In order to gain quantitative understanding of the spectra observed by our experiments, comparison with detailed Monte Carlo simulations is essential. Several simulation codes have been developed by different authors. In particular, the prime tool for the quantitative analysis for the present thesis is SMC (Super Monte Carlo) developed by Tom Huber at Gustavus Adolphus College in Minnesota, USA. In the following section, SMC is described in detail, followed by a brief discussion of other simulation codes used in this thesis.