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

We have measured cosmic ray produced ¹⁰Be (t_½= 1.5 My) and ²⁶Al (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 ²⁶Al is comparable to that for ¹⁰Be . This suggests that the production ratio ²⁶Al:¹⁰Be 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.