PRODUCTION RATES OF COSMOGENIC NUCLIDES IN BOULDERS

Abstract

We study how the production rates of cosmogenic nuclides in solid targets at the Earth's surface depend on the shape and size of a sampled rock and the position of a sample. We use a physical model simulating the interaction of galactic cosmic ray particles with matter. Production rates at boulder surfaces may be up to 10-12% lower than values at the surface of an infinite flat target of the same chemical composition, even when the former sample sees cosmic rays from the full 2π solid angle. This is because cosmic ray neutrons are more easily lost back to the atmosphere from within a non-flat sample than from a flat surface. Therefore, the shape and size of a boulder need to be considered when taking samples, and production rates may have to be corrected accordingly.