New limits on the ordered moments in alpha-Pu and Ga-stabilized delta-Pu
  We present the first muon spin relaxation measurements ever performed on elemental Pu, and set the most stringent upper limits to date on the magnitude of the ordered moment in alpha-Pu and delta-stabilized Pu (alloyed with 4.3 at. % Ga). Assuming a nominal hyperfine coupling field of 1 kOe per Bohr magneton we set an upper limit of 0.001 Bohr magnetons for both materials at T = 4 K. 
R. H. Heffner, G. D. Morris, M. J. Fluss, B. Chung, D. E. MacLaughlin,   L. Shu and J. E. Anderson