Mendelevium stability

The other actinides have been synthesized in the laboratory by nuclear reactions. Their stability decreases rapidly with increasing atomic number. The longest lived isotope of nobelium (102N0) has a half-life of about 3 minutes that is, in 3 minutes half of the sample decomposes. Nobelium and the preceding element, mendelevium (ioiMd), were identified in samples containing one to three atoms of No or Md. 

The isolation and characterization of these elements, particularly the heavier ones, has posed enormous problems. Individual elements are not produced cleanly in isolation, but must be separated from other actinides as well as from lanthanides produced simultaneously by fission. In addition, all the actinides are radioactive, their stability decreasing with increasing atomic number, and this has two serious consequences. Firstly, it is necessary to employ elaborate radiation shielding and so, in many cases, operations must be carried out by remote control. Secondly, the heavier elements are produced only in the minutest amounts. Thus mendelevium was first prepared in almost unbelievably small yields of the order of 1 to 3 atoms per experiment Paradoxically, however, the intense radioactivity also facilitated the detection of these minute amounts first by the development and utilization of radioactive decay systematics, which enabled the detailed properties of the expected radiation to be predicted, and secondly, by using the radioactive decay itself to detect and count the individual atoms synthesized. Accordingly, the separations were effected by ion-exchange techniques, and the elements... 

This oxidation state was indicated in the cocrystallization of Md with CsCl and RbCl after the coreduction of Md + and Sm + with Mg in an ethanol-7 M HC1 solution. Mendelevium was also found enriched in Rb2PtCl precipitates, a specific carrier for the larger ions of the alkali metals. These results were explained by a stabilization of the monovalent ion due to completing the f shell which would give the 5f- electronic configuration. 

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