Protactinium-230
Protactinium-230 has 139 neutrons and a half-life of 17.4 days. It undergoes beta-minus decay to 230U. It is not found in nature because its half-life is so short and it is not found in the decay chains of 235U, 238U, or 232Th. It has a mass of 230.034541 grams/mole.
Read more about this topic: Isotopes Of Protactinium