New interpretation of the Be-10 and Al-26 content in cosmic spherules

The observed concentrations of cosmogenic nuclides in extraterrestrial matter are usually interpreted in terms of the exposure history of the irradiated specimen or in terms of the history of the cosmic radiation itself, For small meteorites in the microgram mass range we present a theoretical approach which allows a new interpretation of the measured concentrations. In particular, we show how to determine the size distribution of the interplanetary dust and how to investigate the related phenomena (radiation pressure, mutual collisions, atmospheric entry). For this, the concentrations of the radioisotopes Be-10 and Al-26 contained in spherules from deep sea sediments were measured by means of the AMS technique. Due to the small sample size, the carrier amount was successfully kept very low: around 50 mu g for Be and between 100 and 200 mu g for Al.