Isotopes of protactinium 镤的同位素
（重定向自Brevium）
Protactinium (Pa) has no stable isotopes. There are three naturally occurring isotopes, allowing a standard mass to be given.
Relative atomic mass: 231.03588(2).
Twenty-nine radioisotopes of protactinium have been characterized, with the most stable being Pa with a half-life of 32,760 years, Pa with a half-life of 26.967 days, and Pa with a half-life of 17.4 days. All of the remaining radioactive isotopes have half-lives that are less than 1.6 days, and the majority of these have half-lives that are less than 1.8 seconds. This element also has 3 meta states, Pa (t1/2 1.15 milliseconds), Pa (t1/2 420 nanoseconds), and Pa (t1/2 1.17 minutes).