# What happens to Cosmic Ray Neutrons at the Earth?

When Cosmic Rays fall down from the sky, they produce lots of neutrons. They are "added" to the Earth system, so what is happening to them?

• Do they decay to protons? It would follow that they then easily catch a free electron and form Hydrogen. Is Earth enriched by more and more Hydrogen over time?
• Are they captured by nuclei as soon as they become thermalized? So they all go into production of radioactive (cosmogenic) nuclei? What happens to neutrons in the ocean, where no heavy nuclei are, do they form Deuterium water?

What is the dominating process and why?

• Good question for which I know only a partial answer. Once you get a ways underground quite a few go into the creation of cosmogenic nuclei, but you might be surprised by how many of them are captured on light isotopes. Surprisingly I don't know how many simply decay---KamLAND certainly has the potential to answer that question, but I don't know that anyone has done the study. Alas, I'm not currently connected to a experiment where I could do the study. – dmckee Aug 14 '14 at 23:05

Actually what I remember reading is that more cosmic ray neutrons are produced in the ground, by fast muon spallation, than in processes like $\mathrm{^{14}N(p,n)^{14}C}$ in the atmosphere. The first data appeared in JETP, the Soviet journal, and mentioned that the thermal flux at ground level was markedly increased by the presence of a half-meter of snow to act as a moderator.