Abstract: Two peak shape functions are selected. They accuratly represent the form of an experimentalalpha peak obtained with semiconductor a-spectrameter. A method is proposed fitting peak pa-rameters by doublet alpha spectra. A MULT program is constructed for multiplet alpha spectra.The program are checked by applying a standard spectrum. The program MULT is used to calcu-late alpha particle emmission probabilities and ~(240)Pu/~(239)Pu atomic number ratio.