Attenuation length for fast nucleon production of 10Be derived from near-surface production profiles

We have measured the fast nucleon production of 10Be to depths of 2.37 m (659 g/cm2) in a granodiorite core of uniform density and composition from the Mt. Givens pluton on the western side of the Sierra Nevada, California, at 37° 14.7′ N, 118° 53.7′ W and 2286 m. The data are well fit with a simple exponential decrease yielding an apparent attenuation length of 10Be production of 177 + 4 (2σ) g/cm2. The shallowest data point is from a depth of 1.24 cm (3.45 g/cm2) and shows no indication of a near-surface flattening of the radionuclide inventory and hence the 10Be production rate.