A program of simulation and optimization is developed for the case of cyclic activation analysis of short-lived isotopes with 14-MeV neutrons. The background line under the photopeaks of interest is simulated using Zikovsky's model. The reliability of the program is checked on real conditions with a geological reference sample "Soil 5" provided by the IAEA. Optimum experimental conditions (timing parameters, number of cycles) are determined, and corresponding detection limits calculated. A systematic study of short-lived isotopes with half-lives lower than 5 min is done for Soil 5, and the results are discussed.