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 de ep drill core (KTB) at Egerer Waldhaeusl, Poppenreuth and Puellersreut h was measured with accelerator mass spectrometry (AMS). These drill c ores are situated in Upper Palatinate (Oberpfalz, Germany) in a region with very low erosion. The cosmogenic production of Al-26 in quartz w as calculated. The calculation is based on two reactions: spallation r eactions on silicon in the first few meters and the capture reaction o f 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 i n silicon to Al-26(5+) was determined by irradiating a quartz sample w ith slow negative muons at PSI in Villigen (Switzerland) and by measur ing the produced Al-26 by AMS. Calculations of Al-26 depth profiles ta king erosion into account were performed. The agreement between the de pth profile calculated with no erosion and the measured preliminary pr ofile is very satisfactory.