Application of self-absorption correction method in gamma spectroscopy for210Pb and137Cs sediment chronology on the continental slope off NW Africa

Abstract

The uppermost 50cm of the high resolution core GeoB9501-4 from the continental slope off NW Africa has been used for improving routine technique of 210 Pb and 137 Cs sediment chronology in the Radioactivity measurement laboratory of the Bremen University. The experimental requirements for 210 Pb and 137 Cs determination were non-destructive analysis of wet sediment samples in cylindrical containers with different heights, unknown elemental composition and density. The method used in this study to deal with self attenuation is applying efficiencies calculated using the LabSOCS TM , Genie 2000 software calibration tool, validated by self-absorption test measurements of different materials with known composition. A mean sedimentation rate of 0.49cm · yr −1 was obtained from the investigated core using the CRS chronological model. This means a relatively increased recent sedimentation rate comparing to an average sedimentation rate at higher depths of an associated gravity core estimated to 0.15cm · yr −1 by 14 C chronology. A further increase of the sedimentation rate was observed in the uppermost part of the studied core (up to 0.90cm · yr −1 ). Life in the semiarid Sahel belt of tropical North Africa strongly depends on the availability of water and has been repeatedly affected by shifts to more arid climate. The most recent drought occurred in the early 1970's and 1980's, with partial recovery during the late 1990's. High resolution fluvial sediments off Senegal offer the opportunity to study the history of the Sahel drought and to assess its imprint on the composition of terrestrial materials deposited at the sea floor, if the material can be accurately dated on historical time scales.