Concerning 5f electron correlation in δ-Pu

Detailed measurements of the Pu 4f, O1s and C1s photoelectron spectra, using synchrotronradiation soft X-rays as the excitation, have been used to investigate the question of the source of the multiplet structure in the Pu 4f spectra of δ-Pu. The conventional wisdom is that the Pu 4f multiplet structure is due to either an Anderson-Impurity-Model mechanism or different types of multi-electronic screening. Here, it is experimentally demonstrated that the multiplet structure in δ-Pu is due to sample impurities, using an extrapolation to zero concentration. This extrapolation is only possible because of the enhanced sensitivity from the synchrotron radiation.