Effective attenuation lengths of cosmic rays producing ¹⁰Be AND ²⁶Al in quartz: Implications for exposure age dating

Abstract

We have measured cosmic ray produced 10 Be (t ½ = 1.5 My) and 26 Al (t ½ = 0.72 My) as functions of depth in a core of quartz sandstone bedrock collected in South Victoria Land, Antarctica. These data were used to place limits on the exposure age and erosion rate of the exposed surface, and to calculate the effective attenuation lengths of cosmic rays producing these nuclides. These latter results indicate that the production attenuation length for 26 Al is comparable to that for 10 Be . This suggests that the production ratio 26 Al: 10 Be does not vary substantially with depth in a rock, and that its value at the surface of exposed rock is not strongly affected by erosional losses, allowing wider use of the ratio in determining exposure ages.