Isochronal annealing studies in Pu and Pu alloys using magnetic susceptibility

The isochronal annealing of the low temperature accumulated damage from the radioactive decay of plutonium in α-Pu, δ-Pu1−xGax (x = 0.043) and δ-Pu1−xAmx (x = 0.224) was characterized using magnetic susceptibility. In each specimen, thermal annealing, as tracked by magnetic susceptibility, only commenced when T > 33 K and the magnetic susceptibility changes due to defects were fully annealed at T ∼ 300 K. The α-Pu magnetic susceptibility isochronal annealing data is similar to earlier measurements of resistivity characterized isochronal annealing. However, the δ-Pu1−xGax (x = 0.043) magnetic susceptibility isochronal annealing data, when compared with similar resistivity data, indicates that for this alloy magnetic susceptibility studies are more sensitive to vacancies than to the interstitials accumulated at low temperatures. The Pu1−xAmx (x = 0.224) alloy shows a remarkable change in properties, over a limited temperature range beginning where interstitial defects are first mobile, and characterized by an induced effective moment of order 1.1 μB/Pu. This transient behavior may be evidence for a disorder driven low temperature phase transition, perhaps indicative of a compositional and structural proximity to a state possessing significant magnetic moments.