α-particle emission probabilities in the decay of 235U

235U decays by α-particle emission to 231Th. The decay scheme of this nuclide is very complex, with more than 20 alpha branches. Recommended values for Pα of this nuclide are based on measurements carried out in 1975. This work presents the results of new measurements made with Si detectors and sources of enriched uranium in the frame of the EUROMET 591 cooperation project. The use of improved measurement techniques and numerical analysis of spectra allowed a new set of Pα values for 13 lines with improved uncertainties to be obtained.