Magnetic and Resistive Properties of Annealing of Radiation Damage in Pu and Pu Alloys

We report a high fidelity radiation damage-isochronal annealing curve based on changes in magnetic susceptibility for $\alpha $-phase Pu from 5-350K with Stage-I annealing at $>$30K and complete annealing at $\sim $315K. These results, while based on changes in magnetic susceptibility, are surprisingly similar to resistivity data reported 40 years ago by Wigley (\textit{Proc. R. Soc.} \textbf{A 284} (1964) 344) and suggest the excess magnetic susceptibility (EMS) is the result of accumulated radiation damage. Additionally, we report the excess magnetic susceptibility as a function of temperature for vacancies alone. We conclude that the vacancy induced EMS shows an inverse-temperature dependence that is much stronger than interstitial induced excess magnetic susceptibility. These results will be compared with resistivity studies of radiation damage accumulation in fcc delta phase Pu( 3.3 at{\%} Ga) (M.J. Fluss \textit{et. al}, \textit{J. of Alloys and Compds.} \textbf{368} (2004) 62--74), where vacancies and vacancy cluster resistance was reported to behave in an anomalous manner with respect to temperature by being proportional to --\textit{ln(T)}, and thus suggesting local moments with a low critical temperature. The possible role of disorder in stabilizing the low density delta phase of Pu will be discussed. \textit{Work performed under the auspices of the U. S. DOE by LLNL; contract W-7405-Eng-48.}