Neptunium compounds isomer shift

Chemical isomer shifts, quadrupole splittings, and magnetic hyperline splittings have been measured in a number of compounds of neptunium with different formal oxidation states [11, 15]. Typical spectra are shown in Fig. 

Fig. 18.5 The known ranges for the chemical isomer shift in neptunium compounds correlated with the formal oxidation state.

Figure 6.27 shows the isomer shifts obtained for a number of actinide conqwunds. The positions of the isomer shifts show the effect of valence states due to different population of the 5f orbitals. The different shifts for compounds of the same valence state is a measure of the variation in the covalmcy of the bonding. The compounds on the left are metallic. The shifts reflects the contributions of conduction electrons to the electron density at the nucleus of neptunium. 

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