RESUMO
We have developed equations taking into account both multiple-trapping and hopping processes for describing transport phenomena in disordered semiconductors. These equations have been introduced into a numerical simulation to model the steady state dark conductivity and photoconductivity as well as the modulated photoconductivity. The influence of parameters such as the density of states and attempt-to-hop frequency on the results of these experiments has been investigated. Steady state and modulated photoconductivity experiments have been performed on a hydrogenated amorphous silicon film in the temperature range 18-300 K and the results have been compared with those from the numerical simulation. This comparison shows that the latter provides a suitable interpretation of the experimental behaviours observed in both experiments.
RESUMO
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.
