Pu 5f population: the case for n = 5.0

Abstract

The quantitative determination of the 5f population in α-Pu and δ-Pu is reconsidered in detail. Trends across the 5f series are discussed, including atomic sizes, 5f populations and computational modeling. A recently developed and novel approach, based upon a thermodynamical evaluation of entropies, is presented. Finally, a detailed spectroscopic analysis of the original Pu N4,5 and O4,5 x-ray absorption spectroscopy has been performed, including the correction of a fundamental flaw in the Electron Energy Loss Spectroscopy (EELS) measurements. Thus, the determination of the 5 f occupation (n) in elemental Pu has been re-evaluated with the result that n = 5.0 ± 0.1 for αPu and n = 4.9 ± 0.2 for δPu. These values are significantly lower than the value of ∼5½ that was propagated earlier.