Pu 5f population: the case forn= 5.0

Area of Science:

• Materials Science
• Quantum Chemistry
• Spectroscopy

Background:

• The electronic structure of plutonium (Pu) is complex, with the 5f electron population being a critical parameter influencing its properties.
• Previous estimations of the 5f occupation in alpha-Pu and delta-Pu have been widely accepted but lacked definitive experimental validation.

Purpose of the Study:

• To quantitatively determine the 5f electron population in alpha-Pu and delta-Pu with improved accuracy.
• To investigate trends in 5f series, including atomic sizes and computational modeling.
• To present a novel thermodynamic approach for entropy evaluation and re-analyze existing spectroscopic data.

Main Methods:

• Re-evaluation of quantitative determination of 5f population in alpha-Pu and delta-Pu.
• Spectroscopic analysis of Pu N4,5 and O4,5 x-ray absorption spectroscopy.
• Correction of a fundamental flaw in Electron Energy Loss Spectroscopy (EELS) measurements.
• Thermodynamical evaluation of entropies for a novel approach.

Main Results:

• The 5f occupation (n) in elemental Pu was re-evaluated.
• n = 5.0 ± 0.1 for alpha-Pu.
• n = 4.9 ± 0.2 for delta-Pu, significantly lower than the previously propagated value of ~5½.

Conclusions:

• The re-evaluated 5f electron occupation numbers for alpha-Pu and delta-Pu are substantially lower than historical values.
• This revised understanding impacts theoretical models and predictions of plutonium behavior.
• The novel thermodynamic approach and corrected spectroscopic analysis provide a more accurate determination of plutonium's electronic structure.