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[en] Potentiostatic, coulometric, potentiometric, and amperometric methods have been used for determining the rate constants of disproportionation (ksub(d)) of plutonium(5) and neptunium (5) and normal real redox potentials (Esub(0)sup(p)) of the following ion pairs in sulphur-phosphoric-acid media: PuOsub(2)sup(2)sup(+) (PuO₂⁺, Pu⁴⁺/Pu³⁺, NpO₂²⁺/NpO₂⁺, NpO₂²⁺/Np⁴⁺, NpO₂⁺/Np⁴⁺, and Fe³⁺/Fe²⁺. The regularities have been shown of changing ksub(d) and Esub(o)sup(p) as a function of H₂SO₄ and H₃PO₄ concentration. It has been established that for plutonium and neptunium a linear correlation is observed between lg ksub(d) and Esub(o)sup(p) of the ion pairs NpO₂²⁺/NpO₂⁺, NpO₂²/Np⁴⁺, NpO₂⁺/Np⁴⁺ and PuO₂²⁺/PuO₂⁺ in a wide range of their values. The correlation coefficient is close to unity in all cases (no less than 0.96). The results of investigations have made it possible to recommend optimum compositions of background electrolytes for performing continuous amperostatic coulometric titration of Pusup((6)) and Npsup((6)) up to four valent state by electrogenerated ions of iron (2)

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[en] Coulometric methods of determining Pu and Np in the products of complex composition containing, in addition to Pu and Np, Cr and Nn have been developed. The methods are based on titration of Pusup((6)) and Npsup((6)) to tetravalent state in H₂SO₄-H₃PO₄ with iron (2) ions generated continuously. A new variant of amperometric method has been proposed for determining end-point of titration. The methods of preparing Pusup((6)) and Npsup((6)) solutions have been developed. It has been shown that, upon dissolution of PuO₂ and NpO₂ by boiling with a mixture of nitric and perchloric acids Pusup((4)) and Npsup((4)) are oxidized quantitatively to Pusup((6)) and Npsup((6)) while Cl₂, Crsup((6)) and Mnsup((7,4,3)) in the solution obtained are selectively reduced by CHOOH and CH₂(COOH)₂. In 6-8 M in terms of H₂SO₄ solution, ammonium bichromate oxidizes Npsup((4)) to Npsup((6)), Pusup((3)) to Pusup((4)), and Mnsup((2)) to Mnsup((3)). Oxidized Mn and excess of Crsup((6)) are selectively reduced by CHOOH and H₂C₂O₄ in 4M in terms of H₂SO₄ solution

[en] A mathematical model of radiative heat exchange in the throats of wide-necked helium cryostats is analyzed. A comparison of the numerical results with known calculated and experimental data shows their good agreement

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