Cross Sections for Nucleosynthesis in Stars and Bombs

Three different processes in which nuclei are synthesized by the multiple capture of neutrons with energies in the keV range are reviewed and compared, namely the $s$-process and $r$-process in stars and the synthesis of very heavy nuclei in thermonuclear explosions. In the $s$-process, neutrons are captured by nuclei in the valley of $\beta$-stability. Knowledge of neutron capture cross sections of $s$-process nuclei can clarify such features of the $s$-process as elemental abundances, time scales, and temperatures. For producing the heaviest possible nuclei by neutron capture in thermonuclear explosions there are advantages in using the heaviest obtainable target nuclei, but for these there is the disadvantage of serious competition from neutron-induced fission. A channel theory of capture to fission ratios shows encouraging agreement with experiment. More data on capture to fission ratios would be valuable, particularly for odd-odd target nuclei. From capture to fission ratios, the number of open channels for fission can be deduced.