Deposition rate and seasonal variations in precipitation of cosmogenic ¹⁰Be

Abstract

The measurement of ¹⁰Be using nuclear accelerators promises to widen the applications of this cosmogenic isotope considerably^1–3. A parameter of fundamental importance in such applications is the production rate of this nuclide in the atmosphere. This production rate has previously been estimated by two methods: (1) by measuring the concentration of ¹⁰Be in marine sediments having known accumulation rates; (2) by using model calculations of cosmic ray interaction rates, combined with estimated cross-sections for production of ¹⁰Be. These two methods have led to an estimated global average ¹⁰Be production rate of 0.015–0.018 atoms cm⁻² s⁻¹ (refs 4,5 and F. Guichard, unpublished work). The increased sensitivity available with the accelerator technique now makes it feasible to measure directly ¹⁰Be deposition rates at the Earth's surface. We report here the results of such a measurement, which lead to an estimated global average production rate more than double the previous estimates. We also give some initial results on the seasonal variation of ¹⁰Be concentration in precipitation, and comment on the possibility that such variations might permit the determination of ancient accumulation rates of polar ice.