The double-humped fission barrier

The concept of the double-humped fission barrier of actinide nuclei has made possible an understanding of a vast amount of data on nuclear fission during the past decade. In this article the analysis of most available relevant data is reviewed, and a synthesis of the fission barrier parameters and their trends over the actinide region is built up. The sequence of the work begins with an outline (but not a critical discussion) of the theoretical foundation of the double-humped barrier, and this is followed by a full account of the nuclear reaction theory required to describe fission reactions within the concept of such a barrier. This reaction theory provides the theoretical tools for a quantitative understanding of a range of phenomena of such kinds as spontaneously fissioning isomers, their half-live and yields, vibrational resonances and narrower intermediate structure in fission cross sections, and the general trends and magnitudes of fission cross sections at excitation energies near the top of the fission barrier. The magnitudes and trends of fission barrier parameters and the level structure of highly deformed nuclei that are extracted from the data on these phenomena are discussed in the light of current concepts of nuclear structure. Also, the possibility of a three-humped and more complex barriers is reviewed