Emerging Magnetism Arising from Self Damage in α- and δ-Pu

As a consequence of the unusual nature of plutonium's electronic structure, point- and extended-defects are expected to, and do exhibit extraordinary properties. Low temperature magnetic susceptibility measurements on Pu and fcc-Pu(Ga) show that the magnetic susceptibility increases as a function of time, yet upon annealing the specimen returns to its initial magnetic susceptibility. This excess magnetic susceptibility (EMS) arises from the alpha-decay and U recoil damage cascades which produce vacancy and interstitials as point and extended defects. The temperature of the first annealing stage defines a temperature (<35K) below which we are able to characterize the time and temperature evolution of the accumulating damage cascades as being a saturation function. The temperature dependence of the EMS is well described by a time independent, Curie-Weiss curve arising from a volumetric region surrounding each U damage cascade. This saturation picture also leads directly to a determination of the microscopic volume of the specimen that is affected by the frozen-in damage cascade. For our measurements in δ-Pu we calculate a diameter of the magnetically affected volume of ∼250Å per damage cascade. This should be compared with an estimated volume that encloses the damage cascade itself (determined from molecular dynamics) of ∼100 Å. Hence, the ratio of these volumes is ∼8. The observed anomalous magnetic behavior is likely a consequence of the highly correlated nature of the electrons. Similarities with defects in hole-doped superconductors suggest a general phenomenon in strongly correlated electron systems, of which Pu may be a particularly unusual or special example.

Point Defects Observed in D-T neutron irradiated Copper, Silver and Gold at 288 K with a Rotating Target in FNS_JAERI

ABSTRACTA 14 MeV D-T(fusion) neutron irradiation was carried out at fusion neutron source facility (FNS) in Japan Atomic Energy Research Institute (JAERI). Specimen temperature was controlled to 288 K. Fluence was 6.1 × 1017to 1.1 × 1021 n/m2. Both TEM thin foil and bulk specimens were irradiated at the same position. At 1018 n/m2, defects observed were single isolated dot defects. With increasing fluence, dot defects changed to complicate structure and made groupings. In a dot group, interstitial clusters and vacancy clusters were observed together. The present result was explained by the modeling that point defects in a nascent damage cascade move in crystal at 288 K and form their defect groupings.