Papers by Author: José Mestnik-Filho

Abstract: For the last 30 years high uranium density dispersion fuels have been developed in order to accomplish the low enrichment goals of the Reduced Enrichment for Research and Test Reactors (RERTR) Program. Gamma U-Mo alloys, particularly with 7 to 10 wt% Mo, as a fuel phase dispersed in aluminum matrix, have shown good results concerning its performance under irradiation tests. Thats why this fissile phase is considered to be used in the nuclear fuel of the Brazilian Multipurpose Research Reactor (RMB), currently being designed. Powder production from these ductile alloys has been attained by atomization, mechanical (machining, grinding, cryogenic milling) and chemical (hydriding-dehydriding) methods. This work is a part of the efforts presently under way at IPEN to investigate the feasibility of these methods. Results on alloy fabrication by induction melting and γ-stabilization of U-10Mo alloys are presented. Some results on powder production and characterization are also discussed.

Abstract: Perturbed gamma-gamma angular correlation (PAC) spectroscopy is a precise and highly efficient tool to follow the temperature dependence of local magnetic fields in any material. Its resolution and efficiency does not depend on temperature and therefore can measure local fields at low as well as high temperature with the same accuracy. Due its versatility in using different probe nuclei it can sense the local magnetic fields at different sites in the crystalline structure of materials. In this review, important results obtained with PAC spectroscopy are shown in two classes of materials: transition metal and transition-metal based compounds and rare earth elements and rare-earth-element based compounds using mainly three different probe nuclei: ¹¹¹Cd, ¹⁸¹Ta and ¹⁴⁰Ce. PAC spectroscopy has contributed to the systematic study of the magnetic hyperfine field in impurities in matrices of Fe, Co and Ni as well as in transition-metal based Heusler alloys. It has also provided important contribution to the investigation of magnetism in rare-earth elements and intermetallic compounds. An still open issue concerning the local fields in metallic magnetic compounds and elements is the exchange interaction between the magnetic ions of the host and a dilute magnetic impurity, which acts as a defect in the magnetic lattice. PAC spectroscopy has been contributing to study this problem with success. Also shown in this review is the crucial role of ab-initio first principle calculations in the interpretation of PAC results.