Production of heavy actinides from interactions ofO16,O18,Ne20, andNe22withCm248

We have measured cross sections for the production of isotopes of Bk through No in bombardments of ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ ions at energies near the Coulomb barrier. In general, the peak of the mass-yield curve for each element is about two mass units larger for ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ than for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, reflecting the neutron excess of the projectiles. The production cross sections and maxima of the actinide isotopic distributions are at least as favorable for production of neutron-rich actinides as those measured for irradiation of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ with very heavy ions. The observation of so many neutron-rich products between the masses of the target and compound nucleus suggests a direct transfer reaction in which the product nuclide is formed with relatively low excitation which minimizes depletion from prompt fission.