Am metal

Am (metal) + PuCl3 (salt) = A111CI3 (salt) + Pu (metal)... 

Ein weiteres Verfahren zur Darstellung von Am-Metall, das auf der Reduktion der Oxyde Am203 oder AmOa mit metallischem Lanthan beruht, beschreiben McWhan et al. (139), (140). Bei diesen Verfahren werden die Oxyde nach folgenden Gleichungen umgesetzt ... 

Die magnetische Suszeptibilitat von Am-Metall wurde ebenfails von McWhan (139) mit Hilfe der Cunninghamschen Quarzpendelwaage (58), (59), (60) bestimmt. Im Bereich —196° C bis + 550° C wurde gefunden ... 

Fig 3-6. Metal ion levels at the surface and in the interior of a solid metal aM. = metal ion energy ... 

Efficient refining of the more volatile actinide metals (Pu, Am, Cm, Bk, and Cf) is achieved by selective vaporization for those (Pu, Am, Cm) available in macro quantities. The metal is sublimed at the lowest possible temperature to avoid co-evaporation of the less volatile impurities and then deposited at the highest possible temperature to allow vaporization of the more volatile impurities. Deposition occurs below the melting point of the metal to avoid potential corrosion of the condenser by the liquid metal. Very good decontamination factors can be obtained for most metallic impurities. However, Ag, Ca, Be, Sn, Dy, and Ho are not separated from Am metal nor are Co, Fe, Cr, Ni, Si, Ge, Gd, Pr, Nd, Sc, Tb, and Lu from Cm and Pu metals. 

Other methods for the preparation of elemental Am, mostly variations on the above two, have been studied (1, 23, 63). Thermal decomposition of the intermetallic compound PtjAm has also been used to prepare Am metal (36, 82,110). 

At the present time, when gram to kilogram amounts of either Am isotope are available, the method of choice for the preparation of Am metal is the metallothermic reduction of Am02 with La (or Th) using a pressed pellet of the oxide and the reductant metal. An oxide reduction-metal distillation still system is shown schematically in Fig. 11. Yields of Am metal are typically >90% and purity levels equal or exceed 99.5 at %. Further purification of the product Am metal can be achieved by repeated sublimations under bigh vacuum in a Ta apparatus (Section III,B Fig. 4). A photograph of 2 g of Am metal distilled in a Ta apparatus is given in Fig. 12. 

Fig. 12. Distilled Am metal (2 g) (center, front) and associated parts of the Ta still.

Table 4. Comparison of Ua Uh, Whyb in the actinide metals series from Th to Am. In the last row, only the qualitative departure from 1, rather than a well defined value for W/Uh is indicated, since evaluations different from those selected, are reported in the literature for Uh and W. Notice the peculiar position of Pu metal and the localized WAJ value for Am metal...

In A.IV, when introducing the Mott-like transition between Pu and Am metals, we have discussed the localization problem as a function of the number of 5 f electrons. In the case... 

For non-magnetic actinide metals, specific heat data have been employed very usefully to corroborate 5 f localization starting with Am, as indicated by the sudden drop in y values (ypu 12 mJ/mol K, yAm 2 mJ/mol K ). It allowed also the discovery of superconductivity in Pa and Am metals ... 

Fig. 25. Mossbauer spectra of NpAs2 at various temperatures against a Am metal source. The solid lines are fit to the data points (which have been omitted in this figure). (Bog6 et al. )...

However, no fingerprint such as a final state multiplet structure, as expected for fully localized 5 f electron and found in Am metal, is observed. The localization of 5 f-states is only weak (band-narrowing and widthdrawal from hybridization) in 6-Pu. This in fact is also consistent with the absence of a magnetic moment formation in 6-Pu (rather, a spin-fluctuation regime is observed ). 

If the 4f core level spectra of the sesquioxides are taken into account (Figs. 31, 32), an interpretation may be forwarded based on a comparison with the spectra of the metals. As we have seen in Part III, to the main 4 f line of Am metal a 6 d screening, and to its low binding energy satellite a 5f screening are attributed. For Pu metal, the main line is attributed on the contrary to 5 f screening (in consistence with the good itinerant... 

On the basis of the known electronic properties of actinides (which have been discussed elsewhere in this book), theoreticians had distinguished the 5f itinerant behaviour of light actinide metals from the 5 f localized behaviour of heavy actinide metals from Am on. The crossover, presented often as a Mott transition, had been predicted to occur between Pu and Am metal, due to the localized character of the 5f state in the latter. Photoemission spectroscopy demonstrates this phenomenon directly with the observation of a 5 f multiplet away from the Fermi level. The detailed description of this peak is certainly complicated, as often happens for response of localized states in photoemission on the other hand (Fig. 17) the contrast to the emission of Pu metal is convincing. 

The 6 d-5 f hybridization of the conduction bands of light actinide metals, which is also predicted by theory, is also demonstrated in photoelectron spectra of Th, U and Pu. In Am metal, on the contrary, the emission at Ep is foimd to be non-f-like, as expected for a lanthanide-like actinide. 

Protein and metal ion(s) Source Resolution of crystallographic data (am) Metal binding sites1 Ref. 

Other important experimental techniques utilized in the molecular transport studies include the mercury-drop junctions52,53 which have been used to study the transport through alkanethiols, and nanorods (a metallic nanowire-S AM-metallic nanowire junction)54 which have been used to measure 16-mercaptohexadecanoic acid. 

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