Iodine-129 (129I)

Iodine-129 (129I) is a rare long-lived radio-isotope of Iodine. Iodine-129 called a cosmogenic nuclide, because it is created by energetic cosmic rays impacting matter in a fission reaction, called spallation. It is also created in nuclear fission reactions and naturally in nature by spontaneous uranium decay.
half-life (λ) 16My
Protons 53
Neutrons 76