The paper contains a description of a method for the analysis of the complex alpha spectra generated during the measurement of the activity of filters outside of a vacuum chamber under environmental conditions. The peaks corresponding to the energies of alpha particles emitted by the specific isotopes are particularly large on the low-energy side of the peak maximum, and the energy resolution strongly depended on the applied filters. The analysis was based on the non-linear regression to a function designed for four, six and eight parameters. Satisfactory results were obtained for each of these functions, and the best-fitting results were achieved for the eight-parameter function. In addition, the uncertainties related to the estimated parameters, as well as the signals corresponding to functions that describe the shape of the energy peak, have been evaluated. There are also examples of the implementation of the method with respect to short-lived radon progeny and thoron decay products.
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