A software package for the simulation of neutron activation spectra has been developed. The simulation of the 14 MeV neutron activation gamma ray spectra has been carried out both for cyclic and conventional modes. The simulation allows the prediction of the optimum parameters for a low level of detection. The parameters are irradiation, counting and decay times. The simulation was based on an accurate calculation of various parameters such as the photoelectric yield, detector efficiency and background estimation. Compton effect, single and double escape are also taken into account. This software was extensively tested using the IAEA certified material Sll lake sediment and AI(OH)3 chemical standard. A high agreement between the theoretical simulated spectra and those measured is obtained. The second part of the package implements the optimization of the timing parameters. The Monte Carlo method was used to search within a constrained time space for the optimum condition resulting in the lowest detection limit for a given reaction. In order to illustrate the validity of the optimisation routine, sodium is determined in SL1 using the reaction 23Na(n,u)20F.