Table of Nuclides Frequently Asked Questions 
1.9: Other Informations 
Transition Probability 
Does this website include information about transition probabilities (e.g., the fraction of radioisotope decays resulting in radiation type and energy of interest)? If not, do you know where I can find this information? Thanks.

You can find transition probabilities by clicking the decay mode(such as beta, EC) in the radionuclide.
If you are not satisfied with this web page, another intersting source of information is the Table of Isotopes: http://isotopes.lbl.gov/isotopes/toi.html 