Crystallography and magnetic properties of transuranium element oxygen compounds (Np, Pu and Am)

This paper includes: 1) The brief description of the experimental techniques used for analyzing very small quantities of solid radioactive compounds (differential thermal micro-analyses, diffraction of X rays, magnetic susceptibility and Moessbauer resonance). 2) The methods of synthesis of the ternary oxides of transuranic elements at oxidation degrees III (Pu2MoO6, Pu2WO6, Pu2(WO4)3, Am2MoO6, Am2WO6, Am2(MoO4)3 and Am2(WO4)3) and at degree IV (Np(VO3)4, Np(MoO4)2, Np(WO4)2 and Pu(MoO4)2). The drawing up of liquid-solid balance diagrams enabled the field of stability of molybdate (or tungstate) systems of alkaline transuranic - mobybdates (or tungstates) to be clarified. 3) The study of the structural properties of the identified phases. These results taken as a whole made it possible to establish a ''comparative crystal - chemistry'' of the oxigenated phases of Np, Pu and Am with those of the thorium and uranium actinide elements and with the rare earths of adjacent ionic radius. 4) The Moessbauer resonance study of 237Np in the solid solution Usub(1-x)Npsub(x)O2 (0 < x <= 1). The analysis of the results obtained is the subject of Part IV of the manuscript. 5) The effects of alpha self-irradiation mentioned in the last part show that it is necessary to gather fresh information on the condensed phases containing heavy radioactive atoms