How long do galactic cosmic rays travel through the Milky Way Galaxy?

Galactic cosmic rays (GCRs) travel through the Milky Way Galaxy for an average of approximately 15 million years.1

This estimated travel time is determined by analyzing the abundance of specific radioactive fragments, such as beryllium-10, found within cosmic rays. Because beryllium-10 has a half-life of 1.5 million years, the quantity of these particles that survive to be detected near Earth serves as a "clock" for their journey. This duration is also consistent with the time required for GCRs to undergo enough collisions with interstellar gas to produce the observed levels of light elements like lithium, beryllium, and boron.1