Papers by Keyword: High Energy Ion Irradiation

Abstract: Positron Annihilation Lifetime Spectroscopy (PALS) is used to study the nanoporosity and fractional free volume in Ultra High Molecular Weight Polyethylene (UHMWPE) and composites with the addition of Martian Regolith (UHMWPE-MR) as-made and irradiated with ⁵⁶Fe heavy ions at an energy of 600 MeV/u to three different doses (10, 32, 64 Gy). The positron lifetime spectra were obtained using ²²Na positron source and the spectra were analyzed to two lifetime components using POSFIT program. First short lifetime component around 0.28 ns is related to positron annihilation in material including vacancy defects and the second long lived component around 1.7 ns is due to Positronium formation in free volume pores. UHMWPE-MR composites were shown to be less porous with much lower nanopores concentration compared to the UHMWPE polymer. The average size of the nanopores is around 0.5 nm (obtained from a simple model). Larger variations in positron lifetime parameters are observed with increasing irradiation dose for UHMWPE polymer compared to UHMWPE+MR composites. The 3-point bend test results also showed larger variations with increasing irradiation dose for the UHMWPE polymer. The variations in PALS parameters may indicate an increasing competition between two processes at higher irradiation doses: 1) vacancy defects aggregation and 2) escape of vacancy defects as the local temperature increases at higher doses resulting in increased vacancy defects mobility. Present results clearly indicate a qualitative inverse relationship between nanoscale porosity measured by positron life time and mechanical properties of UHMWPE and its composite with MR.

Abstract: Different high-Tc superconducting Y-Ba-Cu-O samples of slabs and rings have been investigated. Using differently prepared Y1Ba2Cu3O7-d materials, significant deviations between irradiated and unirradiated specimens have been detected in their properties. These investigations demonstrate that unlikely prepared superconductors are differently sensitive to the external irradiation, although they have the same composition. The irradiation applied during these experiments consisted of high-energy Bi-ions with the flux of 5x1010 ions/cm2 and with the energy of 720 MeV. As is experienced, a considerable variation of the magnetic moment in the extent of 19-44% and a significant increase of the critical current density up to 41% can be detected. These originate from the change of the properties of materials due to the irradiation. For the evaluation of the experiments a new fitting method is elaborated for the temperature dependence of the critical current density, providing fully correct results for the whole temperature interval. The A.C. magnetic measurements show, that the irradiation causes to reach the state of the perfect diamagnetism at higher temperatures, than in the case of unirradiated samples. Similarly, the irradiated specimens have much lower losses, than the unirradiated ones and even these smaller values disappear at low temperatures.