A novel alpha spectrum analysis program which combines the Monte Carlo simulations with spectrum fitting is introduced. The shapes used in the fitting are obtained from the simulations. The program is developed especially to analyze complex alpha particle energy spectra – such as those obtained from non-processed aerosol filters, swipe samples or isolated particles emitting alpha radiation. In addition to activities of the nuclides present in the sample, the program can provide source characterization. In particular, the program can be used to characterize samples of nuclear material, i.e. those containing fissionable isotopes such as U or Pu. In the present paper we illustrate the use of the program to identify and quantify alpha-particle emitting isotopes in a depleted U projectile found in Kosovo and to estimate the depth distribution of alpha-particle emitting aerosols in a glassfibre filter.