Fractionation of U F6 composition in spectrometry ampoules coupled to scintillators, in keV regions

U F6 samples are usually collected inside ampoules by dessublimation. Their chemical analyses by mass spectrometry present irreproductible results. We have collected experimental data and have developed a theoretical mode in order to explain the disparities. We have concluded that there is an equilibrium between the solid surface and gas phase. The solid phase is heterogeneous. The composition of gas phase depends on the initial composition and the collected mass. Other ways of sampling must be developed. (author). 3 refs., 2 figs., 2 tabs