It has often been suggested that fullerenes or fullerene-related nanoparticles might be used for the encapsulation of radioactive materials. If the resulting nanocapsules were shown to be stable, this might provide a new method of nuclear waste disposal. Alternatively, radioisotopes encapsulated in carbon nanoparticles might be useful as tracers or in nuclear medicine. These possibilities have led a number of groups to experiment with the encapsulation of various radioactive atoms inside fullerenes. Actinide carbides encapsulated in carbon nanoparticles have also been prepared and have been shown to be stable for up to one year. To date, the nanocapsules have been prepared using a modification of the arc-evaporation technique for fullerene synthesis. The method generally involves incorporating some of the material to be encapsulated in the graphite cathode and then carrying out arc-evaporation in the usual way. However, there are obvious safety problems with using such techniques in connection with radioactive materials. Also, the overall yield is rather low since in many cases the encapsulated particles are only found in the soot which deposits onto the cathode. We have recently developed a new method for encapsulating material in carbon nanoparticles, which avoids the problems associated with vaporization techniques. The method involves carrying out a simple heat-treatment of a microporous carbon which has been impregnated with a compound of the material to be encapsulated. Here, we show how the new technique can be used to encapsulate crystallites of uranium carbide.
