SYNTHESIS, CHARACTERIZATION, AND NEUTRON-ACTIVATION OF HOLMIUM METALLOFULLERENES

Isolation of the first macroscopic quantities of endohedral holmium me tallofullerenes (principally Ho@C82, Ho-2@C-82, and Ho-3@C-82 by LD-TO F mass spectrometry) has been accomplished by carbon-are and preparati ve HPLC methodologies. The detailed procedure for production and isola tion of the metallofullerenes includes a new technique whereby holmium -impregnated electrodes are prepared simply by soaking porous graphite rods in an ethanolic solution of Ho(NO3)(3) . xH(2)O. Monoisotopic Ho -165 offers a unique combination of advantages for neutron-activation studies of metallofullerenes, and purified samples containing Ho-165@C -82, Ho-165(2)@C-82, and Ho-165(3)@C-82 have been activated by high-fl ux neutron irradiation (phi=4 x 10(13) n cm(-2) s(-1)) to generate Ho- 166 metallofullerenes, which undergo beta(-) decay to produce stable E r-166. Chemical workup of the irradiated samples, followed by re-irrad iation, has been used to demonstrate that observed decomposition of ho lmium metallofullerenes is due mainly to ''fast'' neutron damage rathe r than to holmium atom nuclear recoil (E(max)=200 eV). This implies th at metallofullerene damage can be minimized by using neutron fluxes wi th the highest possible thermal component. A detailed analysis of the neutron-activation results is presented as a prelude to the possible u se of neutron-activated metallofullerenes in nuclear medicine.