A reassessment of 5f occupation in plutonium

A detailed spectroscopic simulation of the original Pu N4,5 and O4,5 X-Ray Absorption Spectroscopy (XAS) has been performed. Additionally, a fundamental flaw in the Electron Energy Loss Spectroscopy (EELS) measurement has been corrected. Thus, the determination of the 5f 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. •The 5f population in αPu is 5.0 ± 0.1.•The 5f population in δPu is 4.9 ± 0.2.•The 2nd Derivative Mode in EELS should not be used in quantitative BR analyses.