 keV to 1.1 MeV. The Barkas effect, i.e. , a difference in the stopping power for antiprotons and protons of the same energy in the same material, shows up clearly in either of the gases. Moreover, below =0.5 keV there is indirect evidence for an increase of the antiproton stopping power. This "nuclear" effect, i.e. , energy losses in quasimolecular interactions, shows up in fair agreement with theoretical predictions. PACS numbers: 34.50.Bw At low projectile velocities (P ( 5 X 10 2) significant differences in collision dynamics were observed [1,2] from one projectile-target system to another. In particular, the p and p stopping powers are expected to be very different around and below the stopping-power maximum where ionization and excitation decrease rapidly and the electronic capture channel for the proton becomes dominant [3]. In the velocity range 10 4~P~5 X 10 3, quasimolecular effects come into play even more strongly and a p will lose energy both through nuclear collisions and through nonadiabatic ionization or excitation of the atom [3 -9]. The p is predicted [5] to have the highest energy loss (the lowest being for p, ) by such collisions between negative-charge projectiles and the atoms of the stopping medium.Moreover, a striking departure from velocity proportionality was reported for protons in He by Golser and Semrad [10] and well reproduced by Kimura [11].In a previous work [2] we found that the stopping power of hydrogen is much smaller for p than for p (Barkas effect [12]) in the energy range from 10 to 120 keV. Moreover, a fast rise of the stopping-power behavior below 1 keV was needed to fit the data in the hypothesis that the capture energy of p lies in the electronvolt range.We report here on the results of new measurements of the p stopping power both in hydrogen and helium. The measurements were performed by the OBELIX spectrometer at the CERN LEAR facility. In hydrogen, new data were taken at the pressures of 2, 5, 10, and 150 mbar [13]. In helium, the measurements were run at target pressures of 4, 8.2, 50, and 150 mbar.By means of suitable thicknesses of material, the highly monocromatic p beam (with an energy of 5.875 MeV and an uncertainty of 10 3) is degraded in order to obtain, at the entrance of the target, a beam with energy continuously distributed starting from E;"=0. Antiprotons enter the target (z = 0) at the time t = 0 and slowdown in a 0.5 T magnetic field oriented along the beam direction 0031-9007/95/74(3)/371(4)$06. 00

The muon tomography technique, based on multiple Coulomb scattering of cosmic ray muons, has been proposed as a tool to detect the presence of high density objects inside closed volumes. In this paper a new and innovative method is presented to handle the density fluctuations (noise) of reconstructed images, a well known problem of this technique. The effectiveness of our method is evaluated using experimental data obtained with a muon tomography prototype located at the Legnaro National Laboratories (LNL) of the Istituto Nazionale di Fisica Nucleare (INFN). The results reported in this paper, obtained with real cosmic ray data, show that with appropriate image filtering and muon momentum classification, the muon tomography technique can detect high density materials, such as lead, albeit surrounded by light or medium density material, in short times. A comparison with algorithms published in literature is also presented.