DETERMINATION OF EROSION RATES WITH COSMOGENIC AL-26

A preliminary depth profile of the long-lived cosmogenic radioisotope Al-26(5+) in quartz samples from pre-drill cores of the continental deep drill core (KTB) at Egerer Waldhaeusl, Poppenreuth and Puellersreuth was measured with accelerator mass spectrometry (AMS). These drill cores are situated in Upper Palatinate (Oberpfalz, Germany) in a region with very low erosion. The cosmogenic production of Al-26 in quartz was calculated. The calculation is based on two reactions: spallation reactions on silicon in the first few meters and the capture reaction of slow negative muons Si(mu-, nu(mu)xn), which is the dominant process below a few meters. The branching ratio of the mu- capture reaction in silicon to Al-26(5+) was determined by irradiating a quartz sample with slow negative muons at PSI in Villigen (Switzerland) and by measuring the produced Al-26 by AMS. Calculations of Al-26 depth profiles taking erosion into account were performed. The agreement between the depth profile calculated with no erosion and the measured preliminary profile is very satisfactory.