Characterization of aerosols from RDD surrogate compounds produced by fast thermal transients

<div><p>Experimental tests have been performed to characterize the aerosols representative of radiological dispersion devices (RDDs, a.k.a. “dirty bombs”) by applying to chosen surrogate compound rapid high temperature transients, vaporizing the sample and forming aerosols mainly by rapid cooling of the vapour. The materials, which were tested in their non-radioactive form, had been chosen from the radioactive sources widely used in industries and nuclear medicine applications, Co, CsCl, Ir and SrTiO₃. Our analyses permitted the characterization of the inhalable fraction of the aerosols released, and the study of the influence of cladding materials on the aerosol release and on its characteristics.</p></div

Unexpected Behavior of Np in Oxo-selenate/Oxo-selenite Systems

A study of neptunium (Np) chemistry in the complex oxo-selenium system has been performed. Hereby, two sets of precipitation experiments were conducted, investigating the influence of the initial oxidation state of selenium using Se^IVO₂ and H₂Se^VIO₄ with Np^V in alkali nitrate solution, keeping the ratio of Np/Se constant. Surprising results were observed. Five novel neptunium and selenium bearing compounds have been obtained by slow evaporation from aqueous solution. The novel Np^IV phase K_4‑<i>x</i>[Np­(SeO₃)_4‑<i>x</i>­(HSeO₃)_<i>x</i>]­·(H₂O)_1.5 (<b>1</b>) crystallizes in green-colored, plate-shaped crystals and was obtained by adding SeO₂ and ANO₃ to a Np^V stock solution. Single-crystal X-ray diffraction reveals one-dimensional chain structures composed of square antiprismatic NpO₈ polyhedra linked via four trigonal pyramidal SeO₃ and HSeO₃ units. Raman spectral analysis supports the presence of both selenite and hydroselenite due to the presence of corresponding modes within the spectra. The addition of selenic acid to a Np^V stock solution resulted in the precipitation of elongated rose prisms of K₂[(NpO₂)₂­(SeO₄)₃­(H₂O)₂]­·(H₂O)_1.5 (<b>2</b>), Rb₂[(NpO₂)₂­(SeO₄)₃­(H₂O)₂]­·(H₂O)₂ (<b>3</b>) and K₉[(NpO₂)₉­(SeO₄)_13.5­(H₂O)₆]­·(H₂O)₁₂ (<b>4</b>) as well as light red plates of Cs₂[(NpO₂)₂­(SeO₄)₃] (<b>5</b>). To our knowledge, this is the first report of Np^VI selenates. All four structures show two-dimensional layered structures with alkali cations acting as charge balancing counter cations. Hereby the layers of compounds <b>2</b> and <b>3</b> are found to be orientational geometric isomers. Distinctly different phenomena are made responsible for the phase formation within these systems. The kinetically driven process of Np^V disproportionation led to the formation of the Np^IV selenites in the Se^IV-based system, whereas the oxidation of Np^V by reduction of nitrate in acidic conditions is responsible for the formation of the Np^VI selenates in the Se^VI system. The influence of air oxygen is also discussed for the latter reaction