The measured and modeled 36Cl concentration in 100-m long limestone core from Vue des Alpes, Switzerland

A 100-m long limestone core was sampled in Vue des Alpes (1256.86m, 47 4'46.8''N, 6 52'14.70E), Switzerland, and analysed for 36Cl with Accelerator Mass Spectrometry at the Laboratory of Ion Beam Physics, ETH Zuerich. The measurements were compared with the theoretical calculation of 36Cl content in the core. The long-lived radionuclide 36Cl (T1/2=301kyr) is produced in limestone by cosmic rays. There are several pathways of 36Cl production in the limestone, and they have different attenuation lengths. At the surface the dominant production pathway is the spallation of Ca by fast neutrons. Under one meter of rock, the slow muon capture on 40Ca starts to take over the lead, while after 10 m depth the fast-muon-induced processes in Ca starts to play a significant role. Three mentioned processes plus U-Th content of the rock also produce thermal neutrons, and these neutrons activate stable 35Cl into 36Cl. These are also important pathways, because concentration of stable chlorine in the sampled core is non-negligible (65 ppm on average). All pathways were combined in a model of 36Cl production and applied to the calculation of 36Cl content of the core. The talk contains the comparison of the measured and calculated 36Cl profiles, and our conclusions on the parameters included into the model.