Lifetimes and preformation factors for the alpha-decay of the even-even actinides

Experimental lifetimes and branching ratios for the -decay of even-even actinide nuclei can be fitted with wavefunctions at the nuclear surface which are practically nucleus independent. This suggests some common preformation process across the entire mass region. Our analysis is achieved without the introduction of a `knocking frequency' and within reasonably well defined limits, the amplitudes that we calculate can be directly related to the -particle preformation factor.