Neutron cerium compounds

The role of the crystal-field interaction remain obscure in all these systems, both for actinides and cerium. Whereas in the other lanthanide NaCl-type compounds, LnX and LnZ, the easy directions are given by straightforward crystal-field considerations and the value of the crystal-field potential varies in a systematic way across the lanthanide series, this is not the case in the materials discussed here. The crystal-field energy levels can be measured in the cerium compounds with neutron inelastic scattering, but have not been observed in the uranium (or higher) actinides. It is assumed that this inability to observe directly the crystal-field levels is because they are strongly broadened by the interaction between the 5f and conduction electrons. This has been the subject of much work by Cooper and his collaborators. 

Commercially available, highly efficient liquid and solid scintillators were tested as standards for comparison with our samples. Ultima Gold (PerkinElmer) is a standard liquid scintillation counting cocktail, containing PPO (ca. 1 wt %) in a mixture of aromatic compounds, and phosphate and succinate surfactants. BC-400 (Bicron) is a plastic scintillator composed of organic fluors, PPO and POPOP, at <3 wt % in PVT. KG2 (Bicron) is a cerium-activated lithium silicate glass scintillator, containing 7.5 wt % of Li (95% i) as a neutron absorber, and Ce as a scintillation material. 

Fig. 12. Korringa slopes for the Gd resonance as observed in Sci. Ce AljCGd) vs the cerium concentration jc. In this compound the valency of Ce can be changed continuously by varying the Ce content. Neutron scattering experiments and susceptibility measurements indicate an intermediate valence state of Ce for concentrations 0.05 <0.4 (Preusse et al. 1981).

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