Mysterious radiation burst recorded in tree rings : Nature News & Comment

Mysterious radiation burst recorded in tree rings : Nature News & Comment: "The 14C isotope is formed when highly energetic radiation from outer space hits atoms in the upper atmosphere, producing neutrons. These collide with nitrogen-14, which then decays to 14C. (The fact that this is always happening because of background radiation is what produces a continuous source of 14C for radiocarbon dating.)"