Cosmic-ray age deduced from the 10Be abundance

The first satellite measurements of the radioactive cosmic-ray species 10Be are reported. The abundance was measured near 100 MeV per nucleon with high-resolution solid-state telescopes on the IMP-7 and IMP-8 satellites during 1973--1974. These two independent measurements yield 10Be/Be ratios of less than 10 percent. Taken together with the galactic propagation model described in the text, these results show that the cosmic-ray ''clock'' lifetime (most probable value of approx.2times107 years) is significantly greater than that deduced for a nonimal interstellar gas density of approx.1--3 atoms cm-3