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Excitation functions have been measured for production of isotopes of Bk through Fm in bombardments of Cm with 234to 294-MeV "Ca ions. and with 239to 318-MeV Ca ions. The maxima of the isotopic distributions for these'elements occur at only 2 to 3 mass numbers larger for Ca than for Ca reactions. The shapes of the distributions and the half-widths of about 2.5 mass numbers are quite similar to those observed previously for reactions of ' 0, ' 0, Ne, and Ne with Cm. In general, the excitation functions for " Ca show maxima near the Coulomb barrier while those for 'Ca are about 20 MeV above the barrier. The cross sections decrease rather slowly with increasing projectile energy over the energy range studied, indicating that the additional projectile energy is not manifested as excitation energy of these actinide products.

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A description of some of the chemical properties and of the methods used in %he separations of elements 99 and 100 is given. The new elements exhibit the properties expected for the tenth and eleventh actinide elements. Attempts to produce an oxidation state greater than 111 of element 99 have been wsuccessful. In normal aqueous media only the 111 state of element 100 appears to exist. The relative spacings of the elution peaks of the new elements in some separations with ion exchange resin columns are the s m e as the relative spacings of the homologous lanthanide elements. The results of experiments involving cation exchange resins with very concentrated hydrochloric acid eluant show that the new elements, like the earlier actinides, are more strongly complexed than the lanthanides. The new elements also exist partially as anions in concentrated hydrochloric acid, as do earlier actinide elements, and they may be partially separated from each other by means of ion exchange resins. With some eluants interesting reversals of elution positions are observed in the region Bk-Cf-99-100, indicating complex ion formation involving unusual factors. UCRL-2591 Rev.